Myotonic dystrophy type 1 involves cardiac conduction disorders. Cardiac conduction disease might cause sudden death or fatal arrhythmias in patients suffering from myotonic dystrophy type 1.

This study enrolled 506 patients with myotonic dystrophy type 1 (aged ≥15 years; >50 cytosine‐thymine‐guanine repeats) and was treated in 9 Japanese hospitals for neuromuscular diseases from January 2006 to August 2016. We investigated genetic and clinical backgrounds, including health care, daily living activities, dietary intake, cardiac involvement, and respiratory involvement during follow‐up. The cause of death or the occurrence of composite cardiac events (i.e., ventricular arrhythmias, advanced atrioventricular blocks, and device implantations) were evaluated as significant outcomes. In the univariate analysis, pacemaker implantations were associated with sudden death. The multivariable analysis revealed that a PQ interval ≥240 ms or QRS duration ≥120 ms) were independent factors associated with a higher occurrence of cardiac events than those observed with a PQ interval <240 ms or QRS duration <120 ms; these cardiac conduction parameters were not related to sudden death.

Cardiac conduction disorders are independent markers associated with cardiac events. Further investigation of the prediction of the occurrence of sudden death is warranted. Sudden death is a critical concern in the management of DM1 and has been associated with cardiac conduction diseases. Appropriate care during hospitalization may assist in resuscitating patients with DM1 from aborted sudden cardiac death because of ventricular tachycardias or critical bradyarrhythmias. In our retrospective analysis, cardiac conduction disorders were associated with documented cardiac events, but not sudden death. This finding emphasizes that physicians should consider the risk of sudden death, even in patients with DM1 without conduction disorders.