Different Response to Cardiac Resynchronization Therapy by QRS Duration in the Patients with Chronic Right Ventricular Pacing

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Background: Effect of upgrade from permanent right ventricular (RV) apical pacing to biventricular (BiV) pacing has not yet delineated. Aims: The aim of this study is to investigate the role of upgrade from RV pacing to BiV pacing. Methods: Sixty four patients with NYHA>class 2 heart failure and LV ejection fraction (LVEF)<35% were divided into two groups: Group-A (primary BiV pacing in 40 patients with intrinsic QRS>130 msec) and group-B (upgrade to BiV pacing in 24 patients with bradycardia and paced-QRS>150 msec). The LV volume and systolic function were assessed with echocardiography at baseline and 6 months after implantation of a cardiac resynchronization (CRT) device. A reduction in LV end systolic volume (LVESV)>15% was defined as responder. Results: LVESV reduced significantly in group-A (204.7 ml to 181.6 ml, P<0.05) and in group-B (152.6 ml to 124.4 ml, P<0.05). Additionally, the reduction in LVESV showed positive correlation with paced-QRS duration at baseline (r=0.46, P<0.05) in group-B. Responder rate was not different in both groups (50.5% vs. 62.5%, P=0.23). Conclusion: CRT upgrade from chronic RV apical pacing is also effective especially in patients with wider QRS duration.