Horizontal QRS axis predicts response to cardiac resynchronization therapy in heart failure patients with left bundle branch block.

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.