It’s been said that “exercise is God’s medicine”. After decades of data, this seems to be somewhat true in that there has yet to be any medicine, or procedure, or intervention that is more beneficial or lifesaving than exercise. In fact, exercise tolerance (one’s maximal exercise output, i.e. how hard and long one can exercise) is the single most important factor is determining longevity of life. Given this fact, exercise tolerance is the single most important metric to be measured in a patient.
Exercise tolerance testing (ETT) is used to determine the presence of significant coronary heart disease. ETT has been quoted as having a sensitivity of 78% and a specificity of 70% in detecting coronary artery disease (CAD).
- ETT consists of exercising on a treadmill following a defined protocol, the Bruce protocol, over approximately 20 minutes. The test begins gently and gradually the level of intensity is increased through a combination of increased treadmill speed and incline.
- Intensity of exercise is measured in metabolic equivalents (METs) where 1 MET is the amount of energy expended at rest or 3.5 ml oxygen per kilogram per minute.
The test is divided into seven stages of three minutes and there is also a less strenuous version called the modified Bruce.
- ECG is recorded throughout and blood pressure measured intermittently.
- ETT might be prematurely stopped for any of the following: development of chest pain, presence of ST elevation, very deep, 2 mm or more, ST depression, arrhythmias, hypotension or if the patient becomes tired and is unable to continue. In addition, elevation of blood pressure to dangerous levels such as >250/115 mm Hg should also lead to termination of the test.
- Beta-blockers and digoxin can interfere with the results so are usually stopped before the ETT.