Q. Evaluate the Magnitude of ST Depression?
It is intuitive that the magnitude of ST depression should correlate with the degree of the ischaemia. In patients with left main or left main equivalent angiographic changes or with other severe degrees of the ischaemia, the magnitude of ST depression is greater. When 2 mm or more of ST depression is present the probability of left main disease increases. The degree of ST depression at higher workloads depends on what is used for the indication to terminate exercise. If patients are pushed enough, or if they have some degree of left ventricular hypertrophy they may have severe ST depression. If patients with single vessel disease are encouraged to exercise strenuously or if they have some degrees of LVH, they may have very severe ST depression.
Bogaty found that in patients with 2 mm or more of ST depression, survival was determined by the duration of exercise on the Bruce protocol, not on the magnitude of depression. Thus the magnitude of ST depression at maximum workload, may not indicate the severity of coronary artery disease. Major ST depression at low workload indicates severe disease.