(PC136) The Role of Hemodynamics in Refining Internal Carotid Artery Stenosis Classification

Objectives: Internal carotid artery (ICA) stenosis is classified as percentage stenosis (%Stenosis) using duplex ultrasound (DUS) velocities or computed tomography angiography (CTA) anatomy. However, variability exists between velocity and anatomic-based %Stenosis classifications and neither classification method accounts for hemodynamics such as flow, pressure gradient (PG), and wall shear stress (WSS), which impact stroke risk. We sought to investigate differences in ICA hemodynamics among %Stenosis groups and define PG/WSS hemodynamic ranges for ICA stenosis. We hypothesize that PG and WSS derived from computational fluid dynamics simulations (CFD) will assist in ICA %Stenosis classification.

Methods: Patients with asymptomatic >70% ICA stenosis on DUS were prospectively enrolled for phase-contrast (PC) magnetic resonance imaging (MRI). Geometric models of the bilateral common carotid artery (CCA), ICA, and external carotid artery (ECA) were created from CTA. PC MRI-derived flow waveforms were prescribed to the CCA and ECA and the ICA outlet was coupled to a 3-element Windkessel model. Navier-Stokes equations were used to solve for velocity and pressures. ICA flow, PG=Pdistal/Pproximal, and WSS were estimated using CFD. DUS and CTA were used to assess %Stenosis of the bilateral ICA. Cases with agreement in %Stenosis on DUS and CTA were used to define average hemodynamics for %Stenosis groups. Average hemodynamics were then used to clarify %Stenosis classification in the cases without agreement on DUS and CTA. Fig 1 depicts the model inputs, outputs, and application.

Results: Thirty arteries were included (average age 71.3 years, 53.3% male). DUS and CTA %Stenosis agreed in 24/30 (80%) cases (6 mild, 3 moderate, 15 severe). Table I depicts standard diagnostics and hemodynamics for cases with %Stenosis agreement. As %Stenosis increased, WSS increased and PG decreased. No significant differences in ICA flow were observed. Six cases had disagreement in %Stenosis classifications (4 cases classified as severe on DUS/velocities but moderate CTA/anatomy; 1 case classified as severe on DUS/velocity but mild on CTA/velocity; 1 case classified as mild on DUS/velocity but moderate on CTA/anatomy). Addition of PG and WSS assisted in clarifying the %Stenosis classification in cases with disagreement between DUS and CTA (1 case re-classified as severe, 4 cases re-classified as moderate, 1 case re-classified as mild).

Conclusions: While velocity and anatomic %Stenosis agree in most cases, 20% show discrepancies. Using hemodynamic parameters (WSS/PG), in addition to velocity and anatomical %Stenosis, provides a comprehensive assessment of stenosis severity and can discriminate %Stenosis in discordant cases.