Long-term follow-up of patients with myotonic dystrophy: an electrocardiogram every year is not necessary.

A high risk of arrhythmias was reported in myotonic dystrophy (MD). The purpose of the study was to evaluate the value of non-invasive and invasive investigations for the arrhythmias detection and when to repeat the investigations. 129 patients, mean age 41 ± 14 years, with MD, were asymptomatic, except 4. Electrocardiogram (ECG), left ventricular ejection fraction determination, Holter monitoring, signal-averaged ECG, electrophysiological study (51) were obtained and repeated each year in patients without conduction abnormalities. Electrocardiogram and Holter monitoring were normal in 72 and 89 patients, respectively. Standard deviation of the mean RR intervals (SDNN) was <100 ms in 30 patients. Late potentials were present in 32 patients, without ventricular tachycardia (VT) correlation. Ejection fraction was normal in all but six patients (60±10.5%). HV interval was prolonged in 0 of 8 patients with normal ECG, 1 of 9 with isolated first degree atrioventricular block, 9 of 16 with hemiblock, and 10 of 15 with bundle branch block. Atrial fibrillation (AF) was induced in 22 patients, non-sustained VT in 6 patients, and sick sinus syndrome noted in 10 patients. The mean time for the ECG change was 5±1 years. After 10±7.5 years, AF occurred in 15 patients; 12 patients died. Multivariate analysis indicated that both AF at ECG and SDNN lower than 100 ms were independent predictors of death. HV increase was noted only in patients with abnormal ECG. The most frequent arrhythmia was AF and was associated with a high risk of death. The repetition of ECG every year is probably not useful.