Hemodynamics in Idealized Stented Coronary Arteries: Important Stent Design Considerations

Abstract

Stent induced hemodynamic changes in the coronary arteries are associated with higher risk of adverse clinical outcome. The purpose of this study was to evaluate the impact of stent design on wall shear stress (WSS), time average WSS, and WSS gradient (WSSG), in idealized stent geometries using computational fluid dynamics. Strut spacing, thickness, luminal protrusion, and malapposition were systematically investigated and a comparison made between two commercially available stents (Omega and Biomatrix). Narrower strut spacing led to larger areas of adverse low WSS and high WSSG but these effects were mitigated when strut size was reduced, particularly for WSSG. Local hemodynamics worsened with luminal protrusion of the stent and with stent malapposition, adverse high WSS and WSSG were identified around peak flow and throughout the cardiac cycle respectively. For the Biomatrix stent, the adverse effect of thicker struts was mitigated by greater strut spacing, radial cell offset and flow-aligned struts. In conclusion, adverse hemodynamic effects of specific design features (such as strut size and narrow spacing) can be mitigated when combined with other hemodynamically beneficial design features but increased luminal protrusion can worsen the stent's hemodynamic profile significantly.

Keywords: Computational fluid dynamics (CFD); Coronary artery disease; Hemodynamics; Stent; Stent design; Wall shear stress (WSS).

Figure 1

Left main coronary blood flow over time prescribed as the inlet boundary condition (adapted from Nichols et al.33). Red circles indicate timepoints selected for transient analysis throughout the manuscript taken from the fourth simulated cardiac cycle.

Figure 2

(a) Struts with 0.83, 1.25, 1.67, and 2 mm spacing (upper to lower) modeled with 81 and 120 µm strut sizes. (b) Biomatrix geometry with 25, 50, and 75% luminal protrusion and malapposition of the stent protruding into the vessel lumen. (c) Biomatrix (left) and Omega (right) geometries with stent design labels.

Figure 3

Strut spacing: (a) Percentage area of adverse stress over the cardiac cycle; WSS < 0.5 Pa (top) and WSSG > 200 Pa/m (bottom), for 81 (left) and 120 µm (right) strut sizes for all strut spacings. (b) TAWSS histogram for 0.83 mm (blue), 1.25 mm (cyan), 1.67 mm (yellow), and 2 mm (red) strut spacing with 81 µm (left) and 120 µm (right) strut sizes.

Figure 4

Strut size: (a) Omega geometry with 81 µm (left) and 120 µm (right) strut size, (b) WSS, (c) TAWSS contour for 81 µm (left) and 120 µm (right) strut size, (d) histogram of TAWSS distribution and (e) percentage areas of low WSS (<0.5 Pa, left) and high WSSG (>200 Pa/m, right) over the cardiac cycle for the 81 µm (blue) and 120 µm (green) Omega geometry.

Figure 5

Stent protrusion comparison between 25, 50, 75% luminal protrusion and malapposition: (a) Percentage area of adverse haemodynamic parameters (WSS < 0.5 Pa and WSSG > 200 Pa/m) over cardiac cycle. (b) Areas of WSS < 0.5 Pa (red) and >2.5 Pa (green) for 25–75% luminal protrusion and malapposition (left to right) at peak flow (2.72 s). (c) High WSS > 2.5 Pa for malapposition over the cardiac cycle. (d) TAWSS distribution for 25, 50, and 75% luminal protrusion (left) and malapposition (right).

Figure 6

Biomatrix vs. Omega: (a) Area of adverse low WSS (<0.5 Pa, left) and high WSSG (>200 Pa/m, right) for Biomatrix (red) and Omega (blue) over the cardiac cycle. (b–d) Comparison between the Biomatrix (left panel) and Omega (center panel) geometries with histograms (right panel, where the Biomatrix is shown in red, and Omega in blue) of (b) WSS at peak flow (2.72 s); (c) TAWSS; and (d) WSSG at peak flow (2.72 s).

Figure 7

WSS at peak flow (2.72 s, left), TAWSS (middle), and WSSG at peak flow (2.72 s, right) along the longitudinal axis of the vessel, crossing the strut peaks for the Biomatrix (red) and Omega (blue) geometries for the first struts to 2 mm within the stented region. Strut positions are indicated by arrows.