exercise tolerance test

An exercise tolerance test is the classic treadmill (or stationary bicycle) test, in which a patient walks at a gradually steepening, faster pace while an electrocardiogram, blood pressure, heart rate, and symptoms are watched throughout. It is the simplest, oldest form of stress test: the exertion raises the heart's demand for oxygen, and the ECG is read for the telltale changes of a struggling, under-supplied heart muscle.

The standard Bruce protocol raises the speed and incline in stages every few minutes until the patient reaches a target heart rate, becomes too tired, or develops chest pain, breathlessness, dangerous ECG changes, or a fall in blood pressure. The key positive finding is ST-segment depression on the ECG, the electrical signature of ischemia. How long the patient lasts, the symptoms, blood-pressure response, and recovery all add prognostic information beyond a simple positive-or-negative result.

Because it relies on the resting ECG showing meaningful changes, the plain exercise test is less reliable when the baseline ECG is already abnormal, in patients on certain drugs, and on average in women. It also says nothing about which artery is affected. When greater accuracy or localization is needed, exercise is combined with imaging — stress echo or perfusion scanning — rather than the ECG alone.