Innovating stents for aneurysm repair: New implant designs informed by thrombosis modeling.

Thoracic endovascular aortic repair (TEVAR) method is an alternative treatment for thoracic aortic aneurysm (TAA) compared to open surgery. It is believed that stent graft implantation can potentially reduce the risk of aneurysm rupture by altering the associated blood flow disturbances within an aneurysm. To investigate the hemodynamics changes of TEVAR intervention to the TAA, three models, namely healthy, aneurysm before treatment, and aneurysm after stent graft implantation models were built. These three models were presented and compared in terms of their flow patterns, time-averaged wall shear stress (TAWSS), oscillating shear index (OSI), and relative residence time (RRT). Reduced TAWSS and OSI with altered flow pattern were found on the aneurysm wall after the deployment of the microporous stent graft. Elevated RRT on the aneurysm sac indicated that red blood cells and platelets tended to stay longer in the aneurysm sac after implantation of the microporous stent graft. The alteration of flow patterns caused by the microporous stent graft revealed its potential to create a beneficial hemodynamic environment, which promotes platelet activation within the aneurysm and elicits localization of thrombus formation that ultimately lead to the recovery of an aortic aneurysm.

Risk prediction for thoracic aortic dissection: Is it time to go with the flow?

Hemodynamic insight into overlapping bare-metal stents strategy in the treatment of aortic aneurysm

Carotid atherosclerotic vascular disease significantly contributes to strokes, presenting a heightened risk of early recurrent ischemia. Computational fluid dynamics (CFD) has shown potential in predicting subsequent stroke recurrence in patients with carotid stenosis. This study aims to investigate the differences in computational time and accuracy of four key hemodynamic indices-wall shear stress (WSS), time-averaged wall shear stress (TAWSS), Oscillatory Shear Index (OSI), and relative residence time (RRT)-across different viscosity models, thereby providing optimal model selection for clinical cases and offering guidance for clinicians' decision-making. A three-dimensional vessel model was established using computed tomography angiography (CTA), followed by CFD simulations to calculate WSS, TAWSS, OSI, and RRT. The accuracy of the simulations was validated by comparing the results with those from Razavi et al. (10.1016/j.jbiomech.2011.04.023). Numerical errors in different parameters under varying stenosis levels and viscosity models were analyzed. In the transient state, when degree of stenosis is 38%, 72%-84%, the performance difference between the two is less than 6%. For TAWSS, the difference is 0% when degree of stenosis is 12%, 18%, 26%, 54%, and 76%. For OSI, the difference is 0% when stenosis is 16%, 18%, 26%. For RRT, the difference between the two is 0% when degree of stenosis is 18% and 84%. WSS exhibited an increasing trend with higher degrees of stenosis. TAWSS demonstrated significant variation in moderate to severe stenosis, while OSI increased markedly in cases of moderate to severe stenosis. High RRT values in severely stenotic regions indicated a propensity for atherosclerotic lesion development. This study systematically quantified the discrepancies between Newtonian and non-Newtonian blood viscosity models in predicting hemodynamic parameters across different degrees of carotid artery stenosis. Statistical analyses revealed significant differences between the two models in WSS, TAWSS, OSI, and RRT (p<0.001 for all parameters). Newtonian models, while computationally efficient, overestimated TAWSS, OSI, and RRT while underestimating WSS, particularly in moderate to severe stenosis. In contrast, non-Newtonian models provided more physiologically accurate predictions, especially in regions with high shear stress variations. The results emphasize the importance of selecting appropriate viscosity models for CFD-based patient-specific risk assessment, particularly in stroke prediction, plaque evaluation, and surgical planning. Non-Newtonian models should be prioritized in high-risk patients where flow disturbances are more pronounced, whereas Newtonian models remain suitable for early screening and rapid assessments.

To compare the hemodynamic performance of three (Bottom Up non-ballet, Top-Down non-ballet, Top Down ballet) idealized stent graft configurations used during endovascular repair of abdominal aortic aneurysms, under the influence of various rheological models. Ten rheological models are assumed and a commercial finite volume solver is employed for the simulation of blood flow under realistic boundary conditions. An appropriate mesh convergence study is performed and five hemodynamic variables are computed: the time average wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), endothelial cell activation potential and displacement force (DF) for all three configurations. The choice of blood flow model may affect results, but does not constitute a significant determinant on the overall performance of the assumed stent grafts. On the contrary, stent graft geometry has a major effect. Specifically, the Bottom Up non-ballet type is characterized by the least favorable performance presenting the lowest TAWSS and the highest OSI, RRT and ECAP values. On the other hand, the Top Down ballet type presents hemodynamic advantages yielding the highest TAWSS and lowest OSI, RRT and ECAP average values. Furthermore, the ballet type is characterized by the lowest DF, although differences observed are small and their clinical relevance uncertain. The effect of the assumed rheological model on the overall performance of the grafts is not significant. It is thus relatively safe to claim that it is the type of stent graft that determines its overall performance rather than the adopted blood flow model.

Background/Objectives: This study compared the hemodynamic performance of fenestrated (FEVAR), branched (BEVAR), and chimney endovascular aortic aneurysm repair (chEVAR) in patients with complex aortic aneurysms. Methods: The pre- (native) and post-endovascular repair (endograft-defined) blood lumen was reconstructed from computed tomography angiographies of nine (9) elective patients treated with FEVAR (n = 3), BEVAR (n = 3), and chEVAR (n = 3). Computational fluid dynamics (CFD) simulations obtained blood flow properties. Velocity magnitude, wall shear stress (WSS), time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and local normalized helicity (LNH) were computed at peak systole and mid-diastole. The hemodynamic data were statistically analyzed to evaluate correlations between FEVAR, BEVAR, and chEVAR, focusing on targeted visceral arteries. Results: Only slight differences were observed regarding RRT, OSI, and TAWSS between FEVAR and BEVAR, whereas the chEVAR group demonstrated a marked deviation from both. In FEVAR, the postoperative helical flow structures appeared more compact, while in BEVAR they were more developed and exhibited a more rotational configuration. The LNH of the visceral vessel patterns exhibited similar qualitative features across groups. Regarding TAWSS, higher values were found in BEVAR, whereas chEVAR showed the lowest. Conclusions: FEVAR, BEVAR, and chEVAR improved postoperative blood flow characteristics toward near-physiological conditions, reducing undesired flow patterns and recirculation zones. FEVAR showed more stable visceral flow, and BEVAR demonstrated higher flow rates and fewer recirculation zones, while chEVAR exhibited more streamlined visceral artery flow with reduced regurgitation at bridging stent entries. Despite variations, all approaches effectively preserved visceral artery perfusion.

Computational fluid hemodynamic based analyisis of the aorto iliac segment before the development of post EVAR iliac branch occlusion.

P3588The synergistic effect of NIRS-detected lipid-rich plaque and 5 different multidirectional wall shear stress metrics on human coronary plaque growth

The patchy anatomical distribution of atherosclerosis has been attributed to variation in haemodynamic wall shear stress (WSS). The consensus is that low WSS and a high Oscillatory Shear Index (OSI) trigger the disease. We found that atherosclerosis at aortic branch sites correlates threefold better with transverse WSS (transWSS), a metric which quantifies multidirectional near-wall flow. Coronary artery disease has greater clinical significance than aortic disease but computation of WSS metrics is complicated by the substantial vessel motion occurring during each cardiac cycle. Here we present the first comparison of the distribution of atherosclerosis with WSS metrics computed for moving coronary arteries. Maps of WSS metrics were computed using dynamic geometries reconstructed from angiograms of ten non-stenosed human right coronary arteries (RCAs). They were compared with maps of fatty streak prevalence derived from a previous study of 1852 RCAs. Time average WSS (TAWSS), OSI, transWSS and the cross-flow index (CFI), a non-dimensional form of the transWSS, gave non-significant or significant but low spatial correlations with lesion prevalence. The highest correlation coefficient (0.71) was for the relative residence time (RRT), a metric that decreases with TAWSS and increases with OSI. The coefficient was not changed if RRT was calculated using CFI, which captures multidirectional WSS only, rather than OSI, which encompasses both multidirectional and oscillatory WSS. Contrary to our earlier findings in the aorta, low WSS in combination with highly multidirectional flow correlates best with lesion location in the RCA, explaining approximately half of its anatomical variation.

The formation of atherosclerosis mainly depends on local hemodynamic blood flow parameters. The spatial and temporal variation of hemodynamic blood flow parameter is considered as an important factor for atherogenesis. The laminar, Newtonian pulsatile blood flow is considered for hemodynamic analysis of the idealized non-stenosis human coronary artery. To model and study the relationship between relative residence time (RRT), time-averaged wall shear stress (WSS) vector (TAWSSV), oscillatory shear index (OSI), and time-averaged WSS (TAWSS) the computational fluid dynamics technique are used. The study shows that higher OSI values are predicted at lower TAWSS and TAWSSV. At the low TAWSS areas the RRT attains a higher value, the region with high RRT correlates with atherosclerotic lesions on the artery wall. The local differences between RRT, OSI, and WSS magnitude may help to find predominantly where the atherosclerotic lesion progresses and develops at specific locations of the artery.

Despite significant progress, malapposed or overlapped stents are a complication that affects daily percutaneous coronary intervention (PCI) procedures. These malapposed stents affect blood flow and create a micro re-circulatory environment. These disturbances are often associated with a change in Wall Shear Stress (WSS), Time-averaged WSS (TAWSS), relative residence time (RRT) and oscillatory character of WSS and disrupt the delicate balance of vascular biology, providing a possible source of thrombosis and restenosis. In this study, 2D axisymmetric parametric computational fluid dynamics (CFD) simulations were performed to systematically analyze the hemodynamic effects of malapposition and stent overlap for two types of stents (drug-eluting stent and a bioresorbable stent). The results of the modeling are mainly analyzed using streamlines, TAWSS, oscillatory shear index (OSI) and RRT. The risks of restenosis and thrombus are evaluated according to commonly accepted thresholds for TAWSS and OSI. The small malapposition distances (MD) cause both low TAWSS and high OSI, which are potential adverse outcomes. The region of low OSI decrease with MD. Overlap configurations produce areas with low WSS and high OSI. The affected lengths are relatively insensitive to the overlap distance. The effects of strut size are even more sensitive and adverse for overlap configurations compared to a well-applied stent.

To explore independent predictors of aortic growth in patients with type B aortic dissection (TBAD) after thoracic endovascular aortic repair (TEVAR), utilizing computational fluid dynamics (CFD) simulation. Patients who underwent TEVAR for TBAD in a single center between April 2014 and April 2023 were evaluated retrospectively. Rapid enlargement (defined as ≥5 mm/year) or aortic rupture were used to categorize patients into aortic growth and nongrowth groups. The analyzed hemodynamic parameters included wall pressure, flow velocity, flow rate, wall shear stress (WSS), time-averaged WSS, oscillatory shear index (OSI), and relative residence time. Four parallel cross-sections (L1-L4) were utilized to extract data from the hemodynamic cloud maps. Multivariate logistic regression analysis was conducted to identify independent predictors. Receiver operating characteristic (ROC) curves and the area under the curve (AUC) for these predictors were also determined. The aortic growth rate was 17.9%. A total of 51 geometric models were successfully constructed, 17 in the growth group and 34 in the nongrowth group. For morphological variables, the growth group exhibited more re-entry tears (p=0.011) and a longer patent false lumen (p=0.028), compared with the nongrowth group. For hemodynamic variables, the growth group had higher L2 pressure (p=0.040), L3 flow rate (p=0.048), and L3 OSI (p=0.020). Multivariate analysis revealed that L3 OSI (OR=7.82, 95% CI 4.122-11.33, p=0.020) and L2 pressure (OR=1.05, 95% CI 1.001-1.099, p=0.044) were independent risk factors for aortic growth. The AUC for L3 OSI and L2 pressure as predictors of aortic growth were 68.25% (95% CI 53.85-82.66) and 64.36% (95% CI 49.13-79.59), respectively. CFD simulation demonstrated that elevated pressure and increased OSI in false lumen could independently predict aortic growth following TEVAR. Monitoring these specific metrics could help identify high-risk patients immediately after stent graft implantation. However, the predictive value of these predictors was low, indicating a need for larger sample, higher-quality studies to validate these findings.Clinical ImpactThoracic endovascular aortic repair (TEVAR) is the important treatment for patients with acute type B aortic dissection (TBAD). However, aortic growth following TEVAR remains an important unresolved issue. Previous case/ cases reports found aortic growth was not solely driven by anatomical factors but influenced by hemodynamics within the false lumen. However, no further higher-quality studies supported the conclusion. In this comparative study, aortic growth and non-growth groups were divided. The computational fluid dynamics (CFD) simulation showed that elevated pressure and oscillatory shear index (OSI) in the false lumen could independently predict aortic growth after TEVAR. Our conclusions allowed vascular surgeons to make a decision on further intervention for distal aortic dissection immediately after stent graft implantation, to prevent potentially post-dissection aortic aneurysm (PDAA) and rupture in the future.

Hemodynamic Consequences of Renal Artery Ostium Positioning After Inner-Branch Endografting for Juxtarenal Aortic Aneurysms.

Hemodynamic characteristics of type I Endoleak and intra-prosthetic thrombus following endovascular aneurysm repair: A computational fluid dynamics study.

Impact on hemodynamics in carotid arteries with carotid webs at different locations: A Numerical Study Integrating Thrombus Growth Model