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.sub.s]/[Q.sub.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.sub.cor] = 0.2-0.6 mmHg*[ml.sup.-1]*min), aortic pressure ([P.sub.a] = 70-130 mmHg), and coronary outflow pressure ([P.sub.b] = 0-15 mmHg). For a given stenosis, FFR increased with decreasing [P.sub.a] or increasing [R.sub.cor]. The sensitivity of FFR to these hemodynamic changes was highest for stenoses of intermediate severity. For [P.sub.b] > 0, FFR progressively exceeded [Q.sub.s/[Q.sub.n] with increasing stenosis severity unless [P.sub.b] was included in the calculation of FFR. Although the [P.sub.b]-corrected FFR equaled [Q.sub.s]/[Q.sub.n] for a given stenosis, both parameters remained equally dependent on hemodynamic conditions, through their direct relationship to both stenosis and coronary resistance. coronary artery stenosis; coronary circulation; coronary stenosis evaluation; coronary flow reserve