Microvasculature in acute myocardial ischemia: part II: evolving concepts in pathophysiology, diagnosis, and treatment.

In the setting of suspected acute myocardial infarction (AMI), a cardiologist needs to know three things: (1) whether there is actually an ongoing infarction, (2) whether reperfusion therapy has succeeded, and (3) how much myocardium was salvaged by reperfusion. Myocardial contrast echocardiography (MCE) can answer the first question by demonstrating the presence of a perfusion defect resulting from reduced microvascular flow because of the presence of a thrombus in an epicardial coronary artery. In a recent multicenter study of 203 patients without ST-segment elevation who presented to the emergency department with chest pain, 21 had AMI, and MCE only missed 1 such patient (sensitivity of 95%).1 Panel A in Figure 1 demonstrates a MCE perfusion defect in a patient presenting to the emergency department with chest pain who was subsequently ruled in for an AMI. The success of reperfusion and degree of myocardial salvage are equally important to know in patients even with ST-elevation AMI. Coronary angiography is not reliable in this regard.2 Figure 1. MCE images of a patient with coronary occlusion (left panel) and reperfusion (right panel) after intravenous administration of microbubbles. Arrows indicate the extent of perfusion defect. Reprinted from Kaul S, Myocardial contrast echocardiography in acute myocardial infarction. In Braunwald E, ed. Heart Disease: A Textbook of Cardiovascular Medicine . Update 1, vol 2, No. 4). Philadelphia, Pa: WB Saunders Co; 2000. Used with permission. The success of attempted reperfusion can also be accurately assessed with MCE. Most currently used clinical and electrocardiographic parameters are accurate in ≈75% of the cases, whereas MCE has an almost 100% accuracy. Panel B in Figure 1 depicts MCE images that were obtained immediately after thrombolysis and showed that most of the myocardium was reperfused. A small region in the apex showed no reflow and failed to exhibit …

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