A family with myotonic dystrophy associated with diffuse cardiac conduction disturbances as demonstrated by His bundle electrocardiography.

In a family with myotonic dystrophy, three siblings showing ECG abnormalities were subjected to His bundle ECG studies. The duration of the disease ranged from 9 to 24 years. All three siblings had prolonged HV intervals (His-Purkinje conduction times) of 70 to 80 msec. The sister with the shortest duration of the disease had second-degree atrioventricular (AV) nodal block as well as left posterior fascicular block, the younger brother had left anterior fascicular block, and the elder brother with the longest history had first-degree AV block without bundle branch or fascicular block. With regard to associated arrhythmias, however, the elder brother developed paroxysmal ventricular tachycardia, apparently due to reentry involving the right bundle branch system, whereas the younger brother and sister had sinus bradycardia alone. This study reveals the prevalence of diffuse conduction disturbances of the specialized conducting system in a family with myotonic dystrophy.