Myotonic dystrophy: ambulatory electrocardiogram, electrophysiologic study, and echocardiographic evaluation.

Myotonic dystrophy is frequently associated with functional and anatomic derangements in the myocardium. Ten myotonic dystrophy patients (seven men and three women, ages ranging from 35 to 58 years) were evaluated with a 12-lead ECG, 24-hour Holter monitor recording, invasive electrophysiologic studies, and echocardiographic examination. Nine patients displayed abnormalities in the conduction system. ECG and Holter monitor abnormalities were first-degree atrioventricular block (n = 8), second-degree atrioventricular block (n = 1) (Wenckebach type), complete left bundle branch block (n = 2), left anterior fascicular block (n = 5), left posterior fascicular block (n = 1), sinus bradycardia (n = 6), sick sinus syndrome (n = 2), frequent premature ventricular complexes (n = 4), and ventricular tachycardia (n = 2). Electrophysiologic study abnormalities included AH interval less than or equal to 140 msec (n = 7), AH interval greater than 140 msec (n = 3), HV interval greater than 60 msec (n = 9), and ventricular tachycardia induction (n = 1). Echocardiographic examination revealed mitral valve prolapse (n = 6). We conclude that diffuse conduction abnormalities were seen in a majority of our patients with myotonic dystrophy. Ventricular arrhythmias, including ventricular tachycardia, were seen in some of these patients, and mitral valve prolapse was a frequent finding.