SPECTRAL-ANALYSIS OF THE CARDIAC CYCLE OF SIGNAL-AVERAGED FRANK LEADSFROM PATIENTS WITH VENTRICULAR-TACHYCARDIA

Identification of the spectral features in electrocardiograms that dis tinguish patients prone to ventricular tachycardia (VT) is a prerequis ite to increasing the diagnostic power of the signal-averaged electroc ardiogram (SAECG). To determine distinguishing features of the magnitu de spectrum, the spectra of SAECGs of sinus beats were analyzed over t he entire cardiac cycle from 32 patients with VT, 30 without VT, and 1 0 normal control subjects. The magnitude spectra of the Frank SAECGs s eparated patients with VT from those without VT over the band from 7 t o 140 Hz with a P value of .000000047. To determine distinguishing fea tures of phase and group-delay spectra, SAECGs of sinus beats over the entire cardiac cycle were analyzed from 57 patients with VT, 65 witho ut VT, and 20 normal control subjects. Unwrapped phase spectra from SA ECGs of the entire cardiac cycle were calculated with respect to the o nset of the Q wave. Phase spectra of SAECGs from patients with VT diff ered from those from non-VT patients at frequencies of 60 Hz or greate r (P = .00085). Average group delays in SAECGs fro patients with and w ithout VT differed (P = .00000069) from 14 to 24 Hz. Group delays in t he VT patients in the 14-24-Hz band were on average 9 ms and 5 ms long er than those of the non-VTs and normal subjects, respectively. Time-d omain reconstructions demonstrated that distinguishing frequency bands were detectable throughout the QRS complex, ST-segment, and T wave in SAECGs from each group. Thus, the spectra of SAECGs over the cardiac cycle contain features that together with temporal features from throu ghout the cardiac cycle are essential in improving methods for stratif ying risk of VT.