Is it possible to identify infrahissian cardiac conduction abnormalities in myotonic dystrophy by non-invasive methods?

Objective-To identify intracardiac conduction abnormalities in patients wit h myotonic dystrophy from their clinical, EGG, and genetic features. Methods-39 consecutive patients (mean (SD) age 42.9 (12.1) years; 16 female , 23 male) underwent clinical examination, genetic studies, resting and 24 hour ambulatory EGG, signal averaged EGG, and electrophysiological studies. Results-23 patients suffered from cardiac symptoms, 23 had one or more card iac conduction abnormality on resting EGG, one had sinus deficiency, and 21 (53.8%) had prolonged HV intervals. No correlation was found between the s everity of the neurological symptoms, onset of disease, cardiac conduction abnormalities on EGG, and the intracardiac conduction abnormalities on elec trophysiological study. The size of the DNA mutation was longer in the abno rmal HV interval group than in the normal HV interval group (3.5 (1.8) v 2. 2 (1.0) kb, p < 0.02). Signal averaged ECG parameters (total QRS duration ( QRSD) and duration of low amplitude signals less than or equal to 40 mu V ( LAS 40)) were greater in patients with an abnormal HV interval than in thos e with a normal HV interval (123.4 (24.6) v 102.8 (12.3) ms and 47.5 (12.8) v 35.3 (8.8) ms, respectively; p < 0.005). Only the association of QRSD gr eater than or equal to 100 ms with LAS 40 greater than or equal to 36 ms id entified patients with an abnormal HV interval with good sensitivity (80%) and specificity (83.3%). Conclusions-Infrahissian conduction abnormalities are common in myotonic dy strophy and can be identified using signal averaged electrocardiography.