The mean LV ejection fractions (LVEF) were 62.7, 62.6, 60.8, and 53.8%, respectively, whereas the prevalence of AF was 10.4%, 10.5%, 14.8%, and 16.8% in patients with normal geometry, concentric remodeling, concentric hypertrophy, and eccentric hypertrophy, respectively. In conclusion, the prevalence of AF was increasing according to LV geometric remodeling patterns in association with LA size and LVEF.This study investigated the relationship between atrial fibrillation (AF) and left ventricular (LV) geometric patterns in a hospital-based population in Japan. We retrospectively analyzed 4444 patients who had undergone simultaneous scheduled transthoracic echocardiography (TTE) and electrocardiography during 2013. A total of 430 patients who had findings of previous myocardial infarctions (n = 419) and without the data on body surface area (n = 11) were excluded from the study. We calculated the LV mass index (LVMI) and relative wall (RWT) and categorized 4014 patients into four groups as follows: normal geometry (n = 3046); concentric remodeling ; concentric hypertrophy ; and eccentric remodeling . The mean left atrial volume indices (LAVI) were 22.5, 23.8, 33.3, and 37.0 mm/m However, as LVH progresses, it is associated with considerable cardiovascular (CV) morbidity and mortality3. Recent studies have focused on the prognostic impact of more subtle LV geometric abnormalities. Patterns of LVH and geometric remodeling have previously been investigated extensively in patients with hypertension and valvular heart diseases5. Concentric LVH has a high mortality risk with preserved ejection fraction (EF)7 or a high mortality risk in patients without regression of abnormal LV geometry8; other studies have reported that relative wall thickness has less impact on prognosis in patients with coronary heart disease3.Left ventricular (LV) hypertrophy (LVH) may be considered a compensatory effect since increasing LV wall thickness reduces LV wall stress9. Atrial fibrillation (AF) is more prevalent among older people with pronounced morbidity and mortality13. AF can cause heart failure, affect quality of life, lengthen the hospitalization period, and increase mortality14. Left atrial (LA) remodeling, LA enlargement, and LV remodeling are related to AF development15. However, the association between LV geometric patterns, LA enlargement, and AF remains unknown. Therefore, in this study, we investigated the association between LV geometric patterns, LA enlargement, and AF.LVH and LV dilatation cause an in increase in end-diastolic pressure, followed by enlargement of the left atriumWe retrospectively analyzed 4444 patients who had undergone simultaneous scheduled transthoracic echocardiography (TTE) and electrocardiography (ECG) at the Cardiovascular Center of Kitano Hospital during 2013. A flowchart of the study population is shown in Fig. The research protocol was approved by the institutional review board of Kitano Hospital . Informed consent was not obtained from each patient since this was a retrospective study. The study protocol conforms to the ethical guidelines of the 1975 Declaration of Helsinki as reflected in a priori approval by the institution’s human research committee. Patients’ records and information were anonymized and de-identified before analysis.From the TTE database, we extracted data for patients’ wall thickness, LV diastolic diameter (LVDd), E/e’, LA diameter (LAD), LA volume index (LAVI), and LV ejection fraction (LVEF). We also extracted the body surface area from the TTE report. From the ECG database, we extracted cardiac rhythm and recorded it as it was documented. Therefore, we could not determine whether the AF was paroxysmal or persistent.3 − (LVDd)3] + 0.6, where LVDd was the LV diastolic diameter, IVSTd was the diastolic interventricular septal wall thickness, and LVPWTd was the diastolic LV posterior wall thickness. In line with the ASE recommendations, a high LV mass index (LVMI) was defined as >115 g/m2 for male patients and >95 g/m2 for female patients. Relative wall thickness (RWT) was calculated using the following formula: (2 × LVPWTd)/(LVDd), which permits physicians to categorize an increase in the LV mass as either concentric (RWT >0.42) or eccentric (RWT ≤0.42) hypertrophy and identify concentric remodeling 17. The LAVI was calculated using the biplane area-length method and body surface area and defined high as a value >42 mL/m215. Data from two-dimensional TTE were analyzed at baseline. The LVEF was measured using the Teichholz method or the modified Simpson rule method and defined low as LVEF <50%.The LV mass was calculated using the formula recommended by the American Society of Echocardiography (ASE), and it was indexed to the body surface area as follows: LV mass = 0.8 × 1.04 [(LVDd + LVPWTd + IVSTd)We then categorized 4014 patients into four groups as follows , hyperlipidemia (ICD-10 code E78), diabetes mellitus , and chronic kidney disease (CKD) (ICD-10 code N18), from electronic medical data at our institution.The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.2). The adjusted odds ratios and 95% confidence intervals were calculated. To show the association of two variables , we presented scatter plots, lines of best fit, and correlation coefficients. To visualize the effect size of each variable, the LogWorth ) scales were presented18. In LogWorth sclaes, a highly significant p-value had a large LogWorth value and a nonsignificant p-value had a low LogWorth value18. We generated the second multivariable regression model (model 2) including the LA size and LVEF to visualize the effect size of the LA size and LVEF as the LogWorth scales. In addition, we generated a multivariable logistic regression model using the same variables in AF for adjustment to analyze factors associated with a high LAVI and a low LVEF. Finally, from a logistic regression model with nominal responses (AF or not) using LVEF and LAVI, we generated a formula for linear combinations of the response levels (x = a + b x LVEF + c x LAVI) and prediction formulas for the response levels predicting the presence of AF (1/ (1 + Exp(x)) and the absence of AF (1/(1 + EXP(-x)), then we compared the two levels and predicted the presence or absence of AF according to the larger response level. We showed a receiver-operating curve with an area under the curve and provided the sensitivity and 1-specificity of this prediction formulas.Categorical variables are presented as numbers and percentages, and were compared using the chi-square test or Fisher exact test. Continuous variables are expressed as a mean ± standard deviation or median (interquartile range). Based on their distributions, continuous variables were compared using the Student t-test or Wilcoxon rank-sum test. To analyze factors associated with AF, we used a multivariable logistic regression model (model 1) involving the following potential independent, clinically relevant variables: age >70 years; sex; LV geometric remodelings that was defined as ordered variables ; and the presence of comorbidities such as ishemic heart disease, hypertension, diabetes mellitus, hyperlipidemia, CKD and overweight .Baseline characteristics of patients are provided in Table 2 in patients with a normal geometry, concentric remodeling, concentric hypertrophy, and eccentric hypertrophy, respectively.Baseline characteristics of echocardiographic findings are provided in Table Overall, 3460 patients had a normal sinus rhythm, 455 had AF, 95 had a pacemaker rhythm, and 15 had other rhythms. The prevalence rates of AF were 10.4, 10.5, 14.8, and 16.8% in patients with a normal geometry, concentric remodeling, concentric hypertrophy, and eccentric hypertrophy, respectively  in end-diastole during sinus rhythm15. Previous work has highlighted the complex mechanisms contributing to AF progression23, as the morphological, electrical, or neurohormonal remodeling along with the ventricular responses were related. Diastolic impairment and an increasing diastolic filling pressure are related to the LA size. With an increase in LA filling pressures, the atrial wall stretches and enlarges. In this study, overweight was not significantly associated with AF, which was inconsistent with the previous studies24. One of the reasons may be the differences in baseline characteristics in Japanese population and in Western population. Body weights in Japan are much lower than those in the US and Europe. Other possible reason may be due to small numbers studied in our study, considering that a marginally significance existed.Concentric remodeling and hypertrophy were often caused by pressure overload that increased the RWT. This was an adaptation to normalize the systolic wall stress. However, LV was shown to be a substrate for LV diastolic dysfunction in concentric remodeling and an incremental risk for diastolic heart failure in concentric hypertrophy. Direct underlying triggers of AF was mainly due to atrial remodeling. Atrial remodeling is caused by multiple factors23. Consequently, LA enlargement in eccentric hypertrophy is suggested to be highest among groups with pressure and volume overload. A larger LA volume is associated with a higher risk of AF15. In addition, patients with AF and patients with a larger LA showed a higher LVMI and a low LVEF in a sub-study of the AFFIRM trial25. In our study analysis of both AF and non-AF populations, LA enlargement and LVEF were significantly related to LV geometric remodeling. Therefore, the rate of AF was increasing per the LV remodeling patterns. This was true for patients with non-valvular AF. The prevalence of LVH was high in patients with non-valvular AF26. Patel et al. reported that LAVI was associated only with LVMI, not RWT21. This is consistent with our present study which showed that the relationship between LA size and RWT was different for normal and high LVMI.Eccentric hypertrophy is typically induced by volume overload, such as in valvular heart disease or systolic heart failure. The prevalence of systolic dysfunction is mostly noted in eccentric hypertrophy. Systolic dysfunction affects LV geometry through enlargement of the LV chamber. A large LV and low LVEF cause congestion of the left atrium26. Thromboembolic events may be one of the mechanisms for the higher mortality in LVH27. Although there are reportedly many factors related to AF and LA enlargement, such as age, the presence of hypertension, and obesity24, LV geometric remodeling has an impact on the presence of AF through the association with LA enlargement and a low LVEF. However, atrial fibrillation can develop without left atrial enlargement28. Atrial size increases with time in patients with atrial fibrillation, without any structural or functional abnormality of LV and the valve28. Since our study is cross-sectional, we could not identify the cause-effect relationship in each patient. Longitudinal follow-up could address this issue in each patient.In addition, LAVI and LVEF accurately predicted the presence of AF in our study; therefore, we performed multivariate analyses excluding these co-linear factors. A linear association with LVMI and LA enlargement was observed; however, the effect of RWT on a low LVEF was different between patients with a normal LVMI and those with a high LVMI. Because LV geometric remodeling was clearly associated with LA enlargement and a low LVEF, a schematic in which that LV morphology was linked to the LV function and LA size is provided Fig. . Further29 and severe AS patients30. In our study, we provided the link between LV geometric patterns and AF prevalence through the contribution of atrial enlargement and decreased LVEF. AF and LA enlargement is a risk factor for ischemic stroke and may contribute to doubling all-cause31 and CV deaths14, and, in a specific condition, non-CV deaths32. However, anticoagulants were sub-optimally prescribed in these patients. Attention should be paid to paroxysmal AF in the LVH population to improve our daily practice.In clinical practice, LVH is a risk factor in hypertensive patients24. Third, we did not consider the effect of valvular diseases such as mitral valve regurgitation. Fourth, patients with short-lasting paroxysmal AF were excluded, because we included patients with AF when they had an AF rhythm according to an ECG examination. Lastly, the data presented provide only hypothesis-generating associations between LV geometry and AF. Since this study had a cross-sectional design, a cause-effect relationship could not be assessed. Further prospective studies are needed to determine the association of LA remodeling, LV geometric changes, LV function, mortality, and the time-course for the development of AF.There are several limitations to the present study. First, the subjects are heterogeneous because of the TTE and ECG findings. The ordering criteria for ECG and TTE were not set. Second, patients’ data were extracted from electronic medical data. A lack of information regarding exercise was an important limitationThe prevalence of AF was increasing according to LV geometric remodeling patterns in association with LA size and LVEF.


Ventricular constraint therapy has been used to prevent and reverse theprogression of heart failure in ischemic and nonischemic cardiomyopathies. Wehypothesized that ventricular restraint should be tried by closing thepericardium that was previously opened following left ventricle topographicalprojection. The surgical technique presentation is illustrated by a remarkable13-year outcome of one patient with dilated cardiomyopathy treated surgically bymitral prosthesis, Cox/Maze III surgery to treat atrial fibrillation, andassociated to the ventricular constraint using the patient's own pericardium.The ventricular pericardial restraint role is unclear, since the patient hadmultiple corrections that could be responsible for the good outcome; however itis viable deserving investigations. It is a public health issueassociated with poor outcomes in the adult population and has become the leadingcause of death in adults. This syndrome has many idiopathic causes as well asrecognized etiologies, among which the most common is coronary artery disease. Otheretiologies include tachycardia-induced cardiomyopathy, storage disorders, andmetabolic disorders, viral and postpartum. As a consequence, the increased volume ofthe left ventricle (LV) causes wall stress and high energy expenditure, triggering amechanism of positive feedback that leads to progressive cardiac remodeling, markedcardiomegaly, spherical LV deformation, and mitral valve insufficiency(MVI).The incidence of heart failure (HF) in the United States has been increasing, with825,000 new cases in 2013. Despite medical and surgical advances, 50% of patientsdiagnosed with HF die within five yearsth century), selected patientswith advanced HF have several alternatives treatments, such as cardiacresynchronization therapy or left ventricular assist devices, as well as surgicalprocedures, including mitral valve (MV) surgery  andpartial left ventriculectomy. These treatments should be considered as alternativesor bridge therapies to orthotropic heart transplantation.Although heart transplantation is still the gold standard of treatment for DC, mostpatients, such as those who are older adult patients and those with comorbidities orsocioeconomic limitations, are excluded. In addition to neurohormonal blockade and a nitinol mesh for ventricular wrapping A 54-year-old male patient was attended for the first time in 2002 for a history ofprogressive dyspnea that had progressed to resting dyspnea (NYHA class IV). Physicalexamination revealed cardiac atrial fibrillation (AF), heart rate 160 bpm, jugularstasis, and a palpable liver situated at 3-4 cm from the right costal margin. He hada history of rheumatic heart disease, alcoholism, and smoking. An initialechocardiogram revealed the presence of mild deficiencies of the mitral andtricuspid valves associated with dilation of the heart chamber and an ejectionfraction (EF) of 20%.During 18 months of nutritional and pharmacologically optimized treatment , the patientremained in the advanced stage of HF. This clinical situation was consistentlyassociated with echocardiographic findings that were incompatible with the severityof his clinical status. Based on these indicators, we diagnosed the patient withdilated cardiomyopathy associated with severe HF, possibly indicating hearttransplantation. The personal circumstances and difficulties inherent in transplantsurgery, MV replacement, and treatment of AF were discussed. On that occasion, itwas proposed that external ventricular constraint related to these procedures (usingthe Acorn CorCap device) could confer additional benefits. After extensivediscussion with the heart team and the patient, it was decided to test thefeasibility of external ventricular restriction using the patient's own pericardium.After obtaining the consent of the patient to this trial, we proceeded with thesurgical treatment.The surgical findings included the following: 1) atrial fibrillation (AF) rhythm; 2)great cardiomegaly at the expense mainly of the left atrium (LA) and LV; 3) cardiacindex (CI) = 1.3; 4) mitral valve (MV) calcified and fibrotic at the edges with someshortening or lengthening chordal; and 5) a great left atrial appendage withoutthrombi. Under cardiopulmonary bypass and myocardial protection with bloodcardioplegia, surgery was performed in four steps:Pericardiotomy following the topography of the heart - Preserving pleuralintegrity, we proceeded to perform a vertical pericardiotomy down to thelevel of the atrioventricular groove, diverting the incision obliquelytoward the apex of the LV, as shown in MV replacement - We used a biological MV prosthesis consisting of bovinepericardium (Braile-M29) and preserved the valve apparatus by performing aresection of the anterior leaflet in a lunate shape, between the edge wherethe chordae were inserted and the anterior annulus. We implanted theprosthesis using 13 wires of Mersilene 2-0-anchored Teflon; the anteriorleaflet points were passed at the free edge of the leaflet and the ringremained.Cox/Maze III surgery for the treatment of AF - The third step compriseddisconnecting and suturing the pulmonary veins; resecting and suturing theleft atrial appendages, and making atrial incisions and sutures. Afteraortic clamp release, ventricular fibrillation reverted to sinus rhythm byway of internal defibrillation. The patient was discontinued fromcardiopulmonary bypass with CI = 2.4, sinus rhythm, with 10 mcg/kg/min ofdobutamine, withdrawal of cannulas, wire pacemaker in right atrium and rightventricle, and hemostasis.Restraint of the ventricles- With the aid of the pericardium flaps, adjustedsnugly by the surgeon at the end diastole, the surgeon narrowed the suturefrom the LV apex to the atrioventricular groove, referring to hemodynamicmonitoring and completing the superior longitudinal pericardium incisionwithout atrial constriction and 1D. During the first two years after surgery, the patient's clinical outcome wasassociated with highly positive echocardiographic data that were consistentlyobserved until the recurrence of AF. Even then, the patient's clinical courseremained well-controlled (NYHA class II). In the eighth year after surgery, however,echocardiographic evidence began to show degeneration of the mitral prosthesis. Thepatient's last hospitalization resulted from severe gastrointestinal bleeding causedby the gastroduodenal artery and required blood transfusions. Duringhospitalization, the patient developed severe HF, and echocardiography showed markeddegeneration with stenosis of the mitral prosthesis. This prosthesis was replaced byanother bovine pericardial valve that was implanted via a transatrial approach,keeping the restrictive pericardium sac. The surgery and the early and four-monthpostoperative outcomes were uneventful. The echocardiogram timeline data ispresented in The first part of this discussion briefly mentions the two well-known surgicalapproaches to treat HF that surely had capitol importance for the remarkable patientoutcome: 1) The mitral prosthesis preserving the valve apparatus, and 2) TheCox/Maze III surgery to treat atrial fibrillation..Bolling et al.,from the University of Michigan, proposed a technique for mitral annulus reductionusing undersized rings in the repair of MVI. Their aim was to obtain the additiveeffect of reshaping the LV to facilitate the return of ventricular ellipsoidalconformation. In other studies, optimal functional improvement after partialventriculectomy (the Batista operation) has been considered when mitralregurgitation is corrected simultaneously, thereby reinforcing thisconcept,7.In 1984, a group at Harvard University postulated that the correction of MVI wouldincrease systolic volume regardless of left ventricular EF. This concept became theimpetus for using MV surgery as an adjunct HF treatment. This group's hypothesis wasbased on possible systolic volume increase, LV volume overload and end-diastolicpressure decrease.The Cox/Maze III surgical procedure remains the treatment with the highest cure rates(over 90%), but the challenging technical nature of the traditional cut-and-sewtechnique has limited its mainstream uptake. After impressive results in sheep models of ischemiccardiomyopathy, in which CorCap reduced left ventricular end-diastolic volume(LVEDV) by 39% and increased EF by 90%, phase 2 studies confirmed its safety andfeasibility in human subjects. Subsequently, results from 300 HF patients in theAcorn Pivotal Trial were published, comparing CorCap with mitral surgeryversus mitral surgery alone, and CorCap plus medical therapyversus medical therapy alone. In this trial, 148 patients weretreated with CorCap. However, despite needing fewer subsequent procedures, havingimproved NYHA class and Minnesota Living with Heart Failure (MLHF) score andfavorable echocardiographic reverse remodeling, patients did not demonstrateimprovement in survival at 1, 3, or 5 years.Because of the enduring belief in its salutary effects on HF patients, strategies forachieving surgical ventricular restoration using fewer invasive methods continue tobe pursued. A number of devices designed to restore LV geometry and decrease wallstress have been tested in both ischemic and nonischemic HF patients. Of all thedevices developed to date, the most tested has been the CorCap Cardiac SupportDevice. The CorCap device consists of a polyester mesh that is placedcircumferentially around the heart, from the apex to the atrioventricular groove. Itprovides diastolic resistance to filling by being adjusted snugly by the surgeon atthe end diastole. In addition, it provides circumferential support, decreases LVwall stress, and resists progressive chamber dilation without any systolicassistance,2. In planning the surgery,the above discussion took into account the hypothesized benefits of using anin situ patient pericardium to constrain the LV. Although thedegree to which the in situ ventricular and pericardial restraintcontributed to the patient's good outcome is unclear, since the patient had multiplecorrections that could be responsible for the good result, however its presentationas a viable technique is pertinent to further investigations.Mortality rates remain significant in patients waiting for heart transplantation,perhaps because treatment alternatives for HF are still part of an open researchfield


Here, we aimed to clarify the relationship between contrast of neuromelanin-sensitive magnetic resonance imaging (MRI) and MR relaxation times using T1-weighted two-dimensional (2D)-turbo spin-echo sequence. To quantitatively evaluate the relaxation time, 2D-image data for the T1, T2, and T2* maps were also acquired. The regions of interest  were manually drawn on neuromelanin-sensitive MRI to measure the contrast ratio (CR) and on relaxation maps to measure the relaxation times.The subjects were 14 healthy volunteers . Neuromelanin-sensitive MRI was acquired using an optimized T1 relaxation times. Moreover, the SNc had significantly lower T2 and T2* relaxation times than the other three regions . Correlation analyses showed no significant correlations between the CRs in the SNc, SCP, and CP and each relaxation time.The CR in the SNc was significantly higher than the CRs in the SCP and CP. Compared to the SCP and CP, the SNc had significantly higher TWe demonstrated the relationship between the CR of neuromelanin-sensitive MRI and the relaxation times of quantitative maps of the human midbrain. Neuromelanin, the dark pigmented granules present in the human central nervous system, was discovered in the 1930s . Until r1-weighted image (T1WI) have revealed that the melanin pigment has T1-shortening effects due to bound paramagnetic metals [in vivo with neuromelanin-sensitive T1WI [2 contrast MRI being better at delineating the SNc [Neuromelanin has the ability to combine with metals, such as iron, and become a paramagnetic agent , 7. Magnc metals . A previive T1WI . Recentlive T1WI , 10, 11, the SNc . However the SNc .1, T2, and T2* relaxation times enables quantitative comparison of MRI across multiple subjects and scanners. The fast measurement of the spin-lattice relaxation time constant (T1) has been popular for determining pathology in brain tissues [1 measurement because it can acquire data quickly [2) measurements were made with a standard spin-echo (SE) sequence [Ex vivo MRI was used to investigate alterations in T2 related to Alzheimer’s disease (AD) pathology and other types of neuropathology common in old age [2* relaxation refers to the decay of transverse magnetization caused by a combination of spin-spin relaxation and magnetic field inhomogeneity. T2* values are always shorter than the underlying T2 values. T2* relaxation is seen with gradient-echo imaging because the transverse relaxation caused by magnetic field inhomogeneities is eliminated by the 180° pulse during SE imaging [1, T2, and T2*). Because they provide an unbiased metric for comparing MR scans, quantitative relaxation maps have been used to reveal the relationship between MR maps and histological evaluations in some disease models [Mapping the T tissues , 14. For quickly –18. In asequence . Ex vivo old age , 20. Fur imaging , 22. Thee models , 18.1, T2, and T2* mapping of the healthy human midbrain. We hypothesized that this contrast would reflect the T1 or T2 relaxation times measured by quantitative mapping.The aim of this study was to clarify the relationship between the neuromelanin contrast in neuromelanin-sensitive MRI and the quantitative relaxation times using TThis study was performed in accordance with the World Medical Association’s Declaration of Helsinki and approved by the local institutional review board . Written informed consent was obtained by all subjects. The subjects in this study were 14 healthy volunteers . These volunteers had never been diagnosed with PD, schizophrenia, or other similar conditions in the past. Any information about the volunteers’ identities was removed from the images and this information was not used in the analysis or interpretation of the data.1WI was acquired as reference images. These images were not used for data analysis. To visualize and identify the bilateral SNc, which is called the neuromelanin-sensitive T1 contrast of the midbrain, the slice having the largest bilateral SNc areas (hyperintense areas) on the 3D-TFE T1WI was determined and set as the center of five consecutive slices on an optimized, T1WI, two-dimensional (2D)-turbo spin-echo (TSE) sequence without MTC preparation pulse. This sequence is able to obtain a TSE-related MTC because it provides the equivalent magnetization transfer effect by refocusing pulse [1, T2, and T2* maps. The location of these slices was the same as the location of the central slice on the 2D-neuromelanin-sensitive MRI. The MRI data sets for the T1, T2, and T2* maps were acquired using an LL sequence [All MRI data were obtained using a 3-Tesla MRI scanner  with a 32-channel head coil, in the form of oblique axial images that were acquired perpendicular to the brainstem. A three-dimensional (3D)-turbo field-echo (TFE) sequence for neuromelanin-sensitive Tng pulse –25. The sequence  based onWe obtained oblique axial images perpendicular to the brainstem and used the slice at the level of lower midbrain for region of interest (ROI) measurements. For semi-quantitative evaluation of the 2D-neuromelanin-sensitive MRI, the ROIs for measuring the signal intensity (SI) were traced manually around the high-signal areas of the bilateral SNc on a single slice, as the SNc neuromelanin-sensitive region. In addition, we measured the SIs in the other regions  of the lower midbrain on the same slice so as to better interpret the characteristics of neuromelanin-sensitive MRI . These R1, T2, and T2* relaxation times, each map was generated using the Relaxation Maps Tool  supported by the PRIDE environment . Since the software used to analyze the neuromelanin-sensitive MRI (ImageJ) and T1, T2, and T2* maps (Relaxation Maps Tool) was not the same, we traced the ROIs on the relaxation maps in a similar way to the neuromelanin-sensitive MRI. However, the SNc was difficult to distinguish from the substantia nigra pars reticulata (SNr) on the relaxation maps. A previous report by Menke et al. parceled the substantia nigra into the SNr and SNc by using connectivity information from diffusion tensor imaging [For measuring the T imaging . A diffe imaging . The lat1, T2, and T2* values and the CRs in each region using Pearson product-moment correlation analyses. A p value of <0.05 was considered significant.All of the values in all of the groups are expressed as the mean ± the standard deviation. To determine the differences of the CRs among three regions  and relaxation times among all regions , Kruskal-Wallis tests and multiple comparisons as a post-hoc test (Dunns method) were performed using Prism 5 . Linear regression analyses were used to assess the correlations between each relaxation time and the CRs in the SNc, SCP, and CP, respectively. For these analyses, the average values of the relaxation times and the CRs in the left and right side of each region were used. We searched for significant correlations between the T1, T2, and T2* maps for healthy volunteers are shown in In the semi-quantitative analysis, the CRs in the three regions  were calculated by using the SIs of neuromelanin-sensitive MRI. The CR averages in the SNc, SCP, and CP were 0.056 ± 0.039, -0.100 ± 0.032, and -0.049 ± 0.038, respectively. The CR in the SNc had a higher signal compared to the other two regions  and the relaxation times.This study investigated the relationship between the contrast of neuromelanin-sensitive MRI and three quantitative relaxation times using T1WI-TSE sequence without MTC preparation pulse was utilized, which provides the equivalent magnetization transfer effect by refocusing pulse [MTC is possible to improve contrast by decreasing the water proton SI where a tight magnetic coupling between water and macromolecules exists –33. Whenng pulse –25. In tng pulse . This mang pulse . Moreoveng pulse , 36. As 1WI with MTC [1-weighted 2D-TSE sequence, which was 0.056 ± 0.039, demonstrated that this region has a relatively high signal compared with the surrounding regions  sequence with MTC pulse resulted in a CR of 9.60 ± 2.36% (0.096 ± 0.024) [1WI-TSE can capture the neuromelanin-generated signals from these nuclei, which show signal suppression of the surrounding brain tissue by T1 prolongation when using high-field MRI [Conventional MRI techniques have failed to depict neuromelanin-containing nuclei of the human midbrain . The higwith MTC . In our ± 0.024) . Langley± 0.024) . The val1WI and T2-weighted image (T2WI) have been proposed for visualizing the SNc of the midbrain [1WI with MTC can distinctly visualize the SNc of the midbrain-level slice [1WI-TSE sequence without MTC preparation pulse. Regardless the low SAR due to no MTC pulse and the relatively short scan time (7 min 18 sec) compared with a previous report (12 min) [2WI was not able to reliably differentiate the details of the midbrain [Some neuromelanin-sensitive sequences utilizing MTC-based Tmidbrain , 37, 40.el slice . On the 12 min) , the resmidbrain , whereasmidbrain . Howevermidbrain . Thus, t min , th1-LL enable the measurement of relaxation times for comparing MR images across subjects and scanners [1-LL sequence is well known for being highly suitable for examining patients with acute myocardial infarction, because it allows for significantly shorter breath-hold time and provides a more accurate estimate of long T1 values at higher heart rates [1 mapping [1-LL sequence for the brain T1 mapping. In our study, the T1 relaxation times in the SNc were 856.4 ± 24.3 ms  on the T1 map in this study  in the SNc in healthy subjects was R2* = 32.8 ± 5.0 s-1, which is equivalent to T2* = 30.5 ± 4.6 ms [2* value in the SNc (2 and T2* relaxation times in the SNc were lower than the relaxation times in the other three regions (2* map reflects this deposition more than the T2 map. The 3-Tesla MRI scanner is sensitive to susceptibility effects, therefore it is believed that the iron deposition leads in a decrease in the T2* value due to the increased magnetic field heterogeneities caused by its paramagnetic effect [2* map in our study and the reduced T2* values in the SNc suggest the existence of iron. However, there were no significant correlations between the CR and the T2 or T2* values (2* measurements [1, T2, and T2* maps such as the 3D-TFE sequence [1 and T2 mapping [The Ton times , 22. A p± 4.1 ms , which i± 4.6 ms . This va regions . This imc effect . As a re* values , showingurements . Some prurements , 51. Sopsequence , 3D-LL tsequence , 54, and mapping  in order1, T2, and T2* maps because the software used to analyze them was different. Furthermore, one person drew the ROIs manually to measure the SIs from the neuromelanin-sensitive MRI and the relaxation times from the maps. Because of this, the reproducibility of the ROI measurements was examined by taking more than one measurements for all ROIs in some of the subjects and it was confirmed that approximately the same values were obtained. One of the technical limitations of neuromelanin-sensitive MRI is the relatively low spatial resolution compared to the size of the SNc, particularly of the slice direction [0 and B1 field heterogeneities. The midbrain location is affected by the magnetic field inhomogeneities and therefore inherent T2* and susceptibility effects are expected to be high in this location. It is believed that correcting the magnetic field heterogeneities would result in obtaining more accurate data. Recently, high 7-Tesla MRI with high-resolution T2*-weighted image, susceptibility-weighted image, and quantitative susceptibility mapping were used to visualize the SNc in healthy volunteers and patients with PD [There were some limitations in this study, one of them being the fact that it was not possible to transfer the ROIs from the neuromelanin-sensitive image to the quantitative Tirection . Also, tirection . These t with PD –59. Quan1WI-TSE sequence. However, the T1-relaxation times in the SNc were longer, while the T2 and T2* values in the SNc were lower than them. There were no correlations between the semi-quantitative CRs on the neuromelanin-sensitive MRI including the CR in the SNc and the quantitative relaxation times. These results suggest that although the neuromelanin-sensitive MRI does not simply reflect the T1 contrast, both T1-shortening due to paramagnetic effects and magnetization transfer effects may contribute to the high SI area of the SNc on T1WI-TSE images. In conclusion, this study demonstrated the relationship between the CR of neuromelanin-sensitive MRI and the relaxation times of quantitative maps of the human lower midbrain. The quantitative evaluation can provide unbiased criteria for making comparisons between patients or healthy subjects, and between different MR scans, while the combination of quantitative and semi-quantitative evaluation has the potential to serve as a useful tool in future studies for further understanding the characteristics of neuromelanin-sensitive MRI.To summarize, the SNc was visualized as a high SI area resulting in high CR compared with the surrounding regions such as the SCP and CP on the 2D-neuromelanin-sensitive MRI using a T


The objective assessment of global and regional cardiac function in children has shown to be clinically relevant but is challenging to conduct. Cardiovascular magnetic resonance (CMR) has emerged as a valuable diagnostic modality especially in patients with cardiomyopathy or congenital heart disease. However, data on the normal cardiac deformation in children assessed by CMR is lacking at present. Thus, the aim of this study was to provide reference values for cardiac strain and strain rate in children and adolescents derived from CMR feature tracking (FT) measurements.In this binational study, eighty children and adolescents  free from cardiac diseases from two centers underwent CMR in 1.5 T whole-body scanners in supine position. Global peak radial, circumferential and longitudinal systolic strains as well as the corresponding early peak diastolic strain rates were assessed applying FT on short axis as well as 3- and 4-chamber views of standard cine steady-state free precession images.p < 0.001).The difference between genders yielded no significance for all assessed strains. Yet, all strains showed a significant parabolic relation to age and an even stronger one to body surface area (BSA). Therefore, BSA-specific reference values were determined using a polynomial regression model. The apical cardiac segments featured significant higher peak circumferential but lower peak radial systolic strains than the midventricular and basal segments  contains supplementary material, which is available to authorized users. The objective assessment of cardiac function in children is still challenging despite the tremendous advances of the last decades . Echocarn = 27) and the Netherlands (n = 53). The age ranged from 0.4 to 18.0 years and both genders were represented nearly equally . The study was approved by the local ethics committees and in accordance with the Declaration of Helsinki. The parents gave informed consent to the participation of their children. A fraction of the study population was part of a previous trial on reference values [The study population consisted of 80 children and adolescents free from cardiac diseases who were recruited at two departments of pediatric cardiology in Germany  [Height and weight were measured and the body surface area (BSA) was calculated using the Mosteller formula (n = 79) .CMR examinations were performed on two different 1.5 T whole body MR scanners  using a phased-array surface coil in supine position. Some of the younger probands (<6 years) needed a mild sedation. However, general anesthesia was required in none of the subjects. A vector electrocardiogram was used for R-wave triggering. Cine images of short axis views, normally covering the entire LV from base to apex, as well as of 3- and 4-chamber views were acquired using a standard SSFP sequence. Imaging parameters were TE 1.1–1.2 ms, TR 40–42 ms, flip angle 80°, field of view (FOV) 160–190 mm x 125–156 mm, matrix 256 × 256 and slice thickness 4–8 mm for the Magnetom Symphony scanner and TE 1.5 ms, TR 3.5 ms, flip angle 45°, FOV 280–370 mm, phase FOV 0.75, matrix 160 × 128 and slice thickness 7–10 mm for the Signa scanner. The number of acquired phases at the Magnetom scanner varied between 20 and 50 per cardiac cycle. Series with a low number of phases were mostly acquired in children with high heart rates. Thus, the temporal resolution was 20.3 (19.0 to 25.6) ms. At the Signa scanner, 30 phases per cardiac cycle were reconstructed consistently resulting in a temporal resolution of 24.7 (22.4 to 27.4) ms.n = 77).Heart rate was measured during the image acquisition and retrieved from the SSFP images used for strain analysis. End-diastolic and end-systolic volumes  as well as LV mass were obtained from short axis stacks and stroke volume (SV) and ejection fraction (EF) were calculated . The endocardial and epicardial borders were manually set in end-diastole and the software tracked image features as signal inhomogeneities, tissue patterns of the myocardium or anatomical structures throughout the entire cardiac cycle. The movement of the features in relation to each other was employed to determine the cardiac strain. A cine mode allowed for a visual control of the tracking quality by showing the tracked endocardial and epicardial borders as well as the resulting strain curves Fig. . In caseFor the assessment of the intra- and interobserver reproducibility, the global peak radial systolic strain as well as the global peak circumferential and longitudinal endocardial systolic strains were measured in 20 subjects. The intraobserver reproducibility was derived from two single measurements. For the interobserver reproducibility, the same cases were evaluated by a second reader who was blinded to the obtained results.t-test, the Welch-test or the Mann-Whitney test were employed as applicable. The Bonferroni correction was applied when necessary. For the definition of reference values, a polynomial regression model with regard to a possible multicollinearity of the variables was applied. The coefficient of variation from duplicated measurements was employed for the assessment of the intra- and interobserver reproducibility. Continuous data are given as mean ± standard deviation and non-parametric data as median (interquartile range). A p-value <0.05 was regarded as statistically significant.Data were analyzed using MedCalc Statistical Software version 15.8 and 16.8 . The Tukey criterion was employed on the global strain and strain rate values for outlier detection and outside as well as far out-values were excluded from further analysis. Normal distribution was assessed by the D’Agostino-Pearson test. Correlation was evaluated by the Spearman’s coefficient of rank correlation for non-parametric data. Linear and parabolic regression models were used to assess the relationship between different variables. For the comparison of two groups the Student’s 2. Age of male and female subjects was similar (13.0 (8.8 to 15.4) years vs. 13.7 (10.8 to 15.6) years, p > 0.4, Fig. 2 vs. 1.5 (1.2 to 1.6) m2, p > 0.6, Fig. p < 0.001, Fig. −1 with slightly higher values in boys than in girls  and a significant age-dependent decrease .The median age of the study population was 13.4 (10.4 to 15.5) years Fig.  and the 2 = 0.64, R2 = 0.61, both p < 0.001) and an association with BSA in the parabolic regression analysis . Accordingly, ESV (34.0 (27.5 to 46.0) ml), which showed a non-parametric distribution, increased significantly with age and BSA . EF (66.0 ± 6.3%) was significantly associated with age and BSA . LV mass (82.9 ± 39.4 g) showed a significant increase with age and BSA . The differences between boys and girls were not significant with regard to EDV, ESV, SV, EF and LV mass in this study population.EDV (106.7 ± 36.8 ml) and SV (70.6 ± 25.1 ml) showed a significant increase with age  and the assessment of the longitudinal systolic strains, using long axis views, in 79 datasets (98.8%).The numbers of outside values, which were identified by the Tukey criterion and excluded from further analysis, were 2 for global peak radial, 5 for global peak circumferential endocardial, 3 for global peak circumferential epicardial, 3 for global peak longitudinal endocardial and 3 for global peak longitudinal epicardial systolic strains. No far-out values were detected.Regarding the early peak diastolic strain rates, the numbers of outside values were 3 for radial, 3 for circumferential endocardial, 0 for circumferential epicardial, 2 for longitudinal endocardial and 1 for longitudinal epicardial measurements. One far-out value of the early peak radial diastolic strain rate was excluded.The numbers of outside values were 4 for the maximum apical endocardial and 1 for the maximum basal endocardial rotation. No far-out values were detected.p > 0.4) for radial, −24.5 ± 3.3% vs. −24.5 ± 2.4% (p > 0.9) for circumferential endocardial, −14.6 ± 2.1% vs. −15.1 ± 1.9% (p > 0.3) for circumferential epicardial, −18.4 ± 3.5% vs. −18.5 ± 3.8% (p > 0.8) for longitudinal endocardial and −15.2 ± 2.7% vs. −15.5 ± 2.9% (p > 0.6) for longitudinal epicardial systolic strains.The differences between boys and girls showed no significance for all assessed strains with global peak values of 23.3 ± 5.0% vs. 24.1 ± 5.0% (−1 vs. −2.0 ± 0.3 s−1 (p > 0.5) for radial, 2.4 ± 0.6 s−1 vs. 2.3 ± 0.4 s−1 (p > 0.2) for circumferential endocardial, 1.4 ± 0.3 s−1 vs. 1.4 ± 0.3 s−1 (p > 0.7) for circumferential epicardial, 1.9 ± 0.4 s−1 vs. 1.9 ± 0.3 s−1 (p > 0.3) for longitudinal endocardial and 1.5 ± 0.3 s−1 vs. 1.5 ± 0.3 s-1 (p > 0.7) for longitudinal epicardial early peak diastolic strain rates.Accordingly, the differences between the gender groups featured no significance for the early peak diastolic strain rates. Values were −2.1 ± 0.4 s2 = 0.18 vs. R2 = 0.14 for radial, R2 = 0.25 vs. R2 = 0.09 for circumferential endocardial, R2 = 0.27 vs. R2 = 0.10 for circumferential epicardial, R2 = 0.20 vs. R2 = 0.15 for longitudinal endocardial and R2 = 0.17 vs. R2 = 0.15 for longitudinal epicardial global peak systolic strains.The regression analysis showed a significant age-dependency for all assessed strains. The parabolic regression equations featured better model fits than the linear equations with values of R2 = 0.22 for radial, R2 = 0.28 for circumferential endocardial, R2 = 0.30 for circumferential epicardial, R2 = 0.21 for longitudinal endocardial and R2 = 0.18 for longitudinal epicardial global peak systolic strains.The model fit could be further improved by using BSA instead of age as the independent variable for the parabolic regression model leading to values of R2 = 0.15, R2 = 0.09, both p < 0.05) showed a significant age-dependency using the parabolic regression model. When the BSA was applied as independent variable, only the parabolic model of the early peak circumferential epicardial diastolic strain rate yielded a statistical significance .Regarding the early peak diastolic strain rates, only the longitudinal endocardial and epicardial values  as well as on the global peak circumferential epicardial systolic strain . However, applying a stepwise multivariable regression model on these strains with age, BSA and heart rate as independent variables, the heart rate did not remain in the final model.Regarding cardiac strains, the regression analysis showed a significant influence of heart rate on the global peak longitudinal endocardial and epicardial systolic strains . Applying a stepwise multivariable regression model with age, BSA and heart rate as independent variables on these early peak diastolic strain rates, heart rate as well as BSA remained in the final model for the radial as well as the circumferential endocardial and the longitudinal endocardial values. Age remained additionally in the final model for the early peak longitudinal endocardial diastolic strain rate. For the early peak circumferential epicardial and longitudinal epicardial diastolic strain rates, heart rate was the only variable remaining in the final model.Regarding the early peak diastolic strain rates, the parabolic regression analysis showed a significant heart rate-dependency of the radial, circumferential endocardial, circumferential epicardial, longitudinal endocardial and longitudinal epicardial values . Yet, the peak radial systolic strain was significantly lower in the apical segments than in the midventricular and basal ones %; midventricular: 25.3 (22.4 to 30.8)%; basal: 29.3 (21.9 to 34.5)%; both p < 0.001). The difference between midventricular and basal segments yielded statistical significance only for the peak epicardial systolic strain (p < 0.001) after applying the Bonferroni correction. For a better readability, all values are given in the non-parametric notation. The results are shown in Fig. The apical cardiac segments featured significant higher peak circumferential endocardial and epicardial systolic strains than the midventricular and basal segments % and −22.7 (−26.0 to −18.6)%; midventricular: −21.6 (−24.4 to −19.6)% and −11.3 (−13.9 to −10.1)%; basal: −23.2 (−25.4 to −21.2)% and −13.1 (−14.5 to −11.8)%; all 2 = 0.10, R2 = 0.11, both p < 0.05). Most of the subjects showed a counterclockwise maximum apical rotation  and a clockwise maximum basal rotation . Of note, in 18.9% of the cases the maximum apical rotation values were negative and in 18.9% of the cases the maximum basal rotation values were positive. The results are given in Tables Both, maximum apical and basal endocardial rotation showed a significant parabolic association with BSA  are interrelated and do not directly reflect the myocardial fiber orientation. For example, the shortening and accompanying thickening of the epicardial and endocardial more longitudinal oriented fibers result in a wall thickening as the myocardium is incompressible. The contraction of the circumferential oriented myocardial fibers contributes to the thickening of the wall as well. In conclusion, the radial strain, which reflects the myocardial wall thickening, results from the contraction of myocardial fibers with different orientations. Notably, an impairment of the more longitudinal oriented endocardial fibers and the associated reduction of the longitudinal strain may cause a compensation by the remaining myocardial fibers resulting in an increase in the radial strain. Consequently, strain values need to be evaluated in relation to each other and not solely.Although the segmental peak systolic strains were measured by FT, we preferred the use of the global peak systolic strain values for further analysis and the determination of reference values due to their lesser variances and higher reproducibility . The sigAlthough a large pediatric study population was recruited at two centers in different countries, most of the subjects were Caucasian and the possible influence of ethnicity on cardiac strain and strain rate could not be assessed. Therefore, the results may not be fully transferable to children from other ethnicities. While the strain measurements were performed at one research institution, the assessment of LV volumes and mass were conducted at the respective centers. Our study population covered a wide age spectrum, however, the youngest subject was 4 months old. Thus, we could not assess the cardiac deformation in neonates. In addition, especially the centiles at the lower end of the age and BSA spectrum may be less precise. The longitudinal strains and strain rates were evaluated in 3- and 4- but not in 2-chamber views, which might have influenced the resulting values. In this study, basic data on cardiac rotation are provided. However, more elaborate analyses including the assessment of cardiac torsion are necessary to achieve a better understanding of the cardiac deformation in children and adolescents. As some of the younger children needed mild sedation for the CMR scans, examinations were conducted in free-breathing in these subjects potentially influencing the obtained images. As the thoracic excursion in this small subgroup of young subjects is little, general anesthesia with controlled ventilation to attain breath hold would not have been appropriate. Although diverse magnetic field strengths do not impair the comparableness of FT-derived strain values, the influence of the scanner design from different manufacturers has not been fully evaluated yet .This is the first study providing CMR-derived reference values for cardiac deformation in children up to 18 years of age using FT. These values may aid to the detection of an impairment of the LV function in clinical routine. As strain values alter during childhood and adolescence, this study provides specific reference values. Further studies may address the incremental benefit of strain measurements for the detection of cardiac dysfunction and the assessment of prognosis in children.


To propose a T2-prepared 3D turbo spin echo (T2prep 3D TSE) sequence for B1-insensitive skeletal muscle T2 mapping and compare its performance with 2D and 3D multi-echo spin echo (MESE) for T2 mapping in thigh muscles of healthy subjects.The performance of 2D MESE, 3D MESE and the proposed T2prep 3D TSE in the presence of transmit B1 and B0 inhomogeneities was first simulated. The thigh muscles of ten young and healthy subjects were then scanned on a 3 T system and T2 mapping was performed using the three sequences. Transmit B1-maps and proton density fat fraction (PDFF) maps were also acquired. The subjects were scanned three times to assess reproducibility. T2 values were compared among sequences and their sensitivity to B1 inhomogeneities was compared to simulation results. Correlations were also determined between T2 values, PDFF and B1.p<0.001) and 2D MESE , but not for T2prep 3D TSE . Reproducibility of T2 expressed by root mean square coefficients of variation (RMSCVs) were equal to 3.5% in T2prep 3D TSE, 2.6% in 3D MESE and 2.4% in 2D MESE. Significant differences between T2 values of 3D sequences (T2prep 3D TSE and 3D MESE) and 2D MESE were found in all muscles with the highest values for 2D MESE (p<0.05). No significant correlations were found between PDFF and T2 values.The left rectus femoris muscle showed the largest B1 deviations from the nominal value (from 54.2% to 92.9%). Significant negative correlations between T2 values and B1 values were found in the left rectus femoris muscle for 3D MESE (r = -0.72, A strong influence of an inhomogeneous B1 field on the T2 values of 3D MESE and 2D MESE was shown, whereas the proposed T2prep 3D TSE gives B1-insensitive and reproducible thigh muscle T2 mapping. Acute inflammatory edematous alterations of skeletal muscles, reflecting disease activity, as well as fatty infiltration of chronically affected muscles are two main characteristics of neuromuscular diseases –3. ConveChemical shift encoding-based water-fat MRI enables the assessment and quantification of the fatty infiltration in muscle tissue using the proton density fat fraction (PDFF) , 8. T2 mIn most clinical settings, T2 is routinely quantified using multi-echo spin-echo (MESE). In addition to fat effects, a major technical challenge in muscle T2 mapping using MESE is the occurrence of stimulated echoes. Stimulated echoes occur because of slice profile effects, transmit B1 calibration errors, transmit B1 inhomogeneity and B0 inhomogeneity . Using 3An adiabatic BIR-4 radiofrequency (RF) pulse previously used for generating T2-weighted contrast  and receA T2-preparation pulse sequence module was developed based on a modified BIR-4 RF pulse, where two gaps with equal duration were introduced to achieve a module with variable TE. The T2-preparation module was followed by a spoiler and a 3D TSE read-out. Ten young and healthy subjects  were recruited for this study. Inclusion criteria were no history of diabetes, neuromuscular disorders and previous quadriceps muscle injuries. The study was approved by the ethics commission of the medical faculty of the Technical University Munich (TUM). Before participation, all subjects gave written informed consent.The bilateral thigh muscles were scanned on a 3 T system  using anterior and posterior coil arrays. The field of view (FoV) was centered at the femur mid-length. To obtain a reproducible positioning, the greater trochanter and the tibial plateau served as anatomical landmarks and the distance between them was halved, as described by Azzabou et al .3, reconstructed voxel-size = 1.75×1.75×4 mm3 and SENSE parallel imaging with reduction factor of 2.T2 mapping was performed using 2D MESE, 3D MESE and T2prep 3D TSE. Spectral Adiabatic Inversion Recovery (SPAIR) was used for suppression of the main fat peaks in all T2 mapping sequences. The common sequence parameters were: FoV = 42×26×8 cm3, echo train length = 50, T2prep durations of 20/30/40/50/60/70 ms and a scan duration of 4:35 min for 20 slices with TR of 1500ms and an effective TE of the TSE shot of 19 ms. The flip angle train of the TSE readout was designed in order to achieve a constant signal plateau throughout the TSE shot  for skeletal muscle: the flip angles of the TSE readout were ramped down to 24° during the first 5 start-up echoes and subsequently increased to 100° to achieve a constant signal plateau and then linearly increased to 125° , according to Gluer et al .Measured T2 values were correlated with transmit B1 field values in the left rectus femoris, as this muscle showed the largest transmit B1 errors in the present experimental set-up. Measured T2 values were also correlated with PDFF values in all muscles.The statistical analyses were performed with SPSS 23.0 . All tests were done using a two-sided level of significance p<0.05. Parameters are presented as mean ± standard deviation (SD). Since the Kolmogorov-Smirnov test partially showed significant differences from normal distribution, correlations between the different MRI-derived parameters were evaluated with the Spearman-Rho correlation coefficient r. t-tests were calculated to compare the different T2 values.p<0.05).Representative T2 maps generated by the three different T2 mapping sequences and the respective B1 map of one healthy volunteer are shown in The T2 values assessed by the three T2 mapping sequences, the B0 field and B1 field inhomogeneities and the PDFF of the segmented muscles are shown in In p<0.001) and 2D MESE , but not for T2prep 3D TSE .When focusing on the B1 mapping and T2 mapping results for the left rectus femoris muscle of all acquired datasets, a significant negative correlation was found between T2 values and B1 field for 3D MESE  for skeletal muscle T2 mapping and compared the developed T2 mapping sequence with standard 2D and 3D MESE in healthy thigh muscles. The results showed a dependency of the T2 values from 2D MESE and 3D MESE on transmit B1 field, whereas the developed T2prep 3D TSE was less affected by the transmit B1 field and showed a good reproducibility in the thigh musculature of young and healthy subjects.In the right rectus femoris, left vastus lateralis and right vastus lateralis muscle the transmit B1 error was relatively small . In thesThe largest B1 errors were reported in the present experimental set-up and volunteer study in the left rectus femoris muscle. Despite the subjects repositioning in the performed reproducibility analysis, B1 errors appeared in a very similar anatomical location independent of repositioning. In the left rectus femoris muscle, 2D MESE as well as 3D MESE resulted in significantly higher T2 values than T2prep 3D TSE, again due to the occurrence of stimulated echoes. Significant negative correlations between left rectus femoris muscle T2 values and B1 values were reported for the two MESE sequences but not for T2prep 3D TSE. In order to remove any effects from intersubject T2 variation in the above correlation analysis, relative T2 differences between the T2prep 3D TSE and the two MESE sequences as a function of the B1 error were also examined. The experimentally measured relative T2 difference between the T2prep 3D TSE and the 2D MESE increased as the B1 field decreased and was in good agreement with the simulation results. A similar trend was also observed between the T2prep 3D TSE and the 3D MESE. The dependence of the relative T2 differences between the T2prep 3D TSE and the two MESE sequences on B1 errors highlighted the dependence of MESE-based T2 quantification on B1 errors.Removing the B1 sensitivity of T2 mapping is a long-standing problem. The developed T2prep 3DTSE enables B1-insensitive T2 quantification, by ensuring B1 insensitivity on the data acquisition side. An alternative way to remove B1 sensitivity is by modeling the B1 effects on the measured signal. Specifically, recent work from Lebel and Wilman has shown that an application of extended phase graphs (EPG) can compensate for stimulated echoes due to B1 effects in MESE-based quantification of T2 values . Such EPAnother important issue is the influence of fatty infiltration on T2 values. In MESE, both inflammatory alterations as well as fatty transformations, are leading to an increase of the T2-weighted signal due to an increase of the water T2 and/or an increase of the fat content  . It has The present study has some limitations. First, only a relatively small and age-homogeneous subject sample was examined. Second, regarding the comparison of the T2 mapping sequences, there was no real gold standard as both the 2D and 3D MESE were affected by the presence of stimulated echoes. The characterization of the B1 sensitivity of all three investigated T2 mapping sequences was the main aim of the present work. Based on the simulations, the proposed T2prep 3D TSE sequence is minimally affected by B1 inhomogeneities and when used as a reference the experimentally measured relative difference between the T2prep 3D TSE and the MESE techniques showed good agreement with the simulations. Third, since age as well as gender affect the muscle composition , the exaIn conclusion, the present work proposed the use of a T2-prepared 3D TSE for robust muscle T2 mapping and was able to show that this method gave B1-insensitive and reproducible T2 values in the thigh muscles of young and healthy volunteers. T2-prepared 3D TSE might therefore be useful as an alternative to standard T2 mapping sequences in settings where strong B1 errors are expected (i.e. in extremities and at high field strengths).S1 TableAge (in years), values (means +/- standard deviations) of B1 (in %), B0 (in %), proton density fat fraction  and T2 relaxation times (in ms) for the investigated muscles using T2prep-3D TSE, 2D MESE and 3D MESE for the four investigated muscles of the thigh region in ten young and healthy subjects. The values are shown for each scan separately. VLL: left vastus laterais muscle,; VLR: right vastus lateralis muscle; RFL: left rectus femoris muscle; RFR: right rectus femoris muscle.(PDF)Click here for additional data file.


Strategies to improve the assessment of patients with suspected acute coronary syndrome continue to evolve, in recognition that fewer than 20% of those attending the Emergency Department with chest pain receive a diagnosis of myocardial infarction. Identifying patients without myocardial infarction at an earlier stage has the potential to reduce hospital admissions for serial cardiac biomarker testing, and facilitate appropriate investigation for alternative causes. However, such strategies are only helpful if it can be demonstrated that they do not compromise patient safety.STAT high-sensitivity cardiac troponin I assay (hs-cTnI). These assays measure different subtypes of cardiac troponin, and there are important differences in the normal reference range, diagnostic thresholds, levels of imprecision and in the lowest absolute concentrations which can be reliably detected, also known as the limit of detection (LoD)  updated their guidance on the evaluation of patients with suspected acute coronary syndrome. For the first time, they recommended clinicians consider ruling out myocardial infarction if a patient has very low concentrations of cardiac troponin at presentation when measured using a high-sensitivity assay.on (LoD) .NICE recommend clinicians apply the LoD as a threshold below which myocardial infarction can be safely ruled out at presentation. Such a strategy is only recommended for patients deemed to be at low risk of myocardial infarction ‘as indicated by a validated tool’. During their appraisal, NICE considered evidence from studies including both the Thrombolysis in Myocardial Infarction (TIMI) score and the Global Registry of Acute Coronary Events score. Both scores were derived and validated in patients with confirmed myocardial infarction to confer prognosis, but over time, these scores have been implemented for risk stratification in patients with suspected, not confirmed, myocardial infarction. Importantly, cardiac troponin concentrations are embedded in both risk scores. NICE ultimately recommend the TIMI score, which has been previously validated in patients with suspected acute coronary syndrome alongside a contemporary troponin assay and serial testing,et al provide the first validation of the NICE guidance in a pooled study of over 5000 patients, in five observational cohorts across two continents, with varying prevalence of major adverse cardiovascular events (4.8% to 15.6%).2I 15.3). For the hs-cTnI, using the LoD (<2 ng/L) and a TIMI score of 0 alongside a non-ischaemic ECG, the sensitivity was 98.9% (95%CI 97.4% to 99.6%) and NPV was 99.5% (95%CI 98.8% to 99.8%). The meta-estimate for sensitivity was similar  but the heterogeneity was high (2I 73.7). The reason for the observed heterogeneity is unclear, but may reflect differences in the assay used for diagnostic adjudication and testing between cohorts. These strategies would identify between 17.9% (95% CI 16.6% to 19.3%) and 21.0% (95% CI 19.9% to 22.2%) of patients as low risk, respectively. The authors evaluate several additional approaches not included in the recommendations of NICE, including the use of thresholds above the LoD in combination with the TIMI score, and their data suggest that higher thresholds  could increase in the proportion identified as low risk without compromising sensitivity or NPV.Carlton While NICE recommend use of the TIMI score, the true need for clinical risk scores in this setting is uncertain. A recent meta-analysis of 9269 patients found a normal ECG and an hs-cTnT result below the LoD provided excellent NPV  and sensitivity  for the diagnosis of myocardial infarction, without the need for additional risk scores.History, ECG, Age, Risk factors, cardiac Troponin) with arbitrary weighting chosen on a pragmatic basis. A recent meta-analysis of 11 217 patients demonstrated this score had a sensitivity of just 96.7% (95% CI 94.0% to 98.2%), below the threshold of 99% which most emergency department physicians deem acceptable.However, there is undoubtedly an appetite for clinical risk scores in some settings, perhaps due to the additional perceived diagnostic confidence they provide. One of the most widely used risk scores, the HEART score, was developed and validated in a suspected acute coronary syndrome population. This score is based on clinical variables selected a priori , and the same applies to the vast majority of studies in this area. A multicentre randomised controlled trial of implementation of a rule-out strategy using a single hs-cTnI concentration (<5 ng/L) has completed recruitment in Scotland (NCT:03005158), and similarly, a randomised controlled trial of the LoD approach for the hs-cTnT is being planned . Both trials will give complementary insight into the safety and efficacy of this approach.For the clinician who plans to implement this strategy prior to the outcomes of these randomised controlled trials, there are some important considerations. Patients who present early after onset of symptoms are challenging to recruit and therefore under-represented in all observational cohort studies. It is therefore recommended that serial testing is performed in all who present early after onset of symptoms. Similarly, any patient with myocardial ischaemia on the ECG should not be considered for early rule out and should undergo serial troponin testing. Of utmost importance is an awareness of the assay in use at your institution, the normal reference range and the appropriate diagnostic and risk stratification thresholds which are not equivalent. Where low concentrations are reported, it is important to ensure appropriate standards for clinical reporting can be met and maintained under routine working conditions. As noted by NICE, implementation of the proposed early rule-out strategy should include clinical audit, with attention paid to the time taken to rule out the diagnosis and on the clinical outcomes of patients with suspected acute coronary syndrome.Clinicians should be confident that newer approaches using low concentrations of cardiac troponin are a magnitude safer than prior strategies using the 99th centile alone at presentation and 3 hours as recommended in the European Society of Cardiology guidelines.


V1.5 is a common feature of Brugada syndrome. Arrhythmias arise preferentially from the right ventricle (RV) despite equivalent NaV1.5 downregulation in the left ventricle (LV). The reasons for increased RV sensitivity to NaV1.5 loss-of-function mutations remain unclear. Because ventricular electrical activation occurs predominantly in the transmural axis, we compare RV and LV transmural electrophysiology to determine the underlying cause of the asymmetrical conduction abnormalities in Scn5a haploinsufficient mice (+/−Scn5a).Loss-of-function of the cardiac sodium channel Na+/−Scn5a vs. wild-type littermates. Only RV transmural conduction was further impaired when challenged with increased pacing frequencies. Epicardial dispersion of activation and beat-to-beat variation in activation time were increased only in the RV of Scn5a+/− hearts. Analysis of confocal and histological images revealed larger intramural clefts between cardiomyocyte layers in the RV vs. LV, independent of genotype. Acute sodium current inhibition in wild type hearts using tetrodotoxin reproduced beat-to-beat activation variability and frequency-dependent CV slowing in the RV only, with the LV unaffected. The influence of clefts on conduction was examined using a two-dimensional monodomain computational model. When peak sodium channel conductance was reduced to 50% of normal the presence of clefts between cardiomyocyte layers reproduced the activation variability and conduction phenotype observed experimentally.Optical mapping and two-photon microscopy in isolated-perfused mouse hearts demonstrated equivalent depression of transmural conduction velocity (CV) in the LV and RV of Normal structural heterogeneities present in the RV are responsible for increased vulnerability to conduction slowing in the presence of reduced sodium channel function. Heterogeneous conduction slowing seen in the RV will predispose to functional block and the initiation of re-entrant ventricular arrhythmias. V1.5) is responsible for the rapid upstroke phase of the action potential (AP) in both atrial and ventricular myocytes. Consequently, this protein plays a critical role in regulating cell excitability and electrical propagation in the heart. Mutations in SCN5A, the gene that encodes the α-subunit of NaV1.5, have been linked to a variety of inherited cardiac arrhythmic disorders.+/−) has emerged as a powerful tool to study arrhythmia syndromes associated with loss-of-function Na-channel mutations,The cardiac sodium channel  coupled with abnormal restitution and AP alternans.,v1.5 and Kv4.2/Kv4.3  are known to exist in both LV and RV of several species. This produces distinct cellular electrical phenotypes between myocytes isolated from the subendocardium and subepicardium, creating the potential for transmural gradients of repolarization.Scn5a+/− mice,In BrS, arrhythmias arise preferentially from the right ventricle (RV), particularly the RV outflow tract (RVOT),to expression.+/− mice. Using optical mapping combined with two-photon (2 P) microscopy to analyse surface and transmural electrical propagation in the isolated perfused mouse heart, we demonstrate that substantial differences in transmural conduction exist between the LV and RV of Scn5a+/− mice. These differences did not arise from increased interstitial fibrosis but rather from normal structural discontinuities present in the RV, but not the LV wall. Selective pharmacological downregulation of INa using tetrodotoxin (TTX) in hearts from young wild-type (WT) mice recapitulated the RV-specific transmural conduction defects seen in Scn5a+/− mice. Computational modelling indicated the key role of non-conducting clefts in evoking activation heterogeneity and transmural dispersion of activation through tortuous conduction pathways when Na channel conductance (gNa) was reduced. Thus, the normal physiological differences in transmural tissue architecture between the RV and LV are major contributors to the RV bias of electrical dysfunction in conditions characterized by loss-of-function of the Na-channel.Problems arise with this view, however, due to the strong electrotonic interaction between well-coupled myocytes in the intact myocardium, which mitigates much of the spatial difference in intrinsic AP duration, even when accounting for gradients in Iin vivo experiments were performed in the animal facility of Nantes University Health Research Institute , which has been accredited by the French Ministry of Agriculture. Experimental procedures were approved by the regional ethics committee . Ex vivo whole heart experiments were approved by the Norwegian Council for Animal Research and were conducted in accordance with the Guide for the Care and Use of Laboratory Animals .All Scn5a+/− mice with a 129/Sv genetic background were genotyped by polymerase chain reaction as previously described.Scn5a+/− mice (63.9 ± 1.8 weeks) and 10 WT littermates (62.2 ± 2.4 weeks) were used in isolated perfused heart experiments. Animals were sedated with a gaseous mixture of 2% isoflurane in 70:30 N2O and O2 and administered an intravenous injection of heparin (1 ml of a 5000-IU solution per kg body weight) to minimize clotting. The excised hearts were cannulated and underwent retrograde perfusion with oxygenated 37 °C Tyrode’s solution containing (in millimole per liter) NaCl (116.0), NaHCO3 (20.0), Na2HPO4 (1.0), MgSO4 (1.0), KCl (5.0), CaCl2 (1.5), Glucose (11.0), Na pyruvate (1.2)—pH 7.4 maintained by continuous bubbling with 95% O2/5% CO2 gas mixture. Flow was adjusted to yield a coronary perfusion pressure of 60–80 mmHg. Heart rate was monitored throughout by a pseudo-ECG recording. Contraction was suppressed with continuous perfusion of blebbistatin (10 µmol/l) and 2, 3-butanedione monoxime (5 mmol/l). Hearts were loaded with the fluorescent indicator di-4-ANEPPS (25 µl of 2 mmol/l stock solution) for voltage measurements. A schematic of the isolated heart setup is shown in Initially, 11 +/Scn5a− mice were unable to tolerate the baseline pacing frequency of 7 Hz used throughout the study, with no signs of ischemia or perfusion issues. The maximum pacing frequency tolerated by these hearts was recorded  after which they were excluded from all subsequent analysis. Data were collected while hearts were paced at 7 Hz initially and then the highest stable pacing frequency possible, defined as the highest frequency where 1:1 capture could be maintained. Trains of 20 APs from each line scan recording were averaged relative to the pacing stimulus pulse to achieve a single transient. No further data filtering was necessary. This allowed temporal information of the transient, particularly from the upstroke, to be preserved. This approach has been verified previously in hearts from several small animal species, including mouse.Equipment and setup is shown in n = 6; +/Scn5a−, n = 5) were fixed in a freshly prepared 4.0% solution of paraformaldehyde and stored at 4 °C overnight, before being transferred to a 0.4% solution of paraformaldehyde until paraffin embedding. Paraffin-embedded tissue was then sectioned into 4 µm-thick slices  at the level of the ventricular midwall using a Leica RM2235 microtome . Cardiac fibrosis was detected by staining slices with Masson’s trichrome. A single value both for fibrosis and non-vascular cleft quantification for the free midwall of each heart was reported from the mean of the eight non-consecutive short-axis slices to obtain a representative estimate of cleft size from the intramural region examined using 2 P.Following the optical experiments, a subset of hearts , chosen from a uniform distribution and arranged randomly in the domain. The Bondarenko mouse ionic model was used to represent ionic membrane dynamics with a global stable time-step of 5µs.x-axis and the diagonal terms of the conductivity tensor were  = S/m. Stimuli were applied to nodes along the (endo) y = 0 line and average measurements were made along the (epi) y = 800 µm line. To numerically represent electrophysiology of the Scn5a+/− myocytes, the maximum sodium channel conductivity  was reduced by a factor of two (low gNa). The APs were also generated from single-cell simulations using the Bondarenko model with and without lowered gNa.Tissue dynamics were simulated using the Cardiac Arrhythmia Research PackageIsolated heart experimenters were blinded to the genotype of the mouse by the technician responsible for animal sacrifice. A separate blinding procedure was used once hearts were preserved for histology. Operators performing either tissue histology image analysis or 2 P image analysis, were unblinded only after each data set was fully analysed. Due to timing of isolated heart experiments relative to histological tissue preparation and analysis, no blinding of RV/LV conduction and structure correlation was possible.t-test (paired where appropriate), two-way analysis of variance (ANOVA) or repeated measures two-way ANOVA with Bonferroni multiple comparisons test, as indicated in figure legends. P <0.05 were considered significant.The 10% point of the AP rising phase relative to stimulus pulse was used as an index of tissue activation at each transmural layer, allowing calculation of transmural CV and beat-to-beat activation variability. AP duration (APD) was calculated at 30, 50, and 80% repolarization levels. WF and 2 P data were analysed using custom written software in Delphi  and Matlab , respectively. Data are expressed as mean ± standard error. Statistical analysis was performed in Graphpad prism 7  using Student’s Scn5a+/− model were initially quantified via ECG, recorded in vivo at 10 weeks of age in all animals. Representative examples are shown in +/Scn5a− mice exhibited marked slowing of ventricular conduction, characterized by a prolonged QRS duration compared with WT mice . Slower AP rise times were found across the region of interest in the RV of Scn5a+/− vs. WT mouse hearts . AP duration in the RV of +/Scn5a− hearts was also found to be significantly longer vs. WT RV at 75% repolarization . To identify specific intramural features of the conduction defect in the +/Scn5a− mice, transmural electrophysiology was investigated using sequential line scan recordings through the LV and RV wall. Typical averaged APs from WT (black trace) and Scn5a+/− (red trace) mouse hearts are shown in Figure  from the sub-epicardium (top) and mid-myocardium (bottom) of the RV. Line-scan recordings with 2 P revealed that AP rise time  was similarly slowed in the LV and RV of Scn5a+/− hearts (dashed lines) throughout the transmural region measured, compared with WT hearts (solid lines). WT LV exhibited significantly longer APDs throughout the epicardial and sub-epicardial regions compared with RV, but this interventricular difference was abolished in +/Scn5a− hearts . No transmural gradient of APD was detected in the LV or RV of either WT or +/Scn5a− hearts.The electrophysiological defects of the Figure ). At 7 Hz, CV in both ventricles was lower in Scn5a+/− hearts compared to WT , and no significant difference was present between ventricles . When transmural conduction was challenged, however, by gradually increasing the stimulation frequency, the maximal rate displaying 1:1 ventricular capture was significantly lower in the Scn5a+/− hearts than in the WT hearts . Crucially, at these maximal stimulus frequencies, CV was significantly reduced in the RV but not LV of Scn5a+/− hearts, whereas CV in the WT hearts was not significantly altered using maximal stimulus frequencies in either ventricle .Defects in transmural conduction leading to conduction block play a major role in the appearance of arrhythmias in Na channel loss-of-function mutations. To better understand the relative impact of Na channel abundance on LV and RV transmural conduction, 2 P line-scans at each epicardial layer were time-matched relative to the endocardial stimulus pulse, and inter-layer CV calculated using the time delay between layer activation and distance of electrical propagation  and Scn5a+/− (lower) hearts, illustrating significant slowing and dispersion of activation in the RV of +/Scn5a− hearts. The time for 95% of whole-field activation was significantly longer in the RV of Scn5a+/− hearts vs. WT hearts; however, no between-group difference was found for LV . Variability in activation time (tAct) on a beat-to-beat basis was assessed in the epicardial layers from a sequence of 25 APs acquired using 2 P excitation. Representative AP upstrokes recorded using this method are overlaid with respect to the timing of the electrical stimulus pulse in Figure  (grey lines). Once again, Scn5a+/− hearts showed a significantly increased variability in tAct preferentially in the RV but not the LV in comparison to WT hearts . Differential RV activation behaviour in Scn5a+/− hearts was also observed upon increasing stimulation frequency. Figure  shows the relative change in time between stimulus and epicardial activation upon increasing stimulation frequency from 7 Hz to maximum stable frequency (10 Hz in the example trace). The increased pacing frequency resulted in a significantly increased stimulus to activation delay in the RV of Scn5a+/− hearts relative to WT hearts, but no observed difference in LV .This RV-specific conduction defect was studied in more detail by examining electrical activation characteristics using both WF and 2 P. Scn5a+/− hearts, we sought to uncover underlying structural differences that may explain these observations. Initial 2 P imaging revealed distinct structural features 50–150 µm below the epicardial surface between the LV and RV in both +/Scn5a− and WT groups (n = 7 for both). Representative LV and RV sub-epicardial 2 P images are shown in Figure . Image analysis revealed that a significantly larger proportion of the RV was occupied by non-vascular clefts compared with the LV in both +/Scn5a− and WT hearts . These observations were explored in more detail using transverse short-axis histological slices taken midway between apex and base and stained with Masson’s trichrome  to quantify the degree of transmural fibrosis (stained blue). No significant difference in fibrosis levels were observed, either between groups or between ventricles within each group . Non-vascular spaces were quantified from histology across the LV and RV freewall for the intramural region observable by 2 P microscopy, from the epicardial surface down to a depth of 400 µm . At a high magnification, the diffuse strand-like architecture of the RV becomes apparent in contrast to the densely compacted LV myocardium. In line with the 2 P-derived image analysis, a significantly larger intramural area is occupied by non-vascular extracellular clefts in the RV vs. LV, with no differences between WT and +/Scn5a− . As shown in Figure , grouping the percentage cleft area by absolute size reveals that LV and RV diverge from each other at the largest cleft sizes (1 × 10−2 and 1 × 10−1 mm2) in both WT and Scn5a+/− hearts.Given the disparity in electrophysiological behaviour between the LV and RV of Scn5a+/− hearts suggests that a RV bias in the electrophysiological phenotype of Na-channel loss-of-function may result as a consequence of RV structure. To test this hypothesis and avoid the influence of confounding age-related changes, gNa was reduced acutely in isolated hearts from young  WT mice using the specific Na-channel inhibitor TTX. Figure  shows representative ECG recordings 20 min after perfusion with 0.5, 2.0, and 5.0 µM TTX, along with the resultant 2 P-derived transmural activation profiles at each concentration. In the presence of 5.0 µM TTX, tissue excitability diminished to such an extent that the voltage threshold for stimulation was increased substantially (>5 V) resulting in marked changes in epicardial activation patterns. At 2.0 µM, however, TTX reduced transmural CV in the LV and RV to 56.8 ± 7.4% and 57.3 ± 4.2%, respectively, of pre-treatment values . TTX treatment significantly prolonged APD in the RV sub-epicardial and mid-myocardial layers but not the LV . Importantly, no transmural gradient in APD developed after TTX treatment over the 450 µm range investigated. Significant slowing of AP rise time also developed in both the RV and LV transmural wall in this subset of hearts following TTX perfusion , an effect which was most pronounced in the RV. Most importantly, differences in transmural conduction and activation characteristics developed between LV and RV after TTX perfusion similar to those found in Scn5a+/− hearts. Analysis of activation time from a train of APs captured with 2 P line scanning close to the epicardial surface revealed a significant increase in tAct variability in the RV, but not the LV, following TTX perfusion . In addition, while increasing pacing frequency from 7  to 10 Hz after TTX perfusion slowed transmural CV in both ventricles , the effect was greater in the RV vs. the LV, with CV decreasing by 36 ± 6% in the RV but only 16 ± 3% in the LV. Taken together, these results suggest that solely reducing gNa acutely via pharmacological inhibition is sufficient to reproduce many of the RV-specific conduction defects present in +/Scn5a− hearts.The observation that cleft size is different between LV and RV but not different between WT and Figure ), mathematically described as non-conducting clefts, using either normal Na-channel conductance  or 50% of normal (low gNa). Representative APs under both conditions from the midwall of modelled tissue with no structural discontinuities (compact) are shown in Figure . An increase in transmural AP rise times was apparent in the low gNa condition in the compact model  which increased further using the largest proportion of structural discontinuities . Transmural activation maps for several different model cleft configurations are displayed in Figure  for normal (left) and low (right) gNa. These maps demonstrate a prolonged transmural activation delay and increasing dispersion of activation with increasing cleft size when gNa is reduced by 50%. The consequence of tortuous conduction pathways that result under these conditions are illustrated in the lower right panel of Figure . Red arrows indicate conduction slowing through the midwall region, while severe activation delay in later activated regions results in conduction block (black arrows). The influence of clefts in the presence of low gNa is also shown in low gNa condition when basic cycle length is reduced from 100 ms (10 Hz) to 75 ms (∼13.3 Hz) . Under these conditions, epicardial activation time is markedly increased, even when cleft size is short. Like the experimental results, prolongation of APD was also demonstrated in the model after reduction of gNa. APD90 over the first 400 µm of the model tissue is shown for compact  and long cleft (closed symbols) scenarios in To quantify the influence of transmural structure on electrical conduction, a simplified 2 D model of transmural conduction was employed with varying degrees of structural heterogeneity  and spatial  activation heterogeneity compared with the RV, despite transmural CV in Scn5a+/− hearts being similarly reduced in both ventricles. Acute Na channel inhibition in WT hearts with TTX (reducing CV to levels comparable to Scn5a+/− hearts) qualitatively recapitulated the differential transmural conduction behaviour between RV and LV seen in +/Scn5a− hearts. The TTX concentration used was close to the previous reported Kd (1.6 µM) based on INa binding curves.The abundance of transmural extracellular clefts between WT and et al.et al. also performed a detailed three-dimensional examination of transmural laminar arrangement in rat LV and found the sub-epicardial layers to be compact with relatively fewer clefts compared with more discontinuous mid-wall, a finding closely resembling the LV structure seen from 2P imaging and short-axis histological images in the current study.et al. to fully address this. Consequently, we believe that this study is the first to investigate the potential influence of interventricular transmural cleft size and distribution on arrhythmia susceptibility in a model of reduced Na channel expression.To the best of our knowledge, an interventricular comparison of non-vascular clefts has yet to be made. LeGrice Activation heterogeneity and increased conduction slowing in RV vs. LV results from tortuous conduction pathways, which depend not only on the total volume of clefts within the intramural wall but also on the frequency of coupling between groups of myocytes. While this is evident to an extent from the short-axis histological slices, this was not explicitly quantified from experimental data. The influence of the coupling frequency is examined in more detail, however, using the computational model, by varying the length of the intramural clefts (rather than area). This more closely approximates the laminar cleft orientation and volume seen experimentally and allowed this aspect to be explored in a controlled manner. Another important aspect is fibre orientation; myocyte layers are known to exhibit pronounced fibre rotation between the endo and epicardial surfaces.Of note is the influence of clefts on APD. In both experimental groups, when Na channel function was reduced, RV APD was prolonged relative to control while LV APD was unaltered. The model demonstrated that in compact tissue , APD was prolonged only slightly (∼5 ms), but the presence of long clefts  increased the magnitude of APD prolongation by ≈2×. Both experiments and model therefore suggest a significantly greater influence of reduced gNa (or Na channel expression) on transmural repolarization in the presence of structural heterogeneities such as those within the RV wall. The change in APD from compact tissue observed in the model was not seen experimentally in the LV, but this could be attributed to the relatively small change being masked by variation in APD between experimental preparations as well as variability associated with the method of measurement. Modelling transmembrane potentials across a region of tissue equivalent to the 2 P experimental imaging (400 µm) revealed a transmural APD gradient between 4 and 5 ms (see V1.5 has been reported to be lower in the RV of Scn5a+/− mice.+/− mice).+/− mouse. In line with this observation, RV rise time from both Scn5a+/− hearts and TTX-treated hearts was not different from that of controls close to the epicardium . These data support the conclusion that structural heterogeneities alone are enough to influence conduction delay and heterogeneity, particularly at increased heart rates.Several aspects of ventricular ion channel heterogeneity have been proposed to explain the increased RV susceptibility to arrhythmias in the presence of Na channel loss-of-function mutations. Expression of Naet al.).Scn5a1798insD/+)The unique developmental origin of the RVOT has emerged in recent years as an explanation for the increased RV susceptibility to arrhythmias , when fibrosis would not be expected to play an appreciable role.,SCN5A loss-of-function mutation found in BrS patients revealed an increased propensity for both pacing induced and spontaneous VF, often originating from the RV free wall.Interstitial fibrosis has been reported among patients with BrS,Transmural electrophysiological data were acquired sequentially as simultaneously examining many layers in intact tissue using 2P imaging was not possible, limiting analysis to steady state behaviour synchronized to the stimulus pulse. Nevertheless, it enabled average transmural conduction behaviour of both ventricles to be examined within the same preparation with minimal physical tissue disruption, maintaining the preparation as close to physiological as possible. Ventricular wedge preparations are routinely used for optical interrogation of transmural electrophysiologyex vivo experiments). This approach was justified, as previous simulations using the full bidomain representation with a highly conducting medium in the cleft produced almost identical results (data not shown). 2 D modelling might be expected to exaggerate phenomena compared to a more realistic 3 D model . The 2 D model in this study was employed primarily to gain mechanistic insight into the role of structure rather than replicate the experimental results. For this purpose, the 2 D representation was more than sufficient. A representative 3 D model requires greater detail of cleft frequency in both short and long axis transmural planes, something that was not possible using histological sections in the current study. Future studies may look to construct a similar model in 3 D using 2P imaging of optically cleared intact hearts. This approach would also aid in mapping the measured electrical activity directly onto the corresponding structure, something that was not possible using the histological sections without physical fiduciary markers.Computational modelling of the ventricular wall in 2 D utilized a verified mouse ventricular cell model to mirror the intact mouse heart used experimentally. The electrophysiological characteristics of the mouse AP are different from humans and other larger mammals, which could introduce disparities when trying to extrapolate results to larger species. To assess the contribution of species differences, parallel simulations were performed using the Luo-Rudy guinea pig ventricular cell model that recapitulates many of the electrophysiological characteristics of human cardiomyocytes.We demonstrate that normal structural heterogeneities present in the RV are responsible for increased vulnerability to conduction slowing in the presence of reduced Na channel function. Indeed, the greater density of transmural clefts in the RV was sufficient to explain the distinct electrophysiological phenotype without the need for additional fibrosis. This heterogeneous conduction slowing will predispose to functional block and the initiation of re-entry, and as such may explain the increased susceptibility to VF in BrS, a condition frequently characterized by loss-of-function Na channel mutations and associated conduction slowing specific to the RV.Cardiovascular Research online.Supplementary DataClick here for additional data file.