The relationship of QRS morphology and mechanical dyssynchrony to long-term outcome following cardiac resynchronization therapy

Abstract

Aims: Because benefits of cardiac resynchronization therapy (CRT) appear to be less favourable in non-left bundle branch block (LBBB) patients, this prospective longitudinal study tested the hypothesis that QRS morphology and echocardiographic mechanical dyssynchrony were associated with long-term outcome after CRT.

Methods and results: Two-hundred and seventy-eight consecutive New York Heart Association class III and IV CRT patients with QRS ≥120 ms and ejection fraction ≤35% were studied. The pre-specified primary endpoint was death, heart transplant, or left ventricular assist device over 4 years. Dyssynchrony assessed before CRT included interventricular mechanical delay (IVMD) and speckle-tracking radial strain using pre-specified cut-offs for each. Of 254 with baseline quantitative echocardiographic data available, 128 had LBBB, 81 had intraventricular conduction delay (IVCD), and 45 had right bundle branch block (RBBB). Radial dyssynchrony was observed in 85% of the patients with LBBB, 59% with IVCD*, and 40% with RBBB* (*P < 0.01 vs. LBBB). Of 248 (98%) with follow-up, LBBB patients had a significantly more favourable long-term survival than non-LBBB patients. However, non-LBBB patients with dyssynchrony had a more favourable event-free survival than those without dyssynchrony: radial dyssynchrony hazard ratio 2.6, 95% confidence interval (CI) 1.47-4.53 (P = 0.0008) and IVMD hazard ratio 4.9, 95% CI 2.60-9.16 (P = 0.0007). Right bundle branch block patients who lacked dyssynchrony had the least favourable outcome.

Conclusion: Non-LBBB patients with dyssynchrony had a more favourable long-term survival than non-LBBB patients who lacked dyssynchrony. Mechanical dyssynchrony and QRS morphology are associated with outcome following CRT.

Figures

Figure 1

Representative speckle-tracking radial strain curves in a heart failure patient with left bundle branch block. Segmental strain curves in mid-left ventricular segments are shown in yellow (anterior septum), light blue (anterior), green (lateral), purple (posterior), dark blue (inferior), and red (septum). Time difference in peak strain in the anterior septum to the peak strain in the posterior wall was used to measure radial dyssynchrony.

Figure 2

(A–E) Five patient examples of different QRS morphology and radial strain dyssynchrony, with ejection fraction (EF) response and long-term outcome following cardiac resynchronization therapy (CRT). LBBB, left bundle branch block; IVCD, interventricular conduction delay; RBBB, right bundle branch block.

Figure 3

The Kaplan–Meier curves demonstrating the probability of freedom from death, transplant, or ventricular assist device after cardiac resynchronization therapy (CRT) comparing patients with left bundle branch block (LBBB), interventricular conduction delay (IVCD), and right bundle branch block (RBBB).

Figure 4

The Kaplan–Meier curves demonstrating the probability of freedom from death, transplant, or ventricular assist device after cardiac resynchronization therapy (CRT) comparing patients with left bundle branch block (LBBB), to those with non-LBBB with or without significant radial dyssynchrony (top panel) or with or without interventricular mechanical delay (IVMD) (bottom panel). Non-LBBB patients with dyssynchrony had similar outcome as those with LBBB, whereas Non-LBBB patients without dyssynchrony had a less favourable outcome.

Figure 5

The Kaplan–Meier curves demonstrating the probability of freedom from death, transplant, or ventricular assist device after cardiac resynchronization therapy (CRT) comparing patients with left bundle branch block (LBBB), to those with interventricular conduction delay (IVCD) with or without significant radial dyssynchrony (top panel) or with or without interventricular mechanical delay (IVMD) (bottom panel). Interventricular conduction delay patients with dyssynchrony had similar outcome as those with LBBB, whereas interventricular conduction delay patients without dyssynchrony had a less favourable outcome.

Figure 6

The Kaplan–Meier curves demonstrating the probability of freedom from death, transplant, or ventricular assist device after cardiac resynchronization therapy (CRT) comparing patients with left bundle branch block (LBBB), to those with right bundle branch block (RBBB) with or without significant radial dyssynchrony (top panel) or with or without interventricular mechanical delay (IVMD) (bottom panel). Right bundle branch block patients with dyssynchrony had similar outcome as those with left bundle branch block, whereas right bundle branch block patients without dyssynchrony had a less favourable outcome.

Figure 7

The Kaplan–Meier curves demonstrating the probability of freedom from death, transplant, or ventricular assist device after cardiac resynchronization therapy (CRT) comparing patients with left bundle branch block (LBBB), to those with non-LBBB with or without significant dyssynchrony by a combined approach of interventricular mechanical delay (IVMD) and radial dyssynchrony by speckle-tracking strain. More favourable outcome was observed in non-LBBB with both markers of dyssynchrony, and least favourable outcome in patients who lacked dyssynchrony by either method. +, positive; −, negative.

Figure 8

Bar graphs of subgroup analysis of absolute changes in ejection fraction (EF, %) and relative changes in end-systolic volume (ESV, %) after cardiac resynchronization therapy. Patients with left bundle branch block (LBBB) are shown in comparison to patients with interventricular conduction delay (IVCD) or right bundle branch block (RBBB) with or without significant radial dyssynchrony by speckle-tracking strain.