Anastomoses of the Coronary Arteries
Inter-coronary Anastomoses
The right and left coronary arteries anastomose with each other at the arteriolar level within the myocardium, chiefly:
- At the apex of the heart — between the terminal branches of the anterior and posterior interventricular arteries.
- In the interventricular septum — between septal branches of both interventricular arteries.
- In the atrioventricular sulcus — between the terminations of the RCA and circumflex artery.
Extra-cardiac Anastomoses
The coronary arteries also anastomose with vessels outside the heart through the pericardium:
| Vessel | Route |
|---|---|
| Vasa vasorum of the aorta | Direct communication near the coronary ostia |
| Vasa vasorum of the pulmonary arteries | Pericardial reflection |
| Internal thoracic arteries | Via pericardiophrenic branches through the pericardium |
| Bronchial arteries | Through pericardial attachments |
| Phrenic arteries | Through the diaphragmatic pericardium |
The last three (internal thoracic, bronchial, phrenic) anastomose through the pericardium and may open up in emergencies when both coronary arteries are severely obstructed.
Functional Significance
Why Anastomoses Are Inadequate in Acute Occlusion
- Coronary arteries are anatomically not end-arteries (anastomoses exist at the arteriolar level).
- However, they are functionally end-arteries — the anastomotic channels are too small and too few to provide adequate collateral flow when a large branch is suddenly blocked.
- Sudden occlusion → arterioles do not have time to dilate → no effective collateral circulation → myocardial infarction.
When Collateral Circulation Can Develop
- Slowly progressive occlusion (e.g., gradual atherosclerotic narrowing) → allows time for existing arterioles to enlarge → functional collateral circulation may develop.
- This is why some patients with chronic coronary artery disease tolerate complete occlusion of a vessel without infarction — collaterals have already opened up.
Retrograde Venous Flow
- In extreme circumstances, retrograde flow through the cardiac veins may provide minimal perfusion to ischaemic myocardium — but this is not a reliable mechanism.
Summary
Coronary anastomoses exist but are clinically insufficient for acute protection. Their value is primarily in chronic, slowly progressive coronary artery disease where collateral channels have had time to develop.