Myocardial contrast echocardiography in acute myocardial infarction: Pathophysiological background and clinical applications

Abstract

Myocardial contrast echocardiography is a technique used in experimental and clinical settings in order to visualize the pattern of intramyocardial perfusion. In the acute phase of myocardial infarction, regional absence of flow during myocardial contrast echocardiography delineates the area at risk of necrosis, while the definitive non-perfused area expresses infarct size. Reopening the infarct-related artery, which may be achieved spontaneously by thrombolysis or percutaneous transluminal coronary angioplasty, is not a reliable indicator of intramyocardial reperfusion. If myocardial ischaemia due to coronary occlusion has been sufficiently prolonged and severe, not only myocyte viability, but also microvascular integrity is lost. Myocardial contrast echocardiography, using intracoronary injection of sonicated contrast medium, gives information about microvascular integrity and the effective presence of intramyocardial reflow. Anatomical integrity of microvasculature does not necessarily imply preserved function, and thus the microvessel vasodilating reserve may also be impaired. Myocardial contrast echocardiography has the potential to assess alterations in microvascular function, showing, in the myocardial area with reduced coronary reserve, a relatively reduced increase in echocontrast signal intensity when an intravenous vasodilator agent is administered.

Elevations in Troponin T and I Are Associated With Abnormal Tissue Level Perfusion

“…Coronary occlusion that is associated with significant myocardial damage may also be associated with disruption of the surrounding microvascular integrity. 24,25 A complex process involving platelets, neutrophils, oxygen radicals, complement, and other inflammatory mediators may then result in localized inflammation and worsening of microvascular obstruction. 23 The inflammatory consequences of microvascular dysfunction may then further limit the extent of blood flow at the tissue level after epicardial reperfusion, leading to further myocardial necrosis.…”

“…Accordingly, the no-reflow phenomenon has been associated with more extensive necrosis and is associated with regional and global ventricular dysfunction. 25,26 …”

Complications of Coronary Intervention

“…45 In the AMICI study, the extent of no-reflow at MCE was demonstrated to be the best predictor of adverse left ventricular remodeling after acute myocardial infarction, being superior to ST-segment resolution and to MBG among patients exhibiting TIMI flow grade 3. 20…”

Mortality in patients with TIMI 3 flow after PCI in relation to time delay to reperfusion

“…Suboptimal myocardial perfusion is associated with impaired coronary microcirculation, increased infarct size and higher mortality rates 11,21 . As a consequence, the focus of treatment is shifting towards the assessment of myocardial reperfusion at microvascular level.…”