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Cardiovascular Engineering

Cardiovascular Engineering - Poster Session E

Poster U4 - Impact of Pressure Wires in Virtual FFR Assessment: A Computational Study

Saturday, October 26, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Coronary artery disease (CAD), one of the most common cardiovascular diseases, is caused by plaque buildup within the vessel wall, leading to coronary artery narrowing and reduced myocardial blood supply. Early diagnosis and treatment are crucial for improving patient outcomes. Fractional flow reserve (FFR) is the current gold standard for the diagnosis of CAD. It is defined as the ratio of time-averaged distal coronary pressure (Pd) to proximal coronary pressure (Pa) during drug-induced maximal hyperemia, and it is clinically obtained through an invasive pressure guidewire. However, the invasive nature of FFR measurement can increase patient discomfort and the risk of catheter-related complications.
Several non-invasive diagnostic methods have been proposed, such as fractional flow reserve derived from computed coronary tomography angiography (FFRCT) and fractional flow reserve derived from machine learning algorithms (FFRML). These techniques primarily rely on computational fluid dynamics (CFD), but have generally produce FFR estimates without considering the impact of the pressure guidewire on the computed hemodynamics.
In this study, we conducted a comprehensive study to quantify the impact of pressure wire on FFR computation under various scenarios, including different stenosis lengths, severity, and types (localized or diffuse). The aim was to improve the accuracy of CFD-based FFR computation and assist in decision-making for CAD diagnosis and treatment.

Materials and

Methods:  Figure 1 illustrates a CFD model for computational FFR assessment constructed from patient-specific CCTA data. The model includes the aortic root and left and right coronary arteries, with four branches on the left and two on the right. A 2.0 mm diameter catheter was first advanced to the proximal segment of the left main coronary artery (LM), and a 0.36 mm diameter guidewire was placed into the distal segment of the left anterior descending artery (LAD) to simulate interventional procedures.
Lumped parameter models (LPM) of the left heart, coronary arteries, and aorta, as shown in Figure 1, were used as boundary conditions to generate pulsatile flow and pressure solutions. The coronary artery LPMs are connected to the ventricular pressure, to produce the well-known diastolic-dominant flow patterns in the coronary arteries. The left coronary arteries were directly connected to the left ventricular pressure, while the right coronary arteries used a reduced transfer coefficient to account for and the smaller right ventricular pressures.
The Navier-Stokes equations were solved to compute velocities and pressures within the 3D domain, using CRIMSON, a widely adopted open-source hemodynamic computation software. Figure 2 presents eight different models, with and without guidewire, for LAD stenosis ranging from 0% to 65% diameter reduction. Locations for Pd and Pa assessment are indicated in the figure. Solutions for FFR with and without wire are referred to as FFRwire and FFRno wire , respectively.

Results, Conclusions, and Discussions: Figure 3(a) and (b) shows that as stenosis percentage increased, both FFRno wire and FFRwire decreased. Across all stenosis severities, FFRwire was consistently lower than FFRno wire. The FFR discrepancy ΔFFR between FFRno wire and FFRwire increased with stenosis severity, reaching a value of 0.41 at the 65% stenosis. To understand the relationship between ΔFFR and stenosis severity, we introduce the blockage ratio, defined as the cross-sectional area of the pressure guidewire divided by the minimum luminal area of the stenosis. This parameter reflects the effective flow area at the narrowest point of the coronary artery.
Figure 3(c) shows that the blockage ratio increases with increasing stenosis severity. For a 65% stenosis, the guidewire obstructs 18.4% of the minimum luminal area. Therefore, the presence of the guidewire exacerbates the impact of the stenosis on the flow, resulting in larger ΔFFR.
Figure 4 shows the relationship between FFRno wire and FFRwire, as indicated by the green line obtained using linear regression. An FFR value of 0.8 or smaller indicates a hemodynamically significant stenosis, and the need for a revascularization procedure. The gray area in the plot represents a ‘misdiagnosis range’, with FFRno wire values larger than 0.8 and FFRwire values smaller than 0.8. The plot indicates that two points fell within this misdiagnosis range, indicating that the diagnostic results shift from normal to abnormal when considering guidewire effects.
In summary, this study investigated the impact of pressure wires on virtual FFR assessment based on CFD. The intervention of the catheter and pressure guidewire resulted in lower virtual FFR values. As stenosis severity increased, the difference between FRR values computed with and without wire became more significant. This difference could lead to potential misdiagnosis for moderate stenosis. These findings highlighted the importance for considering the influence of the guidewire in FFR assessments. Future work will include the impact of additional parameters such as stenosis shape, diffuse vs localized stenosis, and degree of hyperemia.

Acknowledgements (Optional):