Cardiac conduction abnormalities in children with Duchenne's progressive muscular dystrophy: electrocardiographic features and morphologic correlates.

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Abstract
The ECG of 50 boys (5-18 yr old) with Dunchenne''s muscular dystrophy were studied for evidence of cardiac conduction system abnormalities. Among the 24 patients with positive findings (48%), most had intraatrial conduction defects: 16 had an abnormally prolonged PV1 index, 12 had a short PR interval with a normal QRS and 2 had coronary sinus rhythm. Five patients had infranodal conduction defects: 1 had right bundle branch block, 3 had left anterior fascicular block and one had a right bundle branch block with left anterior fascicular block. Only 1 child had 1st-degree atrioventricular (AV) block. About 1/3 of the patients had more than one type of defect. The conduction abnormalities were progressive in some patients. Morphologic features of the conduction systems of 3 patients were studied systematically to find correlates for the observed ECG changes. Compared with normal controls matched for age and sex, each of these 3 hearts showed multifocal areas of degenerative changes, characterized by vacuolization, fatty infiltration, nuclear pyknosis, loss of myofibers and moderate to severe fibrosis. These dystrophic changes were similar in all patients and (with differing severity) involved the sinoatrial node, atrial preferential pathways, approaches to the AV node, the AV one including the upper portion, the bundle of His, and subendocardial as well as infranodal right and left bundle branches. A high prevalence of ECG evidence was indicative of cardiac conduction abnormalities in patients with Duchenne''s dystrophy. Multifocal dystrophic involvement of the cardiac conduction system furnishes the anatomic basis for such changes and may account for the persistence of an infantile pattern of accelerated conduction, which may sometimes manifest clinically as Lown-Ganong-Levine syndrome with or without sinus tachycardia.