Cardiac Resynchronization Therapy in Patients With Intrinsic and Right Ventricular Pacing-Induced Left Bundle Branch Block Pattern

We studied 95 consecutive patients, mean age 70 years, who received cardiac resynchronization therapy (CRT) for class III or IV heart failure with a left ventricular (LV) ejection fractionor =35% and a QRS durationor =120 ms. Sixty-seven patients had intrinsic left bundle branch block (LBBB) (group 1), and 28 patients had right ventricular pacing-induced LBBB (group 2). The time difference (TPW-TDI) between onset of QRS to the end of LV ejection by pulsed wave Doppler and onset of QRS to the end of systolic wave in the basal segment with greatest delay by tissue Doppler imaging was measured before CRT and at the last follow-up after CRT. TPW-TDI50 ms was defined as left ventricular mechanical dyssynchrony. A positive response to CRT was defined as LV volume at end-systole decreasingor =15% after CRT. The percentage of CRT responders in group 2 was significantly greater than that in group 1 (68% versus 42%, P = 0.04) during follow-up of 16 months. After adjusting for age, gender, and clinical features, this pattern of CRT response persisted (P = 0.008). Similarly, there was a greater reduction in QRS duration in group 2 (178 ms) after CRT versus 154 ms for group 1, P = 0.01. There was no significant difference in TPW-TDI between the 2 groups at baseline or at follow-up. There was no significant difference in mortality (15% versus 14%) and Kaplan-Meier survival plot during follow-up. Patients with heart failure and right ventricular pacing-induced LBBB have a better response rate to CRT than patients with intrinsic LBBB. The change in left ventricular mechanical dyssynchrony after CRT was similar in these 2 groups of patients.