The Multi-Artery Fractional Flow Reserve (FFR) Method in The Percutaneous Coronary Intervention (PCI) Practice

Current single-artery FFR-oriented coronary stenosis severity assessment methods (resting Pd/Pa, wave-free iFR and hyperemic FFR) are used successfully in single vessel disease (SVD) cases. In such cases the stenotic artery is in an independent stand-alone position with a proximal intracoronary aortic driving pressure. The treatment decision criteria of each method (FFR threshold value and FFR ‘grey range’) apply to FFR of the artery (denoted FFR^true) which is the remnant fraction left in the stenotic artery of the calculated virtual blood flow of the very same artery prior to the onset of stenosis. As FFR^true can be expressed in terms of the total stenotic resistance Rs of the artery and the microvascular resistance Rmv associated with the artery, FFR^true can be also justifiably regarded as an ad-hoc intrinsic property of the stenotic artery. It doesn’t change unless the artery undergoes revascularization, turning its FFR^true to nearly 1.00. The general scenario however encountered in the PCI practice is one in which a stenotic artery interconnects with other stenotic arteries and it is no longer in an independent stand-alone position since inter-arterial stenosisstenosis interactions take place. Due to this substantial change of circumstances, treatment decision criteria no longer apply to FFR^true of an artery, rather to its actual FFR (denoted FFR^real).

The multi-artery FFR method is not intended to constitute a substitute for any of the current FFR-oriented methods. As single-artery FFRoriented methods cannot resolve complex scenarios of interacting stenotic coronary arteries, in this article the novel multi-artery FFR method extends these methods to the multi-artery domain with no need to alter their associated experimental techniques nor their treatment decision criteria. Reduction of the mathematics to minimal number of simple formulas in this article enables the PCI practitioner to apply the formulas to measured intracoronary pressures in real time.

Keywords: Multi-artery fractional flow reserve; Fractional flow reserve; Percutaneous coronary intervention; Revascularization; Percutaneous transluminal coronary angioplasty

Abbreviations: FFR: Fractional Flow Reserve; PCI: Percutaneous Coronary Intervention; iFR: Instantaneous Wave-Free Ratio; CABG: Coronary Artery Bypass Graft; ISR: In-Stent Restenosis; DES: Drug-Eluting Stent; ST: Stent Thrombosis; MACE: Major Adverse Coronary Event; MVD: Multi- Vessel Disease; SVD: Single Vessel Disease