Prognosis in patients achieving ≥10 METS on exercise stress testing: Was SPECT imaging useful?

The benefit of myocardial perfusion imaging (MPI) over exercise ECG stress testing alone is unclear in individuals attaining a workload of a parts per thousand yen10 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 a parts per thousand yen10 METS regardless of peak exercise heart rate. The authors previously reported a low prevalence of significant ischemia in this patient cohort. Baseline characteristics, ECG stress test findings, and perfusion and function results from quantitative gated (99m)Tc-SPECT MPI were compared by achievement of a maximum age-predicted heart rate a parts per thousand yen85% in 509 consecutive patients who reached a parts per thousand yen10 METS. Events including all-cause and cardiac mortality, non-fatal myocardial infarction (MI), and late revascularization (> 4 weeks after MPI) were prospectively collected. Of the 509 patients achieving a parts per thousand yen10 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 a parts per thousand yen10% 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 a parts per thousand yen5% LV ischemia. Thus, patients at intermediate risk for CAD or known CAD achieving a parts per thousand yen10 METS have a very low prevalence of a parts per thousand yen10% 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 a parts per thousand yen10 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.