SCIENTIFIC LETTER Pharmacological vasodilatation in the assessment of

ssessment of the coronary collateral circulation by intracoronary pressure measurements was first described a decade ago and has rapidly become a clinically accepted standard for quantification of collateral flow. The pressure-derived collateral flow index (CFI) expresses collateral flow in relation to normal maximum myocardial perfusion and is calculated by simultaneous measurement of aortic (Pa), central venous (Pv) and coronary wedge (Pw) pressures, where CFI = (Pw 2 Pv)/(Pa 2 Pv). In addition to these pressure gradients, collateral flow is determined by the resistances of collateral vessels and the myocardial microvasculature. Therefore, a flow index can only be derived from pressure measurements during condi-tions of maximum vasodilatation, when all resistances are minimised and held constant. Maximal and steady-stat