Cardiac critical events in myotonic dystrophy: relationship with the severity of neuromuscular disease

Background: Conduction and ventricular arrhythmic disturbances in myotonic dystrophy (MD) are the main causes of cardiac morbidity and mortality. Methods: To better define the natural history of cardiac involvement and the relationship with severity grade of neuromuscular disease, we followed up 83 MD patients (56 men and 27 women; mean age 37±14 years) for a mean period of 61±38 months (range 2–156 months). Pre-study evaluation included physical examination, 12-lead electrocardiogram, 24-h Holter monitoring, and echocardiography. Results: During the study, cardiac critical events (CCE) occurred in 20 patients (24%), five of whom died of sudden death related to documented ventricular tachycardia, 12 of whom had pacemaker implantation and three of whom experienced ventricular tachyarrhythmias. The incidence of CCE appeared to be related to disease severity; in fact, CCE progressively increased from class I to class III (2% vs. 17% vs. 78%, respectively, P<0.001). Moreover, 8% of the patients experienced CCE in spite of low-grade muscular involvement. Conclusions: Critical cardiac events are significantly associated with the more severe forms of neuromuscular disease, while in some patients cardiac involvement in MD worsens independently from skeletal muscle disease.