Suitable analyzed signal duration and criteria for abnormal signal-averaged electrocardiogram on frequency-domain analysis in patients with Duchenne's muscular dystrophy.

To establish the criteria for an abnormal signal-averaged electrocardiogram (SA-ECG) in patients with Duchenne's muscular dystrophy (DMD), we used the technique of fast-Fourier transformation and studied the effects of analyzed signal phase and attenuation of low frequency components by filter processing. Twenty-three patients with DMD and twenty age-matched healthy volunteers were studied. An abnormal SA-ECG was defined as an area ratio of high frequency components/low frequency components over the 97th percentile of normal controls. Frequency domain analysis of the terminal 40 ms of the QRS complex and 80 ms of the initial ST segment was most predictive for distinguishing DMD patients at risk for ventricular tachycardia (VT). Although filter processing reduced the power of low frequency components and increased the area ratios, the sensitivity for the prediction of VT was not significantly enhanced. The area ratios of 40-100 Hz/0-40 Hz were superior to the area ratios of 20-50 Hz/0-20 Hz for predicting patients with VT.