The exercise treadmill test: Estimating cardiovascular prognosis
ABSTRACTAbnormal hemodynamic responses to exercise treadmill testing may indicate an increased risk of coronary events and death, even if evidence of ischemia is absent. Exercise duration and the blood pressure, heart rate, and heart rhythm responses to exercise have prognostic significance.
KEY POINTS
- Of the prognostic factors, exercise duration is the one most strongly associated with risk of coronary events and death, independent of age, sex, or known presence and severity of coronary artery disease.
- A decrease in blood pressure with exercise can reflect severe coronary artery disease or left ventricular systolic dysfunction.
- A heart rate that does not increase adequately during exercise or does not recover rapidly after exercise is associated with an increased risk of death.
- Exercise training may help to improve the prognosis of patients with an abnormal hemodynamic response to exercise caused by poor general health.
CASE STUDIES REVISITED
As for the two men described at the beginning of this article, patient B has a worse cardiovascular prognosis than patient A.
Both men have the same pretest probability of coronary artery disease (about 50%), based on identical age, sex, and chest pain characteristics. The ST-segment response during exercise—the traditional marker of ischemia used to diagnose coronary disease—is also the same for each patient.
However, hemodynamic variables are markedly different between the two patients: patient B has several adverse prognostic indicators, including lower functional capacity, a hypotensive blood pressure response, and abnormal heart rate recovery.
The most widely used treadmill risk score, the Duke treadmill score,13 can be calculated as:
Exercise time (in minutes, Bruce protocol) minus 5 times the magnitude of ST-segment depression (in millimeters) minus 4 times the treadmill angina index (ie, 0 = no angina, 1 = nonlimiting angina, 2 = angina that is the reason for terminating exercise).
Applying this formula yields a Duke score of 4.5 (estimated annual cardiovascular mortality risk 0.25%) for patient A and a score of –3.5 (estimated annual cardiovascular mortality risk 2%) for patient B.
Because patient A exercised to a high workload, he is more likely to have a false-positive exercise ECG result than patient B. But whether an exercise ECG test is falsely positive or falsely negative can only be determined after coronary angiography.
Exercise hypotension, as seen in patient B, can indicate left ventricular systolic dysfunction with exercise but has not been shown to predict stroke risk.
MANAGEMENT CONSIDERATIONS
How to manage patients with an abnormal hemodynamic response in the absence of ischemia is uncertain. Given the excellent prognosis of patients with well-preserved exercise capacity, it is unlikely that revascularization procedures in these patients would improve outcome.
On the other hand, patients with an abnormal hemodynamic response due to poor general health or autonomic nervous system dysfunction may be able to achieve a better prognosis with interventions that improve some of the abnormal responses. Increased functional capacity through exercise training is associated with a lower mortality rate,42 and coronary artery bypass surgery can abolish exercise-induced hypotension.43
Strategies to further evaluate and treat patients with an isolated finding of chronotropic incompetence, abnormal heart rate recovery, or frequent exercise-induced ventricular ectopy are not clear and require future study.
