Influence of zero flow pressure on fractional flow reserve
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Fractional flow reserve (FFR) is a commonly used index to assess the functional severity of a coronary artery stenosis. It is conventionally calculated as the ratio of the pressure distal (Pd) and proximal (Pa) to the stenosis (FFR=Pd/Pa). We hypothesize that the presence of a zero flow pressure (Pzf), requires a modification of this equation. Using a dynamic hydraulic bench model of the coronary circulation, which allows one to incorporate an adjustable Pzf, we studied the relation between pressure-derived FFR=Pd/Pa, flow-derived true FFRQ=QS/QN (=ratio of flow through a stenosed vessel to flow through a normal vessel), and the corrected pressure-derived FFRC=(Pd−Pzf)/(Pa−Pzf) under physiological aortic pressures (70 mmHg, 90 mmHg, and 110 mmHg). Imposed Pzf values varied between 0 mmHg and 30 mmHg. FFRC was in good agreement with FFRQ, whereas FFR consistently overestimated FFRQ. This overestimation increased when Pzf increased, or when Pa decreased, and could be as high as 56% (Pzf=30 mmHg and Pa=70 mmHg). According to our experimental study, calculating the corrected FFRC instead of FFR, if Pzf is known, provides a physiologically more accurate evaluation of the functional severity of a coronary artery stenosis.
KeywordsFractional Flow Reserve Aortic Pressure Coronary Circulation Flow Relation Coronary Pressure
We thank Stefaan Bliki, Marcel Anteunis, and Martin Vandaele for technical assistance during the realization of the hydraulic model of the coronary circulation. Tom Claessens and Koen Matthys are funded by specialization grants of the Institute for the Promotion of Innovation by Science and Technology in Flanders (IWT 021228 and IWT 993175). Paul Van Herck is a research assistant of the Fund for Scientific Research—Flanders (F.W.O.—Vlaanderen). Patrick Segers receives a post-doctoral grant from the Fund for Scientific Research in Flanders (FWO—Vlaanderen).
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