Interventricular Electrical Delay Is Predictive of Response to Cardiac Resynchronization Therapy.

OBJECTIVES This study was conceived to evaluate the relationship between interventricular electrical delay, as measured by the right ventricle-left ventricle (RV-LV) interval, and outcomes in a prospectively designed substudy of the SMART-AV (SMARTDELAY determined AV Optimization) trial. BACKGROUND Despite the well-documented benefit of cardiac resynchronization therapy (CRT), the nonresponder rate remains an important clinical problem. Implanting LV leads by traditional anatomic criteria has limited impact on outcomes. However, pacing at sites with late electrical activation improves CRT response rates. Thus, we hypothesized that interventricular electrical delay is associated with improved CRT outcomes. METHODS This was a multicenter study of patients with advanced heart failure undergoing CRT implantation. In 419 subjects, the unpaced RV-LV interval was measured in sinus rhythm. LV volumes and ejection fraction were measured by echocardiography at baseline and after 6 months of CRT by a blinded core laboratory. Quality of life (QOL) was assessed by a standardized questionnaire. RESULTS When separated by quartiles based on interventricular delay, the magnitudes of LV volumes, ejection fraction and the QOL measure increased significantly with prolongation of RV-LV delay (p < 0.05). The LV end-systolic volume response rate increased progressively from 30% to 75% (p < 0.001), and the QOL response rate increased from 50% to 65% (p = 0.08). Patients in the highest quartile of RV-LV had a 5.98-fold increase (p < 0.001) in their odds of a reverse remodeling response, with female sex, ischemic etiology, and baseline LV end-systolic volume being the other independent predictors of response. CONCLUSIONS Baseline interventricular delay is a potent independent predictor of remodeling and QOL responses with CRT.