The natural course of cardiac conduction disturbances in myotonic dystrophy.

In this study we noninvasively followed for a mean period of 46 months 21 patients with different grades of myotonic dystrophy to evaluate the course of the involvement of the cardiac conducting system. Six patients (28.6%), 1 affected by a mild and 5 by a severe form of the neuromuscular disorder, showed appearance or deterioration of conduction disturbances suggesting a serious derangement of the specialized tissue; in 3 of them a permanent demand pacemaker was implanted. Conduction defects are the most frequent cardiac manifestations in myotonic dystrophy and become worse with time, mainly in patients with higher degrees of the disease. Furthermore, first-degree atrioventricular block may represent an early sign of developing of more advanced conduction defects.