Purpose:The right ventricular(RV) apical pacing results in progressive left ventricular(LV) dysfunction and contributes to the development of heart failure.In MOST trials, increased heart failure hospitalization was associated with the prevalence of more than 40% RV pacing. This study aimed to assess the prevalence and clinical predictors for development of LV systolic dysfunction after long-term RV apical pacing in acquired atrioventricular block who require permanent pacing. Methods:We studied the clinical outcomes after long-term (>90% ventricular pacing during >6 months) RV apical pacing for acquired AV block in 60 patients without LV systolic dysfunction(EF>50%). We compared age, sex, history of diabetes, hypertension and coronary artery disease, paced QRS duration(pQRSd) and echocardiographic parameters between LV systolic dysfunction and normal LV function. The LV dysfunction was defined as EF<50% at follow-up echocardiography. Results:The mean follow up duration was 64.8짹35.8 months. The patients with LV systolic dysfunction (21 pts) had significantly lower LVEF, larger LV systolic dimension, wider pQRSd and higher incidence of new-onset atrial fibrillation than normal LV function(39 pts). Multivariate analysis showed a LVEF at implant (HR 0.908, p=0.027) and paced QRS duration(HR 1.039, p=0.055) were independent predictors for development of LV systolic dysfunction. Conclusions:The permanent RV apical pacing was associated with LV systolic dysfunction in 35% of patients. The LVEF at implant and pQRSd might predict LV systolic dysfunction.