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 m yotonic dystrophy (MD). This study was performed to determine whether a con -elation exists between electrophysiological (EP) testing data and clinical status, heart function, or size of the DNA abnormality (cytosine-thymine-g uanine 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 conc ordant with endocardial measurements, However, Il of 20 patients with norma l surface ECGs had abnormal subhisian conduction. Atrial arrhythmias were i nducible in 41% of cases and correlated with prolongation of the AH interva l (P=0.02) and a shorter atrial refractory period (P=0.04). Induction of ve ntricular arrhythmias (18%) correlated strongly with age (P=0.0003), After adjustment fur age, the extent of DNA mutation correlated with the Walton s core (P=0.0018) but not with conduction abnormalities or induction of arrhy thmias, Conclusions-Prolongation of the HV interval is the most common conduction a bnormality in MD and can be reliably recognized only by invasive EP testing . It raises the issue of prophylactic pacing to limit the incidence of sudd en death in MD. Atrial and ventricular arrhythmias are often inducible, alt hough their predictive value remains to be determined. Young age emerged as the most powerful predictor of inducible ventricular tachyarrhythmias, Con versely, we found no relationship between ECG or EP abnormalities recorded during invasive testing and the DNA mutation size or severity of peripheral muscle involvement.