The coronary arteries were once thought of as end-arteries. Certainly, they often behave like functional end-arteries, as illustrated by the ischaemia induced by single vessel coronary artery disease. However, we now know that there are interconnecting branches between the main arteries although their clinical relevance has been disputed, since the anastomoses are often incapable of restoring flow to normal levels (figure 1).

Hitherto, 12 studies have investigated the effect of collaterals on survival, the first in 1971,1 but only three have demonstrated a clear benefit leaving unresolved the dispute about their functional relevance.2 The inconsistency is partially explained by the method of assessment used in most of the studies whereby collaterals were ‘quantified’ visually during coronary angiography. This represents a rather crude approach compared with the more accurate intracoronary flow or pressure-based methods (collateral …