ECG Changes in Acute Myocardial Infarction

• Myocardial Ischemia– Symmetrical T wave inversion or elevation and

ST segment elevation or depression

• Myocardial Injury– ST segment elevation or depression

• Myocardial Necrosis– Abnormal Q waves

Abnormal T Wave

• Repolarization begins at the epicardium and progresses toward the endocardium producing a + T-wave.

• Abnormal T waves indicate myocardial ischemia and appear within seconds of the onset of an acute MI. These are caused by a delay or change in direction of repolarization.

• Abnormal T waves are associated with depression or elevation of the ST segment.

Abnormal ST Segments

• Abnormal ST segments are present in myocardial infarction, indicating myocardial ischemia and injury, and in noninfarction-related myocardial ischemia from any cause

• ST Segment Elevation

• ST Segment Depression

ST Segment Elevation• ST elevation is an ECG sign of severe, extensive,

usually transmural, myocardial ischemia and injury in the evolution of an acute Q-wave MI.

• ST elevation is considered > 1 mm above baseline and measure .04 second after the J point.

• ST elevation usually appears within minutes after the onset of infarction, initially indicating extensive myocardial ischemia and a progression to Myocardial injury within 20 to 40 minutes.

• Then to Myocardial Necrosis in about 2 hours and the development of abnormal Q waves.