Background: Myocardial fractional flow reserve (FFR) is a reliable index in coronary intervention. A simple FFR measurement does not predict the true functional severity of an individual stenosis in multiple sequential coronary stenoses because of complex interaction between the stenoses. Application of the theoretical equations to predict the true FFR of individual stenosis is limited in a tandem lesion. Two novel equations applicable to a multiple sequential coronary stenoses are mathematically derived. One predicts the true FFR of each stenosis (equation A), and the other predicts the true FFR after releasing a given stenosis (equation B). The present study aimed to validate the two derived equations in an in vitro model of coronary circulation.
Methods and results: Predictive FFR was compared with true FFR in an in vitro model of three sequential stenoses using linear regression analysis. The difference between apparent FFR and true FFR was compared with the difference between predictive FFR and true FFR. The legitimacy of equation A was first assessed. A close correlation was found between predictive FFR and true FFR (r² = 0.92). The difference between predictive FFR and true FFR was significantly lower compared to the difference between apparent FFR and true FFR (0.18 ± 0.10 vs 0.05 ± 0.05; P<.001). The legitimacy of equation B was also assessed, and a close correlation was found (r² = 0.97). The difference was significantly lower when we applied equation B (0.13 ± 0.06 vs 0.04 ± 0.02; P<.001).
Conclusions: Equations A and B strongly predict the true value of FFR in the experimental model of coronary circulation.