Long-term clinical response of cardiac resynchronization after chronic right ventricular pacing.

Chronic right ventricular (RV) pacing might elicit unpredictably deleterious effects on left ventricular (LV) function similar to that of native left bundle branch block (LBBB). The objective of the present study was to evaluate the clinical and echocardiographic response to cardiac resynchronization therapy after years of chronic RV pacing. In this prospective observational study of 284 consecutive patients, cardiac resynchronization therapy was performed in 194 patients (68%) with a native LBBB and in 90 patients (32%) with a pacing-induced LBBB after chronic RV pacing (upgraded group). Echocardiographic and clinical parameters were evaluated in both groups at baseline and during 2 years of follow-up. The clinical response was defined as survival with improvement of > or =1 in the New York Heart Association class without heart failure hospitalization. Reverse LV remodeling was defined as LV end-systolic volume reduction of > or =15%. At baseline, the New York Heart Association class, quality of life, and exercise capacity were comparable but the LV ejection fraction was significant greater and the LV volumes were significant smaller in the upgraded group. Changes with time in the clinical parameters, echocardiographic parameters, and clinical response were not significantly different between the 2 groups. Reverse LV remodeling was observed in 86% in the upgraded group versus 78% of the native LBBB group after 1 year (p = 0.39). Survival was not significantly different between the 2 groups. In conclusion, comparable clinical and echocardiographic improvement was seen when resynchronization therapy was applied in patients with preceding chronic RV pacing compared with patients with a native LBBB.