Pediatric restrictive cardiomyopathy with rapid complete atrioventricular block progression.

Restrictive cardiomyopathy (RCM) is a rare pediatric cardiomyopathy characterized by ventricular diastolic dysfunction, and poor prognosis that often requires heart transplantation. We report the case of a 7-year-old boy with RCM complicated by complete atrioventricular block (CAVB) in whom pathological examination of the explanted heart demonstrated extensive fibrosis involving the cardiac conduction system. At 1 year and 9 months of age, the patient presented with arrhythmia. Echocardiography revealed marked biatrial enlargement and small ventricles. Cardiac catheterization demonstrated elevated filling pressures confirming RCM. One month after diagnosis, the patient developed severe bradycardia and circulatory collapse, requiring extracorporeal membrane oxygenation. Electrocardiography revealed complete atrioventricular (AV) block, and a permanent pacemaker (PM) was implanted. Despite recurrent heart failure episodes, cardiac function was maintained with medical therapy, including carvedilol and enalapril, without mechanical circulatory support until heart transplantation at 5 years of age. Pathology of the explanted heart revealed extensive interstitial fibrosis involving the conduction system, suggesting that conduction tissue fibrosis caused the CAVB. These findings provide pathological insight into the mechanism of advanced atrioventricular block in pediatric RCM. This case demonstrates that RCM may progress from first-degree AV block to CAVB due to conduction fibrosis. Learning objective: Understanding the clinical and pathological progression of restrictive cardiomyopathy (RCM) complicated by complete atrioventricular block in children is important. This case illustrates that fibrosis of the conduction system can lead to severe bradycardia and circulatory collapse, highlighting the importance of the early detection of conduction abnormalities and timely pacemaker implantation. It has also been demonstrated that appropriate medical therapy combined with pacemaker management can effectively bridge pediatric patients with RCM to heart transplantation.