Aortic Hemodynamics After Thoracic Endovascular Aortic Repair, With Particular Attention to the Bird-Beak Configuration

Analysis of Aortic Arch Hemodynamics With Simulated Bird's Beak Effects

OBJECTIVE

The objective of this study was to investigate the flow effects in different degrees of thoracic aortic stent graft protrusion extension by creating bird beak effect simulations using accurate 3D geometry and a realistic, nonlinear, elastic biomechanical model using computer-aided software SolidWorks.

METHODS

Segmentation in 3D of an aortic arch from a computed tomography (CT) scan of a real-life patient was performed using SolidWorks. A parametric analysis of three models was performed: (A) Aortic arch with no stent, (B) 3 mm bird-beak configuration, and (C) 6.5 mm bird-beak configuration. Flow velocity, pressure, vorticity, wall shear stress (WSS), and time average WSS were assessed.

RESULTS

The flow velocity in Model A remained relatively constant and low in the area of the ostium of the brachiocephalic artery and doubled in the left subclavian artery. On the contrary, Models B and C showed a decrease in velocity of 52.3 % in the left subclavian artery. Furthermore, Model B showed a drop in velocity of 82.7% below the bird-beak area, whereas Model C showed a decline of 80.9% in this area. The pressure inside the supra-aortic branches was higher in Model B and C compared with Model A. In Model A, vorticity only appeared at the level of the descending aorta, with low to non-vorticity in the aortic arch. In contrast, Models B and C had an average vorticity of 241.4 Hz within the bird beak area. Regarding WSS, Model A, and Model B shared similar WSS in the peak systolic phase, in the aortic arch, and the bird beak area, whereas Model C had an increased WSS by 5 Pa on average at these zones.

CONCLUSION

In the present simulations' lower velocities, higher pressures, vortices, and WSS were observed around the bird beak zone, the aortic arch, and the supra-aortic vessels.

Stereolithographic (SLA) 3D Printing for Preprocedural Planning in Endovascular Aortic Repair of a Thoracic Aneurysm

BACKGROUND

When treating aortic aneurysm patients with complex anatomical features, preprocedural planning aided by 3D-printed models offers valuable insights for endovascular intervention. This study highlights the use of stereolithographic (SLA) 3D printing to fabricate a phantom of a challenging aortic arch aneurysm with a complex neck anatomy.

CLINICAL CASE

A 75-year-old female presented with a 58 mm descending thoracic aortic aneurysm (TAA) extending to the distal arch, involving the left subclavian artery (LSA) and the left common carotid artery (LCCA). The computed tomography (CT) scans underwent scrutiny by radiology and vascular teams. Nevertheless, the precise spatial relationships of the ostial origins proved to be challenging to ascertain. To address this, a patient-specific phantom of the aortic arch was fabricated utilizing an SLA printer and a biomedical resin. The thoracic endovascular aortic repair (TEVAR) procedure was simulated using fluoroscopy on the phantom to enhance procedural preparedness. Subsequently, the patient underwent a right carotid-left carotid bypass and a right carotid-left subclavian bypass. After a 24-hour interval, the patient underwent the TEVAR procedure, during which a 37 mm × 150 mm stent graft (CTAG, WL Gore and Associates, Flagstaff, AZ, USA) and a 40 mm × 200 mm stent graft (CTAG, WL Gore and Associates, Flagstaff, AZ, USA) were deployed, effectively covering the LSA and LCCA. Notably, the aneurysm exhibited complete sealing, with no indications of endoleaks or graft infoldings. At the 12-month follow-up, the patient remains in good health, with no evidence of endoleaks or any other surgery-related complication.

CONCLUSION

This report showcases the successful use of a 3D-printed endovascular phantom in guiding the decision-making process during the preparation for a TEVAR procedure. The simulation played a pivotal role in selecting the appropriate stent graft, ensuring an intervention protocol optimized based on the patient-specific anatomy.

Short-term follow-up of proximal aorta remodeling after zone 2 thoracic endovascular aortic repair for acute type B aortic dissection

BACKGROUND

To evaluate the early remodeling of the proximal aorta in patients with acute type B aortic dissection (ATBAD) after zone 2 thoracic endovascular aortic repair (TEVAR).

METHODS

From January 2016 to May 2022, 53 ATBAD patients underwent zone 2 TEVAR were divided into two groups, the Castor single-branched stent-graft (CSS) group (n = 26) and the common stent-graft group (n = 27). Three-dimensional imaging created by computed tomography angiography was used to measure different parameters of the aorta, such as angulation, cross-sectional area (CSA), length and tortuosity. Early remodeling of the proximal aorta was evaluated by comparing geometric parameters of the proximal aorta before and 3 months after surgery.

RESULTS

In terms of angle, the postoperative angle of aortic arch to ascending aorta, descending aorta increased in all patients compared with that before surgery (all P < 0.05), while the angle of aortic arch to left subclavian artery increased after surgery only in the CSS group (P < 0.001); As for CSA, the CSA of distal aortic arch and true lumen increased (all P < 0.05), while the CSA of false lumen decreased in both groups after operation (all P < 0.05); Only in CSS group, the CSA of the ascending aorta, proximal aortic arch and total descending thoracic aorta decreased after surgery (all P < 0.05); In terms of length, the aortic arch prolonged after operation in both groups (P = 0.018 and P = 0.004, respectively). In addition, the ascending aorta tortuosity decreased in the CSS group after surgery (P = 0.011). There was no significant difference in the alterations of other aortic parameters after operation (P > 0.05).

CONCLUSIONS

The CSS implantation provided a more relatively safe and effective treatment for acute type B aortic dissection patients with unfavorable proximal landing zone. It can promote the earlier remodeling of the proximal aorta compared with the common stent-graft implantation after zone 2 TEVAR.

Zone 2/3 lesion and emergency repair as potential mortality predictors of TEVAR for thoracic aortic pseudoaneurysm

OBJECTIVE

Thoracic aortic pseudoaneurysm (TAP) is an uncommon but life-threatening condition. The present study aimed to investigate the early and midterm clinical outcome of TAP patients following TEVAR and identify potential mortality predictors.

METHODS

We retrospectively reviewed a series of 37 eligible patients with TAP admitted to our hospital from July 2010 to July 2020. We explored their baseline, perioperative and follow-up data. Fisher exact test and Kaplan-Meier method were applied for comparing difference between groups.

RESULTS

There were 29 men and 12 women, with the mean age as 59.5 ± 13.0 years (range 30-82). The mean follow-up period was 30.7 ± 28.3 months (range 1-89). For early outcome (≤ 30 days), mortality happened in 3 (8.1%) zone 3 TAP patients versus 0 in zone 4 (p = 0.028); postoperative acute arterial embolism of lower extremity and type II endoleak respectively occurred in 1(2.7%) case. For midterm outcome, survival at 3 months, 1 year and 5 years was 88.8%, 75.9% and 68.3%, which showed significant difference between zone 2/3 versus zone 4 group (56.3% vs. 72.9%, p = 0.013) and emergent versus elective TEVAR group (0.0% versus 80.1%, p = 0.049). Previous stent grafting or esophageal foreign body with Aortoesophageal fistula (AEF), and systemic vasculitis, as etiologies, resulted in encouraging immediate outcome but worse midterm prognosis.

CONCLUSION

TAP lesions at zone 2/3 and emergent TEVAR predict worse midterm outcomes compared to zone 4 lesions and elective TEVAR. The outcomes are also mainly restricted by the etiology of the TAP.

Prediction of bird-beak configuration in thoracic endovascular aortic repair preoperatively using patient-specific finite element simulations

Objectives

Formation of bird-beak configuration in thoracic endovascular aortic repair (TEVAR) has been shown to be correlated with the risk of complications such as type Ia endoleaks, stent graft migration, and collapse. The aim of this study was to use patient-specific computational simulations of TEVAR to predict the formation of bird-beak configuration preoperatively.

Methods

Patient-specific TEVAR computational simulations are developed using a retrospective cohort of patients treated for thoracic aortic aneurysm. The preoperative computed tomography images were segmented to develop three-dimensional geometry of the thoracic aorta. These geometries were used in finite element simulations of stent graft deployment during TEVAR. Simulated results were compared against the postoperative computed tomography images to assess the accuracy of simulations in predicting the proximal position of a deployed stent graft and presence of bird-beak. In cases with a bird-beak configuration, the length and angle of the bird-beak were measured and compared between the simulated and postoperative results.

Results

Twelve TEVAR patient cases were simulated. Computational simulations were able to accurately predict whether the proximal stent graft was fully apposed, proximal bare stents were protruded, or bird-beak configuration was present. In three cases with bird-beak configuration, simulations predicted the length and angle of the bird-beak with less than 10% and 24% error, respectively. Other factors such as a small aortic arch angle, small oversizing value, and landing zones close to the arch apex may have played a role in formation of bird-beak in these patients.

Conclusions

Computational simulations of TEVAR accurately predicted the proximal position of a deployed stent graft and the presence of bird-beak preoperatively. The computational models were able to predict the length and angle of bird-beak configurations with good accuracy. These simulations can provide insight into the surgical planning process with the goal of minimizing bird-beak occurrence.

Analysis of Postoperative Remodeling Characteristics after Modular Inner Branched Stent-Graft Treatment of Aortic Arch Pathologies Using Computational Fluid Dynamics

The modular inner branched stent-graft (MIBSG), a novel interventional therapy, has demonstrated good effects in the endovascular treatment of aortic arch pathologies, especially those involving the supra-aortic branches. Nevertheless, the long-term efficacy of the MIBSG and in-depth quantitative evaluation of postoperative outcomes remain to be examined. Moreover, the regularity of postoperative vascular remodeling induced by MIBSG implantation has yet to be explored. To address these questions, we constructed four models (normal, preoperative, 1 week postoperative, and 6 months postoperative) based on a single patient case to perform computational fluid dynamics simulations. The morphological and hemodynamic characteristics, including the velocity profile, flow rate distribution, and hemodynamic parameter distribution (wall shear stress and its derivative parameters), were investigated. After MIBSG implantation, the morphology of the supra-aortic branches changed significantly, and the branch point moved forward to the proximal ascending aorta. Moreover, the curvature radius of the aortic arch axis continued to change. These changes in morphology altered the characteristics of the flow field and wall shear stress distribution. As a result, the local forces exerted on the vessel wall by the blood led to vessel remodeling. This study provides insight into the vascular remodeling process after MIBSG implantation, which occurs as a result of the interplay between vascular morphological characteristics and blood flow characteristics.

Impact of Thoracic Endografting on the Hemodynamics of the Native Aorta: Pre- and Postoperative Assessments of Wall Shear Stress and Vorticity Using Computational Fluid Dynamics

PURPOSE

To quantify the hemodynamic consequences of thoracic endovascular aortic repair (TEVAR) by comparing the preoperative and postoperative wall shear stress (WSS) and vorticity profiles on computational fluid dynamics (CFD) simulations.

MATERIALS AND METHODS

The pre- and postoperative computed tomography (CT) scans from 20 consecutive patients (median age 69 years, range 20-87) treated for different thoracic aortic pathologies (11 aneurysms, 5 false aneurysms, 3 penetrating ulcers, and 1 traumatic aortic rupture) were segmented to construct patient-specific CFD models using a meshless code. The simulations were run over the cardiac cycle, and the WSS and vorticity values measured at the proximal and distal landing zones were compared.

RESULTS

The CFD runs provided 4-dimensional simulations of blood flow in all patients. WSS and vorticity profiles at the proximal landing zone (located in zones 0-3 in 15 patients) varied in 18 and 20 of the cases, respectively; WSS was increased in 11 cases and the vorticity in 9. Pre- and postoperative WSS median values were 4.19 and 4.90 Pa, respectively. Vorticity median values were 40.38 and 39.17 Hz, respectively.

CONCLUSION

TEVAR induces functional alterations in the native thoracic aorta, though the prognostic significance of these changes is still unknown. CFD appears to be a valuable tool to explore aortic hemodynamics, and its application in a larger series would help define a predictive role for these hemodynamic assessments.

Location of Reentry Tears Affects False Lumen Thrombosis in Aortic Dissection Following TEVAR

Purpose: To report a study that assesses the influence of the distance between the distal end of a thoracic stent-graft and the first reentry tear (SG-FRT) on the progression of false lumen (FL) thrombosis in patients who underwent thoracic endovascular aortic repair (TEVAR). Materials and Methods: Three patient-specific geometrical models were reconstructed from postoperative computed tomography scans. Two additional models were created by artificially changing the SG-FRT distance in patients 1 and 2. In all 5 models, computational fluid dynamics simulations coupled with thrombus formation modeling were performed at physiological flow conditions. Predicted FL thrombosis was compared to follow-up scans. Results: There was reduced false lumen flow and low time-averaged wall shear stress (TAWSS) in patients with large SG-FRT distances. Predicted thrombus formation and growth were consistent with follow-up scans for all patients. Reducing the SG-FRT distance by 30 mm in patient 1 increased the flow and time-averaged wall shear stress in the upper abdominal FL, reducing the thrombus volume by 9.6%. Increasing the SG-FRT distance in patient 2 resulted in faster thoracic thrombosis and increased total thrombus volume. Conclusion: The location of reentry tears can influence the progression of FL thrombosis following TEVAR. The more distal the reentry tear in the aorta the more likely it is that FL thrombosis will occur. Hence, the distal landing zone of the stent-graft should be chosen carefully to ensure a sufficient SG-FRT distance.

Aortic Curvature Remodeling after Thoracic Endovascular Aortic Repair: Assessing Device Conformability, Using Image Vector Analysis

BACKGROUND

Aortic arch curvature can be straightened by endograft placement. However, different measurement methods with dissimilar follow-up and endografts have been published. The aim of this study was to corroborate, for the first time, the pliability of the Conformable Gore TAG Thoracic Endoprosthesis (W.L. Gore and Associates, Flagstaff, AZ, USA) into the aortic arch, using different image vector analysis.

MATERIAL AND METHODS

We, retrospectively, analyzed patients primarily treated for thoracic aortic aneurysms and blunt traumatic aortic injuries by means of a Conformable Gore TAG Thoracic Endoprosthesis endograft proximally sealed into the aortic arch (zones Z1-Z3) in five different Spanish centers, between 2010 and 2017. The preoperative, one-month and six-month postoperative, computed tomography angiographies (CTAs) were obtained, creating accurate 3D center lumen line and external lumen line from the aortic valve to the renal arteries. Three different image analysis methods were used to compare modifications of the aortic curvature: first, segment analysis (angulations of the center lumen line when divided into seven precise segments, examining anterior-posterior, right-left, and cranial-caudal displacement), second, center lumen line analysis (bending of the center lumen line itself in seven definite points), and third, expected behavior (length of the endograft in the external lumen line). Two independent observers performed a blind analysis of all CTAs. Changes between preoperative and postoperative CTAs at one and six months are compared, and differences are viewed between cases sealed proximally (Z1-Z2) and distally (Z3) into the aortic arch.

RESULTS

We analyzed 37 cases. At 1- and 6-month follow-ups, minimal changes occurred first in segment analysis (only a slight decrease of -2.0° in the XY plane at 10 cm from the brachiocephalic trunk at six-month follow-up was seen, P = 0.027). Second, center lumen line analysis again only showed negligible aortic curvature straightening (+3.5° at 10 cm from the brachiocephalic trunk at one month, P = 0.006, disappearing at six-month follow-up). Finally, good device length predictability was shown (interclass correlation coefficients: 0.995 and 0.994 at one and six months, P > 0.001). No differences were seen between cases proximally sealed into the proximal and distal aortic arch.

CONCLUSIONS

Conformable Gore TAG Thoracic Endoprosthesis thoracic endograft showed a good pliability into the aortic arch and proximal thoracic aorta, with minimal changes in the aortic curvature after endograft placement in the short-term follow-up (up to six months). In addition, final endograft length into outer aortic curvature is highly predictable.

Patient-specific CFD modelling in the thoracic aorta with PC-MRI-based boundary conditions: A least-square three-element Windkessel approach

The increasing use of computational fluid dynamics for simulating blood flow in clinics demands the identification of appropriate patient-specific boundary conditions for the customization of the mathematical models. These conditions should ideally be retrieved from measurements. However, finite resolution of devices as well as other practical/ethical reasons prevent the construction of complete data sets necessary to make the mathematical problems well posed. Available data need to be completed by modelling assumptions, whose impact on the final solution has to be carefully addressed. Focusing on aortic vascular districts and related pathologies, we present here a method for efficiently and robustly prescribing phase contrast MRI-based patient-specific data as boundary conditions at the domain of interest. In particular, for the outlets, the basic idea is to obtain pressure conditions from an appropriate elaboration of available flow rates on the basis of a 3D/0D dimensionally heterogeneous modelling. The key point is that the parameters are obtained by a constrained optimization procedure. The rationale is that pressure conditions have a reduced impact on the numerical solution compared with velocity conditions, yielding a simulation framework less exposed to noise and inconsistency of the data, as well as to the arbitrariness of the underlying modelling assumptions. Numerical results confirm the reliability of the approach in comparison with other patient-specific approaches adopted in the literature.

Left ventricular remodeling in patients with acute type B aortic dissection after thoracic endovascular aortic repair: Short- and mid-term outcomes

BACKGROUND

Left ventricular (LV) remodeling remains unknown in patients with acute Type B aortic dissection (aTBAD) after thoracic endovascular aortic repair (TEVAR) during follow-up.

METHODS

Between May 2004 and January 2016, 163 consecutive patients (136 males, mean preoperative age: 51.06 ± 10.79 years) with aTBAD underwent TEVAR. A linear mixed model was used to evaluate risk factor influencing on LV remodeling and investigate longitudinal changes in LV thickness, diameter, volume, function and mass at preoperation, postoperation, short- and mid-term follow-up.

RESULTS

Median follow-up time was 48.0 months (quartiles 1-3, 31-84 months, maximum 147 months). LV thickness and mass followed a continuous downward trend over time. Interventricular septal thickness at end-diastole significantly decreased at mid-term follow-up (time, p < 0.001: preoperative 11.59 ± 0.14 mm vs mid-term 10.82 ± 0.15 mm, p < 0.001; postoperative 11.40 ± 0.14 mm vs mid-term 10.82 ± 0.15 mm, p = 0.006). LV posterior wall thickness at end-diastole was markedly reduced at mid-term follow-up (time, p < 0.001: preoperative 10.89 ± 0.11 mm vs mid-term 10.02 ± 0.11 mm, p < 0.001; postoperative 10.78 ± 0.13 mm vs mid-term 10.02 ± 0.11 mm, p < 0.001; short-term 10.56 ± 0.15 mm vs mid-term 10.02 ± 0.11 mm, p = 0.021). LV mass index markedly decreased during follow-up (time, p = 0.001: preoperative 129.60 ± 3.55 g/m² vs short-term 119.26 ± 3.19 g/m², p = 0.009; preoperative 129.60 ± 3.55 g/m² vs mid-term 115.79 ± 3.62 g/m², p = 0.003). LV function was improved, but not significantly so, during follow-up. Strict blood pressure control had no influence on LV remodeling. True lumen followed a continuous enlargement trend in terms of proximal thoracic aorta and celiac trunk level during follow-up.

CONCLUSIONS

TEVAR can reverse LV remodeling and LV hypertrophy in patients with aTBAD during follow-up.

Blood Flow after Endovascular Repair in the Aortic Arch: A Computational Analysis

BACKGROUND

 The benefits of thoracic endovascular aortic repair (TEVAR) have encouraged stent graft deployment more proximally in the aortic arch. This study quantifies the hemodynamic impact of TEVAR in proximal landing zone 2 on the thoracic aorta and the proximal supra-aortic branches.

METHODS

 Patients treated with TEVAR in proximal landing zone 2 having available preoperative and 30-day postoperative computer tomography angiography and phase-contrast magnetic resonance imaging data were retrospectively selected. Blood flow was studied using patient-specific computational fluid dynamics simulations.

RESULTS

 Four patients were included. Following TEVAR in proximal landing zone 2, the mean flow in the left common carotid artery (LCCA) increased almost threefold, from 0.21 (0.12-0.41) L/min to 0.61 (0.24-1.08) L/min (+294%). The surface area of the LCCA had not yet increased commensurately and therefore maximum flow velocity in the LCCA increased from 44.9 (27.0-89.3) cm/s to 72.6 (40.8-135.0) cm/s (+62%). One of the patients presented with Type Ib endoleak at 1-year follow-up. The displacement force in this patient measured 32.1 N and was directed dorsocranial, perpendicular to the distal sealing zone. There was a linear correlation between the surface area of the stent graft and the resulting displacement force (p = 0.04).

CONCLUSION

 TEVAR in proximal landing zone 2 alters blood flow in the supra-aortic branches, resulting in increased flow with high flow velocities in the LCCA. High displacement forces were calculated and related to stent graft migration and Type I endoleak during 1-year follow-up.

Abdominal aortic aneurysm endovascular repair: profiling post-implantation morphometry and hemodynamics with image-based computational fluid dynamics

Endovascular aneurysm repair (EVAR) has disseminated rapidly as an alternative to open surgical repair for the treatment of abdominal aortic aneurysms (AAAs), because of its reduced invasiveness, low mortality and morbidity rate. The effectiveness of the endovascular devices used in EVAR is always at question as postoperative adverse events can lead to re-intervention or to a possible fatal scenario for the circulatory system. Motivated by the assessment of the risks related to thrombus formation, here the impact of two different commercial endovascular grafts on local hemodynamics is explored through 20 image-based computational hemodynamic models of EVAR-treated patients (N=10 per each endograft model). Hemodynamic features, susceptible to promote thrombus formation, such as flow separation and recirculation, are quantitatively assessed and compared with the local hemodynamics established in image-based infrarenal abdominal aortic models of healthy subjects (N=10). The hemodynamic analysis is complemented by a geometrical characterization of the EVAR-induced reshaping of the infrarenal abdominal aortic vascular region. The findings of this study indicate that: (1) the clinically observed propensity to thrombus formation in devices used in EVAR strategies can be explained in terms of local hemodynamics by means of image-based computational hemodynamics approach; (2) reportedly pro-thrombotic hemodynamic structures are strongly correlated with the geometry of the aortoiliac tract postoperatively. In perspective, our study suggests that future clinical follow up studies could include a geometric analysis of the region of the implant, monitoring shape variations that can lead to hemodynamic disturbances of clinical significance.

Geometric Deformations of the Thoracic Aorta and Supra-Aortic Arch Branch Vessels Following Thoracic Endovascular Aortic Repair

Objective:

To utilize 3-D modeling techniques to better characterize geometric deformations of the supra-aortic arch branch vessels and descending thoracic aorta after thoracic endovascular aortic repair.

Methods:

Eighteen patients underwent endovascular repair of either type B aortic dissection (n = 10) or thoracic aortic aneurysm (n = 8). Computed tomography angiography was obtained pre- and postprocedure, and 3-D geometric models of the aorta and supra-aortic branch vessels were constructed. Branch angle of the supra-aortic branch vessels and curvature metrics of the ascending aorta, aortic arch, and stented thoracic aortic lumen were calculated both at pre- and postintervention.

Results:

The left common carotid artery branch angle was lower than the left subclavian artery angles preintervention ( P < .005) and lower than both the left subclavian and brachiocephalic branch angles postintervention ( P < .05). From pre- to postoperative, no significant change in branch angle was found in any of the great vessels. Maximum curvature change of the stented lumen from pre- to postprocedure was greater than those of the ascending aorta and aortic arch ( P < .05).

Conclusion:

Thoracic endovascular aortic repair results in relative straightening of the stented aortic region and also accentuates the native curvature of the ascending aorta when the endograft has a more proximal landing zone. Supra-aortic branch vessel angulation remains relatively static when proximal landing zones are distal to the left common carotid artery.

Aortic Arch and Thoracic Aorta Curvature Remodeling after Thoracic Endovascular Aortic Repair

BACKGROUND

The objective of this study was to analyze the original curvature of the aortic arch and thoracic aorta, and how it is modified after the placement of a thoracic endograft.

METHODS

We retrospectively analyzed all patients primarily treated for thoracic aortic aneurysms and blunt traumatic aortic injuries by means of an endograft sealed into the aortic arch (zones, Z1-Z3) in 2 different centers (Vascular Surgery Division, Hospital Clinic, UB; and Vascular and Endovascular Surgery Department, Hospital Vall d'Hebron, UAB; Barcelona, Spain), between 2010 and 2015. The last preoperative and early (1-month) postoperative computed tomography angiography (CTA) was obtained for all cases, and an accurate 3-dimensional (3D) center lumen line was created, from the aortic valve to the renal arteries. Angles in 2-dimensional (2D; XY-plane) and 3D (referred to cranial-caudal Z-axis) were analyzed in: the distal ascending aorta, aortic arch, and thoracic aorta (at 5, 10, 15, and 20 cm from the brachiocephalic trunk [BCT]) and celiac trunk (CT). Changes in preoperative-postoperative CTA were compared independently for both diseases. Thirty-six cases were included (20 aneurysms, 16 blunt traumatic injuries; mean age, 69.5 and 42.5 years).

RESULTS

After placement of an aortic endograft (sealed in Z1-Z2 in 30% of aneurysms and 75% of traumatic injuries; mean endograft length: 22.6 cm and 11.3 cm, respectively), a global left anterior displacement of the ascending aorta was observed (2D examination: -13.1° and -7.5°, P = 0.049 and 0.041, respectively). The 3D examination showed an average increase of the aortic angle at 5 and 10 cm from the BCT in the whole sample (+4.0°, +4.9° in reference to the vertical; P = 0.017, 0.001), softening the curvature of the proximal descending thoracic aorta. In addition, in traumatic injuries, a decrease in the aortic arch angle was observed (-3.5°, P = 0.030).

CONCLUSIONS

Placement of an endograft into the aortic arch and proximal thoracic aorta engenders a softening of the proximal descending thoracic aorta curvature, increasing its angle from the vertical. In blunt traumatic aortic injuries (with shorter and more proximally sealed endografts), an additional decrease of the aortic arch angle (3.5° more vertical), was observed.

Activities at Thoracic Aortic Research Center, IRCCS Policlinico San Donato

The Thoracic Aortic Research Center (TARC) of the IRCCS Policlinico San Donato (PSD) aims to promote research on thoracic aortic diseases, to disclose the scientific knowledge and clinical experience and to develop new scientific paths within the Hospital and the aortic community, in collaboration with other national and international centres. Thoracic Aortic Research Center collaborates with many centres in both Europe (e.g. University of Utrecht, the Netherlands) and the USA (e.g. University of Michigan). This has led to multiple highly regarded publications in respected cardiovascular journals and has led to several PhD programmes resulting in doctorate degrees. Within Italy, in association with the Bioengineering School of the University of Pavia, TARC has founded the "BETA-lab" (Biomechanics for Endovascular Treatment of the Aorta laboratory), where MDs, Bioengineers, and PhD fellows conduct experimental studies using in vitro/ex vivo models of the physiologic aorta and aortic diseases. Furthermore, a database (iCardiocloud) where the medical imaging of cardiovascular patients from the PSD is structured, for in silico analysis utilizing computational fluid dynamics, and in vitro studies using also 3D printed aortic models. With the role of principal investigator or co-investigator, TARC at PSD has been participating in other several projects, including the International Registry of Acute Aortic Dissection, the International Aortic Arch Surgery Study Group, the European Registry of Endovascular Aortic Repair Complications, the ADSORB and ASSIST trials, and the GREAT registry. International collaborations have included also studies on predictors of aortic growth after dissection with the Yale University and University of Virginia, and on aortic biomarkers with the University of Tokyo.

An In Vitro Phantom Study on the Role of the Bird-Beak Configuration in Endograft Infolding in the Aortic Arch

Purpose: To assess endograft infolding for excessive bird-beak configurations in the aortic arch in relation to hemodynamic variables by quantifying device displacement and rotation of oversized stent-grafts deployed in a phantom model. Methods: A patient-specific, compliant, phantom pulsatile flow model was reconstructed from a patient who presented with collapse of a Gore TAG thoracic endoprosthesis. Device infolding was measured under different flow and pressure conditions for 3 protrusion extensions (13, 19, and 24 mm) of the bird-beak configuration resulting from 2 TAG endografts with oversizing of 11% and 45%, respectively. Results: The bird-beak configuration with the greatest protrusion extension exhibited the maximum TAG device displacement (1.66 mm), while the lowest protrusion extension configuration led to the minimum amount of both displacement and rotation parameters (0.25 mm and 0.6°, respectively). A positive relationship was found between the infolding parameters and the flow circulating in the aorta and left subclavian artery. Similarly, TAG device displacement was positively and significantly (p<0.05) correlated with the pulse pressure for all bird-beak configurations and device sizes. However, no collapse was observed under chronic perfusion testing maintained for 30 days and pulse pressure of 100 mm Hg. Conclusion: These findings suggest that endograft infolding depends primarily on the amount of aortic pulsatility and flow rate and that physiological flows do not necessarily engender hemodynamic loads on the proximal bird-beak segment sufficient to cause TAG collapse. Hemodynamic variables may allow for identification of patients at high risk of endograft infolding and help guide preventive intervention to avert its occurrence.

Biomechanical Changes After Thoracic Endovascular Aortic Repair in Type B Dissection

Thoracic endovascular aortic repair (TEVAR) has evolved into an established treatment option for type B aortic dissection (TBAD) since it was first introduced 2 decades ago. Morbidity and mortality have decreased due to the minimally invasive character of TEVAR, with adequate stabilization of the dissection, restoration of true lumen perfusion, and subsequent positive aortic remodeling. However, several studies have reported severe setbacks of this technique. Indeed, little is known about the biomechanical behavior of implanted thoracic stent-grafts and the impact on the vascular system. This study sought to systematically review the performance and behavior of implanted thoracic stent-grafts and related biomechanical aortic changes in TBAD patients in order to update current knowledge and future perspectives.