Anisotropic repolarization in ventricular tissue.
Gotoh, Masamichi, Takumi Uchida, Wei Fan, Michael C. Fishbein, Hrayr
S. Karagueuzian, Peng-Sheng Chen.
Division of Cardiology, Department of Medicine (M.G., T.U., W.F.,
H.S.K., P.-S.C.) and Department of Pathology (M.C.F.), Cedars-Sinai
Medical Center, and the School of Medicine, University of California
Los Angeles, Los Angeles, California
APStracts 3:0388H, 1996.
Using extracellular recording and stimulation techniques, it has been
demonstrated that the effective refractory period of epicardial
ventricular cells is significantly influenced by the sequence of
activation. Whether or not myocardial fiber orientation is also
important in determining the repolarization process is unclear. To
determine the importance of fiber orientation on the repolarization
process, we studied 12 blocks of pig right ventricular tissue in
vitro. The size of each tissue block was 30 mm X 30 mm X 2 mm.
Transmembrane action potentials were recorded and effective
refractory periods were measured from the epicardial surface of the
preparation, which showed nearly uniform fiber orientation. Tissues
were paced at 500 ms and 1,000 ms cycle lengths. Sequential
recordings were made at 1, 4, 7, 10, 13, and 16 mm from the site of
stimulation along and across the fibers. The results showed that
propagation of depolarization was much slower in the transverse
direction than in the longitudinal direction. In the transverse
direction, action potential duration was longest at the closest
observation point, i.e., 1 mm away from the site of stimulation
(188+/-14 ms and 267+/-18 ms, respectively, for 500 and 1,000 ms
pacing cycle lengths). It progressively shortened as the recording
site was moved farther away from the stimulating site (p<0.001).
The action potential duration 16 mm from the site of stimulation was
165+/-11 ms and 247+/-12 ms for 500 and 1,000 ms pacing cycle
lengths, respectively. In contrast, the action potential duration in
the longitudinal direction did not change as the distance between
recording site and the S1 site increased. We conclude that, at
physiological temperature and pacing cycle lengths, sequence of
activation significantly influenced action potential duration when
the propagation of activation was transverse to myocardial fiber
orientation. When activation propagated parallel to fiber
orientation, there was little or no change of action potential
duration as distance increased.
Received 18 July 1994; accepted in final form 5 June 1996.
APS Manuscript Number H631-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996