In angina patients who are momentarily not feeling any chest pain, an electrocardiogram is typically normal, unless there have been other cardiac problems in the past. During periods of pain, depression or elevation of the ST segment may be observed. To elicit these changes, an exercise ECG test («bike test») may be performed, during which the patient exercises to their maximum ability before fatigue, breathlessness or, importantly, pain supervenes; if characteristic ECG changes are documented (typically more than 1 mm of flat or downsloping ST depression), the test is considered diagnostic for angina. The exercise test is also useful in looking for other markers of myocardial ischemia: blood pressure response (or lack thereof, particularly a drop in systolic pressure), arrhythmia and chronotropic response.
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Figure 50 — ECG during angina attack (depression of ST segment, inversion of T wave) and after (normalization)
