A 52-year-old woman with acute inferior wall STEMI (ST elevation in II, III, aVF) undergoes emergency coronary angiography. The right coronary artery (RCA) is completely occluded. Which finding best distinguishes RCA occlusion proximal to the right ventricular (RV) branch from distal RCA occlusion?

## Distinguishing Proximal vs. Distal RCA Occlusion ### Anatomical Basis The right coronary artery supplies the inferior wall of the left ventricle and the right ventricle. Proximal RCA occlusion (before the RV branch) affects both the inferior LV and RV; distal RCA occlusion (after the RV branch) spares the RV. ### Right Ventricular Infarction: The Key Discriminator **Key Point:** ST elevation in the right-sided lead V4R (or V3R, V5R) is the most specific finding for proximal RCA occlusion because it indicates right ventricular infarction. The RV is supplied by the RV branch, which arises proximal to the main inferior territory. When the RCA is occluded proximal to the RV branch, both the RV and inferior LV are infarcted. Distal RCA occlusion preserves RV perfusion and does not produce ST elevation in V4R. ### Comparison Table | Feature | Proximal RCA Occlusion (before RV branch) | Distal RCA Occlusion (after RV branch) | | --- | --- | --- | | **ST elevation in II, III, aVF** | Present | Present | | **ST elevation in V4R (RV lead)** | **Present (≥1 mm)** | **Absent** | | **Right ventricular infarction** | **Yes** | **No** | | **Hemodynamic consequence** | RV dysfunction → ↓ preload → hypotension | Isolated inferior infarction | | **Bradycardia/AV block** | Common (RV branch supplies AV nodal artery) | Less common | | **Fluid responsiveness** | Yes (RV preload-dependent) | Standard management | ### Clinical Pearl **Clinical Pearl:** RV infarction is a critical diagnosis because it makes the RV preload-dependent. These patients are exquisitely sensitive to nitrates and diuretics, which can precipitate cardiogenic shock. Recognition of RV involvement (via V4R ST elevation) mandates aggressive fluid resuscitation and avoidance of vasodilators. Distal RCA occlusion does not involve the RV and is managed conventionally. ### High-Yield Summary **High-Yield:** In inferior STEMI, always obtain right-sided ECG leads (V3R, V4R). ST elevation in V4R = RV infarction = proximal RCA occlusion = high-risk presentation requiring fluids and avoiding nitrates/diuretics. **Mnemonic:** **RV STEMI = Proximal RCA** — Right Ventricular infarction indicates the occlusion is Proximal to the RV branch, not distal. [cite:Harrison 21e Ch 297]