Paced QRS morphology mimicking complete left bundle branch block induced by right ventricular pacing is associated with pacing‐induced cardiomyopathy

Abstract Introduction Right ventricular (RV) pacing sometimes causes left ventricular (LV) systolic dysfunction, also known as pacing‐induced cardiomyopathy (PICM). However, the association between specifically paced QRS morphology and PICM development has not been elucidated. This study aimed to investigate the association between paced QRS mimicking a complete left bundle branch block (CLBBB) and PICM development. Methods We retrospectively screened 2009 patients who underwent pacemaker implantation from 2010 to 2020 in seven institutions. Patients who received pacemakers for an advanced atrioventricular block or bradycardia with atrial fibrillation, baseline LV ejection fraction (LVEF) ≥ 50%, and echocardiogram recorded at least 6 months postimplantation were included. The paced QRS recorded immediately after implantation was analyzed. A CLBBB‐like paced QRS was defined as meeting the CLBBB criteria of the American Heart Association/American College of Cardiology Foundation/Heart Rhythm Society in 2009. PICM was defined as a ≥10% LVEF decrease, resulting in an LVEF of <50%. Results Among the 270 patients analyzed, PICM was observed in 38. Baseline LVEF was lower in patients with PICM, and CLBBB‐like paced QRS was frequently observed in PICM. Multivariate analysis revealed that low baseline LVEF (odds ratio OR: 0.93 per 1% increase, 95% confidence interval CI: 0.89–0.98, p = 0.006) and CLBBB‐like paced QRS (OR: 2.69, 95% CI: 1.25–5.76, p = 0.011) were significantly associated with PICM development. Conclusion CLBBB‐like paced QRS may be a novel risk factor for PICM. RV pacing, which causes CLBBB‐like QRS morphology, may need to be avoided, and patients with CLBBB‐like paced QRS should be followed‐up carefully.