ST Segment Elevation and Other ECG Findings in Myocardial Infarction

Abstract

One of the most important uses of the ECG is identifying the presence of occlusion of one of the coronary arteries that provide blood supply to the heart. Myocardial injury is associated with a characteristic evolution of ECG changes. Of all of the ECG changes, ST segment elevation is the most prominent, and evaluation of the ECG can help localize the specific region and amount of cardiac tissue being affected and in turn help predict the culprit coronary artery prior to therapeutic interventions and overall prognosis.

Appendices

Review Questions

• 1. ECG findings associated with myocardial infarction include:

  • A. ST segment elevation

  • B. ST segment depression

  • C. T wave peaking

  • D. All of the above.

• 2. The ECG in Fig. 7.26 shows:

  • A. Inferior wall myocardial infarction

  • B. Anterior wall myocardial infarction

  • C. Lateral wall myocardial infarction

  • D. No evidence for a myocardial infarction

• 3. Atrioventricular block is most commonly associated with:

  • A. Inferior wall myocardial infarction

  • B. Anterior wall myocardial infarction

  • C. Lateral wall myocardial infarction

Fig. 7.26

ECG for Problems #2 and #4 (Courtesy Irwin Hoffman)

• 4. The ECG in Fig. 7.26 is consistent with:

  • A. Proximal right coronary artery occlusion

  • B. Distal right coronary artery occlusion

  • C. Left anterior descending coronary artery occlusion

  • D. Circumflex coronary artery occlusion

Answers

• 1. D. Myocardial infarction can be associated with a number of ECG findings. However, identification of a myocardial infarction associated with ST segment elevation is particularly important (ST elevation myocardial infarction or STEMI), since multiple studies have shown that rapid re-establishment of coronary flow is critical.

• 2. A. The ECG shows an inferior wall myocardial infarction with ST segment elevation in the inferior wall.

• 3. A. Inferior wall myocardial infarction is associated with some form of AV block in 1/3 of patients. Usually, the AV nodal artery branches at the same point as the posterior descending artery. A more thorough discussion of AV block in the setting of myocardial infarction is provided in the clinical cases.

• 4. A. The ECG shows ST segment elevation in the inferior wall with right ventricular infarction (ST segment elevation in RV 4 and absence of reciprocal ST depression in V1 and V2). This constellation of findings is consistent only with a proximal occlusion of the right coronary artery.