Predictors of Atrio‐Ventricular Conduction Disease, Long‐Term Outcomes in Patients with Myotonic Dystrophy Types I and II

BACKGROUND: Patients with myotonic dystrophy (DM) have an annual mortality of approximately 3.5%, one-third of which is sudden cardiac death. The predictors of cardiac conduction disease in these patients are incompletely defined. METHODS: A single-center cohort study included 211 patients with DM type 1 (DM1) and 25 DM type 2 (DM2). A severe electrocardiogram (ECG) abnormality was defined as a PR interval of ≥240 ms or QRS duration of ≥120 ms. RESULTS: A severe ECG abnormality was found in 24% of DM1 patients and 17% of DM2 patients. Among DM1 patients, those with a severe ECG abnormality were older (41.6 ± 14.6 vs 35.4 ± 12.6 years) and more likely to have hypertension (13.2% vs 4.2%, P = 0.038), heart failure (4.4% vs 0%, P = 0.056), atrial arrhythmias (6.6% vs 0.7%, P < 0.001), a higher number of trinucleotide repeats (689 ± 451 vs 474 ± 322, P = 0.01), and a family history of sudden cardiac death (26.7% vs 5.6%, P < 0.001) or pacemaker implantation (20% vs 0.7%, P < 0.001). Pacemakers or defibrillators were implanted in 14% of all patients, including 65% of patients with severe ECG abnormalities. During 57 ± 46 months, 13 patients died (1.16% per year), including three patients who died suddenly, two of whom had normally functioning pacemakers. CONCLUSION: In DM1, atrio-ventricular conduction disease is associated with increasing age, concomitant cardiovascular disease, nucleotide repeat length, and family history. The systematic identification of conduction disease and aggressive use of prophylactic pacemakers is associated with low rate of sudden cardiac death.