Pressure-Derived Fractional Flow Reserve to Assess Serial Epicardial Stenoses: Theoretical Basis and Animal Validation

Abstract

Background —Fractional flow reserve (FFR) is an index of stenosis severity validated for isolated stenoses. This study develops the theoretical basis and experimentally validates equations for predicting FFR of sequential stenoses separately. Methods and Results —For 2 stenoses in series, equations were derived to predict FFR (FFR pred ) of each stenosis separately (ie, as if the other one were 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 coronary artery, FFR pred was compared with FFR app (ratio of the pressure just distal to that just proximal to each stenoses) and to FFR true (ratio of the pressures 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 case of fixed proximal and varying distal stenoses (n=20). The overestimation of FFR true by FFR app was larger than that of FFR true by FFR pred (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 overestimation of FFR true by FFR app was larger for fixed proximal than for fixed distal stenoses. Conclusions —The interaction between 2 stenoses is such that FFR of each lesion separately cannot be calculated by the equation for isolated stenoses (P d /P a during hyperemia) applied to each separately but can be predicted by more complete equations taking into account P a , P m , P d , and P w .