Area-at-risk determination by technetium-99m-hexakis-2-methoxyisobutyl isonitrile in experimental reperfused myocardial infarction.

Abstract

In a canine model of reperfused myocardial infarction, we tested the hypothesis that after reperfusion, technetium-99m-hexakis-2-methoxyisobutyl isonitrile (Tc-MIBI) tomographic imaging still reflects occlusion blood flow when the tracer is injected before reperfusion. Nine anesthetized dogs underwent 2 hours of coronary occlusion followed by 3 hours of reperfusion ending by being killed. Reference coronary blood flow was determined by radioactive microspheres injected during occlusion and after reperfusion. Biopsies in normal and ischemic myocardium and single photon emission computed tomography were obtained during occlusion and after reperfusion. Circumferential profiles were applied to axial slices divided into 5-degree sectors. The sectors were divided into 3 groups selected on the occlusion acquisition (normal, mildly reduced, and severely reduced) and compared with the postreperfusion acquisition. Tissular Tc-MIBI kinetics was assessed both by Tc-MIBI time-activity curves of normal and ischemic tissue obtained by biopsy and by the relative gradient between normal, ischemic, and necrotic postmortem tissue samples. In biopsy samples, Tc-MIBI content remained unchanged during occlusion and after reperfusion in normal as well as in ischemic tissue (4,662 +/- 2,237 counts/min/mg vs. 4,599 +/- 1,577 counts/min/mg in normal tissue, NS; 941 +/- 903 counts/min/mg vs. 1,087 +/- 721 counts/min/mg in ischemic tissue, NS). In postmortem tissue samples, there was a good correlation between occlusion microsphere blood flow and Tc-MIBI activity (r = 0.91). In the necrotic samples, mean normalized Tc-MIBI activity (10 +/- 17%) was slightly higher than the normalized microsphere blood flow (3 +/- 3%, p less than 0.001) but markedly lower than the normalized microsphere reperfusion blood flow (63 +/- 31%, p less than 0.001). Comparing the single photon emission computed tomographic acquisitions before and after reperfusion, Tc-MIBI activity remained unchanged in normal as well as in mildly reduced or severely reduced segments. Thus, our data are consistent with the hypothesis that Tc-MIBI traces blood flow, does not redistribute significantly despite reperfusion, and can be used for imaging the area at risk.

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.…”

Nuclear Cardiology Core Laboratory: State of the Art

“…Among the available myocardial perfusion tracers, 99m Tc-labeledsestamibi has been more extensively tested in clinical trials, and evidence supports the accuracy of 99m Tc-sestamibi SPECT for estimation of the area at risk and final infarct size. Studies in animal models of coronary occlusion/reperfusion have demonstrated a good correlation between measured 99m Tc-sestamibi SPECT defect size and true myocardial infarct size when radiotracer is either injected after coronary reperfusion or under permanent coronary occlusion [12][13][14] Furthermore, the area of reduced tracer uptake seen in images obtained by injection during coronary occlusion showed good correlation with reduced flow in the area at risk, as determined by microspheres [12]. Therefore, the area of salvaged myocardium can be assessed by the difference in defect sizes of images obtained by tracer injection during coronary occlusion, which estimates the total risk area, and the images obtained after tracer injection following reperfusion therapy ( fig.…”