1. Right-Dominant Coronary Anatomy
Scenario: Posterior descending artery (PDA) arises from the RCA — standard anatomy (≈ 80 % of hearts). An inferior STEMI may be due to RCA or LCx occlusion; table below highlights distinguishing ECG / clinical clues.
| ECG / Bedside clue | RCA Culprit | LCx Culprit |
|---|---|---|
| Inferior ST elevation pattern | Lead III > Lead II (right-ward injury vector) | Lead II ≈ III or II > III |
| Reciprocal ST depression in aVL | Marked (≥ 1 mm) | Milder or none |
| Lateral ST elevation (I, aVL, V5-6) | Absent / minimal | Present |
| Right-sided involvement (V1, V4R) | ST ↑ common (RV infarct) | Rare |
| Posterior clues (V7-9, mirror in V1-2) | Minimal | Tall R + ST ↓ in V1-3 or ST ↑ V7-9 |
| Early AV block / brady-arrhythmia | Frequent (AV-node branch) | Less common |
| Haemodynamics | RV-dependent hypotension; fluid responsive | LV posterolateral failure; pulmonary congestion |
Practical bedside memory aid: “III beats II with deep aVL = RCA; lateral or posterior lift = LCx.”
2. Left-Dominant Coronary Anatomy (Circumflex gives PDA)
Scenario: In ≈ 10-15 % of hearts the LCx supplies the PDA and most of the inferior wall. The pattern of inferior STEMI shifts accordingly; RCA infarcts are usually smaller and RV-centred.
| ECG / Bedside clue | Nondominant RCA Culprit | Dominant LCx Culprit |
|---|---|---|
| Inferior ST elevation pattern | Modest; III > II but smaller ΣST | II ≈ III or II > III with larger amplitude |
| Reciprocal ST depression in aVL | Often ≥ 1 mm | Mild / neutralised by lateral ST ↑ |
| Lateral ST elevation (I, aVL, V5-6) | None or < 0.5 mm | Concordant elevation common |
| Posterior involvement | Uncommon | ST ↑ V7-9 or tall R + ST ↓ V1-3 |
| Right-sided ST elevation (V4R, V1) | Possible (RV branch) | Absent |
| AV-nodal block | Can occur | Less frequent |
| Haemodynamics | RV preload sensitive | Higher risk LV failure / cardiogenic shock |
Practical bedside rule: “Inferior plus lateral or posterior lift → LCx dominant; isolated small inferior (III > II) or RV clues → RCA.”
Why it matters clinically
-
RCA occlusion—watch for high-grade AV block and RV infarction; preload-dependent, so give fluids cautiously but early.
-
LCx occlusion—greater posterolateral necrosis risk; may masquerade as a “normal” ECG if posterior only, so record V7-V9 when suspicion is high.
Practical bedside rule in left dominance
Inferior + lateral or posterior lift → think LCx.
Isolated smaller inferior (III > II) or RV signs → think RCA.
Example RCA Infarct/OMI (2nd EKG right -sided leads)
What is the culprit vessel in this inferior wall STEMI?
Answer: Right coronary artery (RCA) is the most likely culprit.
The ECG demonstrates a classic right-dominant inferior MI pattern: larger ST elevation in lead III than II, conspicuous reciprocal depression in aVL, and no concordant lateral ST elevation.
| Key ECG / Bedside clue | Finding on the provided tracing | Interpretation |
|---|---|---|
| ST height: lead III vs II | ST ↑ in III > II | Injury vector points right-inferior → favors RCA occlusion |
| Reciprocal change in aVL | Clear ≥ 1 mm ST depression | Classic RCA signature (deep aVL depression) |
| Lateral leads (I, aVL, V5-6) | No concordant ST elevation | Absence of lateral lift argues against LCx culprit |
| Posterior / right-sided clues | Posterior leads not shown; V1-3 lack tall R / ST ↓; right-sided leads pending | RCA can still involve RV → record V4R to confirm |
| Rhythm / conduction | Sinus rhythm; no high-grade AV block yet | RCA supplies AV node in ≈ 90 % → monitor for late block |
Practical bedside rule to remember
“III beats II with deep aVL depression → think RCA.
Lateral or posterior lift → think LCx.”
Example typical left circumflex infarct:
No comments:
Post a Comment