The Journal of Thoracic and Cardiovascular Surgery, Vol 104, 364-373, Copyright © 1992 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Myocardial oxygen consumption of fibrillating ventricle in hypothermia. Successful account by new mechanical indexes--equivalent pressure- volume area and equivalent heart rate
H Yaku, Y Goto, S Futaki, Y Ohgoshi, O Kawaguchi and H Suga
Department of Cardiovascular Dynamics, National Cardiovascular Center (NCVC) Research Institute, Osaka, Japan.
We studied the effects of cardiac hypothermia on myocardial oxygen
consumption of a fibrillating ventricle and evaluated whether myocardial
oxygen consumption of a fibrillating ventricle in hypothermia can be
accounted for by new mechanical indexes: equivalent pressure-volume area
and equivalent heart rate in the isolated cross- circulated canine heart
preparation. Equivalent pressure-volume area is the area that is surrounded
by a horizontal pressure-volume line at the pressure of a fibrillating
ventricle and the end-systolic and end- diastolic pressure-volume relations
in the beating state in the pressure-volume diagram. Equivalent
pressure-volume area is an analog of the pressure-volume area of a beating
heart and has been proposed to be a measure of the total mechanical energy
of a fibrillating ventricle. Equivalent heart rate was calculated from
myocardial oxygen consumption per minute in both beating and fibrillating
states under unloaded conditions as an estimate of the frequency of
contractions of individual myocytes on the assumption that individual
myocytes during ventricular fibrillation have the same contractility as
that in the beating state. We estimated myocardial oxygen consumption per
minute of the fibrillating ventricle at various ventricular volumes as a
function of both equivalent pressure-volume area and equivalent heart rate.
The myocardial oxygen consumption-equivalent pressure-volume area relation
during ventricular fibrillation in hypothermia was highly linear, with a
correlation coefficient of 0.90 (mean). The relation between estimated and
directly measured myocardial oxygen consumption values of a fibrillating
ventricle in hypothermia was highly linear (r = 0.98), and the regression
line (y = 0.80x + 0.48) was close to the identity line in the working
range. Therefore we conclude that equivalent pressure-volume area is the
primary determinant of myocardial oxygen consumption during ventricular
fibrillation in hypothermia, and myocardial oxygen consumption of a
fibrillating ventricle in hypothermia can be accounted for by the
combination of equivalent pressure-volume area and equivalent heart rate as
in normothermia.
