The coronary circulation supplies oxygen and nutrients to the myocardium and is uniquely adapted to meet high metabolic demand. Impairment of coronary blood flow rapidly leads to myocardial ischaemia, arrhythmia, and infarction. Understanding coronary anatomy and flow dynamics is essential for interpreting ECG changes, managing acute coronary syndromes, and guiding revascularisation.

❤️ Left Coronary Artery (LCA)🫀

Origin: Arises from the left aortic sinus of the ascending aorta.
Main Branches:
- 🌟 Left Anterior Descending (LAD) – Supplies anterior septum and apex; proximal occlusion = “widowmaker”.
- ↪️ Left Circumflex (LCx) – Courses in AV groove; gives obtuse marginal branches.
Supplied Territories:
- LAD: Anterior LV wall, anterior 2/3 of septum, apex.
- LCx: Lateral LV wall ± posterior wall (in left dominance).

💙 Right Coronary Artery (RCA)

Origin: Arises from the right aortic sinus.
Main Branches:
- Posterior Descending Artery (PDA): From RCA in ~85% (right dominance).
- Right Marginal Artery: Supplies RV free wall.
Supplied Territories:
- RCA: Right atrium, RV, SA node (~60%), AV node (~80%).
- PDA: Inferior LV wall, posterior septum.

🫀 Coronary Artery Anatomy

📊 Major Coronary Arteries — Summary

Artery	Origin	Branches	Supplied Areas
LCA	Left aortic sinus	LAD, LCx	Most of LV myocardium
RCA	Right aortic sinus	PDA, Right marginal	RA, RV, inferior LV, conduction system
PDA	RCA (85%) / LCx (8–10%)	—	Posterior LV + septum
LMCA	Left aortic sinus	LAD + LCx	Large LV territory

📉 Coronary Occlusion and ECG Changes

Artery	ECG Leads	Typical Changes	Territory
LAD	V1–V4	ST elevation, Q waves	Anterior/septal LV
LCx	I, aVL, V5–V6	Lateral ST elevation	Lateral LV
RCA	II, III, aVF	Inferior ST elevation	Inferior LV/RV
PDA	V7–V9	Posterior ST elevation	Posterior LV
LMCA	Widespread	Global ST changes	Large LV area

💡 Coronary Blood Flow

Unlike most organs, coronary perfusion occurs predominantly during diastole. During systole, myocardial contraction compresses intramyocardial vessels, particularly in the left ventricle, reducing flow. Tachycardia shortens diastole and therefore reduces coronary perfusion.

⚙️ Coronary Flow Dynamics

⏱️ Diastolic dominance: Maximal perfusion in ventricular relaxation.
🔄 Autoregulation: Maintains stable flow across MAP 60–140 mmHg.
💪 Metabolic coupling: Flow rises in proportion to oxygen demand.
🫀 Subendocardial vulnerability: Inner myocardium is most susceptible to ischaemia.

🧬 Regulation of Coronary Tone

Local metabolites: Adenosine, CO₂, H⁺, K⁺ → vasodilation.
Endothelial factors: Nitric oxide (NO), prostacyclin.
Neurohumoral: Sympathetic tone modulates flow indirectly via demand.
Structural disease: Atherosclerosis reduces vasodilatory reserve.

🚫 Vasoconstrictors

Endothelin-1, Angiotensin II, Thromboxane A2
α-adrenergic stimulation (noradrenaline)
Serotonin (5-HT)

✅ Vasodilators

Nitric oxide (NO), Prostacyclin (PGI₂)
Adenosine, Bradykinin
β₂-agonists
Calcium-channel blockers
Nitrates (clinical use)

🩺 Clinical Integration

Coronary artery disease impairs vasodilatory reserve, meaning flow cannot increase adequately during stress. This results in exertional angina, ECG changes, and myocardial stunning. In acute plaque rupture, abrupt occlusion causes transmural infarction, electrical instability, and cardiogenic shock if untreated.

Reduced diastolic time (tachycardia, AF) worsens ischaemia.
Hypotension reduces coronary perfusion pressure.
LV hypertrophy increases oxygen demand.
Anaemia reduces oxygen delivery.

✅ Makindo Exam & Clinical Pearls

LAD occlusion = highest mortality (large LV territory).
Inferior MI + hypotension → suspect RV infarction (RCA).
Tachycardia worsens angina by reducing diastolic filling.
Subendocardium is always first to become ischaemic.
Left main disease causes global ECG changes and shock.

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Anatomy and Physiology of the Coronary Arteries