Identification and Localization of STEMI: ANTERIOR WALL

The key to identification of ST segment elevation lies in the ability of the provider to recognize patterns and identify elevation above the isoelectric or ECG baseline. Recall that STEMI is identified when a patient has symptoms consistent with Acute Coronary Syndrome (ACS) and the following ECG findings:

1.      ST elevation greater than 1 mm in TWO or more contiguous leads (with a narrow QRS)
(Many references cite >2mm of elevation in the precordial leads)

2.      ST depression greater than 1 mm in V1 and V2 for posterior wall myocardial infarction

In addition, the identification of STEMI is supported by presence of reciprocal change. Reciprocal change occurs when you see “opposite” ST segment changes in corresponding leads. In an inferior wall MI, the paramedic should see ELEVATION in leads II, III, and aVF. Reciprocal ST segment depression should occur in the lateral leads, or leads I and aVL.

ECG tracings DIAGNOSTIC of ST elevation myocardial infarction are displayed and examined for your review. The ECGs are actual tracings from prehospital Lifepak 12 or 15 monitors.

I.                 Recognizing the Anterior Wall STEMI







Note the widespread ST segment elevation in leads V1-V5. Elevation is most prominent in leads V2-V3. These ECG leads, placed across the patient’s precordial area, represent the anterior wall of the heart. This area is usually supplied by the left anterior descending artery. Elevation is at least 4 mm (four small boxes) above the ECG baseline. Since leads V2-V6 represent the anterior wall, these leads are contiguous. Reciprocal change should be seen in the inferior leads, but this ECG does not show clear ST segment depression. This ECG tracing is a classic example of an anterior wall STEMI.

II.                 Recognizing the Anterior Wall STEMI

Courtesy of Dr. Amal Mattu: ECG's for the Emergency Physician

Again, there is clear ST segment elevation in leads V2, V3, and V4. There is corresponding reciprocal changes in leads II, III, and aVF. Note also elevation in leads I and aVL. This patient is experiencing a rather large anterior wall and lateral wall STEMI. There is ST segment elevation in more than two contiguous leads plus the presence of reciprocal change. Anterior and lateral wall myocardial infarction typically occurs because of blockage in the left anterior descending or left main coronary artery.