Collateral vessels are alternative blood vessel pathways that carry blood around a blockage or an area of abnormal development. When a normal artery or vein is obstructed, narrowed, or absent, blood is redirected through smaller, pre-existing vessels that gradually enlarge and remodel over time to compensate. This process, known as collateralisation, is the body’s natural response to chronic ischaemia (reduced blood flow).
In the heart, coronary collateral vessels develop in response to long-standing coronary artery disease. When a coronary artery is progressively narrowed by atherosclerotic plaque, neighbouring small vessels may enlarge to supply the affected area of heart muscle from an alternative route. The extent of collateral development varies considerably between patients and may provide some protection by sustaining partial blood flow to the threatened territory during acute occlusion.
In congenital heart disease, collateral vessels may form before birth or in infancy as a compensatory response to abnormal cardiac anatomy. An important example is major aortopulmonary collateral arteries (MAPCAs), which can develop in conditions such as pulmonary atresia, where the normal connection between the right ventricle and lungs is absent or severely underdeveloped. MAPCAs arise from the aorta and carry blood directly to the lung circulation, partially compensating for the absent or restricted pulmonary blood supply.
Collateral vessels are assessed during coronary angiography and cardiac catheterisation. In surgical planning for complex congenital heart disease, the anatomy of MAPCAs is carefully mapped before repair, as they must be incorporated into or excluded from the reconstructed circulation. In acquired coronary disease, robust collateral supply is associated with smaller infarct size and better outcomes after sudden coronary occlusion.
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