Applied Anatomy of the Coronary Arteries
Coronary Arteries as Functional End-Arteries
Although the coronary arteries anastomose anatomically at the arteriolar level, they behave as functional end-arteries. Sudden occlusion of any large branch leads to ischaemia and necrosis of the myocardium it supplies, because collateral vessels cannot open up fast enough to compensate.
Angina Pectoris
| Feature | Detail |
|---|---|
| Mechanism | Partial (incomplete) obstruction or spasm of a coronary artery → reduced blood supply to myocardium on exertion |
| Symptoms | Moderately severe constricting or crushing pain in the left precordium, radiating to the left shoulder, medial side of the arm and forearm, sometimes to the jaw or neck |
| Timing | Occurs on exertion; relieved by rest |
| Relief | Sublingual nitrates (glyceryl trinitrate) |
Myocardial Infarction (MI)
| Feature | Detail |
|---|---|
| Mechanism | Sudden, complete occlusion of a coronary artery (usually by thrombosis) → myocardial necrosis |
| Symptoms | Severe crushing chest pain lasting >30 minutes, not relieved by rest; nausea, vomiting, sweating, shortness of breath, tachycardia |
| Radiation | Medial side of arm, forearm, and hand; may radiate to jaw or neck |
| Outcome | Infarcted muscle is replaced by fibrous scar tissue; may cause ventricular fibrillation and sudden death |
Key distinction: Angina — pain on exertion, relieved by rest. MI — pain at rest, lasting >30 min, not relieved by rest.
Sites of Coronary Artery Occlusion
| Vessel | Frequency | Territory at Risk |
|---|---|---|
| Anterior interventricular artery (LAD) | 40–50% | Anterior wall of both ventricles, anterosuperior septum, bundle branches |
| Right coronary artery (RCA) | 30–40% | Right ventricle, inferior wall of left ventricle, AV node, SA node |
| Circumflex artery | 15–20% | Lateral and posterior wall of left ventricle |
The LAD is the most commonly occluded coronary artery (“the widow maker”).
Referred Pain of Cardiac Ischaemia
Cardiac pain is referred to the medial side of the left arm and forearm (T1–T4 dermatomes) because the heart and the medial arm share the same spinal segments (upper 4–5 thoracic segments). Pain may also be referred to the jaw, neck, or epigastrium.
Arrhythmias from Coronary Occlusion
Occlusion affecting the SA node, AV node, or bundle branches causes cardiac arrhythmias:
- SA node occlusion → sinus bradycardia or sinus arrest
- AV node occlusion → AV block (heart block) — ventricles continue at a slow intrinsic rate, independent of atrial activity
- Bundle branch occlusion → bundle branch block
The right coronary artery supplies most of the conducting system. RCA occlusion is therefore the most common cause of heart block.
Coronary Angiography
A radiological procedure where contrast medium is injected directly into the coronary arteries via a catheter (typically passed retrogradely through the femoral artery → aorta → coronary ostia). It visualises the lumen of the coronary arteries and localises sites of narrowing or occlusion. Essential before deciding on intervention.
Coronary Angioplasty (Percutaneous Coronary Intervention — PCI)
A catheter with a small inflatable balloon at its tip is advanced into the obstructed coronary artery. The balloon is inflated to flatten the atherosclerotic plaque against the vessel wall and dilate the lumen. An intracoronary stent is often deployed to maintain dilatation and prevent re-stenosis.
Coronary Artery Bypass Grafting (CABG)
A segment of vein or artery is used to bypass the obstruction, routing blood from the aorta to the coronary artery distal to the blockage.
| Graft | Notes |
|---|---|
| Great saphenous vein | Most commonly used; easily harvested, diameter matches coronary artery, provides long segments |
| Left internal mammary artery (LIMA) | Preferred graft for the LAD; superior long-term patency |
| Radial artery | Increasingly used; good long-term results |
Indicated when: multiple sites of obstruction, long segments of occlusion, or failed angioplasty.