[Study of suitable analyzed signal duration and criteria for abnormal signal averaged electrocardiogram on frequency-domain analysis in patients with Duchenne's muscular dystrophy].

We investigated the optimal condition to detect abnormalities on the fast-Fourier transformation of the signal-averaged electrocardiogram (SA-ECG) by studying the effects of analyzed signal duration, attenuation of low frequency components by using filtering processing and the criteria for abnormal SA-ECG. Subjects were 23 patients with Duchenne's muscular dystrophy (DMD) and were divided into two groups by the presence of ventricular tachycardia (VT). Age-matched healthy volunteers were obtained as controls. Abnormal SA-ECG was identified from the data in the controls as over 97 percentile of H/L ratio. Frequency domain analysis from last 40 ms of QRS wave to 80 ms of ST segment was most capable to distinguish the DMD patients with VT from the patients without VT, compared to analysis from last 20 ms. Whereas, analysis from QRS onset failed to detect VT patients. Although filter processing reduce the power of low frequency and increase the H/L ratio, sensitivity for predicting VT was not enhanced significantly. In conclusion, the frequency-domain analysis during the terminal 40 ms of the QRS complex and 80 ms of ST segment was most optimal condition to distinguish the DMD patients with VT.