AJP - Heart and Circulatory Physiology, Vol 271, Issue 3 1094-H1098, Copyright © 1996 by American Physiological Society
Electrophysiological background of individual variability in electrical defibrillation efficacy
Y. Murakawa, T. Yamashita, K. Ajiki, K. Sezaki, Y. Kanese and M. Omata
Second Department of Internal Medicine, University of Tokyo, Japan.
This study was performed to test whether heart-to-heart variability of
defibrillation efficacy is attributable to differences in postshock
refractory state of nondepolarized myocardium. In 30 anesthetized dogs, a
localized potential gradient was created using 1-16 V of stimulus across a
pair of platinum plate electrodes on the right ventricle (5-mm
interelectrode distance). The postshock recovery interval (PSRI) of the
relatively refractory myocardium directly adjacent to the excited area was
estimated by measuring the recovery interval after an appropriately timed
field stimulus. The transcardiac defibrillation threshold (DFT) was also
determined. The results showed that DFT normalized by the weight of the
heart was inversely correlated with the PSRI measured with a field stimulus
of 6 V (local shock intensity approximately 5 V/cm) or more (6 V: r =
-0.502, P < 0.005; 16 V: r = -0.635, P < 0.0005). This observation
suggests that variability of defibrillation efficacy in intact hearts is
largely due to differences in the postshock refractory state of the
nondepolarized myocardium.
