Characterization of the asynergic myocardium in acute coronary syndrome using simultaneous dual radionuclide emission computed tomography

Phantom and clinical studies were undertaken to determine the value of dual SPECT with Tl-201 and Tc-99m pyrophosphate using a simultaneous collection method in evaluating tissue characterization of ischemic myocardium. Phantom experiments revealed that the residual myocardium was detected from the severity of Tl-201 defect images; the influence of cross talk between two radionuclides was negligible; when the Tc-99m layer was located within 50% inside the phantom wall and the other space was filled with Tl-201 solution, the Tc-99m layer was visualized inwardly more clearly than the Tl-201 layer; and transmural infarction 2 to 2.5 cm in diameter was visualized as the total defect of Tl-201. Taking these results into account, scintigraphic characteristics in 84 patients with acute coronary syndrome were evaluated. Seventeen patients in whom asynergy had nearly resolved in the chronic phase were defined as the group of reversible ischemic myocardial damage. Tl-201 uptake in ischemic lesions was improved in the chronic phase when reinfarction was not seen. Both reduced uptake of Tl-201 and Tc-99m uptake in the subendocardial segment were seen in 43% for nontransmural infarction. Total defect of Tl-201 along with transmural uptake of Tc-99m was the most common for transmural infarction. For unstabler angina pectoris, there was no evidence of Tc-99m PYP uptake. Reduced or normal uptake of Tl-201 combined with negative Tc-99m uptake were dominant for reversible ischemic myocardial damage. Patients having relatively good recovery had a significantly higher prevalence of reduced Tl-201 uptake and subendocardial uptake of Tc-99m and a significantly lower prevalence of the total defect of Tl-201 and transmural uptake of Tc-99m. In conclusion, dual SPECT is useful for predicting reversibility in the early stage of acute coronary syndrome. (N.K.)