ABSTRACT
The first diagnostic clinical application of a progressive work exercise test used 12-lead ECG measurements to detect coronary artery disease. Diagnostic exercise electrocardiography remains an essential part of a CPET, although primarily now as a safety measure to detect exercise-associated rhythm abnormalities or ischemia. While exercise ECG changes suggesting ischemia may be detected during a CPET, significant cardiac impairment may only manifest initially as a reduced maximal oxygen uptake associated with a proportionately reduced ventilatory threshold. Maximal oxygen uptake is a reliable surrogate measure of maximal cardiac output in both normal subjects and cardiac disease patients. With progression of any myocardial disease, the VO2 max has proven to be a useful assessment of risk for adverse events. A second, independent, established risk marker for cardiac patients is the averaged VE/VCO2 measurement. Finally, the relatively less-common finding of periodic breathing during exercise constitutes a third independent cardiac risk factor. A progressive increase in systolic blood pressure is expected with heavy effort, and the failure to develop systolic hypertension can be a sign of a significant ischemic or myocardial or valvular abnormality and ordinarily necessitates cessation of the exercise effort. A more specific finding of cardiac impairment is obtained from the course of O2 pulse (VO2/heart rate) measurements during a CPET. The O2 pulse should increase steadily during the CPET, and if it stabilizes or decreases in the later stages of exercise, it indicates that forward stroke volume is decreasing at higher heart rates. This abnormal finding has a wide differential diagnosis including diastolic dysfunction, ischemic heart disease, or valvular heart disease. Postural orthostasis tachycardia syndrome (POTS) represents an abnormality of exercise autonomic regulation without myocardial disease that is most frequently found in young women. The most common CPET manifestation of POTS is a failure to increase systolic pressure with maximal exercise effort.
