Risk Factor Analysis of Bird Beak Occurrence after Thoracic Endovascular Aortic Repair

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.

A computational study of artery curvature and endograft oversize influence on seal zone behavior in endovascular aortic repair

Thoracic endovascular aortic repair (TEVAR) is a minimally invasive procedure involving the placement of an endograft inside the dissection or an aneurysm to direct blood flow and prevent rupture. A significant challenge in endovascular surgery is the geometrical mismatch between the endograft and the artery, which can lead to endoleak formation, a condition where blood leaks between the endograft and the vessel wall. This study uses computational modeling to investigate the effects of artery curvature and endograft oversizing, the selection of an endograft with a larger diameter than the artery, on endoleak creation. Finite element analysis is employed to simulate the deployment of endografts in arteries with varying curvature and diameter. Numerical simulations are conducted to assess the seal zone and to quantify the potential endoleak volume as a function of curvature and oversizing. A theoretical framework is developed to explain the mechanisms of endoleak formation along with proof-of-concept experiments. Two main mechanisms of endoleak creation are identified: local buckling due to diameter mismatch and global buckling due to centerline curvature mismatch. Local buckling, characterized by excess graft material buckling and wrinkle formation, increases with higher levels of oversizing, leading to a larger potential endoleak volume. Global buckling, where the endograft bends or deforms to conform to the centerline curvature of the artery, is observed to require a certain degree of oversizing to bridge the curvature mismatch. This study highlights the importance of considering both curvature and diameter mismatch in the design and clinical use of endografts. Understanding the mechanisms of endoleak formation can provide valuable insights for optimizing endograft design and surgical planning, leading to improved clinical outcomes in endovascular aortic procedures.

Type III aortic arch angulation increases aortic stiffness: Analysis from an ex vivo porcine model

Objective

The relationship among increased aortic arch angulation, aortic flow dynamics, and vessel wall stiffness remains unclear. This experimental ex vivo study investigated how increased aortic arch angulation affects aortic stiffness and stent-graft induced aortic stiffening, assessed by pulse wave velocity (PWV).

Methods

Porcine thoracic aortas were connected to a circulatory mock loop in a Type I and Type III aortic arch configuration. Baseline characteristics and blood pressures were measured. Proximal and distal flow curves were acquired to calculate PWV in both arch configurations. After that, a thoracic stent-graft (VAMF2626C100TU) was deployed in aortas with adequate proximal landing zone diameters to reach 10% t0 20% oversizing. Acquisitions were repeated for both arch configurations after stent-graft deployment.

Results

Twenty-four aortas were harvested, surgically prepared, and mounted. Cardiac output was kept constant for both arch configurations (Type I: 4.74 ± 0.40 and Type III: 4.72 ± 0.38 L/minute; P = .703). Compared with a Type I arch, aortic PWV increased significantly in the Type III arch (3.53 ± 0.40 vs 3.83 ± 0.40 m/second; P < .001), as well as blood pressures. A stent-graft was deployed in 15 aortas. After deployment, Type I arch PWV increased (3.55 ± 0.39 vs 3.81 ± 0.44 m/second; P < .001) and Type III arch PWV increased although not significantly (3.86 ± 0.42 vs 4.03 ± 0.46 m/second; P = .094). Type III arch PWV resulted the highest and significantly higher compared with the Type I arch after stent-graft deployment (3.81 ± 0.44 vs 4.03 ± 0.46 m/second; P = .023).

Conclusions

Increased aortic arch angulation-as in a Type III arch-is associated with higher aortic PWV and blood pressures and this may negatively influence cardiovascular health.

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.

Homemade fenestrated physician-modified stent-grafts for arch aortic degenerative aneurysms

OBJECTIVE

To evaluate early and medium-term outcomes of single and double fenestrated physician-modified endovascular grafts (PMEGs) for total endovascular degenerative aortic arch aneurysm repair.

METHODS

This single-center retrospective analysis of prospectively collected data included 52 patients, from August 2013 through January 2021, undergoing home-made fenestrated thoracic endovascular aortic repair (TEVAR) for degenerative aortic aneurysms. In all cases a distal smaller fenestration for the left subclavian artery (LSA) was fashioned and the only one stented. For double-fenestrated endograft a proximal larger fenestration that incorporated both the brachiocephalic trunk and left common carotid artery was added.

RESULTS

52 patients with degenerative aortic arch aneurysms were treated. There were 36 men and the mean age was 75 ± 8 years. 31% treated with a single LSA fenestration, while 69% had a double-fenestrated TEVAR. 10% (n=5) were emergent procedures. Technical success was 100%. The median time requirement for stent graft modification was 22 ± 6 minutes. Thirty-day mortality was 2% (n=1). 5 patients (10%) had a cerebrovascular event including 2 transient ischemic attack, one minor stroke with full neurological recovery and 2 with sequelae. 2 patients (4%) experienced perioperative retrograde dissection during follow-up. No patient had a type I, type III or type II endoleak from the LSA. No patient required re-intervention. All supra-aortic trunks were patent. During a mean follow up of 18 ± 11 months, there were no conversion to open surgical repair, aortic rupture or paraplegia.

CONCLUSIONS

Single or double PMEG is a safe and suitable tool for the treatment of high morbidity pathology such as aortic arch degenerative aneurysm repair. This device can be used in elective and emergency patients.

Predicting reintervention after thoracic endovascular aortic repair of Stanford type B aortic dissection using machine learning

OBJECTIVES

To construct models for predicting reintervention after thoracic endovascular aortic repair (TEVAR) of Stanford type B aortic dissection (TBAD).

METHODS

A total of 192 TBAD patients who underwent TEVAR were included; 68 (35.4%) had indications for reintervention. Clinical characteristics, aorta characteristics on pre- and postoperative computed tomography angiography, and aorta characteristics on immediate postoperative aortic digital subtraction angiography were collected. The least absolute shrinkage and selection operator (LASSO) regression was applied to identify the risk factors for reintervention. Eight classifiers were used for modeling. The models were trained on 100 train-validation random splits with a ratio of 2:1. The performance was evaluated by the receiver operating characteristic curve.

RESULTS

Seven predictors of reintervention were identified, including maximum false lumen diameter, aortic diameter measured at the level of approximately 15 mm distal to the left subclavian artery, aortic diameter measured at the level of the diaphragm, false lumen diameter measured at the level of the celiac artery, number of bare-metal and covered stents, number of bare-metal stents, and residual perfusion of the false lumen. Logistic regression (LR) yielded the highest performance, with an area under the curve of 0.802. A nomogram built for clinical use showed good calibration. The cutoff value for dividing patients into low- and high-risk subgroups was 0.413. Kaplan-Meier curves showed that the overall survival of high-risk patients was significantly shorter than that of low-risk patients (both p < 0.05).

CONCLUSION

Our nomogram could predict the reintervention after TEVAR in patients with TBAD, which may facilitate patient selection and surveillance strategies.

KEY POINTS

• Seven risk factors of reintervention after TEVAR of TBAD were identified for modeling. • Logistic regression performed best in predicting reintervention with an AUC of 0.802. • Patients with a high risk of reintervention had shorter OS than those with a low risk.

Association between aortic arch angulation and bird-beak configuration after thoracic aortic stent graft repair of type B aortic dissection

OBJECTIVES

The goal of this study was to investigate factors favouring the bird-beak configuration after thoracic endovascular aortic repair (TEVAR) for type B aortic dissection.

METHODS

We retrospectively analysed 76 patients with type B aortic dissection who underwent landing zone 1 and 2 TEVAR from December 2015 to January 2018. Preoperative aortic arch geometry (aortic arch length, maximal diameter and angulation), stent graft details and operative details were evaluated. A bird-beak configuration was defined as a ≥5-mm gap between the proximal end of the stent and the aortic wall of the lesser curvature.

RESULTS

Patients were stratified into those with (n = 46) and without (n = 30) a bird-beak configuration. The baseline demographics, dissection chronicity, clinical features and implanted devices were largely similar between the 2 groups. No significant difference was observed in the arch length or maximal arch diameter. However, the mean aortic arch angulation was greater in patients with than without a bird-beak configuration (61.4° vs 51.3°; P < 0.001). No influence of either the stent graft brand or the proximal stent graft type was observed. The multivariable analysis showed that the aortic arch angulation was an independent risk factor for a bird-beak configuration (odds ratio 1.15, 95% confidence interval 1.07-1.24; P < 0.001). A cut-off angle of 59.15° was predictive of a bird-beak configuration (sensitivity 59%; specificity 77%).

CONCLUSIONS

The preoperative aortic arch angulation was an independent predictor of a postoperative bird-beak configuration in patients with type B aortic dissection who underwent TEVAR that involved the aortic arch. An angle of >59.15° may imply a relatively hostile anatomy with a higher risk of a bird-beak configuration.

Multiaxial pulsatile dynamics of the thoracic aorta and impact of thoracic endovascular repair

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Altered motion of the thoracic aorta after thoracic endovascular aortic repair.

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Geometric analysis with cardiac-gated computed tomography and computer modeling.

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Decreased motion of the stented aorta and increased motion above the stented aorta.

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Longitudinal curvature and diametric deformation affected by presence of endograft.

Purpose

The thoracic aorta is a highly mobile organ whose dynamics are altered by thoracic endovascular aorta repair (TEVAR). The aim of this study was to quantify cardiac pulsatility-induced multi-axial deformation of the thoracic aorta before and after descending aortic TEVAR.

Methods

Eleven TEVAR patients (8 males and 3 females, age 57–89) underwent retrospective cardiac-gated CT angiography before and after TEVAR. 3D geometric models of the thoracic aorta were constructed, and lumen centerlines, inner and outer surface curves, and cross-sections were extracted to measure aortic arclength, centerline, inner surface, and outer surface longitudinal curvatures, as well as cross-sectional effective diameter and eccentricity for the ascending and stented aortic portions.

Results

From pre- to post-TEVAR, arclength deformation was increased at the ascending aorta from 5.9 ± 3.1 % to 8.8 ± 4.4 % (P < 0.05), and decreased at the stented aorta from 7.5 ± 5.1 % to 2.7 ± 2.5 % (P < 0.05). Longitudinal curvature and diametric deformations were reduced at the stented aorta. Centerline curvature, inner surface curvature, and cross-sectional eccentricity deformations were increased at the distal ascending aorta.

Conclusions

Deformations were reduced in the stented thoracic aorta after TEVAR, but increased in the ascending aorta near the aortic arch, possibly as a compensatory mechanism to maintain overall thoracic compliance in the presence of reduced deformation in the stiffened stented aorta.

Determining the Optimal Proximal Landing Zone for TEVAR in the Aortic Arch: Comparing the Occurrence of the Bird-Beak Phenomenon in Zone 0 vs Zones 1 and 2

Purpose: To identify the optimal proximal landing zone for thoracic aortic endovascular repair (TEVAR) of aortic arch pathologies so as to avoid the bird-beak phenomenon that leads to type Ia endoleak. Materials and Methods: A retrospective single-center review was conducted of 164 patients (mean age 70.3±10.8 years, range 29–93; 127 men) who underwent repairs of the aortic arch using hybrid TEVAR from April 2008 to March 2017. The patients were divided into 2 groups according to the proximal landing zone: 43 zone 0 patients (26.2%) had total debranching TEVAR (n=18) or total endovascular aortic repair (n=25) while 121 patients (73.8%) had TEVAR landing in zones 1 (n=41) or 2 (n=80). Bird-beak configurations, endoleaks, and stent migrations were assessed on the postoperative and latest computed tomography angiography (CTA) scans. Overall survival and freedom from the bird-beak configuration, aorta-related death, and aortic events were estimated using the Kaplan-Meier method. Hazard ratios (HR) were calculated with the 95% confidence interval (CI). Results: All procedures were successful, without any 30-day mortality. There were 3 early complications (1.8%; all strokes) and 10 early endoleaks (6.1%; no type Ia). On the first postoperative CTA, 42 patients (25.6%) had a bird-beak configuration. The zone 0 patients had significantly fewer (p<0.001), shorter (p<0.004), and less angulated (p<0.001) bird-beak configurations than in zones 1–2. The mean follow-up period was 4.2 years (range 0.5–8.8). There were 18 late deaths (11.0%); only one was related to the aorta (rupture due to a type Ib endoleak in a zone 0 patient). The 5-year freedom from aorta-related death was not significantly different between groups (zone 0: 96.9% vs zones 1–2: 100%, p=0.080). On the latest CTA, 51 (31.0%) patients had a bird-beak configuration; of those, 22 (13.4%) showed >3-mm progression. The freedom from bird-beak configuration estimate was significantly higher in the zone 0 group (95.4%) vs zones 1–2 (57.8%; HR 0.10, 95% CI 0.02 to 0.31, p<0.001). There were 9 late endoleaks (4 type Ia; none in the zone 0 group). The rate of stent-graft migration was significantly lower in the zone 0 group (2.3% vs 14.1% in zones 1–2, p=0.035). Conclusion: Early and most late results in zone 0 TEVAR were equal to those in zones 1 and 2; however, there were no late type Ia endoleaks and fewer bird-beak configurations associated with zone 0 TEVAR, which suggests that zone 0 landing is advantageous for preventing these complications.

One-Year Results From the SURPASS Observational Registry of the CTAG Stent-Graft With the Active Control System

Purpose: To report the outcomes from the observational SURPASS registry, which was created to assess the performance of the Conformable TAG (CTAG) stent-graft with the Active Control System (ACS) in patients undergoing thoracic endovascular aortic repair (TEVAR) in a real-world setting. Materials and Methods: The SURPASS registry (ClinicalTrials.gov; identifier NCT03286400) was an observational, prospective, single-arm, post-market, international study that enrolled patients undergoing TEVAR using the CTAG with ACS for both acute and chronic thoracic aortic disease between October 2017 and July 2018. The CTAG with ACS features 2-stage deployment of the stent-graft and an optional angulation mechanism that modifies only the proximal end of the stent-graft. During the observation period, 127 patients (mean age 67.1±12.1 years, range 27–86; 92 men) were enrolled and treated for an array of aortic pathologies, including chronic and acute lesions and 4 ruptured descending thoracic aneurysms. The primary outcome of this study was technical success; secondary outcomes were clinical success and major adverse events at 30 days and 12 months. The numbers of 2-stage device deployments and applications of the angulation mechanism were recorded, along with the reasons for use. Results: Technical success of the TEVAR was 97.6% owing to unintentional partial coverage of supra-aortic branches in 3 cases (the vessels were patent on imaging). The stent-graft was repositioned at its intermediate diameter in 79 patients (62.2%), and the angulation feature was applied in 64 cases (50.4%), mainly to improve proximal wall apposition and orthogonality in the aorta. The desired effect was achieved in 60 cases (93.8%). There was no device compression, bird-beak configuration, fracture, or graft occlusion. The 30-day and 12-month clinical success rates were 97.6% and 92.9%, respectively. There were 3 aorta-related deaths at 30 days and a further 3 at 12 months. Fatalities were due to a retrograde type A dissection (0.8%), paraplegia, bowel ischemia, sepsis in the setting of a mycotic aneurysm, aneurysm rupture post aortoesophageal fistula, and multiorgan dysfunction syndrome. Three endoleaks (2 type Ia and 1 type III) required reintervention. Conclusion: In the SURPASS registry, the use of the CTAG device with ACS showed promising outcomes despite the challenging pathologies. The new delivery system enables a controlled staged delivery with in situ adjustments during positioning, facilitating the treatment of complex aortic disease.

Impact of the Bird-Beak Configuration on Postoperative Outcome After Thoracic Endovascular Aortic Repair: A Meta-analysis

Purpose: To investigate the association between the bird-beak configuration (BBC), a wedge-shaped gap between the undersurface of a thoracic endograft and the lesser curvature of the arch after thoracic endovascular aortic repair (TEVAR), and postoperative outcome after TEVAR. Methods: The study was performed according to the PRISMA guidelines. The PubMed, EMBASE, and Cochrane databases were searched to identify all case series reporting BBC after TEVAR between 2006 and April 2018. Data analysis was performed considering the difference in the risk of complications for presence vs absence of BBC. After screening 1633 articles, 21 studies were identified that matched the selection criteria; 12 of these reported detailed information to investigate the postoperative outcome using proportion meta-analysis with a random effects model. The pooled risk difference is reported with the 95% confidence interval (CI). Heterogeneity of the included studies was assessed with the I2 statistic (low 25%, medium 50%, high 75%). Results: Complications occurred within a range of 0 to 72 months in 14.7% (95% CI 7.4% to 27.3%) of patients with BBC and in 6.3% (95% CI 2.5% to 15.4%) of patients without BBC. A cumulative incidence could not be assessed. The summary risk difference was 11.1% (95% CI −0.1% to 22.3%, p=0.052). There was significant heterogeneity ( I2=85.6%). The Egger test did not show evidence of publication bias (p=0.975). When specifically considering type Ia endoleak and endograft migration, the risk difference between BBC and non-BBC patients was 8.2% (95% CI 0.3% to 16.1%, p=0.042; I2=69.0%). The specific risk difference for endograft collapse/infolding and thrombosis was 3.7% (95% CI −3.5% to 11.1%, p=0.308; I2=10.2%). Conclusion: At present the literature does not provide statistical evidence to establish an overall prognostic value of the BBC. Nevertheless, the BBC appears to be associated with a high risk of type Ia endoleak and endograft migration, which warrants specific and long-term surveillance. Clinically relevant values for BBC grading should be established to perhaps define indications for preemptive treatment based on the presence of BBC only.

Unplanned stents in thoracic endovascular aortic repair for type B aortic dissection: A 16-year single-center report

Background

Unplanned stents in thoracic endovascular aortic repair mean additional stents implantation beyond the preoperative planning to achieve operation success. This study aimed to reveal the prevalence and consequences of unplanned stents in thoracic endovascular aortic repair for type B aortic dissection and explore the reasons, risk factors and solutions for unplanned stents.

Methods

Retrospectively analysis consecutive patients diagnosed as type B aortic dissection with initial tear originating distal from the left subclavian artery and underwent thoracic endovascular aortic repair from September 1998 to June 2014 in our center.

Results

Under the criteria, this study enrolled 322 patients, with 83 (25.8%) patients in unplanned group. The incidence rate of unplanned stents in thoracic endovascular aortic repair for type B aortic dissection in each year demonstrates as a bimodal curve. The curve showed that, 2003 and, 2004 was the first and highest peak and 2007 was the second peak. There was no difference in five-year survival rate between planned and unplanned patients (log-rank test, p = 0.994). The unplanned group had higher hospitalization expenses (142,699.08 ± 78,446.75 yuan vs. 175,238.58 ± 34,838.01 yuan; p = 0.019), longer operation time (104.50 ± 93.24 min vs. 179.08 ± 142.47 min; p < 0.001) and hospitalization time (17.07 ± 16.62 d vs. 24.00 ± 15.34 d; p = 0.001). The reasons for unplanned stents were type Ia endoleak (46 patients, 55.4%), bird beak (25 patients, 30.1%), and inappropriate shaping of stent (9 patients, 10.8%). Asymptomatic aortic dissection patients had higher incidence of unplanned stents. Short proximal neck length (2.66 ± 0.59 mm vs. 2.50 ± 0.51 mm; p = 0.016), short stent coverage length (154.62 ± 41.12 mm vs. 133.60 ± 44.33 mm; p = 0.002), and large distal stent oversize (75.44±10.77% vs. 82.68±15.80%; p <0.001) were risk factors for unplanned stents in thoracic endovascular aortic repair.

Conclusion

There are some special risk factors and reasons for unplanned stents in thoracic endovascular aortic repair for type B aortic dissection. Knowing these can we reduce the utilization of unplanned stents with appropriate methods.

Traumatic aortic injury: does the anatomy of the aortic arch influence aortic trauma severity?

Purpose

Traumatic aortic injury (TAI) is a rare but life-threatening type of injury. We investigate whether the anatomy of the aortic arch influences the severity of aortic injury.

Methods

This is a retrospective study of twenty-two cases treated with TEVAR for TAI in our department from 2009 to 2014. Aortic injury was assessed in accordance with the recommendations of the Society of Vascular Surgery. We measured the aortic arch angle and the aortic arch index, based on the initial angio-CT scan, in each of the analyzed cases.

Results

The mean aortic arch index and mean aortic arch angle were 6.8 cm and 58.3°, respectively, in the type I injury group; 4.4 cm and 45.9° in the type III group; 3.3 cm and 37° in the type IV group. There were substantial differences in both the aortic arch index and the aortic arch angle of the type III and IV groups. A multivariate analysis confirmed that the aortic arch angle was significantly associated with the occurrence of type III damage (OR 1.5; 95% CI 1.03–2.2).

Conclusions

The severity of TAI is influenced by the sharpness of the aortic arch. There is an inverse relationship between the severity of aortic injury and the aortic arch index.