AJP - Heart and Circulatory Physiology, Vol 273, Issue 2 583-H592, Copyright © 1997 by American Physiological Society
Severe diastolic dysfunction with preserved energy conversion efficiency after countershock
S. Yasuda, T. Shishido and Y. Goto
Department of Internal Medicine, National Cardiovascular Center, Osaka, Japan.
The left ventricular (LV) mechanical performance and the LV myocardial
oxygen consumption (VO2)-to-pressure-volume area (PVA; LV total mechanical
energy index) relationship were measured in isovolumic contraction of
isolated blood-perfused dog hearts before and after direct current (DC)
countershocks. At a constant LV volume, DC shocks increased LV
end-diastolic pressure progressively and strikingly with the progression of
myocardial edema and a marked prolongation of the time constant of LV
pressure decay. In contrast, DC shocks changed neither the slope of the LV
end-systolic pressure-volume relationship nor the contractile efficiency
(the slope of the Vo2-PVA relationship). The oxygen cost of contractility
(the slope of the relationship between PVA-independent VO2 and LV
contractility) increased 27% after DC shocks. However, the magnitude of
this change was considerably smaller than that previously reported in
postischemic stunned myocardium (123%), suggesting that the adverse effect
of DC shocks on the energy cost of excitation-contraction coupling is
relatively minor. Thus, despite the severe diastolic dysfunction, DC shocks
do not substantially impair either the efficiency of cross-bridge cycling
or calcium cycling. Myocardial interstitial edema is more likely a
potential mechanism of diastolic dysfunction after DC shocks.
