A Coupled Experimental and Computational Approach to Quantify Deleterious Hemodynamics, Vascular Alterations, and Mechanisms of Long-Term Morbidity in Response to Aortic Coarctati

Introduction Coarctation of the aorta (CoA) is associated with morbidity despite treatment. Although mechanisms remain elusive, abnormal hemodynamics and vascular biomechanics are implicated. We present a novel approach that facilitates quantification of coarctation-induced mechanical alterations and their impact on vascular structure and function, without genetic or confounding factors. Methods Rabbits underwent thoracic CoA at 10 weeks of age (~ 9 human years) to induce a 20 mm Hg blood pressure (BP) gradient using permanent or dissolvable suture thereby replicating untreated and corrected CoA. Computational fluid dynamics (CFD) was performed using imaging and BP data at 32 weeks to quantify velocity, strain and wall shear stress (WSS) for comparison to vascular structure and function as revealed by histology and myograph results. Results Systolic and mean BP was elevated in CoA compared to corrected and control rabbits leading to vascular thickening, disorganization and endothelial dysfunction proximally and distally. Corrected rabbits had less severe medial thickening, endothelial dysfunction, and stiffening limited to the proximal region despite 12 weeks of normal BP (~ 4 human years) after the suture dissolved. WSS was elevated distally for CoA rabbits, but reduced for corrected rabbits. Discussion These findings are consistent with alterations in humans. We are now poised to investigate mechanical contributions to mechanisms of morbidity in CoA using these methods

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

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 Multi-Link 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 best- and worst-case orientations of the stent struts relative to the primary blood flow direction. All stents were 18 mm in length and over-deployed 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

Computational simulations demonstrate altered wall shear stress in aortic coarctation patients treated by resection with end-to-end anastomosis.

International audienceBACKGROUND: Atherosclerotic plaque in the descending thoracic aorta (dAo) is related to altered wall shear stress (WSS) for normal patients. Resection with end-to-end anastomosis (RWEA) is the gold standard for coarctation of the aorta (CoA) repair, but may lead to altered WSS indices that contribute to morbidity. METHODS: Computational fluid dynamics (CFD) models were created from imaging and blood pressure data for control subjects and age- and gender-matched CoA patients treated by RWEA (four males, two females, 15 ± 8 years). CFD analysis incorporated downstream vascular resistance and compliance to generate blood flow velocity, time-averaged WSS (TAWSS), and oscillatory shear index (OSI) results. These indices were quantified longitudinally and circumferentially in the dAo, and several visualization methods were used to highlight regions of potential hemodynamic susceptibility. RESULTS: The total dAo area exposed to subnormal TAWSS and OSI was similar between groups, but several statistically significant local differences were revealed. Control subjects experienced left-handed rotating patterns of TAWSS and OSI down the dAo. TAWSS was elevated in CoA patients near the site of residual narrowings and OSI was elevated distally, particularly along the left dAo wall. Differences in WSS indices between groups were negligible more than 5 dAo diameters distal to the aortic arch. CONCLUSIONS: Localized differences in WSS indices within the dAo of CoA patients treated by RWEA suggest that plaque may form in unique locations influenced by the surgical repair. These regions can be visualized in familiar and intuitive ways allowing clinicians to track their contribution to morbidity in longitudinal studies