Repolarization abnormalities in Duchenne-type muscular dystrophy

OBJECTIVES
Duchenne-type muscular dystrophy (DMD) is an X-linked recessive inherited disease affecting mainly the skeletal and cardiac muscles. We aimed to seek associations between the incidence of ventricular arrhythmias and corrected QT (QTc) dispersion and its component, corrected JT (JTc) dispersion in patients with DMD.

STUDY DESIGN
The study included 43 consecutive male patients (mean age 8.8±3.0 years; range 3 to 17 years) with DMD. On standard 12-lead electrocardiograms (ECG) the QT and JT intervals and the corrected QT (QTc) and JTc dispersions were calculated. Ventricular extrasystoles were assessed on 24-hour Holter ECG recordings. Ventricular dysrhythmic patterns were evaluated according to the Lown-Wolf classification. The results were compared with those of a control group of 34 healthy children (mean age 9.5±3.1 years).

RESULTS
The mean QTc and JTc dispersion values were significantly higher in DMD patients compared to controls (QTc: 78.0±20.6 msec vs. 50.9±16.5 msec; JTc: 77.6±20.5 msec vs. 50.8±17.7 msec; p<0.05). The results of Holter monitoring were evaluated in 36 patients and in 33 controls. Ventricular extrasystoles were found in six patients (16.7%) and in one (grade I) control subject (3%). The incidence of pathological findings was significantly higher in the study group (p<0.05), including grade I pathology in four patients, grade II pathology in one patient, and grade IV in one patient. QTc and JTc dispersion values of the patients with and without ventricular extrasystoles showed no statistically significant difference (p>0.05).

CONCLUSION
Similar QTc and JTc dispersion values detected in patients with and without ventricular extrasystoles may suggest that ventricular repolarization abnormalities occur in early life and may predispose to the development of ventricular arrhythmias in the long-term.