Effect of ischemic zone size on nonischemic zone function

Abstract

To study the influence of ischemic zone size on function in nonischemic regions, wall thickening and the end-systolic pressure-thickness (ESPTR) relationship were measured before and during a 90-s coronary occlusion, which produced either a small or large (24 or 35% of left ventricular mass) area of ischemia. With both size ischemic areas, nonischemic zone isovolumic and ejection phase wall thickening increased during occlusion, primarily because of increased preload and, to a lesser extent, a reduced pressure component of afterload. The nonischemic region ESPTR was unchanged from preocclusion control with small ischemic mass. With larger ischemic mass, the nonischemic region ESPTR was shifted downward and to the left, indicating reduced end-systolic performance. The decline in the nonischemic zone ESPTR with large ischemic zone size was not due to reduced blood flow, shortening deactivation, reflex effects, or "tethering" but rather to the associated decline in coronary perfusion pressure. Thus the increase of nonischemic region wall thickening during acute ischemia is due to a change in ventricular loading conditions and not augmentation of contractile performance. Larger ischemic zone size can impair function in nonischemic myocardium by reducing the erectile component of end-systolic performance.

Contribution of asynchrony and nonuniformity to mechanical interaction in normal and stunned myocardium

“…It has been postulated that, during regional ischemia, either a difference in contractility (''weak and strong muscles in series'') or a difference in timing (''asynchrony'') between ischemic and nonischemic regions is responsible for the mechanical interaction (2,16,17,20,23,28). In the present study, we confirmed a role for both mechanisms in regionally stunned myocardium.…”

“…During ischemia, three independent factors have been identified to contribute to mechanical interaction: 1) changes in sympathetic tone, 2) the Frank-Starling mechanism, and 3) direct myocardial unloading (2,7,8,10,12,16,17,20,23,28,30). The proposed mechanism to explain mechanical interaction during ischemia is discussed for the present experimental conditions.…”

Nonischemic End-Systolic Performance

“…Whereas regional ischemia is usually associated with an increase in shortening and thickening in the nonischemic region, it is also accompanied by a decrease in the end-systolic performance of the nonischemic region [1, 2]. Not surprisingly, the size of the ischemic bed appears to be the principal determinant of nonischemic end-systolic function [1, 2].…”

“…Whereas regional ischemia is usually associated with an increase in shortening and thickening in the nonischemic region, it is also accompanied by a decrease in the end-systolic performance of the nonischemic region [1, 2]. Not surprisingly, the size of the ischemic bed appears to be the principal determinant of nonischemic end-systolic function [1, 2]. Ischemia of a large area has been shown to be associated with a decrease in nonischemic end-systolic performance as manifested by a leftward and downward shift of the nonischemic end-systolic pressure-thickening relationship [2](fig.…”

“…Not surprisingly, the size of the ischemic bed appears to be the principal determinant of nonischemic end-systolic function [1, 2]. Ischemia of a large area has been shown to be associated with a decrease in nonischemic end-systolic performance as manifested by a leftward and downward shift of the nonischemic end-systolic pressure-thickening relationship [2](fig. 1) and a rightward and downward shift of the end-systolic pressure-length relationship [1].…”