Effect of Varying Hemodynamic and Vascular Conditions on Fractional Flow Reserve: An In Vitro Study

Abstract

BackgroundThe aim of this study was to investigate the impact of varying hemodynamic conditions on fractional flow reserve (ratio of pressure distal [Pd] and proximal [Pa] to stenosis under hyperemia) in an in vitro setting. Failure to achieve maximal hyperemia and the choice of hyperemic agents may have differential effects on coronary hemodynamics and, consequently, on the determination of fractional flow reserve.Methods and ResultsAn in vitro flow system was developed to experimentally model the physiological coronary circulation as flow‐dependent stenosis resistance in series with variable downstream resistance. Five idealized models with 30% to 70% diameter stenosis severity were fabricated using VeroClear rigid material in an Objet260 Connex printer. Mean aortic pressure was maintained at 7 levels (60–140 mm Hg) from hypotension to hypertension using a needle valve that mimicked adjustable microcirculatory resistance. A range of physiological flow rates was applied by a steady flow pump and titrated by a flow sensor. The pressure drop and the pressure ratio (Pd/Pa) were assessed for the 7 levels of aortic pressure and differing flow rates. The in vitro experimental data were coupled with pressure–flow relationships from clinical data for populations with and without myocardial infarction, respectively, to evaluate fractional flow reserve. The curve for pressure ratio and flow rate demonstrated a quadratic relationship with a decreasing slope. The absolute decrease in fractional flow reserve in the group without myocardial infarction (with myocardial infarction) was on the order of 0.03 (0.02), 0.05 (0.02), 0.07 (0.05), 0.17 (0.13) and 0.20 (0.24), respectively, for 30%, 40%, 50%, 60%, and 70% diameter stenosis, for an increase in aortic pressure from 60 to 140 mm Hg.ConclusionsThe fractional flow reserve value, an index of physiological stenosis significance, was observed to decrease with increasing aortic pressure for a given stenosis in this idealized in vitro experiment for vascular groups with and without myocardial infarction.

Cardiac 3D Printing and its Future Directions

“…CT-derived fractional flow reserve, FFR) against a controlled in vitro forward flow gold standard. (31) Using 3D printed coronary-like vessels, which were fabricated using a clear rigid material (Veroclear, Stratasys), Kolli et al showed that FFR decreased as a function of aortic pressure. This relationship was established using a set of idealized 3D printed vessels with systematically placed stenotic regions that varied from 30% to 70%, resulting in absolute decreases in FFR of 0.03 to 0.2, respectively.…”

Clinical Applications of Three-Dimensional Printing in Cardiovascular Disease

“…Because 3D printing models more accurately replicate the cardiovascular anatomy, the clinical applications have been focused on 'anatomy and function. ' Kolli et al [62] verified the impact of varying hemodynamic conditions on fractional flow reserve in an in vitro setting using 3D printing models. Maragiannis et al [63] demonstrated that patient-specific models using fused dual-material could replicate both the anatomic and functional properties of severe degenerative aortic valve stenosis.…”

Initial evaluation of three-dimensionally printed patient-specific coronary phantoms for CT-FFR software validation

“…22,25,26 Previous in vitro studies using idealized 3D printed coronary phantoms have indicated a dependence on FFR with increasing aortic pressure, making this adjustment in the 3D printed phantoms a necessary step toward replicating physiological conditions. 16 Figure 4(a) shows the setup of the phantoms within the flow loop and Fig. 4(b) shows the phantom setup within the CT gantry.…”

“…15 Previous research has shown the use of 3D printing to create coronary phantoms with stenosis; however, these phantoms were idealized and made out of rigid materials that do not replicate the compliance of vasculature. 16 Recently, 3D printing has been utilized to create patient-specific coronary phantoms that have been successfully used for flow measurements. [17][18][19] Despite a limited number of commercial polymers that are available for 3D printing, these phantoms have been demonstrated to approximately replicate the mechanical properties of vasculature.…”