Stricter criteria for left bundle branch block diagnosis do not improve response to CRT

Background Cardiac resynchronization therapy (CRT) has proved to be effective in patients with heart failure and left bundle branch block (LBBB). Recently, new electrocardiography criteria have been proposed for the diagnosis of LBBB. These criteria are stricter than the current American Heart Association (AHA) criteria. We assessed the rate of echocardiographic response to CRT in patients with traditional LBBB versus patients who met the new criteria (strict LBBB). Methods Consecutive patients undergoing CRT were enrolled in the CRT MORE registry. Patients with no-LBBB QRS morphology according to AHA criteria, atrial fibrillation, right bundle branch block, and right ventricular pacing were excluded. Strict LBBB was defined as: QRS ≥ 140 ms for men and ≥130 ms for women, QS or rS in V1–V2, mid-QRS notching or slurring in ≥2 contiguous leads. Patients showing a relative decrease of ≥15% in left ventricular end-systolic volume (LVESV) at 12 months were defined as responders. Results Among 335 patients with LBBB, 131 (39%) had strict LBBB. Patients with and without strict LBBB showed comparable baseline characteristics, except for QRS duration (166 ± 20 ms vs 152 ± 25 ms, P < 0.001). On 12-month evaluation, 205 patients (61%) were responders; 85 of 131 (65%) had strict LBBB and 120 of 204 (59%) had traditional LBBB (P = 0.267). On multivariate analysis, a history of atrial fibrillation, larger LVESV, and the presence of mid-QRS notching in ≥1 lead (odds ratio 2.099; 95% confidence interval 1.061–4.152, P = 0.033) were independently associated with echocardiographic response. Conclusion Stricter definition of LBBB did not improve response to CRT in comparison to the current AHA definition