Pressure-length loop in the ischemic segment during left circumflex coronary artery stenosis and its modification by afterload reducing in excised perfused canine hearts.

By using excised perfused heart preparations, we investigated the regional myocardial functions in the presence of a flow-limiting coronary stenosis of the left circumflex coronary artery (LCX) (approximately low reduction of pre-ischemic control), as well as global cardiac functions during afterload reducing, while keeping left ventricular end-diastolic pressure (LVEDP) and heart rate constant. After inducing the LCX stenosis, cardiac output (CO), peak left ventricular pressure (peak LVP) and stroke work (SW) decreased from pre-ischemic control values, i.e., 81.1 +/- 3.2%, p less than 0.005, 88.1 +/- 3.8%, p less than 0.02 and 72.2 +/- 5.7%, p less than 0.005, respectively (n = 7), whereas pressure-length (P-L) loop areas changed as follows; ischemic control values of the left anterior descending coronary artery (LAD) and LCX regions were 96.6 +/- 6.0%, n.s. and 72.6 +/- 9.0% of pre-ischemic control, p less than 0.02, respectively. Following afterload reducing with LCX stenosis, CO increased gradually, while the ischemic regional function started to further aggravate, and the initial point of further ischemic aggravation obtained in this experiment occurred at 63.5 +/- 6.9 mm Hg of mean aortic pressure (AoP). These results suggested that the increase of total cardiac function such as CO following afterload reducing was probably induced at the expense of aggravated regional ischemia. Therefore it was concluded that the treatment of ischemic myocardium by reducing afterload pressure should be done very carefully.