Provisional use of myocardial perfusion imaging in patients undergoing exercise stress testing: A worthy concept fraught with challenges

Excerpt

It has been recognized for many years that patients who achieve a high workload on exercise stress testing have an excellent prognosis, particularly in the absence of ischemic ST segment depression.1-4 Outpatients with a low-risk Duke Treadmill Score (based on exercise duration, magnitude of ST deflection and an angina index) had an observed annual mortality rate of only 0.25%.5 Exercise capacity has been shown to be a better predictor of all-cause mortality than maximum exercise heart rate.1 Myers et al1 reported that patients achieving a workload of ≥10 metabolic equivalents (METs), even in the presence of cardiovascular disease, had a relatively low risk of death during follow-up. For every 1-MET increment in peak treadmill workload, there was an associated 12% improvement in survival. These investigators found that, in both healthy subjects and those with cardiovascular disease, the peak exercise capacity was a stronger predictor of an increased risk of death than clinical variables or coronary artery disease (CAD) risk factors such as hypertension, smoking, and diabetes. It had greater prognostic value than peak exercise heart rate, ST depression, or exercise-induced arrhythmias. Morise et al6 found a 14% reduction in cardiac events among subjects <65 years of age, and an 18% reduction among subjects ≥65 years of age for each 1-MET increase in workload. After adjustment for age, the peak METs achieved was the strongest predictor of subsequent mortality. In another study, among patients with a positive exercise ECG, who achieved ≥10 METs, 93% had a negative exercise echocardiogram and less than 1% mortality after 7.2 years of follow-up.7 …