Noninvasive indices of repolarization and its dispersion

In experimental studies using Langendorff perfused, isolated canine hearts immersed in a torso-shaped electrolytic tank we studied repolarization and its dispersion using direct epicardial measurements and newly derived, noni nvasive body surface indices. Activation recovery intervals (ARIs) measured from 64 epicardial sites based on differences between activation times (AT s) and recovery times (RTs) provided direct measures of repolarization. The indirect, torso surface indices were derived from inflections of the root- mean-square (RMS) voltage of the torso tank surface electrocardiograms reco rded simultaneously with the epicardial data. For cycle lengths ranging fro m 300 to 900 ms, and electrolyte temperatures ranging from 32 degrees C to 40 degrees C we calculated mean, variance, and range of ATs, RTs, and ARIs from the epicardium. From epicardial and torso surface RMS waveforms, we us ed times of R and T peal;s and their differences to estimate mean ATs, RTs, and ARIs, respectively. The RMS T wave width as determined from the second derivative inflections on either side of the T peak served as an estimate of the dispersion of RTs. In parallel studies, we showed that the direct me asures of repolarization and its dispersion were reflected in RMS waveforms generated from the epicardial electrograms themselves. In this study, we c onfirm that the torso and epicardial RMS waveforms reflect comparable infor mation for estimating repolarization and its dispersion. Furthermore, the d erived measures provide a method to assess mean ARIs and dispersion of RTs on a beat-to-beat basis and during abnormal (ectopic ventricular) activatio n sequences.