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RESEARCH PAPERS

# In Vitro Quantification of Guidewire Flow-Obstruction Effect in Model Coronary Stenoses for Interventional Diagnostic Procedure

[+] Author and Article Information
Koustubh D. Ashtekar

Department of Mechanical Engineering, University of Cincinnati, Cincinnati, OH 45221

Lloyd H. Back

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91125

Saeb F. Khoury

Department of Internal Medicine-Cardiology, University of Cincinnati, Cincinnati, OH 45221

Rupak K. Banerjee1

Departments of Mechanical Engineering and Biomedical Engineering, University of Cincinnati, Cincinnati, OH 45221rupak.banerjee@uc.edu

Gray zone is defined as the coronary stenosis for which FFR measurement is between 0.75 and 0.8 (15).

1

Corresponding author. Present address: Mechanical (Primary) and Biomedical (Secondary) Engineering Departments, 688 Rhodes Hall, P.O. Box 210072, Cincinnati OH 45221-0072.

J. Med. Devices 1(3), 185-196 (May 21, 2007) (12 pages) doi:10.1115/1.2776336 History: Received October 10, 2006; Revised May 21, 2007

## Abstract

The objective is to quantify the guidewire (diameter of $0.35mm$) flow-obstruction effect in the in vitro model coronary stenoses in relation to trans-stenotic pressure drop, $Δp$, fractional flow reserve (gFFR; “g” represents FFR measurement with guidewire insertion) and coronary flow reserve (gCFR) for steady and pulsatile physiological flows. The sensor tipped pressure or flow measuring guidewire insertion through stenotic lumen increases the trans-stenotic pressure drop or reduces the pharmacologically induced hyperemic flow in the coronary arteries with plaques. These hemodynamic changes may cause error in true FFR and CFR measurements, especially for intermediate coronary stenosis. To quantify guidewire flow-obstruction effect, simultaneous measurements of trans-stenotic pressures and flow were performed by two methods: (a) guidewire based measurements (gCFR and gFFR by inserting sensor tipped guidewire) and (b) true physiological measurements (CFR by in-line Doppler flow cuff and FFR by the radially drilled pressure ports in three epicardial coronary stenotic test sections, postangioplasty, intermediate, and preangioplasty). The diagnostic parameters measured before guidewire insertion (CFR and FFR) and during guidewire insertion (gCFR and gFFR) were validated numerically and correlated with the new diagnostic parameter “lesion flow coefficient (LFC).” There was significant flow reduction with increased trans-stenotic pressure drop due to guidewire insertion. The FFR-gFFR and CFR-gCFR correlations were $FFR=0.92×gFFR+0.097$$(R2=0.99)$ and $CFR=0.91×gCFR+0.44$$(R2=0.99)$, respectively, where gCFR is reported from clinical pressure-flow data. Similar highly regressed $(R2>0.9)$ correlations were obtained for LFC and gLFC with flow ratios and pressure ratios. There was significant difference between steady and pulsatile pressure drops for the same mean flow with and without guidewire insertion. The trans-stenotic hemodynamics was altered due to guidewire insertion. The true FFR and CFR were underestimated because of guidewire insertion. Hence, the FFR-gFFR and CFR-gCFR correlations can be used to find out true FFR and CFR from clinically measured values (i.e., gFFR and gCFR). In addition, the gLFC-gCFR and gLFC-gFFR were correlated significantly for post- and preangioplasty conditions.

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## Figures

Figure 1

(a) Photograph of postangioplasty stenosis test section. A total of 16 pressure ports (diameter of 0.3mm) is drilled radially along the axial direction of stenosis test section, spaced approximately 5mm apart. Port No. 3 is located 3.4mm proximal to the converging section. Port Nos. 5 and 7 are drilled on the opposite side of the shown face and are located at the start and at the end of throat section, respectively. (b) MicroCT images of intermediate and preangioplasty stenotic test sections. The picture is taken only for 2cm in proximity to the stenosis test section. Port Nos. 4 and 5 are shown in this figure. A total of 16 and 14 pressure ports is drilled radially for intermediate and preangioplasty stenotic test sections, respectively. (c) Schematic diagram of stenosis test sections with inserted guidewire for postangioplasty case. (d) Schematic diagram of stenosis test sections without inserted guidewire for postangioplasty case.

Figure 2

Experimental setup showing the flow loop, data acquisition system, and stenotic test section

Figure 3

Hyperemic and basal pulsatile flow versus time generated in the flow loop and applied to the test section. S, start of systole; D, start of diastole. The flow wave form obtained in the in vitro experiment is based on the flow wave form obtained by in vitro calibration (Cho (17)).

Figure 4

(a) Pressure pulse at various times along the axial direction measured by Volcano system in converging, throat, and diverging sections. (b) Pressure drop versus flow characteristic for steady state experiment. (c) Time averaged pressure drop versus flow characteristic for pulsatile flow experiment. Legends: diamonds: postangioplasty; triangles: intermediate stenosis; and circles: preangioplasty. Filled data points: with guidewire insertion; unfilled data points: without guidewire insertion. The solid lines, second order polynomial curve fit for experimental data; the dashed lines: second order polynomial curve fit for numerical data. The Y axis scales are the same for comparison of steady and pulsatile flow condition pressure drops.

Figure 5

CFR-prh line for mean pressure and flow data for pulsatile flow experiment. Hemodynamic hyperemic end points, as shown in Table 2, are represented by red donuts in the figure. The line connecting these three end points is used to limit the experimental data to calculate the hyperemic flows.

Figure 6

(a) FFR-gFFR relation for pulsatile flow and (b) CFR-gCFR relation for pulsatile flow

Figure 7

(a) LFC-(p̃r∕p̃a) correlations. At hyperemia, circled points are FFR or gFFR. (b) LFC-(Q̃∕Q̃b) correlations. At hyperemia, circled points are CFR or gCFR.

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