Effect of coronary reperfusion on technetium-99m methoxyisobutylisonitrile uptake by viable and necrotic myocardium in the dog.

Technetium-99m hexakis-2-methoxyisobutyl isonitrile (99mTc-MIBI) distribution is flow-dependent, permitting the imaging of coronary perfusion defects. However, the behaviour of this tracer in viable and necrotic tissues within the ischaemic area at risk is still being debated. In a clinically relevant canine model, dogs were submitted either to a 24-h permanent occlusion (group 1) of the left descending coronary artery (LAD) or to a 90-min LAD occlusion followed by 22.5 h reperfusion (group 2). 99mTc-MIBI and radiolabelled microspheres were injected 3 h before sacrifice. After delimiting the area at risk and the infarct by Evans blue perfusion and triphenyltetrazolium chloride staining, heart slices were imaged by scintigraphy and tissue radioactivity measured in a gamma-counter. In the necrotic area of both groups, the 99mTc-MIBI distribution was proportional to the myocardial blood flow, approximating a 1:1 ratio (identity line slope 1, intercept 0) with highly significant correlation coefficients (group 1 r = 0.87, group 2 r = 0.86), whereas in the viable-ischaemic area of both groups, the data points are widespread above and below the identity line, indicating both over- and underestimations of blood flow in these tissue areas. These results were more pronounced following reperfusion as compared with permanent occlusion. Multiple linear regression analysis confirms differences (P less than 0.001) in 99mTc-MIBI distributions between the viable-ischaemic and the necrotic zones. Delineation of the ischaemic area at risk was possible only with permanent occlusion. A hypoperfused area was observed after reperfusion but differs from the anatomical infarcted area.(ABSTRACT TRUNCATED AT 250 WORDS)