Influence of cardiac stress protocol on myocardial perfusion imaging accuracy: The role of exercise level on the evaluation of ischemic burden

Background: Some specifics of cardiac stress protocols, i.e., stressor used or exercise level achieved, may impact myocardial perfusion imaging (MPI) accuracy. Methods: Four-hundred and seventy-five patients were submitted to MPI and coronary angiography. MPI was performed after exercise (303 patients) or dipyridamole stress (172 patients). A coronary stenosis ≥70% was considered significant. In case of exercise test, a peak heart rate (HR) <85% of the maximal age predicted was considered submaximal and categorized as follows: >75% and <85% (“Group 1”); <75% (“Group 2”). Results: At coronary angiography, 312/475 (66%) patients showed significant stenosis. In the overall population, MPI showed a high accuracy in unmasking significant coronary stenosis, independently of the stress protocol adopted (AUC.76 for exercise vs.78 for vasodilator; P = NS). However, in case of an exercise stress test, a significant interaction between peak %HR and MPI diagnostic power was evident. While an elevated accuracy was still maintained in “Group 1” patients (AUC.79; P vs maximal exercise = NS), a significant drop was demonstrated in “Group 2” patients (AUC.66; P vs maximal exercise = .012, and P vs “Group 1” = .042). Conclusions: The accuracy of MPI is not influenced by the stress protocol adopted. Exercise MPI maintains an elevated accuracy as long as the %HR remains >75%