While the existence of structural adaptation of coronary anastomoses is undisputed, the potential of coronary
collaterals to be capable of functional adaptation has been questioned. For many years, collateral vessels were thought to
be rigid tubes allowing only limited blood flow governed by the pressure gradient across them. This concept was consistent
with the notion that although collaterals could provide adequate blood flow to maintain resting levels, they would be
unable to increase blood flow sufficiently in situations of increased myocardial oxygen demand.
However, more recent studies have demonstrated the capability of the collateral circulation to deliver sufficient blood
flow even during exertion or pharmacologic stress. Moreover, it has been shown that increases in collateral flow could be
attributed directly to collateral vasomotion.
This review summarizes the pathophysiology of the coronary collateral circulation, ie the functional adapation of coronary
collaterals to acute alterations in the coronary circulation.