collateral circulation

Collateral circulation is the heart's own set of detour roads. When a main coronary artery narrows over time, small connecting vessels can enlarge and carry blood around the bottleneck, supplying the region from a neighbouring artery.

These channels exist as tiny anastomoses between coronary branches. Chronic ischemia is a powerful stimulus for them to grow: as a vessel slowly narrows, the pressure difference drives flow through these connections, and they gradually widen and remodel into a meaningful supply route. This is one reason a person can have a severely narrowed or even fully blocked artery yet relatively little symptom or damage.

Collaterals are most protective when narrowing develops slowly, giving them time to mature. They offer far less protection against a sudden occlusion, as in many heart attacks, where there has been no chance for them to develop. Their extent varies greatly between individuals and is hard to predict.

Well-developed collaterals can limit infarct size and preserve muscle when a vessel finally closes; they are a natural form of bypass, complementing rather than replacing treatments that reopen the original artery.