Computational Fluid Dynamics Evaluation of Equivalency in Hemodynamic Alterations Between Driver, Integrity, and Similar Stents Implanted Into an Idealized Coronary Artery

Abstract

We tested the hypothesis that a slight modification in fabrication from the Driver to the Integrity stent (Medtronic) results in nearly equivalent distributions of wall shear stress (WSS) and mean exposure time (MET), reflective of flow stagnation, and that these differences are considerably less than the MultiLink Vision (Abbott Vascular) or BX Velocity (Cordis) bare metal stents when evaluated by computational fluid dynamics (CFD). Arteries were modeled as idealized straight rigid vessels without lesions. Two vessel diameters (2.25 and 3.0 mm) were studied for each stent and 2.75 mm diameter Integrity stents were also modeled to quantify the impact from bestand worstcase orientations of the stent struts relative to the primary blood flow direction. All stents were 18 mm in length and overdeployed by 10%. The results indicated that, regardless of diameter, the BX Velocity stents had the greatest percentage of the vessel exposed to adverse WSS followed by the Vision, Integrity, and Driver stents. In general, when strut thickness and stent:lumen ratio are similar, the orientation of struts is a determining factor for deleterious flow patterns. For a given stent, the number of struts was a larger determinant of adverse WSS and MET than strut orientation, suggesting that favorable blood flow patterns can be achieved by limiting struts to those providing adequate scaffolding. In conclusion, the Driver and Integrity stents both limit their number of linkages to those which provide adequate scaffolding while also maintaining similar strut thickness and stent:lumen ratios. The Integrity stent also imparts a slight helical velocity component. The modest difference in the fabrication approach between the Driver and Integrity stents is, therefore, not hemodynamically substantial in this idealized analysis, particularly relative to potentially adverse flow conditions introduced by the other stents modeled. This data was used in conjunction with associated regulatory filings and submitted to the FDA as part of the documents facilitating the recent approval for sale of the Resolute Integrity stent in the United States.