Objectives We sought to identify prospectively the prevalence of significant ischemia (≥10% of the left ventricle (LV)) on exercise SPECT imaging relative to workload achieved in consecutive patients referred for myocardial perfusion imaging (MPI). Background High exercise capacity is a strong predictor of a good prognosis, and the role of MPI in patients achieving high workloads is questionable. Methods Prospective analysis was performed on 1,056 consecutive patients who underwent quantitative exercise gated 99mTc-SPECT MPI, of whom 974 attained ≥85% of their maximum age-predicted heart rate (MAPHR). These patients were further divided based on attained exercise workload (<7, 7-9, or ≥10 METS) and were compared for exercise test and imaging outcomes, particularly the prevalence of ≥10% LV ischemia. Individuals reaching ≥10 METS but <85% MAPHR were also assessed. Results Of these 974 subjects, 473 (48.6%) achieved ≥10 METS. This subgroup had a very low prevalence of significant ischemia (2 of 473, 0.4%). Those attaining <7 METS had an 18-fold higher prevalence (7.1%, p<0.001). Of the 430 patients reaching ≥10 METS without exercise ST-depression, none had ≥10% LV ischemia. In contrast, the prevalence of ≥10% LV ischemia was highest in the patients achieving <10 METS with ST-depression (14 of 70; 19.4%). Conclusions In this referral cohort of patients with an intermediate to high clinical risk of CAD, achieving ≥10 METS with no ischemic ST-depression was associated with a 0% prevalence of significant ischemia. Elimination of MPI in such patients, who represented 31% (430/1396) of all undergoing exercise SPECT in this laboratory, could provide substantial cost-savings.

Background The benefit of myocardial perfusion imaging (MPI) over exercise ECG stress testing alone is unclear in individuals attaining a workload of ≥10 METS. The purpose of this prospective study is to determine mortality and nonfatal cardiac events in patients at either intermediate pretest risk for CAD or patients with known CAD, achieving ≥10 METS regardless of peak exercise heart rate. The authors previously reported a low prevalence of significant ischemia in this patient cohort. Methods Baseline characteristics, ECG stress test findings, and perfusion and function results from quantitative gated 99mTc-SPECT MPI were compared by achievement of a maximum age-predicted heart rate ≥85% in 509 consecutive patients who reached ≥10 METS. Events including all-cause and cardiac mortality, non-fatal myocardial infarction (MI), and late revascularization (>4 weeks after MPI) were prospectively collected. Results Of the 509 patients achieving ≥10 METS, follow-up for mortality was obtained in 463 (91%). Those lost to follow-up were older and had higher rates of tobacco use. The prevalences of CAD risk factors, prior known CAD, and MPI abnormalities were higher for the 68 patients failing to reach 85% of their target heart rate. The rate of ≥10% left-ventricular (LV) ischemia by MPI remained very low irrespective of attained heart rate (0.6% (3/463)). Six (1.2%) had an LVEF < 40%. Death occurred in 12 (2.6%) patients, one of which was classified as cardiac (0.1%/year). The other 11 deaths were related to cancer. Additionally, there were three nonfatal MIs (0.7 %) and one late revascularization (0.2%). Only one of these patients had any ischemia on MPI. No cardiac event patient had exercise ST depression or ≥5% LV ischemia. Conclusions Thus, patients at intermediate risk for CAD or known CAD achieving ≥10 METS have a very low prevalence of ≥10% LV ischemia and very low rates of cardiac mortality, nonfatal MI, and late revascularization, irrespective of heart rate achieved. Cardiac events did not correlate with abnormalities on the index MPI study. These results suggest that patients who attain ≥10 METS during exercise stress have an excellent prognosis over an intermediate term of follow-up, regardless of peak exercise heart rate achieved. The added value of MPI to standard exercise ECG testing in this population is questionable.

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