Quantification of area at risk during coronary occlusion and degree of myocardial salvage after reperfusion with technetium-99m methoxyisobutyl isonitrile.

Abstract

Serial myocardial imaging with technetium-99m methoxyisobutyl isonitrile (9'Tc-MIBI) has been proposed for evaluating myocardial salvage after reperfusion. To define 'mTc-MIBI uptake before and after reperfusion, 17 open-chest dogs underwent 3 hours of left anterior descending artery occlusion and 3 hours of reperfusion. 9'Tc-MIBI was injected during occlusion (group 1) or after 90 minutes of reperfusion (group 2). Myocardial 99'Tc-MIBI activity was correlated with microsphere flow during occlusion and reperfusion. Anatomic risk area and infarct area were defined by postmortem vital staining and correlated with the perfusion defects defined by analysis of 99mTc-MIBI macroautoradiographs and gamma camera images of myocardial slices. The left ventricle was divided into 96 segments for gamma well counting. Flow and '9"Tc-MIBI activity were normalized to nonischemic values. Myocardial segments were grouped, based on occlusion flow, into zones: severely ischemic (<30% nonischemic), moderately ischemic (>30%o, .60%o nonischemic), mildly ischemic (>60%o, <90%1 nonischemic), and nonischemic (>90%o, < 120% nonischemic). Among dogs injected with "'Tc-MIBI during coronary occlusion (group 1), myocardial 99'Tc-MIBI activity correlated linearly with occlusion flow for both endocardial (r=0.91) and transmural (r=0.91) segments. The risk area defined by '9mTc-MIBI autoradiography (group 1) correlated with the postmortem risk area (p=0.94) but was 29O smaller than the anatomic risk area (p=0.03), reflecting the contribution of collateral flow. Among dogs injected with "'Tc-MIBI after reperfusion (group 2), myocardial 99"Tc-MIBI did not correlate with reperfusion flow in either endocardial or transmural segments. Among group 2 dogs, myocardial 9'Tc-MIBI activity was significantly less than reperfusion flow at the time of injection in the severely ischemic (25 ±5% versus 74±24% nonischemic,p=0.002), moderately ischemic (54±12% versus 96+15% nonischemic, p=0.001), and mildly ischemic (84±6% versus 93±3% nonischemic, p=0.002) zones. The defect area defined by 'mTc-MIBI autoradiography (group 2) correlated very closely with the postmortem infarct area (p=0.98). Thus, the myocardial uptake of 99mTc-MIBI during coronary occlusion correlates with occlusion flow and reflects the "area at risk." When 99mTc-MIBI was given after 90 minutes of reperfusion following 3 hours of coronary occlusion, the myocardial activity was significantly reduced compared with reperfusion flow in both necrotic and perinecrotic regions, reflecting myocardial viability more than the degree of reperfusion. (Circulation 1990;82:1424-1437 T X ahe current management of myocardial infarcinfarction, the extent of myocardial necrosis is detertion focuses on the application of acute mined by the "area at risk," collateral flow, and the interventional reperfusion techniques to duration of coronary occlusion.2 A noninvasive imagreduce myocardial necrosis.1 During myocardial ing technique that could 1) assess the area at risk, 2)

Validation of Collateral Fractional Flow Reserve by Myocardial Perfusion Imaging

“…Restoration of hyperemic reperfusion flow after balloon deflation does not significantly alter the original distribution of the tracer when injected during coronary occlusion, as demonstrated by Sinusas et al 23 and De Coster et al 24 in open chest dogs. The use of 99m Tc-sestamibi imaging as a measure of myocardial ischemia severity during coronary occlusion not only in the setting of acute coronary syndrome but also during controlled coronary artery occlusion, as in our model, has also been validated before.…”

Extent of Myocardium at Risk for Left Anterior Descending Artery, Right Coronary Artery, and Left Circumflex Artery Occlusion Depicted by Contrast-Enhanced Steady State Free Precession and T2-Weighted Short Tau Inversion Recovery Magnetic Resonance Imaging

“…8,9 More recently, the advent of perfusion imaging, such as by myocardial perfusion single-photon emission computed tomography (MPS), [10][11][12][13][14][15] and tissue characterization by cardiovascular magnetic resonance (CMR) 7,[16][17][18][19] has allowed for visualization of MaR directly. However, only 2 MPS studies with a limited number of patients have looked at the extent of perfusion territories.…”

Myocardium at risk: Reasons and methods for measuring the extent

“…In contrast to the earlier studies involving thallium-201, 12 technetium99m-based perfusion tracers undergo minimal redistribution, allowing image acquisition several hours after injection. [13][14][15] Another advantage of Tc-99m over Tl-201 is the higher peak energy window, which allows a more accurate identification of the boundaries of a perfusion defect and increases accuracy of gated images. However, the limited availability of tracers in the emergency room and intensive care units, the need of injecting isotope in the acute setting and of scanning patients with a gamma camera, let alone radiation exposure for the patient and the operator, limits the actual utilization of SPECT for measuring the area at risk and salvaged myocardium.…”