Effect of ischemia and postischemic dysfunction on myocardial uptake of technetium-99m-labeled methoxyisobutyl isonitrile and thallium-201

Abstract

The myocardial uptake of a new technetium-99m-labeled myocardial perfusion agent, methoxyisobutyl isonitrile (Tc-99m MIBI), and thallium-201 was correlated with microsphere flow in an open chest canine model of low coronary flow and postischemic dysfunction. Eighteen dogs were given an injection of thallium-201 (0.5 mCi) and Tc-99m MIBI (5 mCi) either after 40 min of partial left anterior descending artery occlusion (Group I, 10 dogs) or during reperfusion after 15 min of left anterior descending artery occlusion (Group II, 8 dogs). Regional dysfunction was documented during injection in both groups by quantitative two-dimensional echocardiography. Regional blood flow was assessed by radiolabeled microspheres. The heart was excised 15 min after radionuclide injection and the left ventricle divided into 96 segments for gamma well counting. Among Group I dogs, central ischemic thallium-201 and Tc-99m MIBI activity (expressed as a percent of the activity in the corresponding nonischemic zone) was comparable, respectively, for endocardial (54 +/- 17% and 52 +/- 17%), mid-wall (71 +/- 20% and 69 +/- 17%) and epicardial (89 +/- 13% and 94 +/- 9%) segments and increased proportionally with flow. There was a good linear correlation among these endocardial segments between flow and both thallium-201 (r = 0.78) and Tc-99m MIBI (r = 0.85) activity. Among Group II dogs, central ischemic endocardial flow (59 +/- 14%) was comparable to thallium-201 (70 +/- 18%) and Tc-99m MIBI (74 +/- 12%) activity. Similarly, relative endocardial flow in the intermediate ischemic region (71 +/- 11%) was comparable to thallium-201 (77 +/- 11%) and Tc-99m MIBI (81 +/- 10%) activity. Thus, myocardial uptake of Tc-99m MIBI and thallium-201 is comparable under conditions of low coronary flow and postischemic dysfunction and closely parallels flow alterations.

Comparison of thallium deposition with segmental perfusion in pigs with chronic hibernating myocardium

“…They noted that relative thallium uptake in the subendocardial samples was linearly proportional to relative microsphere flow (correlation coefficient of 0.78). Consistent with redistribution, the relative thallium uptake was systematically and significantly greater than relative perfusion (23). When thallium was allowed to accumulate for 2.5 h, there was a further increase in relative thallium uptake (22).…”

“…Although the subsequent time points continued to show linear correlations, there was a progressive decrease in the slope at 2 h (slope ϭ 0.58; r ϭ 0.79) and 4 h (slope ϭ 0.39; r ϭ 0.66) after thallium administration. Thus thallium redistribution progressed but was still incomplete at 4 h. Similarly, Sinusas et al (23) evaluated thallium accumulation in dogs over the final 20 min of a 1-h partial coronary occlusion. They noted that relative thallium uptake in the subendocardial samples was linearly proportional to relative microsphere flow (correlation coefficient of 0.78).…”

Single-day combined evaluation of regional myocardial perfusion and function at rest and peak exercise with99mTc-MIBI in patients with coronary artery disease

“…Therefore, > 80% regional diagnostic accuracy was obtained even in submaximal (i.e. at lower risk) exercise tests, confirming that 9~mTc-MIBI results are not affected by the exercise level very much, in comparison with 2~ [34], probably because of the different characteristics of the 2 tracers [4,5,7].…”

The noninvasive assessment of myocardial viability

“…("TI is dependent on regional blood flow and the extraction fraction 0f")~T1 by the myocardium.-w3h In a canine model of myocardial stunning resulting in severe postischemic dysfunction, reduced flow, and no necrosis, normal myocardial 201T1 extraction and washout kinetics are observed.". 37 After injection and initial uptake of 'o'T1 into the myocardium, continuous exchange occurs between viable myocardium and the blood pool. If ?…”