• Acute ST depression can be associated with ischemia, non-Q wave infarction, electrolyte abnormalities, osmolality changes, hyperventilation, standing, and certain drugs. An ECG should be obtained in any patient with chest pain of uncertain etiology because an acute ST shift can confirm that it is due to ischemia. The amount of ST depression is measured from the PR segment (the iso-electric line).
• Chronic ST depression is a non-specific marker for cardiac disease, but is associated with a poor outcome. It can be due to electrolyte abnormalities and drugs, particularly digoxin. It may be associated with subendocardial damage, as opposed to Q waves, which are associated with transmural damage due to infarction. It is controversial whether or not rest ST depression ever represents chronic ischemia associated with hibernating myocardium.

The patient must be questioned as to the past or present history of cardiac ischemic pain. Obtain blood chemistries including electrolytes, glucose, calcium, magnesium, BUN and creatinine. Carefully record all medications and be sure of their non-prescription drugs that can contain diuretics and even digoxin. If ischemic chest pain is described, the Duke Angina score can be used to estimate prognosis. A treadmill test usually will be indicated to evaluate the chest pain.