Backgound : Fractional flow reserve (Pd/Pao) means 'flow of stenosis (Qs)/flow of normal coronary artery(Qn) by Ohm's law. In a stenotic area where pressure drop occurs, the velocity of blood flow (v) can be calcluated by Bernoulli equation (Δp=4v²). With this equation, Qs = √Δp/2 * stenotic area, and Qn can be expressed as (√Δp/2 * stenotic area)/FFR. Hence, Coronary flow reserve without stenosis (hyperemic Qn/baseline Qn) can be calculated and defined as 'microvascular flow reserve(MFR)'in this study.
Methods : MFR was defined as (√hyperemicΔp* baseline FFR)/(√baselineΔp *hyperemic FFR). In 18 patients with relatively short lesion (<30 mm) with normal looking vessel other than the lesion, coronary pressure wire study was done before and after stenting to acquire MFR. The first MFR was acquired in de novo lesion with the MFR equation. After stenting, repeated MFR measurements for second and third MFR were done at random baseline Pd/Pao values with undersized balloon obstruction. And then, pressure wire derived CFR by thermodilution was done again to measure post PCI CFR.
Results: Each measured MFR in either de novo lesion or random artificial balloon obstructions was not significantly different each other. Moreover, each MFR also significantly corresponded with its post-PCI CFR.
Conclusions: MFR appears to be a reliable parameter that can be simply measured by pressure wire. Predicting post PCI CFR in advance with MFR equation may be helpful to determine lesion significance before PCI.
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