Differential uptake of myocardial perfusion radiotracers in normal, infarcted, and acutely ischemic peri-infarction myocardium.

OBJECTIVES

We measured the uptake of technetium-99m tetrofosmin (99m Tc) and thallium-201 (201 TI) in areas of healed transmural myocardial infarction and in the regions of acute peri-infarction ischemia.

METHODS

Anesthetised pigs with a 1-month old transmural infarction elicited by permanent ligature of the left anterior descending (LAD) coronary artery below the first branch underwent one hour of proximal LAD occlusion followed by injection of 99m Tc-tetrofosmin and 201TI either in the left atrium (GI, n= 19) or in the jugular vein (GII, n = 6). Twelve other pigs (GIII) with similar acute peri-infarction ischemia received 99m Tc-tetrofosmin and 201Tl into the left ventricle during cardiocirculatory arrest to rule out the effect of coronary collaterals. Radiotracer counting was determined in samples from normal, acute ischemic and necrotic regions.

RESULTS

Uptake of 99m Tc-tetrofosmin and 201 Tl was greater in the infarct scar (median % of normal tissue: 20 for 99m Tc and 8.6 for 201 Tl in GI; 22 and 15 in GII) than in acute ischemic myocardium (3.2 and 2.5 in GI; 6.4 and 3.3 in GII). Radiotracer injection in arrested hearts (GIII) depicted a similar pattern (median % of injected dose: 6.2 for 99m Tc and 10 for 201Tl in the scar; 2.3 and 4.0 in acute ischemia; 2.9 and 3.5 in normal tissue). The infarcted region showed connective tissue and lack of viable myocardium.

CONCLUSION

A 1-month old infarct scar with no viable myocardial tissue can take up significant fractions of 99mTc-tetrofosmin and 201Tl even in the absence of coronary collateral perfusion. Data suggest that the infarct scar can extract these radiotracers from the intraventricular blood.