[Patency, perfusion and prognosis in acute myocardial infarct]

Early restoration of bloodflow in the infarct-related coronary artery is the principal mechanism by which early reperfusion therapies may improve outcome in patients with acute myocardial infarction. The beneficial effect of reperfusion is independent of the therapy used (thrombolysis or PTCA), but, as shown in many studies, depends very much on the time to reperfusion. The achievement of a normal bloodflow in the infarct vessel, the so called TIMI 3 patency is considered to be the gold standard for the evaluation of the success of reperfusion therapy. However, there is increasing evidence from recent studies, that restoration of epicardial bloodflow does not necessarily indicate perfusion at the myocardial level. As unequivocally shown by contrast echocardiography using intracoronary injections of microbubbles, this is true even for TIMI Grade 3 flow, which correlates most strongly with prognosis and usually is associated with a very low mortality of about 3 to 4%. Angiographic patency not only is a sometimes unreliable indicator of myocardial reperfusion, but also involves an invasive procedure, is expensive and not universally available. A readily available and simple indicator of reperfusion is the early resolution of ST segment elevation. Complete ST resolution at 90 or 180 minutes after the initiation of treatment is associated with an excellent prognosis, even better than TIMI 3 patency. In contrast, no ST resolution indicates an in-hospital mortality which is about 8-fold greater than with complete ST resolution. Since ST resolution may be more closely related with the relief of ischemia than angiographic patency, the prognostic power of the combination of both indicators should be greater than that of either of them alone. Thus, it is evident from many studies that patency of the infarct-related artery is necessary for myocardial salvage in acute myocardial infarction, but it has to be achieved rapidly and has to be complete and sustained. However, even an early and perfect angiographic result achieved by thrombolysis or PTCA, does not consistently indicate myocardial reperfusion, and the mechanisms of the often called no-reflow phenomenon are still poorly understood. The possible contribution of reperfusion injury to poor clinical outcomes after adequate epicardial flow has been restored is also a matter of controversy and deserves further research. Promising results were derived from studies with GP IIb/IIIa inhibitors, in which improved microvascular flow and myocardial reperfusion were observed, when these agents were used as adjunct to thrombolysis and PTCA.