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

Pressure-based fractional flow reserve (FFR) is used clinically to evaluate the functional severity of a coronary stenosis, by predicting relative maximal coronary flow (Q(s)/Q(n)). 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 (P-a = 70-130 mmHg), and coronary outflow pressure (P-b = 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 P-b > 0, FFR progressively exceeded Q(s)/Q(n) with increasing stenosis severity unless P-b was included in the calculation of FFR. Although the P-b-corrected FFR equaled Q(s)/Q(n) for a given stenosis, both parameters remained equally dependent on hemodynamic conditions, through their direct relationship to both stenosis and coronary resistance