MET is an abbreviation for metabolic equivalent. It is arrived at by measuring the oxygen consumed by the patient, which reflects the energy the patient is expending. One MET is 3.5 ml 02/kg/min, the oxygen consumption by an average individual at rest. It is estimated that most people need to be able to perform exercise at an intensity of at least 5 METs in order to carry out adequately activities of daily living.
What are the differences between a normal and abnormal exercise ECG?
The single most reliable indicator of exercise-induced ischemia is ST-segment depression. One millimeter or more of horizontal or downsloping ST depression is generally considered indicative of an abnormal ischemic change. Greater amounts of ST depression and downsloping morphology increase specificity for ischemia. Upsloping ST depression is a less specific ECG change. Some suggest that 1.5 mm of upsloping ST depression should be considered diagnostic of ischemia, but more rapidly upsloping ST depression is a nondiagnostic finding.
ST elevation with exercise is an infrequent finding that may represent severe ischemia. When it occurs in an area of prior infarction (in leads with pathologic Q waves), it is a nonspecific finding that is thought to be caused by abnormal wall motion. ST elevation in lead aVR is also a nonspecific finding.
T wave changes, such as inversion or pseudonormalization,‚ in the absence of ST-segment shift are also nonspecific findings. Finally, changes in R-wave amplitude and in U-wave axis have been associated with ischemia but are not of great clinical utility.