Effects of ectopic pacing on left ventricular repolarization were
studied in six anesthetized open-chest chickens. In each animal,
unipolar electrograms were acquired from as many as 98 sites
with 14 plunge needles (seven transmural locations between
epicardium and endocardium in each needle). Activation-recovery
intervals (ARIs), corrected to the cycle length, were used for
estimating repolarization. At baseline, the nonuniform ARI
distribution in the left ventricle resulted in the apicobasal
differences being greater than the transmural gradient.
Nonuniform ARI prolongation caused by ectopic pacing resulted
in decreasing the transmural repolarization gradient and
increasing the differences in the apex-to-base direction. The
basal, but not apical transmural differences contributed to the
total left ventricular transmural gradient. The total left ventricular
apicobasal gradient was contributed by the apicobasal differences
in mid-myocardial and subendocardial layers more than in
subepicardial ones. Thus, in in situ chicken hearts, the transmural
and apicobasal ARI gradients exist within the left ventricle with
the shortest ARIs in the basal subepicardium and the longest
ARIs in the subendocardium of the apical and middle parts of the
left ventricle. Apicobasal compared to transmural heterogeneity
of local repolarization properties contributes more to the total left
ventricular repolarization gradient.
Sympathetic modulation of the relation between ventricular repolarization and cycle length.
