Long-term arrhythmia follow-up of patients with myotonic dystrophy

Myotonic dystrophy (MD) is the most common muscular dystrophy in adults and is associated with sudden death. Reported predictors of sudden death in this population include atrial tachyarrhythmias, a PR interval greater than 240 milliseconds, aberrant QRS conduction, and any degree of AV block.

We sought to report on the arrhythmic outcome of a cohort of patients with a new diagnosis of genetically proven MD.

We performed a retrospective review of 37 patients with genetically confirmed MD referred to our electrophysiology clinic for primary cardiac screening.

There were 25 patients with MD type 1 (MD1) and 12 patients with MD type 2 (MD2). Eight patients with MD1 (32%) had atrial fibrillation, compared to only one patient with MD2 (8.3%). Patients with MD1 were more likely to have evidence of conduction disease abnormalities (40% vs. 8.3%, P = ns) and had a higher all-cause mortality (16% vs. 0%) than those with MD2. Criteria for recommending ICD implantation were based on sudden death risk factors suggested by published literature. Eleven patients were offered an ICD, 2 refused and died within the next year. Of the 9 patients who received an ICD, 8 had MD1. Three patients received appropriate shocks, 2 for monomorphic VT, and one for polymorphic VT.

The presence of AV conduction disturbance in MD patients is associated with a greater risk for ventricular arrhythmias. MD1 was more likely to be associated with cardiac arrhythmias than MD2. The incidence of ventricular arrhythmias among those who received a primary prevention ICD was 33% over 22 months, with 2 patients experiencing monomorphic VT and one experiencing polymorphic VT.