Cardiac rhythm and conduction in Duchenne's muscular dystrophy: a prospective study of 20 patients.

This study was designed to determine the types and prevalence of rhythm and conduction disturbances in Duchenne's muscular dystrophy, and examine the results in light of known morphologic abnormalities of the myocardium and the small coronary arteries, and in the context of left ventricular function, regional wall motion, mitral valve prolapse and left atrial size. The observed disorders of impulse and conduction extended from the sinus node to the His-Purkinje system. Rhythm disturbances included persistent and labile sinus tachycardia (gradual or abrupt), sinus arrhythmia, sinus pauses, atrial ectopic beats, atrial ectopic rhythm, junctional rhythm, atrial flutter and ventricular premature beats (uniform, multiform, bigeminal and repetitive). Disorders of conduction included abnormal intraatrial or interatrial conduction, Mobitz type I block, nonconducted atrial premature beats, short PR interval, right ventricular conduction delay and rightward axis compatible with left posterior fascicular block. The role of dystrophic involvement of specialized conduction tissues and of the small vessel coronary arteriopathy remains speculative, but mitral valve prolapse, left atrial size and left ventricular size, function and regional wall motion played no discernible part in the genesis of the rhythm and conduction disturbances. Except for end-stage atrial flutter, these disturbances were not clinically deleterious.