Mechanical and surgical interventions for the reduction of myocardial ischemia

To reduce myocardial ischemia effectively, mechanical or surgical interventions must achieve either augmentation in coronary blood flow, a reduction in myocardial oxygen demand, or a combination of both. Coronary bypass graft procedures can achieve an immediate augmentation in coronary blood flow distally through the involved vessel and thereby improve myocardial perfusion and oxygen delivery and thus have the potential for reversing myocardial ischemia both acutely and for the long term. Although myocardial revascularization may resolve the ventricular functional alterations associated with acute myocardial ischemia it remains uncertain whether revascularization can reverse ischemic myocardial cellular injury and in what time framework, as related to reversible vs. irreversible ischemic cellular changes. Mechanical circulatory assistance (MCA) using diastolic counterpulsation effectively reduces myocardial ischemia by the physiologic mechanisms of 1) decrease in left ventricular after-load and left ventricular wall tension, 2) improvement is cardiac output by diastolic counterpulsation and 3) augmentation of coronary blood flow by diastolic pressure augmentation. The most effective indication for either MCA or myocardial revascularization is for interruption of myocardial ischemia prior to the development of infarction. Clinical sudies have demonstrated that acute myocardial ischemia can be effectively interrupted by intraaortic balloon pumping (IABP) including reversal of left ventricular dysfunction associated with acute myocardial ischemia. In most instances, cessation of IABP resulted in recurrence of myocardial ischemia indicating the need for urgent revascularization surgery. In the management of medically refractory myocardial ischemia. IABP has been effective in complete suppression of ischemia in 80 percent and resulted in marked improvement in all, allowing safe revascularization surgery with an operative mortality in the range of 5% and perioperative myocardial infarction incidence of 2%. In patients with acute myocardial infarction and cardiogenic shock (AMI-CS), IABP can resolve CS in 75 percent. The combination of IABP and surgery has resulted in survival approaching 45 percent indicative of a significant improvement in salvage in this group of patients where expected mortality approaches 100 percent.