T wave changes

There are two major changes seen in T waves in the setting of myocardial ischemia and infarction: 1.) peaked or "hyperacute" T waves and 2.)T wave inversion. These are important changes that may be part of a Q-wave or non Q-wave infarction.

The T wave in a normal electrocardiogram shares the same polarity as the preceeding QRS complex in any given lead (Why?). In myocardial ischemia, repolarization of the affected area is delayed and therefore remains electrically negative (i.e., depolarized) for a longer period of time.

If the ischemia only affects the subendocardium, the delay of depolarization, the negative charge maintained by the ischemic area unopposed by the rest of the myocardial wall. This results in peaked or "hyperacute T waves."

Peaked T wave

When ischemia affects the epicardium, repolarization will occur in an endocaridal to epicardial direction (i.e., reversed). Therefore, the vector of ventricular repolarization in the affected area will reverse. For this reason, an electrocardiogaphic electrode placed over a zone of transmural ischemia will record an inverted T wave.

Inverted T wave

References: Chou, p.14,121