The P wave may appear flat, but the QRS complex is mostly positive. The QRS complex will be primarily positive. Detecting trouble Myocardial ischemia, injury, and infarction interfere with repolarization, so you'll see changes in the ST segment and T wave. A change in the ST segment of 1 mm above or below the isoelectric baseline is significant, as is T-wave inversion. Because of abnormal repolarization, the T waves will become inverted and the ST segment will become depressed at least 1 mm below the baseline.
Myocardial ischemia is reversible, but if it continues, myocardial injury results.
Myocardial injury is reversible, but it indicates ongoing ischemia consistent with a coronary artery occlusion. Without prompt intervention, an MI may occur. Because the injured cells can't depolarize or repolarize fully, you'll see the ST segment elevate at least 1 mm above the baseline in the leads that monitor the area of occlusion. Myocardial infarction occurs when one or more coronary arteries are completely occluded. ST-segment elevation in the leads monitoring the area of myocardial ischemia.