How are the results of an exercise tolerance test interpreted?

Updated: Nov 20, 2018
  • Author: Richard S Krause, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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The primary finding resulting in a “positive” exercise tolerance test is ST depression on the ECG monitor. A test is considered positive when one or more cardiac leads shows ST depression of 1 mm or greater. The probability and severity of CAD is related directly to the amount of depression and downslope of the ST segment. It is also correlated with the lowest workload at which the depression occurs.

An exercise test will be terminated and considered positive if significant chest pain develops during the test. It is more predictive of CAD if it is also associated with ST depression. Other symptoms such as lightheadedness, vertigo, or peripheral cyanosis may be indicative of inadequate cardiac output.

Secondary endpoints of note in exercise tolerance testing include exercise capacity and hemodynamic response. Exercise capacity is measured in METs. One MET is the equivalent of the resting oxygen uptake while sitting quietly. An exercise of capacity of 5 METs or less is associated with poor prognosis in patients younger than 65 years. An exercise capacity of 13 METs or more indicates a good prognosis even when an abnormal ECG response is noted. [8]

Systolic BP at peak exertion is consider a clinically useful estimation of the inotropic capacity of the heart. A drop of systolic BP below that at rest is associated with an increased risk in patients who have known CAD. Heart rate response to exercise can be affected by left ventricular dysfunction, ischemia, arrhythmias, cardioactive drugs, and autonomic dysfunction. Failure to achieve at least 80% of the age-predicted maximum exercise heart rate is associated with an 84% increase in all-cause mortality in the subsequent 2 years. [9]  The heart rate and BP recovery patterns after cessation of exercise also hold prognostic significance. Slower return to baseline vital signs is associated with higher long-term mortality.

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