Prognostic value of thallium-201 single-photon emission computed tomographic myocardial perfusion imaging according to extent of myocardial defect. Study in 1,926 patients with follow-up at 33 months.

Objectives: This study was designed to assess the prognostic value of thallium-201 single-photon emission computed tomographic (thallium SPECT) perfusion imaging in patients evaluated for stable angina pectoris and to examine the relation, if any, between the presence and extent of myocardial defect and future fatal or nonfatal cardiovascular events (revascularization, secondary myocardial infarction).
Background: Compared with planar scintigraphy, thallium SPECT enables better evaluation of the extent of myocardial perfusion defect. However, its prognostic value has not yet been studied in a large population of patients.
Methods: Between 1987 and 1989 we studied 3,193 patients. After exclusion of patients with unstable angina, myocardial infarction during the previous month or earlier revascularization, 1,926 patients were followed up for 33 +/- 10 (mean +/- SD) months after stress thallium SPECT imaging (performed after exercise in 1,121 patients or during dipyridamole infusion in 805 patients). Thallium SPECT imaging of the left ventricle was divided into six segments.
Results: After normal thallium SPECT imaging (715 patients), the annual total and cardiovascular mortality rates were, respectively, 0.42%/year and 0.10%/year and were significantly higher after abnormal thallium SPECT imaging (respectively, 2.1%, relative risk 5, p = 0.012; 1.5%, relative risk 15, p < 0.0001 [log-rank test]). There was a significant relation between the number of abnormal segments and cardiovascular mortality during follow-up (p < 0.02) or the occurrence of nonfatal events (p < 0.001). The extent of defect on the initial scan provided the best SPECT variable for long-term prognosis. Thallium SPECT imaging provided additive prognostic information compared with other clinical variables (gender, previous myocardial infarction) and exercise electrocardiogram.
Conclusions: In patients with stable angina, normal thallium SPECT imaging indicates a low risk patient, and the extent of myocardial defect is an important prognostic predictive factor.