A normal resting electrocardiogram should not change your diagnosis. It is common in patients with angina pectoris and significant underlying coronary artery disease.
ECG during angina
If an electrocardiogram is taken during an episode of angina pectoris, different patterns of ST-T wave change may be seen. The most common is that of subendocardial injury associated with ST-segment depression. In the less common variant or Prinzmetal's angina, ST-segment elevation is seen. In other patients with myocardial ischemia, deep, symmetric T wave inversion may be present. Examples of these patterns follow.
Subendocardial injury
This electrocardiogram shows diffuse acute subendocardial injury. The characteristic feature demonstrated here is the ST-segment depression seen in most leads. This indicates that the current of injury is arising from the insde layer of the ventricle, that is, the subendocardium. Patients with coronary artery disease may develop these changes during an episode of angina pectoris.
Prinzmetal's angina
These tracings demonstrate the electrocardiographic features of Prinzmetal's angina. The first strip was taken during an episode of chest pain and shows anterior wall subepicardial injury with marked ST-segment elevations in leads V2 through V5. The second strip was taken after the chest pain resolved. The ST-segments have returned to the baseline.
Myocardial ischemia
This electrocardiogram shows myocardial ischemia. The characteristic feature demonstrated here is most marked in the precordial leads, specifically the deep symmetric T wave inversion seen especially in leads V2 through V5. Ischemic T wave changes are often transient. If they persist, they may be the result of prolonged ischemia, as may be seen with unstable angina or a non-Q wave infarction. Enzyme studies would be necessary to differentiate between these two possibilities.