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INTRODUCTION

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Second-Degree AV Block (Mobitz I, Wenckebach). The PR interval gradually increases until a P wave is not followed by a QRS and a beat is “dropped.” The process then recurs. P waves occur at regular intervals, though they may be hidden by T waves. (ECG contributor: James Paul Brewer, MD.)

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PART 1: ST-T ABNORMALITIES

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ACUTE ANTERIOR MYOCARDIAL INFARCTION

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FIGURE 23.1A

Acute Anteroseptal Myocardial Infarction. (ECG contributor: James V. Ritchie, MD.)

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ECG Findings
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  • ST segment elevation in the anterior precordial leads.

  • V1-V4: Anteroseptal injury.

  • V3-V4: Anterior 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).

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Pearls
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  1. The left anterior descending artery supplies blood to the anterior and lateral left ventricle and ventricular septum.

  2. Normal R-wave progression (increasing upward amplitude with R wave > S wave at V3 or V4) may be interrupted.

  3. 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.

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FIGURE 23.1B

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.

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ACUTE INFERIOR MYOCARDIAL INFARCTION

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FIGURE 23.2A

Acute Inferior-Posterior Myocardial Infarction. (ECG contributor: James V. Ritchie, MD.)

Graphic Jump Location
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ECG Findings
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  • ST segment elevation in inferior leads (II, III, aVF)

  • ST segment depressions in the anterior leads (V1-V3) and possibly high lateral leads (I, aVL)

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Pearls
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  1. The right coronary artery supplies blood to the right ventricle, the sinoatrial (SA) node, the inferior portions of the left ventricle, and usually to the posterior portion of the left ventricle and the atrioventricular (AV) node.

  2. Infarctions involving the SA node may produce sinus dysrhythmias including tachycardias, bradycardias, and sinus arrest.

  3. Infarctions involving the AV node may produce AV blocks.

  4. In the presence of acute inferior injury, 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.

  5. Since the right coronary artery so often supplies the posterior left ventricle, look for evidence ...

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