AJP - Heart and Circulatory Physiology, Vol 250, Issue 5 778-H785, Copyright © 1986 by American Physiological Society
Analysis of phases of contraction during graded acute myocardial ischemia
M. Akaishi, R. M. Schneider, R. J. Mercier, J. B. Agarwal, R. H. Helfant and W. S. Weintraub
The quantitative effects of graded ischemia on the phases of contraction in
ischemic and nonischemic myocardium were studied in 10 open-chest dogs.
During progressive coronary stenosis, an index of the overall severity of
ischemia, total myocardial blood flow deficit (TMFD), was measured using
microspheres. Segment shortening (% delta L) during the isovolumic and
ejection phases of systole in the ischemic and nonischemic zones was
obtained with ultrasonic crystals. In the ischemic zone, total systolic and
ejection phase % delta L decreased progressively as stenosis increased;
isovolumic phase % delta L showed segment elongation (bulging) during mild
ischemia, which was unchanged as ischemia became severe. Total % delta L in
the nonischemic zone increased progressively with increasing stenosis,
reaching 132 +/- 20% of the control value when TMFD was 24.8 +/- 6.5% of
total expected left ventricular (LV) myocardial blood flow. The increase in
total % delta L was entirely attributable to increased ejection % delta L
and correlated with indices of preload (multivariate r = 0.65) and
afterload (multivariate r = 0.62). Multiple linear regression analysis
revealed that augmented contraction in the nonischemic zone was best
described (multivariate r = 0.94) by a combination of four hemodynamic
variables estimating LV preload and afterload, which correlated in turn
with the overall severity of ischemia. Thus systolic bulging in the
ischemic zone is primarily an isovolumic phase phenomenon that develops
initially with mild ischemia. Little additional change occurs in the
isovolumic phase as ischemic severity increases, although further
reductions in shortening occur in the ejection phase.(ABSTRACT TRUNCATED AT
250 WORDS)
