Background: QRS duration and morphology are associated with poor prognosis in many different populations, but the predictive value, particularly of the risk of sudden cardiac death (SCD), in asymptomatic patients with aortic stenosis (AS) has not been well studied. Methods: Clinical examination, electrocardiography and echocardiography were obtained in 1,873 asymptomatic AS patients randomized to simvastatin/ezetimibe combination vs. placebo in the Simvastatin and Ezetimibe in Aortic Stenosis (SEAS) study. Association of QRS duration, evaluated as a categorical variable of <85 msec vs. 85-99 msec and ≥100 msec (excluding bundle branch block [BBB]) and QRS morphology in those with BBB, with the risk of cardiovascular morbidity and mortality was assessed by adjusting for biomarkers, clinical- and echocardiographic covariates as well as randomized treatment. Results: QRS data were available in 1,542 patients; followed for a mean of 4.3±0.8 years (6,631 patients-years of follow-up). QRS duration was <85 msec in 900 patients (58.4%), 85-99 msec in 396 (25.7%), ≥100 msec without BBB in 144 (9.3%) and 102 (6.6%) had BBB. In multivariable analyses, those with QRS duration ≥100 msec had, compared to those with QRS duration <85 msec, a 4.9-fold higher risk of sudden cardiac death (95% confidence interval [CI], 1.4 to 16.9, p=0.01) and a 2.7-fold higher risk of cardiovascular death (CI, 1.3 to 5.8, p=0.01). In univariate analyses, left BBB (n=43) was, compared to QRS duration <85 msec, associated with a 3.8-fold higher risk heart failure and right BBB combined with left anterior fascicular block (n=20) with a 4.6-fold higher risk of myocardial infarction (both p<0.05). Conclusion: QRS duration and morphology in asymptomatic patients with AS are independently associated with poor prognosis, particularly the risk of SCD. Figure : Incidence of Sudden Cardiac Death According to Baseline QRS Duration and Morphology: During 4.3 Years of Follow-Up.