Prolonged Corrected QT Interval in Patients with Myotonic Dystrophy Type 1

BACKGROUND AND PURPOSE Sudden cardiac death is one of the leading causes of death in patients with myotonic dystrophy type 1 (DM1). It has been proposed that a prolonged QT interval is associated with sudden cardiac death in several neurological diseases, including multiple system atrophy, idiopathic Parkinson's disease, and diabetic autonomic neuropathy. However, analyses of the corrected QT (QTc) interval in DM1 patients are rare in the literature. The purposes of this study were to determine the association between the QT interval and DM1, and the affecting factors. METHODS Thirty-nine patients diagnosed with DM1 through genetic testing were enrolled. The QTc interval (calculated using Bazett's formula: QTc=QT/√RR) was compared between these patients and 39 normal healthy controls. The clinical and laboratory factors affecting QTc interval in the patient group were investigated. RESULTS The QTc interval was significantly longer in the DM1 group (411.2±44.7 msec, mean±SD) than in the normal control group (355.6±20.6 msec). Intragroup analysis revealed that a prolonged QTc interval in DM1 patients was associated with being female and older, having a longer disease duration, and exhibiting abnormal electrocardiography findings. CONCLUSIONS The higher incidence of sudden cardiac death in the DM1 population is associated with the observed prolonged QTc interval in those patients.