Relationships among electrophysiological findings and clinical status, heart function, and extent of DNA mutation in myotonic dystrophy.

BACKGROUND: Impulse-conduction abnormalities and arrhythmias are common in myotonic dystrophy (MD). This study was performed to determine whether a correlation exists between electrophysiological (EP) testing data and clinical status, heart function, or size of the DNA abnormality (cytosine-thymine-guanine sequence repeat). METHODS AND
RESULTS: Eighty-three MD patients underwent invasive EP studies prompted primarily by the presence of asymptomatic conduction abnormalities. AV conduction disturbances were common and mainly distal (HV interval, 66.2+/-14 ms). AV conduction observed from the surface ECG was generally concordant with endocardial measurements. However, 11 of 20 patients with normal surface ECGs had abnormal subhisian conduction. Atrial arrhythmias were inducible in 41% of cases and correlated with prolongation of the AH interval (P=0.02) and a shorter atrial refractory period (P=0.04). Induction of ventricular arrhythmias (18%) correlated strongly with age (P=0. 0003). After adjustment for age, the extent of DNA mutation correlated with the Walton score (P=0.0018) but not with conduction abnormalities or induction of arrhythmias.
CONCLUSIONS: Prolongation of the HV interval is the most common conduction abnormality in MD and can be reliably recognized only by invasive EP testing. It raises the issue of prophylactic pacing to limit the incidence of sudden death in MD. Atrial and ventricular arrhythmias are often inducible, although their predictive value remains to be determined. Young age emerged as the most powerful predictor of inducible ventricular tachyarrhythmias. Conversely, we found no relationship between ECG or EP abnormalities recorded during invasive testing and the DNA mutation size or severity of peripheral muscle involvement.