Greater response to cardiac resynchronization therapy in patients with true complete left bundle branch block: a PREDICT substudy

Cardiac resynchronization therapy (CRT) benefits patients with heart failure and a wide QRS complex. Still, one-third derive no clinical benefit and a majority of patients demonstrate no objective improvement of left ventricular (LV) function. Left bundle branch block (LBBB) is a strong predictor of response to CRT. We evaluated whether absence of electrocardiogram (ECG) markers of residual left bundle (LB) conduction in guideline-defined LBBB predicted a greater response to CRT. An r wave epsilon 1 mm in lead V1 (r-V1) and/or a q wave epsilon 1 mm in lead aVL (q-aVL) was used to identify patients with residual LB conduction. Forty patients with a wide QRS were prospectively enrolled and subdivided into three groups: complete LBBB (cLBBB), LBBB without r-V1 or q-aVL (n 12); LBBB with residual LB conduction (rLBBB), LBBB with r-V1 and/or q-aVL (n 15); and non-specific intraventricular conduction delay (IVCD), (n 13). Following CRT: mean change in left ventricular ejection fraction was 11.9 11.9 in cLBBB, 3.8 5.4 in rLBBB (P 0.045), and 2.5 4.4 in IVCD (P 0.02 cLBBB vs. IVCD); mean reduction in left ventricular end-systolic volume was 26.4 39.2 in cLBBB, 14.3 22.9 in rLBBB (P 0.35), and 5.6 17.3 in IVCD (P 0.11 cLBBB vs. IVCD); mean change in native QRS duration was 8.0 11.0 ms in cLBBB, 0.8 8.24 ms in rLBBB (P 0.07), and 0.15 8.0 ms in IVCD (P 0.048 cLBBB vs. IVCD). In patients with guideline-defined LBBB, the absence of ECG markers of residual LB conduction was predictive of a greater improvement in LV function with CRT.