190 PREVALENCE, SPECTRUM AND PATHOGENESIS OF EKG EVIDENCE OF CONDUCTION SYSTEM INVOLVEMENT IN DUCHENNE'S MUSCULAR DYSTROPHY (DMD)

Abstract

Twelve-lead electrocardiograms were analyzed in 50 boys, 5 to 18 years of age, with clinical, biochemical and muscle biopsy evidence of DMD. Cardiac conduction system abnormalities were noted in 27 patients (54%). Intra-atrial conduction abnormalities were most common and included: abnormal PV1 index in 14 patients, a short P-R interval in 11 and coronary sinus rhythm in 2. Intraventricular conduction abnormalities were noted in 5 patients: right bundle branch block in 2, left anterior hemiblock in 2 and bifascicular block in 1. First-degree atrioventricular block was seen in 1 patient. Seven patients had more than one type of condution defect. Serial follow-up observations disclosed that the conduction abnormalities were progressive. Morphology of the cardiac conduction system was studied systematically in 4 patients. In each case, within 1-2 hours of death, hearts were perfused at 4°C for four hours either with 2.5 glutaraldehyde or with 10% formalin. By contrast to age and sex-matched normal controls, DMD hearts showed multi-focal areas of degenerative changes characterized by vacuolozation, fatty infiltration, and nuclear pyknosis. Other changes included variation in size and staining of myofibers, splitting and loss of myofibers and moderate-to-severe fibrosis. These dystrophic changes at the cellular level were similar in each patient and involved, with varying degrees of severity, the sino-atrial node, atrial preferential pathways, the atrioventricular node, bundle of His and subendocardial as well as intraventricular right and left bundle branches. Our observations indicate a high prevalence of cardiac conduction abnormalities in patients with DMD and establish that the EKG abnormalities result from dystrophic involvement of the cardiac conduction system.