Regional load dependence of postischemic myocardium

Few studies have examined how load affects the contraction of the myocardium following ischemia. We have therefore developed a canine model in which preload (left atrial pressure) and afterload (mean arterial pressure) are independently varied and heart rate is kept constant. Systolic contraction was found to increase in proportion to preload under preischemic conditions. However, postischemic systolic contractions were reduced and the response to preload was also markedly diminished. Response of systolic thickening to preload was significant in controls (p = 0.003, N = 8) but nonsignificant after 10 minutes of ischemia and 1 hour of reperfusion. Effects of inotropic stimulation were also examined. Dobutamine restored systolic thickening and myocardial contraction to baseline levels following ischemia. However, contraction following dobutamine treatment remained lower than that observed under preischemic conditions. The ideal treatment of the postischemic myocardium should provide low afterload, high heart rate, and high contractility.