Dystrophica myotonia. Correlative electrocardiographic, electrophysiologic, and conduction system study.

Correlative ECG, electrophysiologic (EPS), and pathologic findings of the conduction system (CS) in dystrophica myotonia has not been documented to our knowledge in the English literature. We present such a correlation in two cases. The first at age 55 had right bundle branch block, left anterior fascicular block, and first-degree AV block. At age 65, ECG demonstrated type 1 AV block, and EPS revealed block proximal to the His bundle. Two years later, he died of pneumonia. The CS showed marked degenerative changes and fatty infiltration in the atrial septum and the approaches to the AV node, with marked fibrosis of the right bundle branch and partial interruption of the left bundle branch. Case 2 at age 32 had complete left bundle branch block. At age 35, she had syncope, and the ECG revealed type 2, 2:1, and complete AV block, as well as nonsustained polymorphic ventricular tachycardia; EPS showed block distal to the His bundle. A year later, she died in ventricular fibrillation. The CS revealed fatty infiltration in the approaches to the AV node, fibrosis completely interrupting the left bundle branch, and marked fibrosis of the right bundle branch. In both cases, there was fibrosis of the summit of the ventricular septum with irregularity in the size of the cells, vascular changes, and fatty infiltration of the atrial septum. There was good but not perfect correlation among ECG, EPS, and CS findings. The discrepancy was in the approaches to the AV node in case 2. It appears that dystrophica myotonia is a striated muscle disease and possibly a pan-muscle disease.