IN VIVO, IN VITRO AND IN SILICO COMPARISON OF TWO DEVICES TO MEASURE FRACTIONAL FLOW RESERVE

Background: Fractional flow reserve (FFR) can be measured with a wire or a microcatheter with built-in pressure-sensor. We sought 1)
to quantify the impact on the pressure gradient (ΔP) of each device in silico in a modeled coronary artery stenosis validated by in vitro
measurements and 2) to assess our clinical experience with both systems.
Methods: In a validated test bench mimicking any blood flow rate pattern, 50 mm-long tubes with a inner lumen diameter of 2.5 mm (3D
printed in polylactic acid) with or without a 15 mm-long 60 % diameter stenosis (DS) were studied. Measured ΔP at flow rate (Q) up to
100 ml/min with or without a FFR device inserted were compared with computational fluid dynamic (CFD software FineOpen™, Numeca)
solving the Navier-Stokes equations in a mesh of ~1.106 nodes reproducing the in vitro setup. Clinical cases from our cathlab were also
reviewed over the last 2 years (1009 coronary angiography and 315 PCI).
Results: Without a stenosis, ΔP at Q=100 ml/min was 7, 8 and 9 mmHg respectively without any device, with a 0.014' Boston Scientific
Comet™ FFR-wire and with a Acist Navvus™ 0.022' microcatheter. CFD gave the same values when each system was placed close to the
wall, but gradients twice larger with the FFR device simulated in the center. In the tube with a 60% stenosis, ΔP at Q=50 ml/min was 17,
30 and 74 mmHg respectively. In silico, other geometries demonstrated a decreased influence of any device on ΔP with a larger residual
lumen: in a 2.5 mm tube with a 50% DS, ΔP for Q=50 ml/min was 11, 15 and 25 mmHg, respectively a true FFR of 0.89, a wire-FFR of 0.85
and a microcatheter-FFR of 0.75, for a 100 mmHg proximal pressure. Conceptually, a pressure-wire might not cross difficult lesions while
a workhorse wire would, on which a FFR-microcatheter could be advanced. However, we found in our clinical data base that we tried to
measure FFR with 41 Navvus™ and failed to cross 3 lesions, while we crossed all 71 attempted stenosis with a Comet™ wire.
Conclusion: We demonstrate in vitro and in silico in small diseased coronary arteries that clinically significantly higher ΔP are added by a
FFR-microcatheter than by a FFR wire. In our daily practice, these microcatheters had also a higher failure rate to cross tortuous lesions.