Acute Anterior Myocardial Infarction
- ST segment elevation in the anterior precordial leads.
- Commonly-used terminology for injury location:
- V3-V4: Anterior injury.
- V1-V4: Anteroseptal injury.
- V3-V6: Anterolateral injury. Leads I and aVL may also be involved, especially if the circumflex artery is affected (high lateral injury).
- Reciprocal ST segment depressions are often present in the inferior leads (II, III, aVF).
Acute Anteroseptal Myocardial Infarction. (ECG contributor: James V. Ritchie, MD.)
Pathologic ST-segment elevation beyond 1 mm (double arrow) with pathologic Q waves (arrow) in lead V3. The ST segment demonstrates a convex upward, or "tombstone" morphology.
The left anterior descending artery supplies blood to the anterior and lateral left ventricle and ventricular septum.
Normal R-wave progression (increasing upward amplitude with R wave > S wave at V3 or V4) may be interrupted.
The development of pathologic Q waves in any of the V leads other than V1 strongly suggests that the injury has progressed to an infarction, as seen in this example.
Acute Inferior Myocardial Infarction
- ST segment elevation in inferior leads (II, III, aVF)
- Reciprocal ST segment depressions in the anterior leads (V1-V3) and possibly high lateral leads (I, aVL)
Acute Inferior-Posterior Myocardial Infarction. (ECG contributor: James V. Ritchie, MD.)
ST-segment elevation is present in the inferior leads (II, III, aVF) (arrow), with reciprocal ST depression in the anterior leads (V2-V4) (arrowhead) and high lateral leads (I, aVL).
The right coronary artery supplies blood to the right ventricle, the SA node, the inferior portions of the left ventricle, and usually to the posterior portion of the left ventricle and the AV node.
Infarctions involving the SA node may produce sinus dysrhythmias including tachycardias, bradycardias, and sinus arrest.
Infarctions involving the AV node may produce AV blocks.
In the presence of acute inferior injury, especially if the ST segment elevation in III is higher than in II, a right-sided ECG should be obtained to look for right ventricular involvement. The administration of nitroglycerin in the presence of acute right ventricular infarction can precipitate profound hypotension, as these patients are preload dependent.
Since the right coronary artery so often supplies the posterior left ventricle, look carefully for evidence of a posterior infarction (as present in the example) and consider obtaining an ECG with posterior leads.
Acute Right Ventricular Myocardial Infarction
- ST elevation in right-sided V leads (V4R, V5R)
- ST elevation greater in lead III than lead II suggests RV MI
- ST elevation in the normally-obtained V1 also strongly suggests RV MI
- Often associated with inferior MI and/or posterior MI
Right Ventricular Myocardial Infarction. This ECG was obtained with right-sided lead placement. (ECG contributor: Thomas Bottoni, MD.)
ST elevation in V4R and V5R (arrows), with the V4 and V5 leads placed in their mirror-image locations on the right side of the chest. Any ST elevation seen in the right-sided precordial leads is significant.
The smaller muscle mass of the right ventricle produces a less intense injury pattern that is overwhelmed by the left ventricle in the normally obtained ECG. Placement of right-sided V leads, with V1-V6 in mirror-image locations on the right side of the chest, is important in detecting right ventricular injury.
The heart with an injured right ventricle is very preload-dependent. Beware of lowering preload with nitrates in any patient with suspected RV MI as severe hypotension may occur. Treat hypotension with volume.
Obtain a right-sided ECG in any patient with inferior or posterior MI, and in any patient with a significant hypotensive response to nitrates.
Acute Posterior Myocardial Infarction
- With acute injury pattern—ST segment depression in lead V1 and/or V2 with acute injury pattern.
- With infarction pattern—Small S wave and large R wave greater than 4 ms duration in lead V1 or V2 with infarction.
- With infarction pattern—R-wave/S-wave ratio greater than 1 in lead V1 or V2 with infarction.
Acute Posterior-Lateral Myocardial Infarction. (ECG contributor: Ian D. Jones, MD.)
This tracing demonstrates injury in the posterior LV, manifesting as acute ST depression in V2 (arrow).
By inverting and rotating the EKG, the "classic" ST-elevation injury pattern is easily seen (arrow).
The ST depression is subtle and downsloping. However, the R-wave amplitude approximates that of the S wave and the R wave duration is significant (>4 ms). This is actually an "inverted Q wave" from this patient's posterior infarction that ...
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