Relationship between myocardial perfusion scintigraphy and workload for identifying patients at high risk for myocardial ischemia

Abstract

The stress and rest myocardial perfusion scintigraphy (MPS) measures the workload achieved using metabolic equivalents (METs) and verifies the presence of ischemic changes in electrocardiographic exams. Thus, this study aimed to evaluate these variables and identify which ones would be useful in identifying patients with severe myocardial ischemia. This cross-sectional retrospective study analyzed 2,388 medical records of patients who had been referred for MPS; they were recruited using non-probabilistic convenience sampling. The patients were divided into two groups according to the METs achieved, and the prevalence of severe ischemia was measured using the Wackers-Liu software. A total of 506 patients achieved 10 METs without electrocardiographic changes in the ST segment during stress; they were classified as group B. Of these, 0.4% presented severe myocardial ischemia. Patients from group A did not reach 10 METs (n = 515 patients) and presented ischemic electrocardiographic changes in the ST segment; 3.6% of them presented severe myocardial ischemia, which was significantly different (p < 0.0002). These findings highlight that patients presenting ischemic electrocardiographic changes in the stress phase with a workload <10 METs were 9-fold more likely to have severe myocardial ischemia than those who achieved ≥10 METs without ischemic electrocardiographic changes. Therefore, a workload that reaches ≥10 METs without electrocardiographic changes compatible with ischemia may be a good predictor for the absence of severe myocardial ischemia in MPS.