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Cardiovascular Engineering

Cardiovascular Engineering - Poster Session A

Poster H10 - Comparison of Hemodynamics Amongst Patients with Different Internal Carotid Artery Stenosis Severity

Thursday, October 24, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Internal carotid artery (ICA) stenosis is an atherosclerotic narrowing of the extra-cranial ICA and is a leading cause of death and long-term disability. ICA stenosis can cause ischemic stroke via hypoperfusion and/or embolism, with the latter being more common. Duplex ultrasound (DUS) is the first-line diagnostic modality, and provides a surrogate estimate of percentage stenosis (%Stenosis) via velocity profiles. Computed tomography angiography (CTA) can be used as an adjunctive diagnostic modality. In patients with mild (0-49%) or moderate stenosis (50-69%) medical therapy is superior to surgery (carotid endarterectomy (CEA) or carotid artery stenting). However, patients with severe stenosis (70-99%) or those experiencing symptoms (transient ischemic attack (TIA) or stroke) may benefit from surgical intervention. While reduced stroke risk following CEA has been demonstrated in symptomatic patients with greater than 50% stenosis, the benefit of CEA in asymptomatic patients is debated. In fact, many surgeons reserve operative intervention to those with stenotic lesions >80%. Moreover, %Stenosis does not account for key hemodynamic indices such as pressure gradient (PG), wall shear stress (WSS), or oscillatory shear index (OSI), which play an important role in atherosclerotic embolism. The objective of this work was to utilize magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) to evaluate the hemodynamic differences in patients with varying degrees of ICA stenosis. By examining the variability within the different stenosis groups, we seek to determine if these parameters can better identify patients who would benefit from surgical intervention, thus leading to more individualized treatment for these patients.

Materials and

Methods:  Patients with asymptomatic severe ICA stenosis (70-99% from DUS velocities) were prospectively enrolled. Prior DUS and CTA were required for inclusion. An MRI consisting of a 3D time-of-flight (TOF) of the head/neck for anatomic characterization and 2D cardiac-gated phase contrast (PC) at the common carotid artery (CCA), external carotid artery (ECA), and ICA distal to the lesion was obtained. Vessel-specific velocity encoding based on DUS-derived peak systolic velocity (PSV) was utilized. MRI data was collected at the bilateral ICA, irrespective of the contralateral ICA %Stenosis.
3D geometric CFD models were created in the open source software CRIMSON using a path planning and vessel contouring technique. Phase-contrast (PC-MRI) derived waveforms were prescribed at the CCA inlet and ECA outlet for each patient’s geometric model. Each ICA outlet was coupled to a three-element Windkessel model, whose parameters were iteratively estimated to match the patient’s blood pressure. Blood was modeled as an incompressible Non-Newtonian fluid with a dynamic viscosity of 0.004 kg m−1s−1 and a density of 1060 kg m-3. Incompressible Navier-Stokes equations were used to solve for velocity and pressures.
PSV and end diastolic velocity (EDV) were collected at each ICA from DUS. Average area of the lumen (ALumen) at the maximum stenosis was measured on CTA. ICA hemodynamics (PG=Pdistal/Pproximal, WSS, OSI) were collected, at the stenosis, from CFD models. The above metrics were then compared between arteries with mild (0-49%), moderate (50-69%), and severe (70-99%) ICA stenosis on DUS. Figure 1 shows a summary of the model inputs and outputs.

Results, Conclusions, and Discussions: Twenty-five arteries from 15 patients (average age 69.8 years, 52% male, 44% right) were included (Figure 2). All stenoses were asymptomatic (20% mild, 12% moderate, and 68% severe). Average PSV was 286.4 cm/s, average EDV was 90.0 cm/s, and average ALumen at the maximum stenosis was 8.6 mm2. There was no difference in the average age, sex, or laterality between stenosis groups (p>0.05). PSV (94.0 vs. 127.7 vs. 371.0 cm/s; p=0.002) and EDV (28.8 vs. 43.7 vs. 116.1 cm/s; p=0.005) increased from mild to moderate to severe stenosis. Average ALumen at the maximum stenosis decreased as %Stenosis increased from mild to moderate to severe (17.1 vs 12.8 vs 5.3 mm2; p=0.006). The average WSS increased from mild to moderate to severe stenosis (2.8 vs 5.6 vs 14.1 Pa; p=0.001). Although there was no difference between OSI in mild and moderate stenosis (0.06), patients with severe stenosis had a trend for lower OSI (0.03 vs 0.06; p=0.087). The average PG decreased as %Stenosis increased (mild: 0.99, moderate: 0.98, severe: 0.94) (Table 1).
In the severe stenosis cohort, four arteries had a larger ALumen at the maximum stenosis than the average of those with moderate stenosis. Additionally, six patients in the severe stenosis cohort were found to have WSS values that were more consistent with the moderate stenosis cohort, and five patients were found to have PG values that were more consistent with the moderate stenosis cohort (Figure 2).

Non-invasive assessment of hemodynamic metrics (WSS and PG) might be a more accurate metric for determining a severe ICA stenosis than %Stenosis from DUS velocity.

Although hemodynamics (WSS and PG) in ICA stenosis change with different degrees of %Stenosis, within the severe stenosis group there is considerable variability. Nearly one-third (5/17) of patients classified as having severe stenosis via DUS velocity exhibit hemodynamics (WSS and PG) that are more characteristic of the moderate stenosis group. Additionally, some of these patients still fall within the 70-99% stenosis range when measuring ALumen at the maximum stenosis on CTA. DUS velocity does not account for variations in hemodynamics in patients with severe ICA stenosis.

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