Horizontal QRS Axis Predicts Response to Cardiac Resynchronization Therapy in Heart Failure Patients with Left Bundle Branch Block.

Abstract

Background: Electrocardiogram criteria for left bundle branch block (LBBB) inadequately predict left ventricular electrical dyssynchrony, complicating cardiac resynchronization therapy (CRT) candidate selection.

Objective: To investigate the predictive value of the horizontal QRS axis for CRT response in heart failure (HF) patients with LBBB patterns.

Methods: The direction and magnitude of the horizontal QRS axis were calculated using the net amplitudes in leads V₂ and V₆. CRT response was defined as a ≥10% increase in left ventricular ejection fraction (LVEF) and at least one New York Heart Association (NYHA) class reduction one-year post-CRT implantation. The composite endpoint included HF hospitalization or all-cause mortality.

Results: Among 244 consecutive CRT recipients, 156 (63.9%) responded favorably, while 88 (36.1%) were non-responders. The horizontal QRS axis demonstrated significant backward deviation [-75.5° (-79.7°, -69.0°) vs. -65.0° (-73.0°, -46.5°), P <0.001] and larger magnitude (35.5±10.9 mm vs. 25.5±10.5 mm, P <0.001) in CRT responders compared to non-responders. The direction and magnitude independently predicted CRT response with an area under the curve (AUC) of 0.778 (95% CI: 0.717, 0.839) and 0.749 (95% CI: 0.685, 0.814), respectively. Combining both parameters increased the AUC to 0.814 (95% CI: 0.760, 0.868). Moreover, the direction and magnitude of the horizontal QRS axis, or their combination, predicted the composite endpoint of HF hospitalization or all-cause mortality, with hazard ratios (HR) of 0.36 (95% CI: 0.22, 0.60), 0.41 (95% CI: 0.25, 0.67), and 0.25 (95% CI: 0.15, 0.41), respectively.

Conclusion: Horizontal QRS axis accurately predicts CRT response and prognosis in HF patients with LBBB.