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.