The effect of changes in afterload on systolic bulging

It has been previously shown that after acute coronary occlusion, the extent of systolic bulging is dependent on preload and the function of the remote nonischemic myocardium is influenced by the motion of the ischemic myocardium as well as by the loading conditions. To examine the isolated effects of changing afterload on the movement of acutely ischemic and nonischemic myocardium, seven open-chest, anesthetized dogs were paced from the left atrium at a rate of 100 beats/min after crushing of the sinus node. The pulmonary artery was perfused artificially and the left ventricular end-diastolic pressure (LVEDP) was carefully controlled with a right heart bypass system. Twenty minutes after occlusion of the left anterior descending artery, the peak left ventricular pressure (LVP) was adjusted to three levels (70, 90, and 110 mm Hg) by blood withdrawal or aortic constriction, while the LVEDP was kept constant (8.3 +/- 2.3 mm Hg). Segment length in the ischemic (IZ) and nonischemic zones (NZ) were measured with sonomicrometers and total, isovolumetric, and ejection systolic shortening (% delta L) were calculated. Changes in left ventricular minor-axis diameter were measured with diameter crystals. Increasing the peak LVP increased the LVP both at aortic valve opening and closing. To keep the LVEDP constant as peak LVP was increased, the cardiac output had to be decreased (p less than .0001).(ABSTRACT TRUNCATED AT 250 WORDS)