Pressure-derived fractional flow reserve to assess serial epicardial stenoses - Theoretical basis and animal validation

Background-Fractional flow reserve (FFR) is an index of stenosis severity v alidated for isolated stenoses. This study develops the theoretical basis a nd experimentally validates equations for predicting FFR of sequential sten oses separately. Methods and Results-For 2 stenoses in series, equations were derived to pre dict FFR (FFRpred) of each stenosis separately (ie, as if the other one wer e removed) from arterial pressure (P-a), pressure between the 2 stenoses (P -m), distal coronary pressure (P-d), and coronary occlusive pressure (P-w). In 5 dogs with 2 stenoses of varying severity in the left circumflex coron ary artery, FFRpred was compared with FFRapp (ratio of the pressure just di stal to that just proximal to each stenoses) and to FFRtrue (ratio of the p ressures distal to proximal to each stenosis but after removal of the other one) in case of fixed distal and varying proximal stenoses (n=15) and in c ase of fixed proximal and varying distal stenoses (n=20). The overestimatio n of FFRtrue by FFRapp was larger than that of FFRtrue by FFRapp (0.070+/-0 .007 versus 0.029+/-0.004, P<0.01 for fixed distal stenoses, and 0.114+/-0. 01 versus 0.036+/-0.004, P<0.01 for fixed proximal stenoses). This overesti mation of FFRtrue by FFRapp was larger for fixed proximal than for fixed di stal stenoses. Conclusions-The interaction between 2 stenoses is such that FFR of each les ion separately cannot be calculated by the equation for isolated stenoses ( P-d/P-a during hyperemia) applied to each separately but can be predicted b y more complete equations taking into account P-a, P-m, P-d, and P-w.