FRACTIONAL FLOW RESERVE - THE IDEAL PARAMETER FOR EVALUATION OF CORONARY, MYOCARDIAL, AND COLLATERAL BLOOD-FLOW BY PRESSURE MEASUREMENTS ATPTCA

To overcome the fundamental limitations of coronary arteriography to a ssess the functional significance of coronary artery disease, it is ne cessary to obtain direct information about coronary blood flow. Recent ly we validated three pressure-flow equations, which enable calculatio n of maximum coronary, myocardial, and collateral flow by merely measu ring aortic, central venous, and distal coronary pressures under the c ondition of maximum vasodilation and using an ultra thin pressure moni toring guide wire for distal coronary pressure recording. In this pape r, the first clinical experiences of this method are described. For th at purpose, the concept of fractional flow reserve (FFR) is important. Fractional coronary flow reserve (FFR(cor)) is defined as the maximum achievable blood flow in a stenotic artery, divided by normal maximum flow in that same artery, i.e. maximum flow in that artery in the cas e that it would be completely normal. Fractional myocardial flow reser ve (FFR(myo)) is defined in a similar way, and recruitable collateral blood flow is expressed as a fraction of normal maximum myocardial pow . Fractional flow reserve, defined in this way, is easy to obtain at p ercutaneous transluminal coronary angioplasty (PTCA) by the pressure-f low equations, is independent of pressure changes, applicable to three vessel disease, and enables calculation of the separate contribution of coronary and collateral flow to total myocardial perfusion. In 18 p atients a very close correlation was demonstrated between FFR(myo), ca lculated by pressure recordings at PTCA by the first pressure-flow equ ation, and FFR(myo) obtained by positron emission tomography, which is considered the gold standard for myocardial perfusion. In 60 other pa tients, maximum recruitable collateral blood flow at balloon inflation (Q(c)/Q(N)) was calculated according to the third pressure-flow equat ion and correlated to the presence or absence of ischemia. It could be demonstrated that Q(c)/Q(N) exceeds 22% in all 23 patients without is chemia, whereas Q(c)/Q(N) was less than 22% in 34 but of 37 patients w ho experienced ischemia during balloon inflation. This margin value of 22% is very close to the theoretically expected value of 20%, based u pon a coronary flow reserve of 5 under standard physiologic conditions . It can be concluded that the concept of fractional flow reserve prov ides a rapid, accurate, and elegant way for quantitative assessment of maximum coronary and myocardial blood flow before and after PTCA. Mor eover, this is the first method that enables quantitative calculation of collateral blood flow in clinical practice.