Electrophysiological studies in two patients with dystrophia myotonica and atrioventricular conduction block.

Two patients with dystrophia myotonica showed high-grade atrio-ventricular block. Both underwent electrophysiological studies which revealed sinus and A-V nodal disease with normal intraventricular conduction in 1 case and His-Purkinje conduction disease in the other. Dystrophia myotonica may, therfore, involve all parts of the cardiac conduction system and may affect the generation of cardiac impulses. Pacemaker implantation may be necessary especially if drugs such as procainamide, which in addition to controlling myotonic symptoms may aggravate conduction disorders, are to be used.