Myocardial contrast echocardiography (MCE) has profoundly extended our understanding of myocardial microvascular perfusion after acute myocardial infarction, and intravenous contrast application with bedside imaging is now feasible. Ito and colleagues showed that all patients with TIMI grade 2 flow after PTCA showed substantial no-reflow on MCE, defined as contrast defects after angioplasty of more than 25% of the risk zone (determined before recanalisation). But even with TIMI grade 3 flow, 16% of the patients showed no-reflow, and significant improvement of left ventricular function was only observed in the patients with reflow.6 Comparing microvascu-lar perfusion and regional myocardial contractile recovery,
Ragosta and associates concluded that microvascular integrity, as assessed by MCE, is closely related to myocyte viability.7 Sakuma and colleagues demonstrated that the size of the risk area, determined before reperfusion, as well as a low peak grey scale ratio on MCE one day after primary PTCA for acute myocardial infarction, strongly predicted major cardiac events within the next 22 months.8 Risk factors for the development of perfusion defects on MCE were not consistent in different studies, but most of them reported a higher incidence of no-reflow with longer elapsed time from onset of symptoms to reperfusion, older age, large anterior myocardial infarction, low admission blood pressure, and, interestingly, with the absence of pre-infarction angina, which might be interpreted as a clinical correlate of microvascular preconditioning.
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