A Normal Electrocardiogram Does Not Exclude Infra-Hisian Conduction Disease in Patients With Myotonic Dystrophy Type 1.

Abstract Objectives This study aimed to identify electrocardiographic (ECG) predictors of a prolonged His-ventricular (HV) interval in patients with type 1 myotonic dystrophy (DM1). Background Patients with DM1 have an increased risk of sudden cardiac death. The presence of His-Purkinje system disease/prolonged HV interval (≥70 ms) is associated with a higher risk of potentially life-threatening bradyarrhythmic events. Methods Electrophysiology studies (EPSs) were performed in all DM1 patients referred to 2 tertiary centers for routine cardiac assessment. In a subgroup of patients, the EPS was repeated at varying intervals. Results A total of 154 patients (mean age: 43.7 ± 13.3; 58.1% male) underwent 202 diagnostic EPSs. HV ≥70 ms was found on 58 EPSs (28.7%); 9 of 59 patients (15.2%) with PR  Conclusions ECG parameters have a poor predictive value for infra-Hisian conduction block in DM1 patients. QRS and PR intervals are normal in up to 15.2% of DM1 patients with prolonged HV, and 66.1% of those with PR ≥200 ms and/or QRS ≥100 ms do not have advanced His-Purkinje conduction system disease on EPS. Electrophysiology testing should be a mandatory part of screening for all patients to guide prophylactic pacemaker implantation.