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[Characterization of the asynergic myocardium in acute coronary syndrome using simultaneous dual radionuclide
Abstract:
The purpose of the present study was to evaluate the tissue characterization of the ischemic myocardium by dual single photon emission computed tomography (SPECT) with thallium-201 (Tl-201) and technetium-99m pyrophosphate (Tc-99m PYP) using the simultaneous collection method. The subjects consisted of 84 patients with acute coronary syndrome followed by protracted left ventricular asynergy. For precise interpretation of clinical scintigraphy, we used phantom experiments and the results were as follows: 1. The residual myocardium in the infarcted area could be evaluated to some extent from the severity of the defect on Tl-201 SPECT with optimal and unified image processing standardized by maximal pixel counts in the myocardium. 2. The influence of cross talk between two radionuclides on each tomographic image was negligible under usual clinical conditions. 3. In a subendocardial infarction model where the Tc-99m layer was located within 50% inside the phantom wall and the other space was filled with 201TlCl solution, the Tc-99m layer was clearly visualized inwardly as compared with the Tl-201 layer on dual SPECT with optimal image processing. 4. Transmural infarction could be visualized as a total defect on Tl-201 SPECT only when its diameter was greater than 2 to 2.5 cm. Taking these results into account, we evaluated clinical cases. According to the peak CK value and Tl-201 SPECT in the chronic phase, the subjects were categorized as transmural infarction (TMI), nontransmural infarction (NTMI) and unstable angina pectoris (UAP), and the scintigraphic characteristics of each group were compared. Short-axis tomographic features of all lesions were classified in nine types from 1A to IIIC by the combination of Tl-201 uptake grades (total defect: I, reduced uptake: II, normal: III) and the condition of Tc-99m PYP accumulation (negative: A, transmural: B, subendocardial: C). The relationship between recovery from asynergy and the dual scintigraphic findings was also evaluated and 17 patients in whom asynergy had nearly resolved in the chronic phase was especially classified in a reversible ischemic myocardial damage (RIMD) group. The clinical results were as follows: 1. In cases without reinfarction, a Tl-201 uptake in ischemically-injured lesions was variably improved in the chronic phase. In 9% of all the lesions of NTMI, a Tl-201 uptake showed total defects in the acute phase. 2. Type IIC lesions were most frequently observed, accounting for 43% of all lesions of NTMI.(ABSTRACT TRUNCATED AT 400 WORDS)