Assessment of preload reserve in myocardial ischemia--the relation between preload reserve and ischemic size differs between anterior descending and circumflex coronary artery occlusions in a canine model.

Abstract

The role of changes in preload in maintaining stable hemodynamics during coronary obstruction was assessed in the presence of myocardial ischemia due to occlusions of the left anterior descending (LAD) and left circumflex (LCX) coronary arteries. Changes in preload (mean left atrial pressure) to maintain a constant stroke volume after coronary occlusion were examined in 18 anesthetized dogs (LAD occlusion in 9 dogs, LCX occlusion in 9 dogs). The level of ischemia was assessed sonomicrometrically. Ventricular function curves relating left atrial pressure to stroke volume were assessed during a control state and after 1 min of coronary occlusion. The extent of preload reserve after coronary occlusion was examined on the ventricular function curves and was defined as the change in mean left atrial pressure required to maintain stroke volume at the level of the control state under conditions of regional ischemia. Ischemic size was determined by a stereo-angiogram after the animals were sacrificed. The extent of preload reserve (X) was linearly related to the ischemic size (Y) in both LAD (Y = 0.90 + 0.16X, r = 0.76, p < 0.001) and LCX (Y = -1.79 + 0.19X, r = 0.79, p < 0.001) occlusions. The slopes of the regression lines in LAD and LCX occlusions were the same. The X intercepts of these lines were -5.6% and 9.4% of the left ventricular weight in LAD and LCX ischemia (p < 0.001), respectively. Thus, the presence of systolic wall motion abnormalities due to coronary occlusion can be compensated for hemodynamically by changes in the preload reserve.(ABSTRACT TRUNCATED AT 250 WORDS)