Aims: Dilated cardiomyopathy (DCM) can occur in infants with congenital complete atrioventricular block (CCAVB) treated by permanent pacemaker (PM), even without other congenital heart defects. The objective is to find the risk factors of this complication.
Methods and results: Retrospective analysis of a single-centre experience. Since 1992, 25 patients, aged 25 (1-355) days [median (range)], with normal ejection fraction (EF), underwent PM implantation (13 DDD, 12 VVIR) with an RV-pacing site. Follow-up was 4 (0.3-16) years. DCM occurred after 4 (3-23) months in eight patients (32%). Univariate analysis identified the following risk factors: younger age at implantation [5 (1-85) days vs. 90 (1-355) P = 0.007], a broad QRS (50 vs. 18% P = 0.03), prolonged QTc at implantation (63 vs. 0%, P = 0.001), and greater duration of heart rate >160 bpm during the first month after implantation (18 vs. 2%, P = 0.03). By multivariate analysis prolonged QTc was the only significant risk factor for DCM (hazard ratio: 23, P < 0.001, 95% confidence interval: 4-128). One patient died of heart failure, one was lost to follow up, and two were compensated on anticongestive therapy. EF normalized in four patients after resynchronization therapy (two patients), normalization of AV conduction or changing pacing mode to allow predominant narrow QRS junctional rhythm (one patient each).
Conclusions: Neonates with CCAVB without other congenital heart defects and prolonged QTc are at high risk for DCM possibly due to electromechanical dyssynchrony induced by high-rate RV pacing. In patients in whom RV pacing was discontinued, EF became normal.