The four ECG complexes, shown here for review, are from the tracings just presented. They are representative of some of the electrocardiographic changes associated with acute myocardial ischemia and infarction. TQ and ST segment changes resulting in ST depression, as in (A) or elevation, as in (B) are the initial changes and may be followed by the development of Q waves (B) or QS complexes (C) and/or by T wave changes (D).