Pathophysiology of technetium-99m stannous pyrophosphate and thallium-201 scintigraphy of acute anterior myocardial infarcts in dogs.

Abstract

A B S T R A C T In 17 dogs with acute myocardial infarcts produced by ligation of the proximal left anterior descending coronary artery, a comparative study was made of myocardial scintigrams obtained with technetium-99m stannous pyrophosphate ("mTc-PYP) and thallium-201 ('Tl), tissue levels of 'Tc-PYP and 'Tl uptake, histopathologic alterations, and regional myocardial perfusion measured with radioactive microspheres. 9 of the 10 hearts examined histologically had transmural infarcts with outer peripheral, inner peripheral, and central zones characterized by distinctive histopathologic features. A progressive reduction in myocardial blood flow was demonstrated between normal myocardium and the centers of the infarcts, and correlated well with progressive reduction in 'Tl uptake in the same regions. Marked mTc-PYP concentration occurred in areas with partial to homogeneous myocardial necrosis and residual perfusion located in the outer peripheral regions of the infarcts. The latter areas also were characterized by the presence of muscle cell calcification. The patterns of distribution of "'Tc-PYP and m'°Tl explained the filling defects on 'Tl myocardial scintigrams and the doughnut patterns on 99mTc-PYP myocardial scintigrams in dogs with transmural infarcts. One dog with a subendocardial infarct had a small homogeneous area of activity on the "Tc-PYP myocardial scintigram, and showed marked uptake of 'mTc-PYP in subendocardial areas of extensive necrosis and calcification still receiving some coronary perfusion.Dr.

Sites and Mechanisms of Localization of Technetium-99m Phosphorus Radiopharmaceuticals in Acute Myocardial Infarcts and other Tissues

“…Hearts with proximal LAD occlusion had transmural anterior infarcts with histopathologically distinct central and peripheral regions as previously described (3,4).…”

“…A more detailed analysis was undertaken of the distribution of 99mTc-P and calcium in infarcted myocardium. Study of corresponding histologic sections allowed assignment of samples for tissue assay to the various histopathologically defined infarct zones (3,4). Total number of infarct samples assayed for each dog ranged from 15 to 35.…”

“…Bonte and associates first showed that the 99mTc-P bone scanning agents concentrate in areas of acute myocardial infarction, and suggested that this phenomenon was related to labeling of calcium deposits in the infarcts (2). Our previous experimental studies have demonstrated that a positive 99mTc-P myocardial scintigram results from selective concentration of the agent in areas with partial to homogeneous myocardial necrosis, mtultifocal mtusele cell calcification, and residual blood flow (3)(4)(5)(6). These findings were interpreted as supporting the proposed role of tissue calcification in concentration of the agent, but as not excluiding the possibility of other mechanisms (3)(4)(5)(6).…”

“…Our previous experimental studies have demonstrated that a positive 99mTc-P myocardial scintigram results from selective concentration of the agent in areas with partial to homogeneous myocardial necrosis, mtultifocal mtusele cell calcification, and residual blood flow (3)(4)(5)(6). These findings were interpreted as supporting the proposed role of tissue calcification in concentration of the agent, but as not excluiding the possibility of other mechanisms (3)(4)(5)(6). Other reports (7)(8)(9)(10)(11)(12)(13)(14)(15)(16) have confirmed the dependence of 99mTc-P concentration on the presence of myocardial necrosis, and the importance of blood flow for modulating the level of 99mTc-P uiptake.…”

Contrast enhancement of myocardial infarction: dependence on necrosis and residual blood flow and the relationship to distribution of scintigraphic imaging agents.

“…In each dog in this group the residual blood flow in the center of the infarct was 3% or more of normal myocardial blood flow. cells, but do not accumulate in normal myocardial cells.8' 12-14 Although both experimental" and clinical15 studies have raised the possibility that "mTc-PYP can accumulate to a slight degree in reversibly damaged myocardial cells, accumulation of "9mTc-PYP generally indicates irreversible myocardial damage.6 7,13 A recent study from our laboratory using scanning electron microscopy with elemental x-ray dispersive microanalysis indicated that substantial levels of iodine were measured in myocardial cells within the infarcted region, but no iodine was detected in normal myocardium. 15 The damaged myocardial cells that accumulated iodine showed drastic alteration of intracellular sodium-potassium ratio, suggesting the loss of cellular membrane integrity and probably irreversible cellular damage.…”