Left ventricular mechanical dyssynchrony by cardiac magnetic resonance is greater in patients with strict vs nonstrict electrocardiogram criteria for left bundle-branch block

Abstract

Background Left bundle branch block (LBBB) is a marker of increased delay between septal and left ventricular (LV) lateral wall electrical activation, and is a predictor of which patients will benefit from cardiac resynchronization therapy (CRT). Recent analysis has suggested that one third of patients meeting conventional ECG criteria for LBBB are misdiagnosed and new strict LBBB criteria have been proposed. We tested the hypothesis that strict LBBB patients have greater LV mechanical dyssynchrony than patients meeting non-strict LBBB criteria while there is no difference between patients with non-strict LBBB and LV conduction delay with QRS duration 110–119 ms. Methods Sixty-four patients referred for primary prevention implantable cardioverter-defibrillators (ICD) underwent 12-lead ECG and cardiac magnetic resonance (CMR) myocardial tagging. The patients were classified as strict LBBB, non-strict LBBB or non-LBBB (nonspecific LV conduction delay with QRS duration 110–119 ms). The time delay between septal and lateral LV wall peak circumferential strain (septal-to-lateral wall delay) was measured by CMR. Results Patients with strict LBBB (n=31) had a greater septal-to-lateral wall delay, compared to patients with non-strict LBBB (n=19) (210±137 ms vs. 122±102 ms, p=0.045). There was no significant difference between non-strict LBBB and non-LBBB (n=14) septal-to-lateral wall delay (122±102 ms vs. 100±86 ms, p=0.51). Conclusions Strict-LBBB criteria identify patients with greater mechanical dyssynchrony compared to patients only meeting non-strict LBBB criteria, while there was no significant difference between non-strict LBBB and non-LBBB patients. The greater observed LV dyssynchrony may explain why strict-LBBB patients have better response to CRT.

Comparison of the Relation Between Left Ventricular Anatomy and QRS Duration in Patients With Cardiomyopathy With Versus Without Left Bundle Branch Block

“…7,9,10 Multiple independent studies have shown that they improve prediction of which patients benefit from CRT, 11,12,13 likely identifying which patients have a true LBBB. 14,15 …”

The Prognostic Impact of New‐Onset Persistent Left Bundle Branch Block Following Transcatheter Aortic Valve Implantation: A Meta‐analysis

“…It was reported that strict LBBB patients had greater mechanical dyssynchrony compared with nonstrict LBBB patients. 41 However, Sundh et al have reported that the majority of the new-onset LBBB following TAVI met the strict LBBB criteria, and therefore we consider that the difference between strict and nonstrict LBBB criteria would have minimal effects on our outcomes. 42 …”

New York Heart Association functional class, QRS duration, and survival in heart failure with reduced ejection fraction: implications for cardiac resychronization therapy

“…In the present study, there was a trend towards worse prognosis in subjects with non‐LBBB morphology, found in approximately one‐third of patients with prolonged QRS, compared with LBBB. Causing a characteristic U‐shaped activation pattern of the left ventricle, LBBB has been closely linked to left intraventricular dyssynchrony between the septum and the lateral wall, while QRS prolongation of non‐LBBB type may result in various other electromechanical abnormalities . This may explain why patients with LBBB have especially large effects by CRT while non‐LBBB morphology is a predictor of non‐response .…”