Biventricular pacing (BVP) is the established treatment to perform cardiac resynchronization therapy (CRT) in patients with heart failure (HF) and left bundle branch block (LBBB). However, BVP is an unnatural pacing modality still conditioned by the high percentage of non-responders and coronary sinus anatomy. Conduction system pacing (CSP)—His bundle pacing (HBP) and Left bundle branch area pacing (LBBAP)- upcomes as the physiological alternative to BVP in the quest for the optimal CRT. CSP showed promising results in terms of better electro-mechanical ventricular synchronization compared to BVP. However, only a few randomized control trials are currently available, and technical challenges, along with the lack of information on long-term clinical outcomes, limit the establishment of a primary role for CSP over conventional BVP in CRT candidates. This review provides a comprehensive literature revision of potential applications of CSP for CRT in diverse clinical scenarios, underlining the current controversies and prospects of this technique. Cardiac resynchronization therapy (CRT) by means of biventricular pacing (BVP) is the mainstay treatment on top of guideline-directed medical therapy for patients with heart failure (HF) with reduced ejection fraction, especially when coupled with electro-mechanical ventricular dyssynchrony determined by left bundle branch block (LBBB) . SeveralIn this complex scenario, conduction system pacing (CSP)—His bundle pacing (HBP) and Left bundle branch area pacing (LBBAP)- stimulating the specialized His-Purkinje (HP) system can reproduce the physiological and evolutionary form of intrinsic ventricular electro-mechanical coordination and may represent a valuable alternative in the quest of the optimal cardiac resynchronization therapy .Selective and non-selective HBP  are the terminologies used to describe the capture of the His bundle (HB): S-HBP results in the capture of the His bundle alone without myocardial capture, whereas in NS-HBP, in addition to HB there is the capture of surrounding septal myocardium.In LBBAP, the different grades of penetrance of the pacing lead within the interventricular septum (IVS) and the demonstration of the capture of the conduction system (left bundle branch) discriminate between selective or non-selective-left bundle branch pacing  and left ventricular septal pacing (LVSP) where only myocardial capture of the left side of the IVS is obtained.Despite the promising results of CSP in observational studies, only few pilot RCTs are currently available, and technical obstacles, along with the lack of information on safety issues and long-term clinical outcomes, limit the establishment of a primary role for CSP over conventional BVP in CRT candidates. This review provides a comprehensive literature revision of potential applications of CSP for CRT, highlighting current controversies and future perspectives .The electrical activation pattern of the human heart was first described in the late 1960s .The ventricular electrical activation starts in endocardial areas on the left surface of the interventricular septum , then proceeds towards the apicobasal direction of the ventricles through the presence of Purkinje system terminations within the endocardium .Cardiac resynchronization therapy’s paradigm is to correct the delayed activation of the left ventricular (LV) free wall as induced by abnormalities within the HPS, namely left bundle branch block (LBBB). Previous studies showed that QRS narrowing after BVP implantation is prognostically essential mainly in patients with LBBB, and the degree of QRS duration narrowing strongly predicts clinical outcomes .Several mechanisms have been postulated by which CSP normalizes the QRS duration in patients with BBBs. In the functional longitudinal dissociation concept, it is hypothesized that BBBs are likely secondary to a delay/block within the fibers in the His bundle (HB) already predestined to the right or left bundle branch and, therefore, can be customarily recruited pacing the His bundle .Upadhyay and colleagues also proved the evidence for the proximal disease by detailed intracardiac mapping of the LV septum in 72 patients with LBBB(10). The authors reported a complete conduction block in 64% of the patients  corrigible by pacing distally to the site of the block. Conversely, in the remaining 36% of the cases they reported absence of conduction block and intact Purkinje activation. In this latter situation HBP led to inefficient QRS correction as the delayed LV activation was likely to be due to distal conduction myocardial tissue disease (commonly observed in intraventricular conduction delay - IVCD). Other supposed mechanisms of BBBs correction with CSP may include the virtual electrode effect, transverse connections between the bundles, and the retrograde activation of HB and the right bundle branch (RBB), especially with LBBAP (11).HBP, with either selective or non-selective capture, appears as the most physiological pacing modality that preserves or restores electrical and mechanical synchrony by simultaneously activating both ventricles. LBBAP, on the other hand, by direct capturing the LBB and manifesting electrocardiographically as an incomplete RBBB with a relatively narrow QRS duration, preserves or restores mainly the physiological activation of the LV (5). However, the clinical impact of a delayed RV activation deriving from LBBAP is still unknown, and whether atrioventricular (AV) delay adjustments or bipolar stimulation  could mitigate it through the contemporary right septal activation need further investigations . NeverthCRT with BVP is currently recommended with class I indication by guidelines for symptomatic heart failure patients with QRS duration>150 msec (LBBB morphology), and an LVEF <35% despite optimized medical treatment as BVP has solidly demonstrated in RCTs to improve long-term survival and HF hospitalizations . Howevervia the coronary sinus was not achievable. Direct His-bundle pacing corrected basal conduction disturbances in 13 of the 16 patients (81%) selected. In four patients in whom HBP was attempted, the electrode was not successfully fixed. In the nine remaining patients , a definitive resynchronization by HBP was achieved, with consequent improvement in functional class and parameters of LV function as assessed by echocardiography   . After aIn a retrospective multi-center study of HBP for CRT in 106 patients performed as a primary (73 patients) or rescue (33 patients) strategy, Sharma and colleagues reported an overall success rate of 90%. During a mean follow-up of 14 months, in both groups demonstrated a significant narrowing of QRS durations, an increase in LVEF, and improvement in NYHA functional class .versus BVP are available . The median LVEF improvement in HBP was higher but not significantly different from BVP   . No signp < 0.01) and at 6-month follow-up . This study was limited by the high rate of cross-over that was mainly related to the technical impossibility of achieving the target QRS duration in the HBP group . Pacing thresholds were higher for HBP compared with BVP both at implantation  in CRT candidates in whom coronary sinus lead implantation is unsuccessful . AlthougThe procedural challenges faced with HBP and the evidence of a high rate of instability of pacing parameters at follow-up opened the way for LBBAP . The feaIn 2017, Huang and colleagues pioneered LBB pacing in a patient in whom HBP failed to correct LBBB at the highest pacing output. They were able to capture the proximal trunk of LBB at lower and stable output advancing the lead tip distally from HB towards the ventricle, obtaining the best QRS narrowing (after adjusting the AV delay), and observing a remarkable increase in LVEF at 1 year follow-up .p <.001) and there were no deaths or HF hospitalizations. Vijayaraman and colleagues, in a multicenter study, reported an 85% LBBAP success rate among 325 patients with LVEF<50% who were referred for CRT. During a mean follow-up of 6 months, there was a significant decrease in QRS duration and an improvement in clinical and echocardiographic response with LBBAP (p <.001) and LVEF improvement from 29% ± 10% at baseline to 40% ± 12% (p <.001)  .p = 0.039). LBBP also appeared to have greater reductions in LV end-systolic volume  and NT-proBNP  than BVP whereas comparable changes in NYHA functional class, 6-min walk distance, QRS duration, and rates of response were reported  and LBBB with a 6-month follow-up . This streported .p = 0.003], QRS area , and significantly higher increase in dP/dtmax  compared to BVP.A recent study compared in a crossover fashion, instead, the acute improvement of electrico-mechanical synchrony, and hemodynamics between LBBAP and BVP in 21 patients with HF (predominantly NICM- 90% of the cases) and LBBAP . LBBAP aIn the published results from a large multicenter cohort of patients with HFrEF requiring CRT, CSP (either HBP or LBBAP) was associated with a significant reduction in the composite outcomes of all-cause mortality or HF hospitalizations compared to conventional BVP with a difference more pronounced in the subgroup of patients with LBBB . No direp < 0.001 for non-inferiority). Both groups showed a similar change in left ventricular end-systolic volume  and similar rates of mortality or heart failure hospitalizations   patients allocated to CSP, with an implant success in 4 of 7 (57%) patients. In 28 of 35 patients, LBBP was pursued with an implant success in 23 of 28 (82%) patients. Eight (23%) patients crossed over from CSP to BVP; 2 patients (6%) crossed over from BVP to CSP. A similar decrease in LVAT - evaluated with the non-invasive 3-dimensional mapping system (ECGi) - was achieved by CSP and BiVP  .Current international guidelines do not reserve indications for LBBAP in routine clinical practice but the effect of LBBAP on electro-mechanical parameters seems impressively promising.Further confirmation of LBBAP impact on clinical endpoints at long-term is deeply necessary from larger RCTs to favor the adoption of this technique over BVP in patients undergoing CRT.The incremental diffusion of CSP is laden by troubleshooting issues for HBP and concerns about long-term performances for LBBAP . Since tDespite LBBAP advantages , some safety issues are still unknown as it has been widely used only since 2017 . Some coIn addition to strengths and limitations, CSP brings some controversies that need further explanation. For example, LVSP showed better interventricular synchrony but prolonged LV lateral wall depolarization than LBBP in bradycardia patients and comparable short-term hemodynamic and electro-mechanical improvements with BVP and HBP . Since LFinally, as most of the studies on CSP for CRT were conducted in patients with non-ischemic cardiomyopathy, its generalizability should be extensively validated also in patients with ischemic substrates, genetic or acquired cardiomyopathies  where the necrotic scar and the fibrotic process may involve the target zone of CSP lead placement.Several conditions beyond LBBB can lead to cardiac dyssynchrony and may be targeted by CRT through physiological pacing.It has been demonstrated that BVP-CRT is less effective in patients with RBBB since conventional LV pacing from a coronary sinus vein is not presumed to correct the delayed activation of the RV.Conversely, both HBP and LBBAP overcame the abovementioned limitations, conferred a significant QRS narrowing, and improved LVEF and NYHA functional class in this setting . MoreoveIt is renowned that conventional right ventricular pacing (RVP) induces an unnatural ventricular activation sequence dependent on slow conduction through the myocardial tissue rather than the specialized electrical system, portending to the so-called pacing-induced cardiomyopathy (PICM): a dyssynchronous ventricular activation with the consequent risk of systolic and diastolic dysfunction. However, upgrading from RVP to CSP, either with HBP or LBBAP, showed significant QRS width reduction and improvement in LVEF, suggesting that electrical and structural changes induced by chronic RVP may be reversed effectively with the adoption of CSP . MoreoveAV junction ablation (AVJA) aims to render atrial fibrillation patients pacing dependent to optimize ventricular rate control and response to CRT. Still, at the same time, it could favor the occurrence of PICM, especially in those with pre-existing impaired LV function. This seems more likely with chronic RVP, even though BVP also resulted in dyssynchrony in patients with normal QRS at baseline. The potential advantage of CSP is that it can preserve ventricular synchronization in patients undergoing AVJA that are vulnerable to PICM. Preliminary studies showed that AVJA is technically feasible in the presence of a CSP lead, portending significant improvement in QRS duration, LVEF, and better clinical outcomes  compared with RVP and BVP . RecentlCSP, in particular LBBAP, is currently performed using leads not designed and conceived initially with this scope ; therefoMoreover, in the CROSS-LEFT pilot study in patient candidates for CRT, an LBBAP lead connected to a DF-1 dual-chamber implantable cardioverter-defibrillator provided safe ventricular arrhythmia sensing and efficient electro-mechanical resynchronization . With thin lieu of BVP in patients requiring CRT.The up-to-date clinical evidence for BVP outnumbers that for CSP; therefore, the results of larger prospective RCTs with long-term follow-up are awaited to establish a definitive principal role for CSP Meanwhile, a tailored analysis of the underlying ventricular desynchronization patterns and optimal patient selection may help identify HF patients amenable to benefit most from CSP-CRT as an alternative or in combination with BVP.


The sympathetic cotransmitter, neuropeptide Y (NPY), is released into the coronary sinus during ST‐segment–elevation myocardial infarction and can constrict the coronary microvasculature. We sought to establish whether peripheral venous (PV) NPY levels, which are easy to obtain and measure, are associated with microvascular obstruction, myocardial recovery, and prognosis.r=0.92; P<0.001) and associated with multiple coronary and imaging parameters of microvascular function and infarct size . We therefore assessed the prognostic value of PV NPY during follow‐up, where 34 patients (20.7%) developed heart failure or died. Kaplan‐Meier survival analysis demonstrated that high PV NPY levels (>21.4 pg/mL by binary recursive partitioning) were associated with increased incidence of heart failure and mortality . This relationship was maintained after adjustment for age, cardiovascular risk factors, and previous myocardial infarction.NPY levels were measured immediately after primary percutaneous coronary intervention and compared with angiographic and cardiovascular magnetic resonance indexes of microvascular function. Patients were prospectively followed up for 6.4  years. PV (n=163) and coronary sinus (n=68) NPY levels were significantly correlated (Both PV and coronary sinus NPY levels correlate with microvascular function and infarct size after ST‐segment–elevation myocardial infarction. PV NPY levels are associated with the subsequent development of heart failure or mortality and may therefore be a useful prognostic marker. Further research is required to validate these findings. CScoronary sinusNPYneuropeptide YPPCIprimary percutaneous coronary interventionPVperipheral venousNeuropeptide‐Y levels, when measured from a peripheral vein at the time of primary percutaneous coronary intervention, correlate with coronary microvascular dysfunction, greater myocardial injury, reduced left ventricular ejection fraction 6 months after ST‐segment–elevation myocardial infarction, and subsequent heart failure and mortality over a median follow‐up of 6.4 years, even after adjustment for age and cardiovascular risk factors.We provide a definition of high peripheral venous neuropeptide Y that is associated with subsequent heart failure and mortality.Neuropeptide Y, which can easily and safely be measured from a peripheral vein at a single time point after primary percutaneous coronary intervention, may be a useful biomarker to guide prognosis.It may also be a useful theranostic biomarker to guide the use of neuropeptide‐Y receptor antagonists given previous observations of the ability of such drugs to reduce infarct size in an animal model.In patients with acute ST‐segment–elevation myocardial infarction (STEMI), the immediate aim is to restore coronary perfusion by expeditious revascularization of the infarct‐related epicardial vessel using primary percutaneous coronary intervention (PPCI). Despite this, one third of patients do not regain satisfactory myocardial reperfusion, experiencing a phenomenon known as “no‐reflow.” This involves an ongoing flow restriction in the microcirculation and is associated with prolonged ST‐segment elevation, larger infarct volume, lower left ventricular ejection fraction (LVEF), recurrent heart failure admission, and death.Neuropeptide Y (NPY) is a cotransmitter that is released alongside norepinephrine from sympathetic nerve terminals, particularly during conditions of sympathetic hyperactivity, such as myocardial infarction.Accordingly, we examine a large cohort of patients to see whether peripheral venous (PV) NPY or the transcardiac NPY gradient  is closely associated with severe microvascular obstruction and reduced myocardial recovery, as seen with CS NPY. Given that the most pragmatic measurement to obtain clinically is PV NPY, we sought to ascertain whether this was associated with the development of heart failure or death in the OxAMI  Study.See Data r=0.92; n=67; P<0.001). There was no significant correlation between the CS‐A difference  and CS NPY levels .A total of 164 patients with STEMI were recruited and underwent PV (n=163) and/or CS and coronary arterial (n=68) blood sampling immediately after PPCI. The baseline clinical characteristics of these patients are summarized in Table Like CS NPY levels, PV NPY levels (but not a CS‐A difference) correlated significantly with a lower coronary flow reserve measured via coronary flow wire Table . PV NPY P=0.03)  years following the index event. During follow‐up, 20 patients (12.2%) developed heart failure, 20 patients (12.2%) died, and 34 patients (20.7%) in total experienced events, reaching the composite primary end point of heart failure or mortality. Patients in the events group were more likely to experience hypertension, diabetes, or hypercholesterolemia, and admission heart rate was significantly higher (Table P<0.001). A multivariable Cox proportional hazard model, adjusting for age, sex, smoking, hypertension, hypercholesterolemia, diabetes, family history of cardiovascular disease, and previous myocardial infarction, did not affect the association of PV NPY with the combined end point . We then used binary recursive partitioning analysis to define a PV NPY threshold that best identifies patients reaching the primary outcome. This cutoff (21.4 pg/mL) had a C statistic of 0.62  for the combined end point (heart failure or death), whereas heart failure diagnosis as an independent end point had a C statistic of 0.67 . Patients with high PV NPY were older, but otherwise the 2 groups were well matched in terms of cardiovascular risk factors (Table P=0.02), heart failure , or both   or heart failure , but PV NPY was not a significant independent risk factor for death alone following adjustment (P=0.66), as shown in Figure – Panels PV NPY as a continuous variable was associated with heart failure or death, with an estimated hazard ratio (HR) of 1.014 . Mechanistically, this is consistent with the hypothesis that NPY contributes to microvascular dysfunction and subsequent infarct size, leading to heart failure and mortality following STEMI, rather than having other independent effects outside that of influencing infarct size.Also, there are other ways in which NPY plays an important mechanistic role in the pathophysiology of atherosclerosis, STEMI, and ischemic heart failure. For example, genetic polymorphisms in the NPY gene and those of several of its receptors are associated with early‐onset atherosclerosis.Measuring PV NPY levels may identify patients in whom closer monitoring and more aggressive interventions are required. It is cheaper and more practical to measure PV NPY than routinely perform coronary flow wire measurements of microvascular function or undertake cardiovascular magnetic resonance at both 2 days and 6 months following the event, which also offer valuable prognostic information but are not readily available in all centers.Conceivably, CS NPY could more strongly correlate with events, given its stronger association with microvascular resistance, and a further study powered to evaluate this association would be informative. In addition to this, more precise temporal dynamics of circulating NPY following PPCI for STEMI may be more strongly correlated with poorer outcomes, although this would be more challenging to obtain clinically compared with a test at a single time point when NPY levels are at their highest.Both PV and CS NPY levels significantly correlate with microvascular function and infarct size after STEMI, whereas the CS‐A difference in NPY levels does not, presumably as both cardiac and peripheral NPY release is extremely high and equilibrated by the time of PPCI. High PV NPY levels, which are easy to obtain and measure following coronary intervention, are independently associated with subsequent heart failure and death and could prove to be a useful biomarker in risk stratifying these patients.Robin P. Choudhury, DM; Rajesh K. Kharbanda, MBChB, PhD; Adrian P. Banning, MBBS, MD; Jeremy P. Langrish, MB BCh, PhD; Andrew Lucking, MBChB, PhD; Sam Dawkins, MBBS, DPhil; Giovanni Luigi De Maria, MD, PhD; Vanessa M. Ferreira, MD, DPhil; Keith M. Channon, MD, PhD.The study was supported by a British Heart Foundation Senior Clinical Research Fellowship (FS/SCRF/20/32005) to Dr Herring, a BHF Chair award (CH/16/1/32013) to Dr Channon, the BHF Oxford Centre of Research Excellence (RE/13/1/30181), and the National Institute for Health Research Oxford Biomedical Research Centre.None.Data S1References Click here for additional data file.


Moderate aortic stenosis (AS) is associated with an increased risk of adverse events. Because outcomes in patients with AS are ultimately driven by the condition of the left ventricle (LV) and not by the valve, assessment of LV remodelling seems important for risk stratification. This study evaluated the association between different LV remodelling patterns and outcomes in patients with moderate AS.2) were identified and stratified into four groups according to the LV remodelling pattern: normal geometry (NG), concentric remodelling (CR), concentric hypertrophy (CH), or eccentric hypertrophy (EH). Clinical outcomes were defined as all-cause mortality and a composite endpoint of all-cause mortality and aortic valve replacement (AVR). Of 1931 patients with moderate AS , 344 (18%) had NG, 469 (24%) CR, 698 (36%) CH, and 420 (22%) EH. Patients with CH and EH showed higher 3-year mortality rates  when compared with patients with NG (19%) (P < 0.001). After multivariable adjustment, CH remained independently associated with mortality , whereas both CH  and EH  were associated with the composite endpoint of death or AVR.Patients with moderate AS (aortic valve area 1.0–1.5 cmIn patients with moderate AS, those who develop CH already have an increased risk of all-cause mortality. Assessment of the LV remodelling patterns may identify patients at higher risk of adverse events, warranting closer surveillance, and possibly earlier intervention.  Although risk stratification in AS has traditionally been based on symptoms and left ventricular (LV) ejection fraction (EF),9 the LV remodelling response to AS-related pressure overload is noted before a reduction in LVEF occurs, with several studies demonstrating that LV structural changes are already apparent despite preserved LVEF.11 Moreover, adverse LV remodelling is an important predictor of cardiovascular morbidity and mortality in many cardiovascular diseases,12–14 including severe AS.16 Indeed, while LV remodelling is initially a benign response to increased wall stress, it eventually may lead to development of myocardial fibrosis with a progressive deterioration in LV diastolic relaxation and performance, which are both associated with adverse clinical outcomes in severe AS.17–19 In addition, patients with LV hypertrophy may not always show reverse LV remodelling after aortic valve replacement (AVR), leading to worse postoperative outcomes. These observations underscore the need to identify echocardiographic parameters beyond LVEF to detect the consequences of AS afterload on the LV. Current guidelines recognize four patterns of LV remodelling that could be used to describe the LV response to AS: normal geometry, concentric remodelling, concentric hypertrophy, and eccentric hypertrophy.20 The prognostic implications of these four patterns of LV remodelling in patients with moderate AS, however, have not been investigated. In this study, we aimed to investigate the clinical and echocardiographic characteristics of these four LV remodelling patterns and their prognostic implications in patients with moderate AS.Aortic stenosis (AS) is the most common valvular heart disease in developed countries, affecting 4–5% of patients aged over 65 years.2.8 The definition of moderate AS based on aortic valve area was used to avoid inclusion of patients with severe, low-flow, low-gradient AS and was based on previous papers.22 Patients with previous aortic valve surgery, congenital heart disease, bicuspid aortic valve, supra- or subvalvular AS, or dynamic LV outflow tract obstruction were excluded. All patients underwent complete clinical and echocardiographic evaluation at the time of first diagnosis of moderate AS. Patient information was prospectively collected from the departmental cardiology information system and retrospectively analysed. Clinical data included demographic characteristics, cardiovascular risk factors, New York Heart Association (NYHA) functional class, and comorbidities. The study complies with the Declaration of Helsinki and was approved by the institutional review boards of each centre. Due to the retrospective design of the study, the medical ethics committee of each participating centre waived the need for written informed consent.From the ongoing registries of patients with moderate aortic valve disease from three academic institutions , patients ≥ 18 years who presented between October 2001 and December 2019 with a first echocardiographic diagnosis of moderate AS were identified. Moderate AS was defined as an aortic valve area (AVA) between 1.0 and 1.5 cm20 In the parasternal long-axis view, LV dimensions were assessed, and LV mass was calculated using Devereux’s formula and indexed for body surface area (LVMi).20 Relative wall thickness (RWT) was calculated with the formula: /.20 The echocardiographic variables that define LV geometry (LVMi and RWT) were subsequently used to categorize patients into four patterns of LV remodelling: normal geometry , concentric remodelling , concentric hypertrophy (increased LVMi and RWT >0.42), and eccentric hypertrophy (increased LVMi and RWT ≤0.42)20 . Normal LVMi was defined as LVMi ≤95 g/m2 for women and LVMi ≤115 g/m2 for men.20 LV volumes were assessed and LVEF was calculated according to biplane Simpson’s method.20 Left atrial volumes were measured by the biplane method of disks and indexed for body surface area.20 From the apical three- or five-chamber views, continuous-wave Doppler recordings were obtained to estimate peak aortic jet velocity.23 Mean and peak transvalvular pressure gradients were calculated using the Bernoulli equation.23 AVA was calculated using the LV outflow tract diameter and velocity time integrals of the aortic valve and LV outflow tract.23 Severity of mitral and tricuspid regurgitation was graded using a multiparametric approach, as recommended by current guidelines.24 Pulsed-wave Doppler recordings of the transmitral flow were used to obtain peak early (E) and late (A) diastolic velocities.25 Using tissue Doppler imaging of the mitral annulus on the apical four-chamber view, the e′ was measured at both the lateral and septal side, and averaged to calculate the E/e′ ratio.25 The right ventricular systolic pressure was calculated from the peak velocity of the tricuspid regurgitant jet according to the Bernoulli equation, by adding the right atrial pressure determined by the inspiratory collapse and diameter of the inferior vena cava.26 For the evaluation of right ventricular systolic function, anatomical M-mode was applied to the focused apical four-chamber view of the right ventricle to measure tricuspid annular plane systolic excursion.26All echocardiographic studies were performed using commercially available ultrasound systems and images were retrospectively analysed in each centre according to current guidelines.All patients were followed-up for all-cause mortality and the occurrence of AVR . The primary outcome was all-cause mortality, which was obtained by review of hospital records linked to the governmental death registry database.post hoc analysis or the Kruskal–Wallis test was used for normally and non-normally distributed variables, respectively. Categorical variables were compared using the Pearson χ2 test. The inter- and intra-observer variability of LVMi was assessed by calculating the intra-class correlation coefficient on 50 randomly selected patients. The intra-class correlation coefficients for inter- and intra-observer variability were 0.91  and 0.94 , respectively. Event-free survival curves were generated using the Kaplan–Meier method, and differences between groups were analysed using the log-rank test. Uni- and multivariable analyses of time to events were performed using Cox proportional hazard models with the different patterns of LV remodelling as an independent variable. The following covariables, considered to have a potential prognostic impact, were included: age, sex, diabetes mellitus, arterial hypertension, dyslipidaemia, coronary artery disease, previous myocardial infarction, atrial fibrillation, estimated glomerular filtration rate, NYHA functional class ≥II, LVEF, left atrial volume index, and AVA. The occurrence of surgical or transcatheter AVR was entered as a time-dependent covariate. A separate analysis of time to events using Cox proportional hazard models was performed in the subgroup of patients with preserved LVEF (LVEF ≥50%), and in the subgroup of patients without concomitant significant (≥ moderate) aortic regurgitation. The entry criterium for the multivariable regression analysis was an amount of missing values that did not exceed 10% of the total study population. For both uni- and multivariable analyses, hazard ratios (HRs) with 95% CI were presented. A two-sided P value <0.05 was considered statistically significant. Statistical analysis was performed using SPSS for Windows, version 25.0 .Continuous data are presented as mean ± standard deviation when normally distributed and as median (interquartile range) when not normally distributed. Categorical data are presented as frequencies and percentages. For comparison of continuous variables between groups, the one-way analysis of variance with Bonferroni’s Figure S1). Normal geometry was present in 344 (18%) patients, concentric remodelling in 469 (24%) patients, concentric hypertrophy in 698 (36%) patients, and eccentric hypertrophy in 420 (22%) patients. The clinical characteristics of the overall population and according to the different patterns of LV remodelling are shown in Table 1. Most patients had arterial hypertension (80%) and dyslipidaemia (74%), while diabetes mellitus was observed in one-third of the patients (34%). A history of coronary artery disease was noted in 865 (45%) patients of whom 362 (19%) had a previous myocardial infarction. Dyspnoea, defined as NYHA functional class ≥II, was observed in 828 (43%) patients and one-third of the patients (34%) used diuretic agents. In per-group analysis, patients with concentric hypertrophy were older than patients with normal geometry and were more likely to be female, had more arterial hypertension, more impaired renal function, and more severe symptoms  compared with patients with concentric remodelling. Patients with eccentric hypertrophy had more coronary artery disease and previous myocardial infarction, more impaired renal function, and more severe symptoms compared to patients with concentric remodelling.A total of 1931 patients  were included in the study (Table 2 summarizes the echocardiographic data of the study population. Mean LVEF was 58 ± 13% with 372 (19%) patients having LVEF <50%. Mean AVA was 1.22 ± 0.15 cm2, mean aortic gradient 23 ± 9 mmHg, and peak aortic jet velocity 3.0 ± 0.6 m/s. In the per-group analysis, patients with concentric hypertrophy had more severe LV diastolic dysfunction , whereas patients with eccentric hypertrophy had larger LV dimensions, lower LVEF, more severe LV diastolic dysfunction, and higher systolic pulmonary artery pressures compared to patients with normal geometry. In addition, patients with eccentric hypertrophy had a higher prevalence of concomitant significant aortic and mitral regurgitation. Interestingly, patients with concentric hypertrophy had higher peak aortic jet velocities and mean aortic gradients compared to patients with normal geometry.n = 613; 48%) or died  during a median follow-up of 35 (14–60) months. Of the 613 patients who underwent AVR, 250 (41%) patients underwent transcatheter AVR, and 363 (59%) patients underwent surgical AVR.During a median follow-up of 51 (25–83) months, 833 (43%) patients died. The cumulative 1-, 3-, and 5-year survival rates were 88%, 74%, and 61%, respectively. For the composite endpoint of death or AVR, 1286 (67%) underwent AVR . Similarly, patients with concentric hypertrophy and eccentric hypertrophy showed significantly lower 1-, 3-, and 5-year event-free survival rates for the composite endpoint of death and AVR  when compared with patients with normal geometry  . Similar relationships were observed in patients without significant aortic regurgitation . In the subgroup of patients with preserved LVEF (LVEF ≥50%), patients with concentric hypertrophy, but not with eccentric hypertrophy, had significantly worse survival outcomes (P = 0.001), as well as event-free survival outcomes for the composite endpoint of death and AVR (P = 0.009), compared to patients with normal geometry .The Kaplan–Meier survival curves demonstrated significantly lower survival rates at 1-, 3-, and 5-year follow-up in patients with concentric hypertrophy  and eccentric hypertrophy , when compared with patients with normal geometry  , whereas both concentric hypertrophy  and eccentric hypertrophy  were independently associated with the composite endpoint of death and AVR. Similar associations with outcomes were observed for patients with LVEF ≥50% (Table S1), while in patients without significant aortic regurgitation, only concentric hypertrophy was significantly associated with all-cause mortality and the composite endpoint of death and AVR (Table S2). When considering LV remodelling according to LVMi as a continuous variable (instead of the 4 remodelling patterns), LVMi was independently associated with all-cause mortality , as well as the composite endpoint of death and AVR .The multivariable Cox model is shown in P < 0.001). There was no interaction between the type of intervention  and remodelling patterns with outcomes (P = 0.248).Interestingly, AVR was significantly associated with a lower mortality rate  LV remodelling varies significantly in patients with moderate AS, and (ii) LV concentric hypertrophy is independently associated with all-cause mortality after adjusting for various clinical and echocardiographic variables.27 Indeed, as the LV hypertrophies, myocardial oxygen demand increases while coronary flow reserve decreases due to concomitant microvascular dysfunction, low coronary perfusion pressure, increased extravascular compressive forces, and reduced diastolic perfusion time.29 This disbalance between oxygen demand and delivery eventually causes ischaemia and leads to LV myocardial fibrosis, which is known to be a major determinant of clinical progression from compensated LV hypertrophy to heart failure and is independently associated with mortality in patients with severe AS.30–32 Previous studies have already demonstrated the association between LV mass and LV myocardial fibrosis detected by CMR,32 which could explain why a higher LV mass detected by echocardiography is associated with an increased risk of heart failure in AS33 and is associated with worse outcomes in this study.Although LV remodelling is considered a compensatory mechanism to reduce wall stress and maintain LVEF in AS, it eventually becomes maladaptive, leading to a progressive impairment in LV diastolic relaxation and LV performance which are both associated with worse outcomes in patients with AS.34–36 In addition, if no timely intervention is performed, the compensatory mechanisms to overcome the increase in wall stress could eventually become insufficient, leading to a progressive reduction in LVEF. Inverse correlations between LVEF and LV myocardial fibrosis have been demonstrated by Hein et al.,30 suggesting that LV myocardial fibrosis significantly contributes to the progression of LV systolic dysfunction. These observations demonstrate that the LV response to valvular afterload occurs through a continuous spectrum of LV remodelling and emphasize the importance of a timely intervention at the level of the aortic valve, maybe even when AS severity is still moderate.Although AVR relieves the imposed valvular afterload on the LV, LV diastolic dysfunction may persist due to the underlying presence of irreversible LV myocardial fibrosis. Therefore, end-diastolic LV pressure remains high after AVR and this could generate a vicious cycle of reduced coronary artery perfusion with further progression of LV mid-wall fibrosis. These findings might explain why maladaptive LV remodelling does not necessarily reverse after AVR.et al.37 showed that patients with essential arterial hypertension and concentric hypertrophy had a two-fold increase in cardiovascular deaths compared to patients with eccentric hypertrophy. Similarly, in 436 hypertensive patients, Muiesan et al.13 demonstrated that cardiovascular morbidity and mortality were significantly higher in patients with concentric hypertrophy compared to patients with eccentric hypertrophy. In addition, Capoulade et al.15 demonstrated that LV concentric hypertrophy was independently associated with an increased risk of mortality in patients with severe AS. Our data expand on these results by demonstrating a strong, independent link between concentric LV hypertrophy and outcomes in a large population of patients with moderate AS.Although the traditional focus of AS assessment has been on the valve, it is increasingly acknowledged that AS is not only a disease of the aortic valve but also of the LV. Current guidelines strongly recommend AVR for patients with severe AS who are either symptomatic or develop LV systolic dysfunction, demonstrating that the decision to intervene is ultimately driven by the condition of the LV myocardium and not by the valve. This study shows that LV remodelling in patients with moderate AS already varies considerably and that different patterns of LV remodelling have a different impact on prognosis. Interestingly, only concentric hypertrophy remained independently associated with all-cause mortality after adjusting for other clinical and echocardiographic variables. The observation that concentric hypertrophy is associated with outcomes in patients with a pressure overloaded LV has been previously demonstrated. Koren 38 Nonetheless, it has been demonstrated that in patients with a combination of moderate AS and reduced systemic arterial compliance, global LV afterload is equivalent, and has similar adverse effects on LV remodelling, compared to patients with isolated severe AS.39 Any significant decrease in LV afterload may therefore contribute to the improvement of LV remodelling and future trials are needed to investigate if treating moderate AS in well-selected patients with a markedly increased valvulo-arterial impedance could reverse LV remodelling and improve outcomes.In this study, patients with concentric hypertrophy had higher peak aortic jet velocities and mean aortic pressure gradients with a non-significant trend to a smaller AVA compared to patients with a normal geometry. These observations suggest that AS severity might need to be considered as a continuous variable, with each incremental increase in AS severity imposing an additional pressure load on the LV, thereby facilitating LV remodelling. In addition, it is important to notify that LV remodelling is not only a manifestation of the underlying AS, but rather an expression of the complex interaction between the LV myocardium, valvular afterload, and arterial afterload. In the current study, patients with moderate AS had a high prevalence of concomitant cardiovascular comorbidities, such as diabetes mellitus, arterial hypertension, coronary artery disease, and significant concomitant aortic and mitral regurgitation, which are all known to have an impact on LV remodelling (and the development of LV fibrosis) as well.9 However, as shown in this study, the clinical and echocardiographic presentation of patients with moderate AS already varies considerably with a large proportion of patients showing marked LV remodelling. Because different patterns of LV remodelling are closely related to prognosis, characterizing these patterns in patients with moderate AS is important in daily clinical practice. Whether these data should expand current indications for AVR before progression to severe AS and outweigh the risk of intervention remains uncertain, especially considering the high prevalence of concomitant cardiovascular comorbidities. Nonetheless, future trials investigating the risk-to-benefit ratio of AVR in patients with moderate AS at increased risk appear warranted. The PROGRESS Trial  (NCT 04889872) is currently recruiting patients to explore the hypothesis that transcatheter AVR could improve outcomes in patients with moderate AS.Current guidelines recommend AVR for patients with severe AS who are symptomatic or in whom LV systolic dysfunction develops in the absence of symptoms.The limitations of this study are inherent in its retrospective design. Evaluation of LVMi according to Devereux’s formula is based on geometrical assumptions and may not always be applicable . Echocardiographic measurements were not performed in an independent echocardiographic laboratory. A time span of 18 years was used for inclusion of patients to acquire the large cohort as presented. Specific indications for surgery during follow-up were not recorded in the present database. However, follow-up was performed by cardiologists with expertise in valvular heart disease and surgical decisions were made in accordance to current practice guidelines. Patients had a high prevalence of concomitant cardiovascular comorbidities, which could have an impact on LV remodelling. In addition, measuring the valvulo-arterial impedance could provide additional information, but the retrospective design precluded obtaining the necessary data for its calculation. All-cause mortality was chosen as the primary endpoint because the exact cause of death was not systematically recorded.Different patterns of LV remodelling are observed in patients with moderate AS with LV concentric hypertrophy being independently associated with all-cause mortality at long-term follow-up. Risk stratification according to the different patterns of LV remodelling may help to identify patients with moderate AS who are at increased risk of adverse events and may benefit from close monitoring and follow-up.European Heart Journal - Cardiovascular Imaging online.J.S. received funding from the European Society of Cardiology (ESC Training Grant App000064741). S.C.B. received funding from the European Society of Cardiology (ESC Research Grant App000080404). S.M.P. received funding from the European Society of Cardiology (ESC Training Grant T-2018-17405).jeac018_Supplementary_DataClick here for additional data file.


We aimed to describe the morphology of the border zone of viable myocardium surrounded by scarring in patients with Chagas heart disease and study their association with clinical events.Adult patients with Chagas heart disease  were included. Patients underwent high-resolution contrast-enhanced cardiac magnetic resonance using myocardial delayed enhancement with postprocessing analysis to identify the core scar area and border zone channels number, mass, and length. The association between border zone channel parameters and the combined end-point  was tested by multivariable Cox proportional hazard regression analyses. The significance level was set at 0.05. Data are presented as the mean (standard deviation [SD]) or median (interquartile range).A total of 44 border zone channels (1[1-3] per patient) were identified. The border zone channel mass per patient was 1.25 (0.48-4.39) g, and the extension in layers of the border zone channels per patient was 2.4 (1.0-4.25). Most border zone channels were identified in the midwall location. Six patients presented the studied end-point during a mean follow-up of 4.9 years (SD 1.6). Border zone channel extension in layers was associated with the studied end-point independent from left ventricular ejection fraction or fibrosis mass .High-resolution contrast-enhanced cardiac magnetic resonance can identify border zone channels in patients with Chagas heart disease. Moreover, border zone channel extension was independently associated with clinical events. Although this neglected disease occurs mainly in Latin America, it is increasingly recognized as a new public health challenge in non-endemic countries due to migration,Cardiac magnetic resonance imaging (MRI) permits the evaluation of the prognostic value of cardiac fibrosis in CHD. Indeed, cardiac fibrosis was reported to be associated with the occurrence of ventricular arrhythmiasHigh-resolution contrast-enhanced cardiac MRI (ce-CMR) precisely differentiates the scar core and the morphology of the border zone (BZ) of viable myocardium surrounded by the scar core and/or the mitral annulus, and that connect two areas of normal myocardiumIdentifying BZ channels in CHD is important since sudden death is the primary mode of death in CHDTherefore, our study aimed to evaluate if ce-CMR image postprocessing could identify BZ channels in patients with CHD and describe their morphology and association with clinical events.This paper is the continuation of a previous project on the study of cardiac MRI in patients with CHD with and without ventricular arrythmiasThe exclusion criteria were as follows: clinical history of another concomitant heart disease, atrial flutter/fibrillation, thyroid disease, chronic kidney disease, two or more risk factors for coronary artery disease, pregnancy, and any contraindication to undergo cardiac MRI.CHD classification criteria followed the Brazilian CD consensusPatients were clinically evaluated, had their epidemiological data collected, and underwent two-dimensional echocardiography, ECG, and treadmill exercise testing. Holter monitoring exams were completed for 14 patients at baseline. All exams for each patient were obtained within one month. After this evaluation was complete, patients were scheduled to undergo ce-CMR.The 12-lead ECG tracing was interpreted following the Minnesota Code Manual of Electrocardiographic Findings (modified for CD)All ce-CMRs were acquired using a 3.0-T Siemens Verio  equipped with a cardiac 12-element phased-array coil and advanced cardiac-dedicated software. The images obtained were stored de-identified into DICOM format for offline analysis.3). Images were acquired with 1.4 mm slice thickness with no space between slices up to the LV apex.The LV images were acquired during a 15 s inspiratory breath-hold to decrease breathing movement artifacts. Longitudinal and short axis LV images were acquired by two ECG-triggered pulse sequences at the same spots. LV diameters, volumes, and ejection fraction, right ventricular (RV) volume and ejection fraction, and left atrial (LA) volume were evaluated by cine-CMR using the steady-state free precession protocol. LV mass was the result of the multiplication of LV myocardial volume by its myocardial tissue density  to identify cardiac fibrosis. Fibrosis location and pattern were qualitatively determined. Fibrosis mass was calculated using a visual sub-segmental analysis as previously describedImages in the longitudinal and short axis projections were obtained using an inversion-recovery prepared gradient-echo for myocardial delayed enhancement (MDE) protocol 10 to 20 min after intravenous injection of 0.1 mmol/kg of gadolinium-based contrast (Dotaremhttp://www.gimias.org). The LV epicardial and endocardial borders were automatically traced using three anatomic landmarks  and manually corrected as needed.The postprocessing ce-CMR analyses were performed in Spain, as previously describedTwenty concentric surface layers  were created through the myocardial wall from the endocardium to the epicardium . A 3D shThe software enables the 3D identification of the core, BZ channel number, mass, location, and extension using a specific function to calculate the geodesic distance between two given points in a shell. The BZ was coded light blue, with the BZ channels coded white .The study end-point was a composite of cardiovascular death or ICD implantation. Patients were regularly followed up at Clementino Fraga Filho University Hospital during the study follow-up, and phone contact was made if a patient missed their clinical appointments. Additional Holter monitoring exams were performed whenever patients developed new symptoms of syncope or near syncope. Amiodarone was prescribed for all patients with: 1 - LV ejection fraction under 40% and non-sustained VT on Holter, and history of syncope or sustained VT or ventricular fibrillation (VF) inducible during electrophysiological study; 2 - sustained VT/VF associated with symptoms or not. Electrophysiological studies were performed in case of ICD implantation indication or the presence of non-sustained VT and LV ejection fraction under 40%. ICD implantation was indicated for all patients with either: 1-sudden cardiac arrest due to sustained VT/VF and LV ejection fraction under 35%; or 2-sustained VT and LV ejection fraction under 35%; or 3-non-sustained VT and LV ejection fraction under 35% and sustained VT/VF inducible during electrophysiological study.Death was classified as sudden if a previously stable patient died within 1 h of symptom onset, during sleep, or unwitnessed. Acute non-cardiac illness, drug overdose, terminal disease, metabolic causes, and vascular non-cardiac disease should be ruled out before the etiology was considered cardiact-test or Mann-Whitney test, as appropriate. Separate multivariable Cox proportional hazards regression analyses adjusting for LV ejection fraction and LV fibrosis mass were performed to test if the BZ channel parameters were associated with the studied end-point. LV ejection fractionCalculations were performed using MedCalc 12.5.0.0 statistical software. Normally distributed continuous variables are expressed as the mean and standard deviation (SD), while skewed distributed variables are expressed as the median (interquartile range). Kolmogorov-Smirnov tests demonstrated that the continuous variables were normally distributed if the obtained P-values were >0.10. Categorical variables are expressed as absolute and percentage values. Comparisons between groups were performed using an unpaired Student’s This study was approved by the institutional ethics committee of the Federal University of Rio de Janeiro , conforms to standards applied by the Brazilian National Committee for Research Ethics and Resolution 466/2012 of the National Health Council of the Ministry of Health, and complies with the Declaration of Helsinki, 1964, as revised in 1975, 1983, 1989, 1996, and 2000. All patients gave informed consent before participating.A total of 22 patients  were included in this study. Most of the patients were in the earlier stages of CHD (stage A or B1). Nine of these patients (40.9%) presented the associated digestive form. There was a similar sex distribution. Most patients were white, originated from the Northeast Brazilian region, and had arterial hypertension. The most common symptoms were palpitations, near syncope, and syncope .The most common ECG abnormalities were primary T wave changes, right bundle branch block, left anterior hemiblock, and premature ventricular complex . The mosThe LV volumes, end-diastolic diameter and ejection fraction, LA volume, and RV end-diastolic volume and ejection fraction are depicted in The fibrosis pattern was focal in 13 patients (59.1%), transmural in four (18.2%), and diffuse in five (22.7%). The number of walls with areas of fibrosis was 117 of 374 (31.3%), while the percentage of the walls presenting fibrosis areas was as follows: basal anteroseptal (31.8%), basal anterior (18.2%), basal anterolateral (36.4%), basal inferolateral (77.3%), basal inferior (45.4%), basal inferoseptal (18.2%), mid anteroseptal (18.2%), mid anterior (18.2%), mid anterolateral (36.4%), mid inferolateral (40.9%), mid inferior (18.2%), mid inferoseptal (22.7%), apical septal (27.3%), apical anterior (27.3%), apical lateral , apical inferior (27.3%), and apex (31.8%). The segmental fibrosis pattern was midwall in 82 segments, transmural in 32, subendocardial to midwall in two, and subepicardial to midwall in one.A total of 44 BZ channels were identified . One patSix patients presented the studied combined end-point during a mean follow-up of 4.9 years (SD 1.6). Five patients had cardiac sudden death, and two underwent ICD implantation due to inducible sustained VT during an electrophysiological study that was performed due to non-sustained VT and LV ejection fraction under 40%. One of the patients who underwent ICD implantation died 22 months after placement. Those patients who presented the studied end-point during the study follow-up had larger LV fibrosis mass, larger BZ channel mass, and higher BZ channel extension in layers at baseline .The results of the univariable analyses are depicted in BZ channel extension in layers was associated with the studied end-point independent from LV ejection fraction or LV fibrosis mass, while other BZ channel characteristics (mass and number) had a borderline univariable association with the studied end-point. However, the BZ channel mass and number were not associated with the studied end-point after multivariable analysis , and 5. To our knowledge, this is the first study to evaluate BZ channels and cardiac fibrosis by postprocessing ce-CMR analyses using ADAS-VT software in patients with CHD. This software performs a 3D analysis of the scar and BZ, allowing the identification of the conducting channels corresponding to the electrophysiological substrate of the VT isthmus,The architectural scar pattern in patients with coronary artery disease is pyramidal, with the subendocardial area being more extensive than the subepicardial area and a more significant number of BZ channels having a subendocardial location. Moreover, the BZ channels with a subepicardial location correspond to 35% of the BZ channels in transmural scar zones,-As sudden cardiac death (SCD) is the primary mode of death in CHDOne fact that could contribute to the mortality of patients with CHD despite ICD implantation is the large number of inappropriate versus appropriate shocks. In fact, among patients with CHD and ICD for secondary prophylaxis, those who received more shocks within 30 days had higher cardiac mortality rates,The small sample of patients and clinical events included in the current study limit the conclusions. The small number of events precluded the inclusion of other relevant adjustment variables, such as age, sex, and medications used, and may cause overfitting. The small sample size also did not allow the necessary statistical power to imply conclusions over variables not associated with the combined outcome. The BZ mass was not analyzed in this study. This variable was described by others as a predictor of cardiovascular outcomes in other clinical settingsIn this group of CHD patients, ce-CMR with ADAS-VT allowed the identification of BZ channels as well as their characteristics, precise location, and trajectory. Moreover, BZ channel extension was independently associated with the occurrence of clinical events. Our findings underscore the potential importance of BZ channel identification by ce-CMR for therapeutic guidance and identification of high-risk patients. Further studies are warranted in this area.


Early and accurate assessment of lumbar intervertebral disc degeneration (IVDD) is very important to therapeutic strategy. This study aims to correlate and compare the performances of T1ρ, T2 and T2* mapping for Pfirrmann grades and morphologic changes in the IVDD.This prospective study included 39 subjects with 195 lumbar discs. T1ρ, T2 and T2* mapping were performed, and T1ρ, T2 and T2* values of nucleus pulposus (NP), and anterior and posterior annulus fibrosus were measured. IVDD was assessed with Pfirrmann grading and morphologic changes . The performances of T1ρ, T2 and T2* relaxation times were compared for detecting early (Pfirrmann grade II-III) and advanced degeneration (Pfirrmann grade IV–V), as well as for morphologic changes.P < 0.01) for early IVDD, and the AUCs of T1ρ and T2 relaxation times for assessing advanced degeneration and morphologic changes were similar (P > 0.05) but significantly higher than that of T2*relaxation time (P < 0.01).T2 relaxation times was strongly corelated with T1ρ and T2* relaxation times. Areas under the curves (AUCs) of T1ρ, T2 and T2* relaxation times of NP were 0.70, 0.87 and 0.80 for early degeneration, and 0.91, 0.95 and 0.82 for advanced degeneration, respectively. AUCs of T1ρ, T2 and T2* relaxation times of NP were 0.78, 0.83 and 0.64 for bulging discs, 0.87, 0.89 and 0.69 for herniated discs, and 0.79, 0.82 and 0.69 for annular tearing, respectively. The AUC of T2 relaxation time was significantly higher than those of T1ρ relaxation times (both T2 mapping performed better than T1ρ mapping for the detection of early IVDD. T1ρ and T2 mapping performed similarly but better than T2* mapping for advanced degeneration and morphologic changes of IVDD.The online version contains supplementary material available at 10.1186/s12891-022-06040-y. Low back pain affects up to 40%–80% of the population at some point during their lifetime, with considerable negative impacts on quality of life and social economy , 2. InteMRI is an important tool for evaluating IVDD. The Pfirrmann semi-quantitative classification is the most widely used for visual grading of IVDD , which iIn recent years, various quantitative MRI have been applied to assess alterations of microenvironment of IVDD , such asSince T1ρ, T2 and T2* mapping have different mechanisms, thus they may have different sensitivity to compositional changes throughout IVDD , we hypoThe study was approved by the institute’s research ethics committee, and written informed consent was obtained from each participant prior to enrollment. Subjects with body mass index > 25, spinal fractures, tumors, infections, metabolic disease, previous lumbar disc surgery or interventional treatment, and contraindications for MR imaging were excluded. This study included 39 subjects  with single or recurrent episodes of low back pain and excluding other spine diseases except IVDD.All subjects underwent MRI in the morning to reduce the potential impact of diurnal changes in the discs. Lumbar MRI including sagittal T2-weighted imaging, T1ρ mapping, T2 mapping, T2* mapping and axial T2-weighted imaging were performed at 3.0 T scanner  with a dedicated 15-channel SENSE spine coil. The imaging parameters are shown in Table A total of 195 discs covering L1–L2 to L5–S1 were analyzed. The morphological analyses were performed by the consensus of 2 experienced radiologist without knowledge of the quantitative MRI measurements. The assessments included Pfirrmann classifications on sagittal T2-weighted images , as wellThe raw data of T1ρ mapping were fitted on a pixel-by-pixel basis to the exponentially decaying T1ρ function using IDL 6.3  to generate a T1ρ map, and the T2 and T2* maps were generated and analyzed by using Image J software . Regions of interest (ROIs) were manually placed on the NP, anterior annulus fibrosus (AAF) and PAF of the T1ρ, T2, and T2* maps  were calculated, and ICC values that were ≥ 0.75 were considered excellent agreement . WilcoxoP < 0.001). The T1ρ value in NP was significantly correlated with T2 and T2* values , but no significant correlation was observed in AF between T1ρ and T2 values (P > 0.05), neither between T1ρ and T2* values (P > 0.05). The T1ρ, T2 and T2* values for NP, AAF and PAF at each disc level were not significantly correlated with subject age (Tables EP = 0.02).The reproducibility between the two measurements for T1ρ, T2 and T2* relaxation times at different ROIs was excellent (ICCs = 0.88 ~ 0.93). The median values of NP and AF were 136.60 ms and 100.52 ms for T1ρ mapping, 93.53 ms and 36.99 ms for T2 mapping, and 46.05 ms and 21.18 ms for T2* mapping, respectively. There were significant differences in T1ρ, T2 and T2* values between NP and AF .Of all 195 discs, the Pfirrmann grades were categorized as: I, 32 (16.4%) discs; II, 64 (32.8%) discs; III, 52 (26.7%) discs; IV, 40 (20.5%) discs; and V, 7 (3.6%) discs. The Pfirrmann grade was significantly corelated with subject age .T1ρ, T2 and T2* relaxation times of NP and AF were summarized in Table P < 0.005) except for between grades I and II and between grades IV and V (both P > 0.005). For T2 relaxation times in NP, Kruskal–Wallis test and post-hoc tests showed significant differences between all of the Pfrrmann grades  except between grades IV and V (P > 0.005). Kruskal–Wallis test and post-hoc tests of the T2* relaxation time of NP showed significant differences between all pair-wise comparisons of Pfirrmann grades  except for between III and V and between grades IV and V (both P > 0.05).Regarding T1ρ relaxation times of NP, Kruskal–Wallis test and post-hoc tests showed significant differences between all pair-wise comparisons of Pfirrmann grades , but the AUCs of NP in T2 and T1ρ value were not significantly different from that in T2* values (adjusted P > 0.05). For assessing advanced IVDD, the AUC of NP in T2 value was significantly higher than that in T2* values (P < 0.001), but the AUCs of T2 and T1ρ values did not showed significant difference (adjusted P > 0.05). The AUC of NP in T1ρ value was significantly higher than that in T2* values (P = 0.004).The ROC curves of T1ρ, T2 and T2* relaxation times for early and advanced IVDD are presented in Fig. P < 0.01), while there were no significant differences between bulging discs and herniated discs in all the MRI parameters (P > 0.05).Of all 195 discs, 50 were labeled as bulging discs, 21 were herniated discs; 45 showed an HIZ in the PAF, reflecting annular tearing. T1ρ, T2 and T2* relaxation times of NP and AF for IVDD morphologic changes were showed in Table P < 0.01), and the AUCs of T1ρ and T2 relaxation times were significantly higher than that of T2* relaxation time (P < 0.01).The ROC curves of T1ρ, T2 and T2* relaxation times for morphologic changes of IVDD are presented in Fig. P < 0.01).Calculating a ROC for discriminating herniated discs from normal discs, the AUCs of T1ρ, T2 and T2* relaxation times of NP were 0.87 (95%CI: 0.81–0.94), 0.89 (95%CI: 0.83–0.94) and 0.69 (95%CI: 0.57–0.80), respectively. Furthermore, the AUCs of T1ρ and T2 relaxation times were significantly higher than that of T2* relaxation time (P < 0.01).Calculating a ROC for identifying HIZ of PAF from discs without tear, the AUC of T1ρ, T2 and T2* relaxation times of NP and T1ρ relaxation time of PAF were 0.79 (95%CI: 0.72–0.85), 0.82 (95%CI: 0.76–0.89) and 0.69 (95%CI: 0.61–0.77), respectively. In addition, the AUCs of T1ρ and T2 relaxation times of NP were significantly higher than that of T2* relaxation time  of NP and Pfirrmann grades, and T2 relaxation times was strongly corelated with T1ρ and T2* relaxation times. For identifying early IVDD (grade II-III), T2 mapping yielded greatest AUCs with high sensitivities, followed by T2* mapping and T1ρ mapping, indicating T2 mapping may be more accurate for the early disc degenerative changes. Additionally, T1ρ, T2 and T2* values of NP in normal discs differed significantly from those in bulging disc, herniated disc and annular tears. The AUCs of T1ρ and T2 mapping of NP were significantly higher than that of T2* mapping in detecting advanced IVDD (grade IV–V), bulging discs, herniated discs and annular tearing, implying T1ρ mapping and T2 mapping are more accurate than T2* mapping for late changes during IVDD.Our present finding is consistent with previous studies that T1ρ, T2 and T2* relaxation times of NP decreased linearly with increasing Pfirrmann grades , 21–23. With regard to advanced degeneration and morphologic changes of IVDD , the AUCs of NP in T2 and T1ρ mapping were similar (AUCs: 0.78–0.95) but significantly higher than that in T2* mapping AUCs: 0.64–0.82). With ongoing IVDD, hydrophilic glycosaminoglycans within the NP is reduced or absent, result in structural defects such as annular tears and disc herniation –0.82. Wi.Our results showed that T2 relaxation times was strongly correlated with T1ρ and T2* relaxation times. This may imply T2, T1ρ and T2* relaxation times are correlated to each other fundamentally, as all of them are associated with proteoglycan and water content , 19, 20.There are some limitations in present study. First, the number of patients included in this study was relatively small. However, power analysis depicted a minimum required number of 35 subjects with an alpha value of 0.05 and a specificity of 90%. Second, we only used Pfirrmann grade to assess IVDD, this grading system is subjective and cannot fully reflect the composition change during IVDD . MeanwhiIn conclusion, our resulted showed T2 mapping performed better than T1ρ mapping for the detection of early IVDD, and T1ρ and T2 mapping performed similarly but better than T2* mapping for advanced degeneration and morphologic changes of IVDD. T2 mapping may be of great utility for detecting the early and later changes of IVDD, as well as for monitoring the treatment response to emerging regeneration therapies.Additional file 1: Table E1. Correlation between subject age and T1ρ, T2* and T2 relaxation times of NP for each spinal level. Table E2. Correlation between age and T1ρ, T2* and T2 relaxation times of AAF for each spinal level. Table E3. Correlation between age and T1ρ, T2* and T2 relaxation times of PAF for each spinal level. Table E4. T1ρ, T2 and T2* relaxation times in AAF, PAF and AF for different Pfirrmann grades. Table E5. T1ρ, T2* and T2 relaxation times in AAF, PAF and AF for different Pfirrmann grades. Table E6. T1ρ, T2 and T2* relaxation times in AAF, PAF and AF for lumbar disc bulging, herniation and annular tears. Table E7. Diagnostic performance of T1ρ, T2 and T2* relaxation times in annulus fibrosus for lumbar disc bulging, herniation and annular tears.


MI) and microsphere (PMICRO) perfusion measurements were related through regression by PMI = 0.98 PMICRO + 0.03 (r = 0.97), while the MS (PMS) and microsphere (PMICRO) perfusion measurements were related by PMS = 0.62 PMICRO + 0.15 (r = 0.89). The accuracy of the MI and MS techniques in detecting functionally significant stenosis was 93% and 84%, respectively. The motion-immune (MI) perfusion technique provides accurate myocardial perfusion measurement in the presence of motion without image registration.The aim of this study was to validate a motion-immune (MI) solution to dynamic CT myocardial perfusion measurement, in the presence of motion without image registration. The MI perfusion technique was retrospectively validated in six swine (37.3 ± 7.5 kg) with a motion-susceptible (MS) perfusion technique performed for comparison. In each swine, varying severities of stenoses were generated in the left anterior descending (LAD) coronary artery using a balloon under intracoronary adenosine stress, followed by contrast-enhanced imaging with 20 consecutive volume scans per stenosis. Two volume scans were then systematically selected from each acquisition for both MI and MS perfusion measurement, where the resulting LAD and left circumflex (LCx) measurements were compared to reference microsphere perfusion measurements using regression and diagnostic performance analysis. The MI (P That said, CTA cannot assess myocardial perfusion in such low- to intermediate-risk patients2, where ischemia-guided coronary revascularization is superior to angiography-guided revascularization3. Hence, functional testing such as SPECT and CMR are recommended, but such modalities remain limited as they only provide metrics of relative perfusion5. Of course, dynamic PET has the highest accuracy for diagnosis of myocardial ischemia6, yet, radiotracer availability and cost largely limit its routine application. Thus, the ability of dynamic CT to assess perfusion and ischemia in quantitative terms (mL/min/g) is of clinical merit9. More importantly, evidence supports the combined or tiered use of coronary CTA with dynamic CT perfusion for morphological and physiological assessment of CAD12. That said, routine use of dynamic CT perfusion remains limited by the added contrast and radiation dose required to measure perfusion. Specifically, dynamic CT techniques rely on ECG-gated scanning of the myocardium over 10 to 20 heart beats. While ECG-gating ensures the same cardiac phase is captured for each scan; unfortunately, beat-to-beat variation and imperfect breath-holding necessitates image registration between consecutive acquisitions. Nevertheless, registration itself inherently alters the myocardial CT number, incurring errors in quantitative perfusion measurement. Moreover, dynamic CT perfusion techniques underestimate perfusion as compared to quantitative PET, especially under hyperemic conditions13, where such inaccuracies are further exacerbated by cardiac and respiratory motion despite registration14. Hence, a better solution to dynamic CT perfusion measurement remains necessary.Coronary artery disease (CAD) is the leading cause of mortality in the United States. Fortunately, coronary computed tomography angiography (CTA) can accurately detect or rule out high-grade CAD and is non-inferior to functional testing in patients with low- to intermediate-risk of CAD18. Yet, a remaining limitation of this motion-susceptible (MS) FPA technique is its reliance on image registration to minimize motion between the two volume scans of interest.Prior work in first-pass analysis (FPA) dynamic CT perfusion measurement has addressed some of these limitations via a new technique capable of accurate perfusion measurement with only two volume scans, where one volume scan may also double as a coronary CTAHence, this study aimed to validate a motion-immune (MI) solution to FPA dynamic CT perfusion measurement using quantitative microsphere perfusion measurement as the reference standard. The central hypothesis was that accurate myocardial perfusion measurement is feasible with the MI perfusion technique in the presence of motion without image registration.16, after which both techniques were compared to reference standard microsphere perfusion measurement. Of note, the raw data used were previously acquired to validate the MS perfusion technique with registration15, but the analysis and validation presented in this study are new and independent.The study was performed on six male Yorkshire swine (37.3 ± 7.5 kg). It was approved by the Institutional Animal Care and Use Committee at UC Irvine (IACUC Protocol Number: AUP-22-015) and was carried out in accordance with all relevant regulations, as well as in compliance with the ARRIVE guidelines. In each animal, several different intermediate severity balloon stenoses were generated in the left anterior descending (LAD) coronary artery, after which dynamic imaging was performed. The data were then processed, in the absence of image registration, using the motion-immune (MI) perfusion technique as well as the previously validated motion-susceptible (MS) perfusion techniqueAVG) is approximately proportional to the first-pass rate of contrast mass entry into the compartment over time (dMC/dt: in grams of Iodine per minute), normalized by the average incoming aortic blood pool contrast concentration (CIN: in grams of Iodine per milliliter of blood) and total left ventricular tissue mass (MT: in grams), assuming no contrast mass outflow at the time of measurement16. Importantly, since the mass of Iodine is related to the enhancement of tissue and blood by the same physical constant which cancels in ratio, only the tissue and blood enhancement  of two whole-heart volume scans acquired at the base and peak of the aortic enhancement (V1 and V2) are needed for perfusion measurement, where V1 is effectively a non-contrast volume scan while V2 is effectively a coronary CTA, as previously validated16. Differently, however, the integrated enhancement of V2 is determined by summating all myocardial enhancement values within V2. The integrated enhancement of V1 is then approximated by multiplying the average myocardial enhancement of V1 by the total number of myocardial voxels, n, within V2. Taken in difference, dMC/dt is calculated and normalized by the blood pool contrast concentration (CIN: the average aortic enhancement between V1 and V2) and total tissue mass  to yield the average perfusion (PAVG), shown in Eq. (AVG) is then calculated as the average difference in voxel values between the V2 and V1 volume scans. Finally, the average enhancement of V1 is subtracted per-voxel from V2 to estimate the voxel-by-voxel differences in myocardial enhancement between V1 and V2 (ΔHU*). In combination, MI perfusion (PMI) in mL/min/g is derived, as described by Eq.  were then placed in both femoral arteries, one carotid artery, both femoral veins, and one jugular vein. Using the femoral arterial sheaths, a pigtail catheter was placed into the left ventricular blood pool for injection of microspheres, while a multipurpose catheter was placed into the abdominal aorta for withdrawal of reference blood. Using the carotid arterial sheath, a Judkins right catheter was placed, after which a fractional flow reserve wire (FFR)  was advanced down the LAD. A balloon was then passed into the LAD to generate stenoses with incrementally increasing FFR severities of 1.0, 0.9, 0.8, 0.7, and 0.6 at maximal intracoronary hyperemia . Note that intracoronary hyperemia was used to minimize the hypotension and reflex tachycardia characteristic to intravenous adenosine, but limited stress perfusion measurement to the LAD alone. Next, the jugular vein sheath was set up for contrast injection, while the femoral vein sheaths were used for intravenous fluids and medications. Finally, the heart rate, end-tidal CO2, pulse oximetry, and arterial-line blood pressure were monitored continuously  and logged every 15 min. Using these metrics, the intravenous fluid drip rate, anesthesia depth, and ventilation settings were adjusted accordingly to maintain the mean-arterial pressure greater than 65 mmHg and pulse oximetry greater than 92% for adequate myocardial perfusion and tissue oxygenation, respectively. The animal setup is shown in Fig. Induction of anesthesia was accomplished with Telazol (4.4 mg/kg), Ketamine (2.2 mg/kg), and Xylazine (2.2 mg/kg), followed by maintenance with 1.5–2.5% Isoflurane . Introducer sheaths  was injected  then chased by saline (0.5 mL/kg at 7 mL/s) with one microsphere color also injected. Dynamic whole-heart volume scanning was then performed at 100 kVp and 200 mA, where each volume scan was acquired as a full projection with a rotation time of 0.35 s and 320 × 0.5 mm collimation . After each twenty-scan acquisition, a 15-min delay was observed. Then the stenosis severity was incrementally increased (as described above in 2.3), and the acquisition process was repeated, until all five of the available microsphere colors were used. The 32 cm diameter volumetric CT dose index . After all the microsphere colors had been injected, each animal was euthanized. Their hearts were surgically removed, and 10-g tissue plugs were extracted from the proximal and distal LAD, as well as from the left circumflex (LCx) perfusion territories. All tissue and blood samples were analyzed by IMT Laboratories.The 15.5 µm diameter NuFlow HydroCoat fluorescent microspheres (IMT Laboratories) were used as the reference standard for quantitative perfusion measurement in mL/min/g18. For V1, volumetric region growing was used to measure the average enhancement of the aortic blood pool . For V2, region growing was again used to measure the average enhancement of the aortic blood pool, while segmentation was used to extract and export the entire left ventricular myocardium. All data were then imported into custom in-house software for MI and MS perfusion calculation.All volume scans were reconstructed with AIDR 3D  at 75% of the R-R interval with a voxel size of 0.43 × 0.43 × 0.50 mm. The V1 and V2 volume scans were then systematically selected for analysisC/dt), was then normalized by the average incoming aortic blood pool contrast concentration (CIN) and left ventricular myocardium tissue mass (MT) to yield the average MI perfusion (PAVG_MI). Next, using the V2 segmentation, the average enhancement of the V1 myocardium was subtracted from each voxel of V2 (ΔHU*). Each voxel value was then normalized by the difference in average enhancement between the V2 and V1 myocardium (ΔHUAVG) to yield a perfusion ratio map. The average MI perfusion (PAVG_MI) was then multiplied by the perfusion ratio map (ΔHU*/ ΔHUAVG) to yield voxel-by-voxel MI perfusion measurements (PMI).The integrated enhancement of V2 was first determined by summating all the myocardial enhancement values within the segmented left ventricular myocardium. Next, volumetric region growing was used to measure the average enhancement of the lateral wall of the V1 myocardium, which approximated the average enhancement of the total V1 myocardium. The integrated enhancement of V1 was then estimated by multiplying the average enhancement of the lateral wall of the V1 myocardium by the total voxel volume of the segmented myocardium from V2. The total difference in integrated enhancement between V2 and V1 (dMC/dt) was then determined through image subtraction. After which, normalization by the average incoming aortic blood pool contrast concentration (CIN) and left ventricular myocardium tissue mass (MT) was performed to yield the average MS perfusion (PAVG_MS). Next, each voxel of the V1 myocardium was subtracted from each corresponding voxel of V2 (ΔHU) then normalized by the difference in average enhancement between the V2 and V1 myocardium (ΔHUAVG), yielding a perfusion ratio map. The average MS perfusion (PAVG_MS) was then multiplied by the perfusion ratio map (ΔHU/ ΔHUAVG) to yield voxel-by-voxel MS perfusion measurements (PMI).The segmented myocardium of V2 was applied as a binary mask to segment the myocardium of V1. The difference in integrated enhancement between V2 and V1 . P-values less than 0.05 indicate significant differences. Statistical software was used .As multiple measurements were made per animal, the intra-cluster correlation of measurement was first computed and found to be 0.12. Hence, there was minimal correlation between intra-animal measurements, i.e., all measurements were treated as independent. Overall, MI and MS measurements were compared to microsphere measurements with t-testing, regression, Bland–Altman, Pearson’s correlation coefficient (r), Lin’s concordance correlation coefficient (CCC), root-mean-square-error (RMSE: accuracy), and root-mean-square deviation (RMSD: precision). The diagnostic performance of the MI and MS techniques in identification of functionally significant stenoses, i.e., LAD microsphere perfusion less than 1.0 mL/min/g at hyperemiaThe average body mass of the six male Yorkshire swine was 37.3 ± 7.5 kg, where the average left ventricular mass of the swine was 52.1 ± 12.7 g. During image acquisition, the average heart rate of the swine was 73 ± 5 beats per minute, while their average mean arterial blood pressure was 73 ± 10 mmHg. Following image acquisition and image processing, the average time delay between the V1 and V2 volume scans was 4.7 ± 1.2 s, corresponding to an average change in myocardial enhancement over that time of 25.0 ± 13.5 HU.For the LAD coronary artery, the average MI perfusion was 2.60 ± 1.94 mL/min/g, the average MS perfusion was 1.79 ± 1.34 mL/min/g, and the average microsphere perfusion was 2.62 ± 1.94 mL/min/g, where the result of corresponding t-testing was p = 0.72 and p = 0.00, respectively. For the LCx coronary artery, the average MI perfusion was 0.85 ± 0.40 mL/min/g, the average MS perfusion was 0.67 ± 0.56 mL/min/g, and the average microsphere perfusion was 0.87 ± 0.34 mL/min/g, where the result of corresponding t-testing was p = 0.75 and p = 0.05, respectively. Notably, LAD perfusion measurements were performed during intracoronary hyperemia (stress flow), while LCx perfusion measurements were not (rest flow).MI) to microsphere perfusion (PMICRO) was PMI = 0.98 PMICRO + 0.03, where the Pearson’s and Lin’s correlations were r = 0.97 and ρ = 0.97, respectively, while the RMSE and RMSD were 0.42 mL/min/g and 0.42 mL/min/g, respectively. Alternately, the regression equation relating MS perfusion (PMS) to microsphere perfusion (PMICRO) was PMS = 0.62 PMICRO + 0.15, where the Pearson’s and Lin’s correlations were r = 0.89 and ρ = 0.77, respectively, while the RMSE and RMSD were 1.07 mL/min/g and 0.58 mL/min/g, respectively. All regression analyses are listed in Table The regression equation relating MI perfusion .MI perfusion measurement agreed well with microsphere perfusion measurement, with near unity regression slope, excellent Pearson’s and Lin’s correlation, and minimal RMSE and RMSD. MI perfusion measurement also identified functionally significant stenoses with high accuracy, while only requiring two volume scans per measurement. Hence, accurate myocardial ischemia assessment, in the presence of motion without image registration, is feasible at a low dose  leading to higher false positive rates, reduced specificity, and increased positive predictive value14. Of course, static CT perfusion techniques are less impacted, only displaying gantry rotational-motion induced blurring, but dynamic techniques perform superiorly in detection of intermediate severity CAD, especially under stress conditions24. Yet, even dynamic techniques, such as the maximum slope model, underestimate perfusion, since they rely on small tissue volumes-of-interest (VOI) for measurement, where these VOIs are subject to contrast mass entry and exit over the measurement time, especially at hyperemia. Whereas the MI technique defines the entire myocardium as a single large VOI, where measurements are made prior to hyperemic transit; thus, solving the problem of perfusion underestimation. Hence, the MI technique represents a “best-of-both-worlds” solution as it provides the diagnostic advantages of dynamic CT perfusion, while mathematically eliminating the negative impacts of motion and registration.Notably, the MS perfusion technique was previously validated versus microsphere perfusion, using fully co-registered, motion-corrected data. As a result of registration, the RMSE, RMSD, and diagnostic performance were all improved as compared to the present MS technique without registration. Hence, image registration does improve the accuracy of dynamic CT perfusion measurement in the presence of motion between image acquisitions. However, the MI perfusion technique, in the absence of registration, demonstrated a lower RMSE and RMSD with better diagnostic performance than the MS perfusion technique both 25, where spotty myocardial calcifications may also be present (rarely)26. Hence, in the case of scar, both rest and stress perfusion may be underestimated, but the relation between coronary flow reserve and stress perfusion, i.e., coronary flow capacity, can be used to accurately discriminate scar from ischemia27.While referred to as “motion-immune,” it is important to note that the MI perfusion technique does not eliminate gantry motion blurring, which is inherent to cardiac CT image acquisition. Nevertheless, for motion between consecutive acquisitions caused by beat-to-beat variation (as in this study) or by imperfect breath-holding (to be studied in future work), the mathematics of the MI technique effectively eliminate the impact of such motion; thus, bypassing the need for and errors inherent to image registration. Additionally, the MI perfusion theory assumes that the unenhanced myocardial tissue density is relatively uniform within V1, i.e., that the average myocardial enhancement approximates the per-voxel enhancement with minimal variance. While this assumption holds true for patients without a prior history of myocardial infarction, chronically infarcted myocardium is known to be hypoattenuating secondary to reduced capillary density with increased adiposity28. Alternatively, dynamic bolus tracking combined with a peak timing relation enables acquisition of V2 at approximately the aortic peak (within ± 2 cardiac cycles) while maintaining perfusion measurement accuracy29. In both cases, future clinical implementation will also require incorporation of breath-holding, to be initiated directly after contrast injection but before acquisition of V1, with exhalation after acquisition of V2. Meaning, V1 and V2 should be acquired during the same breath hold. Fortunately, such breath-holding is easily prompted on most clinical CT scanners and should not pose an issue to translation of the MI technique.Dynamic scanning was intentionally performed over many cardiac cycles to retrospectively develop and validate the two-volume MI technique. Hence, prospective validation remains necessary, and will require specialized acquisition timing of V1 and V2 at the base and peak of the aortic enhancement. Fortunately, a diluted test bolus protocol can be used, but requires extra contrast and radiation dose15, while this study only assessed perfusion in the LAD and LCx territories within the left ventricle. Specifically, image registration of V1 and V2 enables maximum intensity projection (MIP) image generation, where the resulting biventricular opacification can be used for segmentation of the main wall of the right ventricular for RCA perfusion measurements15. Without registration, however, only left ventricular segmentation can be performed. That said, if a triphasic injection protocol were to be employed, left and right ventricular opacification can be achieved within the V2 volume scan alone30, enabling biventricular perfusion measurement. Moreover, regarding the perfusion territories assessed, spatially matched virtual tissue plugs were used primarily for perfusion validation. In practice, however, minimum-cost-path perfusion territory or sub-territory assignment will be used for automatic delineation of the coronary perfusion territories, as previously validated31.Additionally, prior work assessed perfusion in the LAD and LCx territories of the left ventricle along with the RCA territory of the right ventricle15 were discussed above. Additionally, as the raw data were previously acquired15, the limitations attributed to study design—central contrast injection, intracoronary adenosine, coronary balloon stenosis, small effective chest diameter, and acquisition timing—were all already addressed in detail and did not significantly impact the results of this work29.Finally, this study did not evaluate the impact of different registration algorithms on perfusion measurement accuracy. However, our prior CT perfusion results that employed image registrationThe motion-immune FPA perfusion technique provides a solution to dynamic CT perfusion measurement in the presence of motion without image registration. By eliminating image registration and using only two volume scans for dynamic CT perfusion measurement, the motion-immune perfusion technique can improve the quantitative accuracy of CT-based CAD risk assessment while also reducing the radiation dose.