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: This study aimed 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 and at least 1 New York Heart Association class reduction 1 year after CRT implantation. The composite end point included HF hospitalization or all-cause mortality.

Results: Of 244 consecutive CRT recipients, 156 (63.9%) responded favorably; 88 (36.1%) were nonresponders. The horizontal QRS axis demonstrated significant backward deviation (-75.5° [-79.7° to -69.0°] vs -65.0° [-73.0° to -46.5°]; P < .001) and larger magnitude (35.5 ± 10.9 mm vs 25.5 ± 10.5 mm; P < .001) in CRT responders compared with nonresponders. The direction and magnitude independently predicted CRT response with an area under the curve of 0.778 (95% confidence interval [CI], 0.717-0.839) and 0.749 (95% CI, 0.685-0.814), respectively. Combining both parameters increased the area under the curve 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 end point of HF hospitalization or all-cause mortality, with hazard ratios 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.

Keywords: CRT response; Cardiac resynchronization therapy; Heart failure; Horizontal QRS axis; Left bundle branch block.