Key result
Submaximal exercise performance is linked to ~7-fold higher annual cardiac event rates vs. high capacity.
Why the study?
Submaximal stress testing achieving less than 85% MPHR may lead to nondiagnostic results, and the prognostic value of submaximal versus high exercise capacity stress echocardiography needed evaluation.
Cohort (n=1,781)
Submaximal normal stress echo signals intermediate risk; leaves open whether ischemia findings should guide management at performance extremes.
BACKGROUND: Submaximal stress testing or achieving <85% maximum predicted heart rate (MPHR) may lead to nondiagnostic results and indeterminate outcomes. High exercise capacity (≥ 10 metabolic equivalents, METS) is a predictor of favorable prognosis. The purpose of this study was to evaluate the prognostic value of submaximal or high exercise capacity stress echocardiography. METHODS: We evaluated 1781 patients (55 ± 13 years; 59% male) undergoing treadmill stress echocardiography divided into 811 patients with submaximal (<85% MPHR) and 970 patients with high exercise capacity (≥ 10 METS). Resting left ventricular ejection fraction and regional wall motion were assessed. The left ventricle was divided into 16 segments and scored on 5-point scale of wall motion. Abnormal stress echocardiography was defined as stress-induced ischemia (wall-motion score of ≥ 1 grade). Follow-up (3.3 ± 1.5 years) for nonfatal myocardial infarction (MI) (n = 40) and cardiac death (n = 52) were obtained. RESULTS: By univariate analysis, echocardiographic variables of ejection fraction, peak wall-motion score index (WMSI) and number of new ischemic wall-motion abnormalities were significant predictors of cardiac events. Cumulative survival was significantly worse in patients with abnormal (ischemic) versus normal (nonischemic) stress echocardiography in submaximal (4.4%/year vs. 1.3%/year, P < 0.0001) and high exercise capacity (1.5%/year vs. 0.2%/year, P < 0.0001) studies. Multivariate Cox proportional hazards analysis identified number of new ischemic wall-motion abnormalities as the strongest predictor of cardiac events (P < 0.05) in both groups. CONCLUSIONS: Despite normal stress echocardiography, the inability to achieve 85% MPHR conferred a higher, intermediate cardiac event rate of 2.9%/year. The ability to achieve 9 minutes (≥ 10 metabolic equivalents, METS) conferred an overall low cardiac event rate of 0.4%/year. However, the absence or presence of ischemia by stress echocardiography was able to further risk stratify patients with either submaximal or high exercise capacity studies.
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Yao et al. (2013) conducted a cohort in Undergoing treadmill stress echocardiography (n=1,781). Submaximal exercise (<85% maximum predicted heart rate) vs. High exercise capacity (≥ 10 metabolic equivalents) was evaluated on Cardiac events (nonfatal myocardial infarction and cardiac death). Submaximal exercise performance (<85% maximum predicted heart rate) conferred a higher cardiac event rate compared to high exercise capacity (2.9%/year vs. 0.4%/year), although the presence of ischemia further stratified risk.
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