An S wave in ECG lead V6 predicts poor response to cardiac resynchronization therapy and long-term outcome

Abstract

Background: Cardiac resynchronization therapy (CRT) is a standard treatment for selected patients with chronic heart failure (HF). However, up to 30%-50% of patients still do not respond to CRT.

Objective: Our aim was to identify the predictive value of an S wave in lead V₆ in CRT response in patients with complete left bundle branch block (CLBBB).

Methods: The CLBBB definition included the Strauss left bundle branch block criteria and the absence of q waves in leads I, V₅, and V₆. According to the electrocardiogram at baseline, CLBBB patients were divided into 3 groups: T-CLBBB group (CLBBB without an S wave in lead V₅ or V₆), V₅S group (CLBBB with an S wave in lead V₅ and no S wave in lead V₆), and V₅&V₆S group (CLBBB with S waves in leads V₅ and V₆). CRT response was defined as left ventricular end-systolic volume reduction ≥ 15% at 6-month follow-up. The combined end point included HF rehospitalization or all-cause death.

Results: Of 181 patients with left bundle branch block-like pattern, 112 patients with CLBBB were included into 3 groups: 54 in the T-CLBBB group, 32 in the V₅S group, and 26 in the V₅&V₆S group. The CRT response rate was 85.2% (46), 65.6% (21), and 38.5% (10), respectively (P < .001). Kaplan-Meier curves demonstrated that patients in the V₅&V₆S group had a higher incidence of HF rehospitalization or all-cause death than those in the other 2 groups (P < .001). In a multivariate logistic regression model analysis, an S wave in lead V₆ was significantly associated with CRT nonresponse (hazard ratio 0.33; 95% confidence interval 0.11-0.96; P = .042).

Conclusion: An S wave in lead V₆ can predict poor response to CRT and long-term outcome.

Keywords: CLBBB; CRT; CRT response; Heart failure; QRS morphology.