Influence of hemodynamic conditions on fractional flow reserve: parametric analysis of underlying model

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Abstract
Pressure-based fractional flow reserve (FFR) is used clinically to evaluate the functional severity of a coronary stenosis, by predicting relative maximal coronary flow (Qs/Qn). It is considered to be independent of hemodynamic conditions, which seems unlikely because stenosis resistance is flow dependent. Using a resistive model of an epicardial stenosis (0–80% diameter reduction) in series with the coronary microcirculation at maximal vasodilation, we evaluated FFR for changes in coronary microvascular resistance ( R cor= 0.2–0.6 mmHg · ml−1 · min), aortic pressure (Pa = 70–130 mmHg), and coronary outflow pressure (Pb = 0–15 mmHg). For a given stenosis, FFR increased with decreasing Pa or increasing R cor. The sensitivity of FFR to these hemodynamic changes was highest for stenoses of intermediate severity. For Pb > 0, FFR progressively exceeded Qs/Qn with increasing stenosis severity unless Pb was included in the calculation of FFR. Although the Pb-corrected FFR equaled Qs/Qn for a given stenosis, both parameters remained equally dependent on hemodynamic conditions, through their direct relationship to both stenosis and coronary resistance.