Going With the Flow: In Vitro Assessment of FFR in >2 Stenoses

By Naritatsu Saito

As many physicians know, a simple fractional flow reserve (FFR) measurement does not predict the true functional severity of an individual stenosis in multiple sequential coronary stenoses because of the complex fluid dynamic interaction between the stenoses. Theoretical equations to predict the true FFR of individual stenosis in a tandem lesion were developed more than 10 years ago, and the equations have been cited repeatedly in many articles. However, the application of the equations is limited in a tandem lesion. We mathematically derived two novel equations applicable to multiple sequential coronary stenoses with more than 3 stenoses. One is the equation which predicts the true FFR of each stenosis (equation A), and the other predicts the true FFR after releasing a given stenosis in multiple sequential stenoses (equation B).

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One may consider that both equation A and equation B are difficult to apply in daily clinical practice since both equations require wedge pressure measurement during the maximum hyperemia. However, both equations are important when considering the theoretical background of the FFR assessment in a sequential lesion. Equation A suggests that the true FFR of individual stenosis is always smaller than the apparent FFR value. The severity of individual stenosis is always underestimated in multiple sequential stenoses. Equation B suggests that the true FFR of entire stenoses after releasing a given stenosis is always smaller than the apparent FFR value obtained by a simple addition of baseline FFR of the entire stenoses plus ∆FFR across the target lesion. A better understanding of the background theory helps to improve the performance of daily practice.

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A selection of articles on Fractional Flow Reserve available at http://www.invasivecardiology.com

 

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