Yield of downstream tests after exercise treadmill testing: a prospective cohort study

Abstract

Objectives: The purpose of this study was to estimate the frequency and results of downstream testing after exercise treadmill tests (ETTs).

Background: The utility of additional diagnostic testing after ETT is not well characterized.

Methods: We followed consecutive individuals without known coronary artery disease referred for clinical ETT at a large medical center. We measured the frequency and results of downstream imaging tests and invasive angiography within 6 months of ETT and the combined endpoint of survival free from cardiovascular death, myocardial infarction, and coronary revascularization.

Results: Among 3,656 consecutive subjects who were followed for a mean of 2.5 ± 1.1 years, 332 (9.0%) underwent noninvasive imaging and 84 (2.3%) were referred directly to invasive angiography after ETT. The combined endpoint occurred in 76 (2.2%) patients. The annual incidence of the combined endpoint after negative, inconclusive, and positive ETT was 0.2%, 1.3%, and 12.4%, respectively (p < 0.001). Rapid recovery of electrocardiography (ECG) changes during ETT was associated with negative downstream test results and excellent prognosis, whereas typical angina despite negative ECG was associated with positive downstream tests and adverse prognosis (p < 0.001). Younger age, female sex, higher metabolic equivalents of task achieved, and rapid recovery of ECG changes were predictors of negative downstream tests.

Conclusions: Among patients referred for additional testing after ETT, the lowest yield was observed among individuals with rapid recovery of ECG changes or negative ETT, whereas the highest yield was observed among those with typical angina despite negative ECG or a positive ETT. These findings may be used to identify patients who are most and least likely to benefit from additional testing.

Keywords: downstream testing; exercise testing; imaging.

Figure 1

Frequency of inconclusive exercise treadmill test results (ETT) (1A). The flow diagram depicts patterns of downstream testing after ETT (1B). MPHR = maximum predicted heart rate.

Figure 2

Results of downstream testing. Results of noninvasive imaging (2A), invasive angiography (2B), and all imaging (2C) obtained within six months after exercise treadmill testing (ETT) stratified by test results. The rate of positive results (yield) ranges from 0% to 21%, being lowest after rapid recovery of ECG changes; and highest after typical angina despite negative ECG or a positive ETT. 2C combines results from 2A and 2B. Obstructive disease denotes stenosis ≥ 50% in the left main coronary or ≥70% in all other coronary vessels. Positive angiography results denote either obstructive disease or coronary revascularization within six months after the most recent test. Negative angiography denotes absence of obstructive disease.

Figure 2

Results of downstream testing. Results of noninvasive imaging (2A), invasive angiography (2B), and all imaging (2C) obtained within six months after exercise treadmill testing (ETT) stratified by test results. The rate of positive results (yield) ranges from 0% to 21%, being lowest after rapid recovery of ECG changes; and highest after typical angina despite negative ECG or a positive ETT. 2C combines results from 2A and 2B. Obstructive disease denotes stenosis ≥ 50% in the left main coronary or ≥70% in all other coronary vessels. Positive angiography results denote either obstructive disease or coronary revascularization within six months after the most recent test. Negative angiography denotes absence of obstructive disease.

Figure 2

Results of downstream testing. Results of noninvasive imaging (2A), invasive angiography (2B), and all imaging (2C) obtained within six months after exercise treadmill testing (ETT) stratified by test results. The rate of positive results (yield) ranges from 0% to 21%, being lowest after rapid recovery of ECG changes; and highest after typical angina despite negative ECG or a positive ETT. 2C combines results from 2A and 2B. Obstructive disease denotes stenosis ≥ 50% in the left main coronary or ≥70% in all other coronary vessels. Positive angiography results denote either obstructive disease or coronary revascularization within six months after the most recent test. Negative angiography denotes absence of obstructive disease.

Figure 3

The results of invasive angiography in patients who underwent imaging after exercise treadmill testing. The figure includes all invasive angiography studies that occurred within 6 months after imaging. The yield of invasive angiography was higher after positive imaging (56%) than after negative imaging (25%). Obstructive disease denotes stenosis ≥ 50% in the left main coronary or ≥70% in all other coronary vessels.

Figure 4

Kaplan-Meier Curves examining outcomes according to exercise treadmill testing (ETT) results. Panel A shows survival free from myocardial infarction (MI) or cardiovascular death (CVD). The rates of MI or CVD were higher among patients with inconclusive ETT (hazard ratio, (HR) 5.4, P=0.004) and positive ETT (HR 8.6, P=0.006) than among those with negative ETT. Panels C and D show survival free from the combined endpoint of MI, CVD, or coronary revascularization. The rates of the combined endpoint were higher among patients with inconclusive ETT (HR 5.1, P<0.001) and positive ETT (HR 36.1, P<0.001). Patients with typical angina despite negative ECG had a higher incidence of the combined endpoint than other types of inconclusive ETT. *Hazard ratios were derived from Cox proportional hazards models adjusted for age and gender. HR = hazard ratio.

Figure 5

Kaplan-Meier curves describing survival free from the combined endpoint of myocardial infarction, revascularization or cardiovascular death for inconclusive exercise treadmill tests (ETT) stratified by functional capacity as measured by metabolic equivalents of task (METs) achieved during ETT (4). While there are no differences in event-free survival by functional capacity in the inconclusive ETT and typical angina groups, among patients with submaximal exercise, patients who achieved ≥ 7 METs had a lower event rate (P=0.013 by the log-rank test).