Assessing coronary artery stenosis severity: In vitro validation of the concept of fractional flow reserve

Fractional flow reserve (FFR) is an index to assess the functional obstruct ion of an isolated coronary artery stenosis, It can be measured using only pressure measurements proximal (P-a) and distal (P-d) to the stenosis: FFR = P-d/P-a. We studied the relation of pressure and flow-derived measurement s of FFR in a pulsatile, hydraulic model of a coronary artery under physiol ogical aorta pressure (80-110 mm Hg) and coronary flow (140-260 ml/min) con ditions, Measurements were done at baseline and for several stenosis levels obtained with an external occluder, We found good correlations (r(2) > 0.9 5) between pressure and flow-derived FFR, irrespective of isolated changes in myocardial resistance or aortic perfusion pressure. The basic assumption , i.e,, that myocardial resistance is constant, was identified as most cruc ial in the validity of the concept of pressure-derived FFR. The agreement b etween our data and published animal and human studies indicates that this is most probably the case in hyperaemic conditions. (C) 1999 Wiley-Liss, In c.