Electrocardiographic determination of perioperative myocardial ischemia and stunning.

Many modalities are available for monitoring for ischemia. Electrocardiography (ECG) is the most suitable modality for monitoring for perioperative ischemia. The detection and monitoring of myocardial stunning is more difficult. T wave inversion or peaking may be caused by ischemia. However, numerous nonischemic causes may lead to perioperative T wave changes. Inverted T waves may also indicate myocardial stunning. ST deviation is the most commonly used feature of ischemia. ST depression may be indicative of subendocardial ischemia while ST elevation may be associated with transmural ischemia or injury. Perioperatively, ST deviation may be caused by many nonischemic causes. Fixed ST deviation may be caused by left ventricular hypertrophy (LVH), cardiac conduction changes, old MI, coronary artery disease, and other causes such as drugs, including digitalis. New ST deviation may be caused by changes in body position. During cardiopulmonary bypass, ST deviation may be caused by hypothermia and defibrillation. ST deviation may be caused by new cardiac conduction changes and pericarditis. Ischemia may cause changes in other features of the ECG including the R wave, Q wave, U wave, QRS axis, and the angle between QRS axis and T wave axis. However, the specificity of these features for ischemia is even lower than that of the ST segment.