the clinical implications of left axis deviation ( lad ) in patients with left bundle branch block ( lbbb ) have not been clearly elucidated . some studies have reported that patients with lad do not have a significantly different prognosis compared with patients with a normal qrs axis,1)2)3 ) while others have shown that patients with lad have a higher incidence of conduction abnormalities and a poor prognosis , including cardiovascular death.4)5)6 ) regardless of the differences in prognosis , previous studies have proposed that diseased myocardium is a plausible mechanism for axis deviation.3)4 ) the selvester qrs scoring system evaluates myocardial scarring based on 12-lead electrocardiogram ( ecg ) readings and has been updated for extensive application : it can be used to evaluate patients with bundle branch block and also those with pacing rhythm.7)8)9 ) the 12-lead ecg has valuable clinical significance and has been validated with cardiac magnetic resonance imaging.10)11 ) furthermore , since the 12-lead ecg is a widely used diagnostic tool that is highly accessible , the myocardial scar score derived from ecg may be valuable in clinic environments . in this study , the association between the qrs axis and the myocardial scar score was investigated in patients with lbbb . in addition , the importance of a left axis deviation concomitant with lbbb was evaluated . this was a retrospective , observational cohort study . from october 2004 to june 2014 , 829 patients were evaluated by 12-lead ecg and diagnosed with lbbb at seoul national university hospital ( seoul , korea ) . one hundred five patients were excluded because they did not have ecg results available for review , or they had been misdiagnosed with lbbb . an additional 410 patients were excluded due to one or more of the following : severe valvular heart disease , presence of an implantable cardiac defibrillator or cardiac resynchronization therapy ( crt ) device , history of cardiac surgery or intervention , ischemic heart disease documented by imaging studies , symptoms of ischemic heart disease or heart failure , or previously proven cardiomyopathy or myocarditis ( fig . we obtained demographic data , data on the presence of underlying diseases , clinical presentation , laboratory test results , and the initial diagnosis of lbbb from the hospital electronic medical records . blood sampling and tests were performed as part of routine practice by laboratories certified by the korean association of quality assurance for clinical laboratory . the criteria for diagnosing lbbb by 12-lead ecg were defined as : qr or rs in leads v1 or v2 ; mid - qrs notching or slurring in 2 of leads v1 , v2 , v5 , v6 , i , and avl ; and qrs duration 140 ms ( male ) or 130 ms ( female).12)13 ) normal axis was defined as -30 r axis < 90. in addition to information on gender and age , a myocardial scar score was calculated according to the previously reported selvester scoring protocol , which was applicable for lbbb patients.8)10 ) the primary endpoint was any major adverse cardiovascular event ( mace ) , defined as a composite of sustained ventricular tachycardia or ventricular fibrillation , pacemaker implantation due to complete atrioventricular block , crt implantation , hospital admission due to heart failure , or cardiovascular death . data are described as meanstandard deviation for continuous variables and as numbers and frequencies for categorical variables . the  test or fisher 's exact test was applied for categorical variables , and an unpaired student 's t - test was used for continuous variables . a receiver - operating - characteristics curve was used to evaluate the predictive power of the myocardial scar score on lad . kaplan - meier estimates were applied to evaluate the chronological inclination of outcomes , and the log - rank test was used to analyze the differences between groups ( subjects with lad , subjects with normal axis ) . a multivariable cox proportional - hazards regression model variables associated with mace with p<0.1 in the univariate analysis were included as confounding factors in the multivariate analysis . this was a retrospective , observational cohort study . from october 2004 to june 2014 , 829 patients were evaluated by 12-lead ecg and diagnosed with lbbb at seoul national university hospital ( seoul , korea ) . one hundred five patients were excluded because they did not have ecg results available for review , or they had been misdiagnosed with lbbb . an additional 410 patients were excluded due to one or more of the following : severe valvular heart disease , presence of an implantable cardiac defibrillator or cardiac resynchronization therapy ( crt ) device , history of cardiac surgery or intervention , ischemic heart disease documented by imaging studies , symptoms of ischemic heart disease or heart failure , or previously proven cardiomyopathy or myocarditis ( fig . we obtained demographic data , data on the presence of underlying diseases , clinical presentation , laboratory test results , and the initial diagnosis of lbbb from the hospital electronic medical records . blood sampling and tests were performed as part of routine practice by laboratories certified by the korean association of quality assurance for clinical laboratory . the criteria for diagnosing lbbb by 12-lead ecg were defined as : qr or rs in leads v1 or v2 ; mid - qrs notching or slurring in 2 of leads v1 , v2 , v5 , v6 , i , and avl ; and qrs duration 140 ms ( male ) or 130 ms ( female).12)13 ) normal axis was defined as -30 r axis < 90. in addition to information on gender and age , a myocardial scar score was calculated according to the previously reported selvester scoring protocol , which was applicable for lbbb patients.8)10 ) the primary endpoint was any major adverse cardiovascular event ( mace ) , defined as a composite of sustained ventricular tachycardia or ventricular fibrillation , pacemaker implantation due to complete atrioventricular block , crt implantation , hospital admission due to heart failure , or cardiovascular death . data are described as meanstandard deviation for continuous variables and as numbers and frequencies for categorical variables . the  test or fisher 's exact test was applied for categorical variables , and an unpaired student 's t - test was used for continuous variables . a receiver - operating - characteristics curve was used to evaluate the predictive power of the myocardial scar score on lad . kaplan - meier estimates were applied to evaluate the chronological inclination of outcomes , and the log - rank test was used to analyze the differences between groups ( subjects with lad , subjects with normal axis ) . a multivariable cox proportional - hazards regression model was used to investigate the independent prognostic indicators of mace . variables associated with mace with p<0.1 in the univariate analysis were included as confounding factors in the multivariate analysis . statistical tests were performed using ibm spss statistics version 22 ( spss inc . , chicago , il , usa ) . the mean age was 68 years , 105 patients ( 33% ) were male , 107 patients ( 34% ) had hypertension , 89 patients ( 28% ) had diabetes mellitus , and 32 patients ( 10% ) had dyslipidemia . when classified according to qrs axis , a total of 91 patients ( 29% ) were classified with lad , and the remaining 71% had a normal axis . the meanstandard deviation myocardial scar score was 3.62.0 for the normal axis group and 5.12.0 for the lad group . the lbbb patients with normal qrs axis were younger and had comparable prevalence of hypertension , diabetes mellitus , and dyslipidemia to those with left axis deviation . there was a significant inverse correlation between the myocardial scar score and the qrs axis ( r=-0.356 , p<0.001 ) ( fig . the myocardial scar score was also significantly associated with age ( r=0.184 , p=0.001 ) and hemoglobin level ( r=-0.165 , p=0.007 ) ; it was not correlated with body mass index ( r=-0.028 , p=0.627 ) , total cholesterol level ( r=-0.039 , p=0.526 ) , or serum creatinine level ( r=0.040 , p=0.504 ) . in the roc curve analysis , the area under the curve of the myocardial scar score to predict lad was 0.700 ( 95% ci 0.639 - 0.761 , p<0.001 ) ( fig . the median follow - up duration was 30 months ( interquartile range : 6 to 63 months ) . during the follow - up period , 10 of 314 patients died ( including two cardiovascular deaths caused by ventricular fibrillation ) . four patients underwent pacemaker implantation due to complete atrioventricular block , and two patients were admitted to the hospital due to de novo acute heart failure ( table 2 ) . stratification according to the qrs axis indicated that patients in the lad group were older and demonstrated a higher incidence of mace compared with patients with a normal axis ( 5.5% vs. 1.3% , log - rank p=0.010 ) ( fig . lad was a significant prognostic indicator of mace in the univariate analysis [ hazard ratio ( hr ) 5.400 ; 95% confidence interval ( ci ) 1.281 - 22.758 ; p=0.022 ] , while myocardial scar score failed to show prognostic implication ( hr 0.877 ; 95% ci 0.619 - 1.243 ; p=0.460 ) . the lad predictive value was marginally attenuated in multivariate analysis ( hr 4.117 ; 95% ci 0.955 - 17.743 , p=0.058 ) after adjusting for the confounding variables of age , sex , and diabetes mellitus ( table 3 ) . the mean age was 68 years , 105 patients ( 33% ) were male , 107 patients ( 34% ) had hypertension , 89 patients ( 28% ) had diabetes mellitus , and 32 patients ( 10% ) had dyslipidemia . when classified according to qrs axis , a total of 91 patients ( 29% ) were classified with lad , and the remaining 71% had a normal axis . the meanstandard deviation myocardial scar score was 3.62.0 for the normal axis group and 5.12.0 for the lad group . the lbbb patients with normal qrs axis were younger and had comparable prevalence of hypertension , diabetes mellitus , and dyslipidemia to those with left axis deviation . there was a significant inverse correlation between the myocardial scar score and the qrs axis ( r=-0.356 , p<0.001 ) ( fig . the myocardial scar score was also significantly associated with age ( r=0.184 , p=0.001 ) and hemoglobin level ( r=-0.165 , p=0.007 ) ; it was not correlated with body mass index ( r=-0.028 , p=0.627 ) , total cholesterol level ( r=-0.039 , p=0.526 ) , or serum creatinine level ( r=0.040 , p=0.504 ) . in the roc curve analysis , the area under the curve of the myocardial scar score to predict lad was 0.700 ( 95% ci 0.639 - 0.761 , p<0.001 ) ( fig . the median follow - up duration was 30 months ( interquartile range : 6 to 63 months ) . during the follow - up period , 10 of 314 patients died ( including two cardiovascular deaths caused by ventricular fibrillation ) . four patients underwent pacemaker implantation due to complete atrioventricular block , and two patients were admitted to the hospital due to de novo acute heart failure ( table 2 ) . stratification according to the qrs axis indicated that patients in the lad group were older and demonstrated a higher incidence of mace compared with patients with a normal axis ( 5.5% vs. 1.3% , log - rank p=0.010 ) ( fig . lad was a significant prognostic indicator of mace in the univariate analysis [ hazard ratio ( hr ) 5.400 ; 95% confidence interval ( ci ) 1.281 - 22.758 ; p=0.022 ] , while myocardial scar score failed to show prognostic implication ( hr 0.877 ; 95% ci 0.619 - 1.243 ; p=0.460 ) . the lad predictive value was marginally attenuated in multivariate analysis ( hr 4.117 ; 95% ci 0.955 - 17.743 , p=0.058 ) after adjusting for the confounding variables of age , sex , and diabetes mellitus ( table 3 ) . the study analysis indicated that the qrs axis of lbbb patients was associated with the myocardial scar score , and lad concomitant with lbbb was a prognostic indicator of mace . the clinical prognostic importance of lad in lbbb patients has been reported in numerous studies ; however , the results remain controversial.1)2)3)4)5)6)14)15 ) a recent study designed to include subjects without clinical cardiovascular disease reported that lad was associated with a higher risk of mortality and cardiovascular disease regardless of concomitant lbbb.16 ) the reason for the different prognostic impact between studies , including ours , may be explained by the different study populations , definition of lad , and study period ( table 4 ) . although the exact mechanism for developing lad is still uncertain , it has been suggested that comorbidities such as hypertension and diabetes mellitus exert an influence and result in conduction disturbance of fascicles and the main left bundle.3)16 ) in addition to prolonged and asynchronous contraction due to concomitant lbbb , this could also cause poor clinical outcomes . myocardial scarring is generated by both ischemic and nonischemic damage.17)18)19 ) the electrical depolarization initiates from the free and septal walls of the right ventricle in lbbb patients , but this vector may be interrupted and recorded differently in an ecg if myocardial scarring is present.8 ) because myocardial scarring is considered to be a cumulative indicator reflecting myocardial damage , we speculated that the qrs axis is related to the myocardial scar score . the selvester qrs score , a quantitative scoring system calculated from 12-lead ecg , can be used to estimate the myocardial scar amount in the left ventricle . the scoring system was established to estimate the myocardial infarct size and has been improved and updated for applications in various conditions , including lbbb.7)8)9)10 ) in lbbb patients , the myocardial scar calculated by the selvester qrs score and that measured by cardiac magnetic resonance imaging were significantly correlated ( r=0.80 , p<0.001 ) and showed a mean difference of 7.6% overestimation . in regard to reproducibility , absolute differences of 0.4 and 0.6 myocardial scar scores were observed in intraobserver and interobserver examination , respectively . the intraobserver and interobserver agreement were =0.96 and =0.86 , respectively , in a previous report.10 ) in this study , we measured the myocardial scar with the selvester qrs scoring system based on the accuracy and reproducibility of the test . our data was similar to previous studies that investigated the prognosis of patients with lbbb and lad and demonstrated a significant negative correlation between the myocardial scar score and the qrs axis in patients with lbbb . despite the significant inverse relationship between myocardial scar score and qrs axis , a high myocardial scar score was not a statistically significant prognostic indicator , in contrast to the presence of lad in lbbb patients ( table 3 ) . results have indicated that lad , not the myocardial scar score , was a prognostic indicator in lbbb patients , and that lad might be partially influenced by myocardial scarring as well as by other confounding pathologic factors . this was a retrospective cohort study , rather than a prospective cohort study ; therefore , there could be unmeasured confounding variables that influenced the results . additionally , although we only included asymptomatic patients who did not have abnormal cardiac imaging studies , we were not able to completely eliminate patients had asymptomatic structural or functional heart disease who therefore did not undergo a cardiac evaluation before the recruitment . finally , the r / s or r / q ratio at lead ii was included in the selvester qrs scoring system , suggesting that patients with lad had higher myocardial scar scores . however , the myocardial scar score difference between the two groups was larger than the scoring point of lead ii . concomitant lad is a prognostic indicator that can predict poor prognosis for patients with lbbb and may be associated with greater myocardial scarring . there was a significant inverse correlation between the qrs axis and the myocardial scar score based on 12-lead ecg results . this was a retrospective cohort study , rather than a prospective cohort study ; therefore , there could be unmeasured confounding variables that influenced the results . additionally , although we only included asymptomatic patients who did not have abnormal cardiac imaging studies , we were not able to completely eliminate patients had asymptomatic structural or functional heart disease who therefore did not undergo a cardiac evaluation before the recruitment . finally , the r / s or r / q ratio at lead ii was included in the selvester qrs scoring system , suggesting that patients with lad had higher myocardial scar scores . however , the myocardial scar score difference between the two groups was larger than the scoring point of lead ii . concomitant lad is a prognostic indicator that can predict poor prognosis for patients with lbbb and may be associated with greater myocardial scarring . there was a significant inverse correlation between the qrs axis and the myocardial scar score based on 12-lead ecg results .