Atrial Fibrillation and Flutter in a Contemporary Cohort of Patients With Myotonic Muscular Dystrophy.

Background: Literature on the prevalence and management of atrial arrhythmias in patients with myotonic muscular dystrophy type 1 (MMD1) or myotonic muscular dystrophy type 2 (MMD2) is limited.

Objectives: This study sought to describe incidence, prevalence, and predictors of atrial fibrillation (AF) and atrial flutter (AFL) in a contemporary cohort of patients with myotonic muscular dystrophy (MMD).

Methods: Associations between patient factors and incident AF/AFL were analyzed in patients with MMD referred for routine electrophysiology evaluation between January 2013 and September 2023.

Results: We identified 120 patients (96 MMD1, 24 MMD2) seen for new electrophysiology clinic visits for MMD cardiac evaluation. Median age at MMD diagnosis was 34.6 years (Q1-Q3: 21.8-51.0 years), with a younger age at diagnosis for MMD1 patients (P < 0.001). AF or AFL was diagnosed in 31% of patients (31 of 96 MMD1 patients vs 6 of 24 MMD2 patients; P = 0.656) during the study period. AF occurred in 34 (28%) patients, AFL in 9 (8%), and 6 of 37 had both AF and AFL. Anticoagulation (AC) was prescribed at initial AF/AFL diagnosis in 41% (n = 15 of 37) of patients. The CHADS-VASc score was higher in patients who received AC (P < 0.001). Twelve (32%) patients underwent catheter ablation. One stroke occurred in the AF/AFL group (no AC, CHADS-VASc score 0). Female MMD1 patients were less likely to develop AF/AFL (HR: 0.08). Diagnosis of MMD1 at a younger age (HR: 0.95 per year) and greater CTG nucleotide repeats (HR: 1.09 per 50 repeats) were associated with incident AF/AFL.

Conclusions: There was a high prevalence of AF/AFL in this single-institution MMD cohort. The CHADS-VASc score may not be an effective tool in this population.