Which electrocardiogram (ECG) leads are most likely to show changes in the event of a right coronary artery (RCA) occlusion?

ECG Changes in Right Coronary Artery Occlusion

Occlusion of the right coronary artery (RCA) most commonly causes ECG changes in leads II, III, and aVF (option C). This pattern reflects inferior wall myocardial infarction, which is the characteristic presentation of RCA occlusion 1.

Pathophysiological Basis

When the RCA is occluded, the inferior wall of the left ventricle becomes ischemic, resulting in a specific pattern of ECG changes:

• ST-segment elevation in leads II, III, and aVF (the inferior leads)
• Greater ST-segment elevation in lead III than in lead II
• ST-segment depression in leads I and aVL (reciprocal changes)

The spatial vector of the ST segment in RCA occlusion is directed inferiorly, rightward, and sometimes anteriorly, which explains this characteristic pattern 1.

Distinguishing Features of RCA Occlusion

Several key features help identify RCA occlusion:

1. Proximal RCA occlusion:

   • ST-segment elevation in leads II, III, aVF
   • ST-segment elevation in lead III > lead II
   • ST-segment depression in leads I and aVL
   • ST-segment elevation in right-sided leads (V3R, V4R) and often V1, indicating right ventricular involvement 1

2. Distal RCA occlusion:

   • ST-segment elevation in leads II, III, aVF
   • Less likely to have right ventricular involvement
   • Positive T wave without ST elevation in V4R 2

Differentiating from Left Circumflex Artery Occlusion

Both RCA and left circumflex artery (LCx) occlusions can cause inferior wall infarction, but several features help distinguish them:

• In RCA occlusion, ST elevation is typically greater in lead III than in lead II
• RCA occlusion often shows ST depression in leads I and aVL
• Proximal RCA occlusion uniquely causes right ventricular infarction with ST elevation in right precordial leads (V3R, V4R)
• LCx occlusion more commonly shows ST elevation in lateral leads (V5-V6) and ST depression in anterior leads (V1-V3) 3, 4

Clinical Implications

The ability to identify RCA occlusion on ECG has important clinical implications:

• Proximal RCA occlusion may involve the right ventricle, which requires specific management considerations
• Right ventricular involvement should be suspected when ST elevation is seen in right precordial leads (V3R, V4R)
• ST elevation in right-sided leads is transient and should be recorded as early as possible after symptom onset 1

Important Caveats

• Right-sided leads (V3R, V4R) should be recorded in all patients with inferior ST elevation to assess for right ventricular involvement
• In rare cases, RCA occlusion may present with a normal ECG or minimal changes 5
• The diagnostic accuracy of ECG patterns depends on coronary dominance patterns 6
• ST elevation in inferior leads has high sensitivity (>90%) for RCA occlusion in patients with inferior STEMI 6

In conclusion, when evaluating a patient with suspected coronary artery occlusion, ST-segment elevation in leads II, III, and aVF is the hallmark ECG finding that suggests RCA occlusion.