Axis deviation in nonischemic cardiomyopathy with left bundle branch block: Insights from left bundle branch pacing

Introduction: Biventricular pacing has shown excellent results in patients with heart failure and left bundle branch block (LBBB). Studies have shown that the patients with abnormal axis deviation may benefit less from cardiac resynchronization therapy (CRT) as compared to those with the normal axis. The exact reason for left axis deviation (LAD) in LBBB is not known but could be due to diseased left anterior fascicle, left ventricular enlargement, or due to advanced electrical remodeling.

Methods: The aim of the study was to analyze the incidence of LAD in nonischemic cardiomyopathy (NICM) with LBBB and the clinical outcomes following left bundle branch pacing (LBBP).

Results: We have included 64 consecutive patients with NICM and LBBB, who underwent successful LBBP. Patients were divided into two groups-Group I with baseline normal axis (n = 40; 63%) and Group II with LAD (n = 24; 37%). The mean axis changed from +23.6 ± 28.8° at baseline to +16.5 ± 35.1° and from -40.4 ± 10.3° at baseline to 7.08 ± 41.1° after LBBP in Group I and Group II, respectively. LBBP retained the normal axis in 93% of Group I patients and normalized the axis in 75% of Group II patients. The percentage changes in QRS duration, left ventricular ejection fraction, and left ventricular end-diastolic diameter were similar in both the groups (+40% vs. +32%; p = .52, +64% vs. +50%; p = 0.34, -8% vs. -6%; p = .76, respectively). Capturing the proximal LBB would correct the LAD by recruitment of left anterior fascicles and pacing proximal to the site of the septal breakthrough of the right bundle branch activation wavefront during LBBB.

Conclusion: LBBP as an alternative strategy for CRT could result in similar improvement in LBBB patients with LAD as in those with the normal axis.