Coronary Arteries
The two coronary arteries arise from the aortic sinuses just above the aortic valve and supply the myocardium. Their territories, anastomoses, and ECG correlations are the cornerstone of acute cardiology.
✦ The Mnemonic
"Left Anterior Descends; Right Circles Around"
LAD supplies anterior wall; RCA supplies inferior wall; LCx supplies lateral wall
Clinical Breakdown
Right dominance (70%): the RCA gives the posterior descending artery (PDA), which supplies the posterior septum and inferior wall. In left-dominant systems (10%), the LCx gives the PDA — making LCx occlusion more dangerous. The SA node is supplied by the RCA in 60% and LCx in 40%.
ECG correlation: LAD occlusion → anterior STEMI (leads V1–V4). RCA occlusion → inferior STEMI (leads II, III, aVF) ± right ventricular infarction (V4R). LCx occlusion → lateral STEMI (I, aVL, V5–V6) ± posterior changes (dominant R wave in V1–V2, ST depression V1–V3).
LMCA (left main stem) occlusion is immediately life-threatening — it supplies 75% of the LV myocardium. ECG shows diffuse ST depression with ST elevation in aVR. This pattern should trigger immediate coronary angiography and revascularisation.
⭐ Clinical Pearl
Ventricular septal rupture post-MI occurs at day 3–5 in the softened infarcted septum. It is a mechanical complication of both anterior (LAD) and inferior (RCA) MI. New harsh pansystolic murmur + acute haemodynamic deterioration after MI = urgent echo. Temporary mechanical support then emergency surgical or percutaneous repair.