A Reassuring ECG Is Not Enough in Myotonic Dystrophy Type 1: A Systematic Review and Meta-analysis

Cardiac involvement is a major determinant of morbidity and premature mortality in myotonic dystrophy type 1 (MD1), yet a reassuring surface electrocardiogram (ECG) may not exclude clinically important distal conduction disease. We conducted a systematic review and meta-analysis of cardiac electrical risk stratification in MD1, focusing on occult His-ventricular (HV) prolongation, prognostic ECG and HV abnormalities, and sudden cardiac death (SCD). PubMed/MEDLINE, Scopus, and ScienceDirect were searched from inception through January 31, 2026. The review followed PRISMA 2020 guidance and was prospectively registered in PROSPERO (CRD420261329528). Thirty-three studies were included. Among EPS-evaluated patients, the pooled prevalence of prolonged HV at the 70-ms threshold was 39.8% (95% CI, 36.1%-43.6%). HV ≥70 ms was present in 20.0% (95% CI, 13.5%-28.5%) despite study-defined normal or low-risk ECG findings. Surface ECG abnormalities were associated with a higher risk of SCD (pooled relative prognostic effect, 3.11; 95% CI, 1.75-5.52) and, separately, with serious cardiac or conduction-related outcomes (4.77; 95% CI, 2.75-8.28). HV ≥70 ms was independently associated with major bradyarrhythmic events and complete atrioventricular block in two adjusted cohorts; these estimates were not pooled because the endpoints differed and cohort independence was uncertain. Across broader longitudinal MD1 cohorts, the pooled cumulative proportion of SCD was 4.0% (95% CI, 3.0%-5.4%). Surface ECG is prognostically informative but cannot reliably exclude clinically relevant His-Purkinje disease. Cardiac risk assessment should therefore be longitudinal, with ECG and ambulatory monitoring forming the foundation and selected EPS providing direct assessment of distal conduction when concern persists.