SUMMARY To determine whether a reduction in myocardial oxygen demand or an increase in coronary blood flow or both are responsible for the salutory effect of intraaortic balloon counterpulsation (IABP) in relieving medically refractory angina, we assessed these variables in six patients in whom IABP was required for relief of myocardial ischemia. IABP decreased the rate7pressure product and aortic enddiastoliczpressure, and the peak systolic aortic pressure and regional myocardial oxygen consumption declined in-all but one patient. Peak and mean aortic diastolic pressures increased. Changes in regional coronary blood flow paralleled changes in peak systolic aortic pressure (r = 0.92, p < 0.007). Thus, relief of angina during IABP could not be ascribed to an increase in regional coronary blood flow. Reduction of myocardial oxygen consumption is the most likely mechanism by which IABP relieves myocardial ischemia in patients with unstable angina pectoris. The mechanism-by which IABP relieves myocardial ischemia is unclear. Possible explanations include enhancementof coronary blood flow through obstructed or collateral coronary vessels,3-22reduction in myocardial oxygen demand,23-28 or both. An increase in coronary blood flow during IABP might be anticipated because marked augmentation of diastolic blood pressure is a fundam'ental and consistent effect of this intervention. Nevertheless, data reported regarding the coronary blood flow response are inconsistent. An important limiting factor in assessing the coronary hemodynamic effect of IABP in patients with coronary artery disease -has been the difficulty in measuring regional-rather than global left ventricular myocardial blood flow.An investigation from our laboratory using a fixed, high-grade coronary stenosis in the awake pig indicates that coronary-blood flow to ischemic myocardium does not consistently increase with IABP.29 Rather, regional blood flow distal to the stenosis tends to decrease in association with the observed reduction in myocardial oxygen demand that results from IABP. Accordingly, the results of our animal study suggest the hypothesis that IABP lessens myocardial ischemia primarily by reducing myocardial oxygen demand rather than by increasing oxygen supply. The objective of the present investigation was to test this hypothesis in patients with medically refractory unstable angina pectoris.Methods The patients were carefully selected to include only those with high-grade left anterior descending stenosis and objective evidence of anterior wall ischemia to permit regional assessment of coronary blo'od flow and myocardial metabolism in the area of myocardium responsible for the clinical syndrome. Nine patients were identified as being suitable candidates for investigation. The thermodilution catheter could not be properly positioned in two patients and satisfactory. diastolic augmentation was not achieved in one patient. The remaining six patients constitute the study group. There were four males and two females, ages 48-71 years (mean 62 year...
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