Objective: For preoperative radionuclide myocardial perfusion imaging, metabolic equivalent is one of the key factors to evaluate the appropriateness. Duke Activity Status Index is a practical method to calculate metabolic equivalents. We intended to validate Duke Activity Status Index in our population for the assessment of preoperative myocardial perfusion imaging appropriateness.
Methods: A total of 542 patients referred for myocardial perfusion imaging were recruited. A questionary compiled from Duke Activity Status Index was filled out based on which metabolic equivalents were calculated. Demographic data and history of cardiac risk factors were also collected. Myocardial perfusion imaging was performed using a 2-day stress-rest protocol either by exercise tolerance test or by pharmacologic stress through injection of Tc-MIBI and imaging by a dual-head gamma camera.
Results: Out of 542 patients, 369 (68.1%) were evaluated for preoperative risk assessment. Metabolic equivalents (oxygen consumption/min/kg) were calculated at 9.3 ± 5.1, 10.8 ± 4.8, and 8.7 ± 5.1 in total, preoperative patients and patients evaluated for ischemia due to nonsurgical purposes, respectively (p = 0.001). The myocardial perfusion imaging was rarely appropriate in 291 (79.5%), maybe appropriate in 67 (18.3%), and appropriate in 8 (2.2%) patients. The prevalence of abnormal myocardial perfusion imaging was 22.5%, 28.4%, and 12.5% in "rarely appropriate," "maybe appropriate," and "appropriate" scenarios, respectively. Metabolic equivalents were similar between patients with normal and abnormal myocardial perfusion imaging (8.7 ± 5.0 vs. 8.5 ± 5.4).
Conclusion: Either Duke Activity Status Index is not a proper tool for calculation of metabolic equivalents or the appropriate use criteria is not operational in the population of Iranian preoperative patients in which cultural factors may contribute.
Keywords: Duke Activity Status Index; appropriateness use criteria; metabolic equivalents; radionuclide myocardial perfusion imaging.