DM1 Patients with Small CTG Expansions are also at Risk of Severe Conduction Abnormalities.

BACKGROUND AND OBJECTIVES: A high risk of cardiac arrhythmias was reported in myotonic dystrophy type 1 (DM1). The purpose of the study was to evaluate the risk of severe electrocardiographic abnormalities in DM1 patients with small CTG expansions.
METHODS: We assessed the ECG done at DM1 diagnosis for 127 patients with ≤200 CTG repeats and for 82 of them who had ≥1 ECG over a period of follow-up of 11.7 ± 7.6 years (mean ± SD). Criteria of severe ECG abnormality are at least one of the following features: PR interval ≥240 msec, QRS duration ≥120 msec, second-degree or third-degree atrioventricular block, atrial fibrillation or flutter, insertion of a pacemaker or cardioverter-defibrillator.
RESULTS: At baseline, ECG was normal for 109 patients out of 127 (85.8%) and only 4 patients (3.1%) presented severe ECG abnormalities. At follow-up, 46 patients out of 82 (56.1%) had a normal ECG and 25 (30.5%) developed severe ECG abnormalities (p < 0.0001) including 6 of them who needed permanent pacemaker insertion. There were also 3 sudden deaths during the follow-up period. Using multivariate Cox regression analysis, age at entry (relative risk RR, 1.05; (95% CI 1.01-1.08; p = 0.012) and muscular weakness (MIRS) at the entry (RR, 2.03; 95% CI 1.28-3.22; p = 0.003) were significant risk factors for the development of severe ECG abnormality.
CONCLUSIONS: An increased risk of severe ECG abnormalitiesy and cardiac events is observed even in DM1 patients with small CTG expansions and warrants close cardiac follow-up similar to DM1 patients with larger CTG expansions.