Design and implementation of mechanical property testing equipment for thoracic aortic stent grafts.

The mechanical properties of the stent graft are important factors influencing the outcome of TEVAR treatment and the occurrence of postoperative complications. The aim of this study is to improve and design a mechanical performance testing equipment for thoracic aortic stent grafts. The mechanical performance testing equipment consists of a radial force testing equipment of the stent graft designed by the wire compression grip method and a dynamic straightening force testing device with stable and controllable test conditions and continuously variable test angles. By constructing the testing equipment to physically measure the stent specimen, the experimental results reflect the trend of change and the simulation results are basically consistent, i.e. the mechanical properties of the thoracic aortic stent designed in this study is feasible and the measured data are valid. The testing equipment can provide the basis and reference direction for the quality testing of stent graft products, optimisation of mechanical properties of stent grafts and R&D innovation.

Effects of Long Term Fatigue Cycling on In Situ Fenestrations of Polyethylene Terephthalate and Expanded Polytetrafluorethylene Thoracic Aortic Stent grafts: An Experimental Study.

OBJECTIVE: In this study, the long term durability of fenestrations after in situ fenestration (ISF) of five commercial thoracic aortic stent grafts was evaluated in an in vitro experiment after a simulated 10 year period. METHODS: Five different thoracic aortic stent grafts (Relay, Valiant, Hercules, TAG, and Ankura, with a diameter of 34 mm) received both needle and laser ISF in vitro. A Viabahn (11 × 50 mm) was released in each fenestration as a bridging stent graft. Long term fatigue tests (simulating 10 years) of each of the fenestrated stent grafts were then conducted in a flow fatigue test system. The area, shape, margin, and the long and short axis of all the fenestrations were evaluated with light microscopy before and after the fatigue test. The leakage from the fenestration junction before and after the long term fatigue was also measured. RESULTS: The experimental results showed no obvious difference between needle and laser fenestrations. The long axes of all the fenestrations remained unchanged, while the short axes increased after the fatigue test, which was significant in Relay, Valiant, and Hercules polyethylene terephthalate stent grafts. The shape scores of fenestrations improved after the fatigue test in Valiant and Hercules, remained unchanged in Relay and Ankura, and worsened in the TAG. After the fatigue cycling, the average leakage from the fenestration junction decreased in all the stent grafts, and the Ankura had the maximum decline rate. CONCLUSION: The ISF technique was durable over a simulated 10 year period. The fenestrations were positively remodelled to be more circular, and the leakage from the junction decreased after long term fatigue testing.

Rapid Morphological Measurement Method of Aortic Dissection Stent Based on Spatial Observation Point Set.

OBJECTIVES: Post-operative stent morphology of aortic dissection patients is important for performing clinical diagnosis and prognostic assessment. However, stent morphologies still need to be manually measured, which is a process prone to errors, high time consumption and difficulty in exploiting inter-data associations. Herein, we propose a method based on the stepwise combination of basic, non-divisible data sets to quickly obtain morphological parameters with high accuracy. METHODS: We performed the 3D reconstruction of 109 post-operative follow-up CT image data from 26 patients using mimics software. By extracting the spatial locations of the basic morphological observation points on the stent, we defined a basic and non-reducible set of observation points. Further, we implemented a fully automatic stent segmentation and an observation point extraction algorithm. We analyzed the stability and accuracy of the algorithms on a test set containing 8 cases and 408 points. Based on this dataset, we calculated three morphological parameters of different complexity for the different spatial structural features exhibited by the stent. Finally, we compared the two measurement schemes in four aspects: data variability, data stability, statistical process complexity and algorithmic error. RESULTS: The statistical results of the two methods on two low-complexity morphological parameters (spatial position of stent end and vascular stent end-slip volume) show good agreement (n = 26, P1, P2 < 0.001, r1 = 0.992, r2 = 0.988). The statistics of the proposed method for the morphological parameters of medium complexity (proximal support ring feature diameter and distal support ring feature diameter) avoid the errors caused by manual extraction, and the magnitude of this correction to the traditional method does not exceed 4 mm with an average correction of 1.38 mm. Meanwhile, our proposed automatic observation point extraction method has only 2.2% error rate on the test set, and the average spatial distance from the manually marked observation points is 0.73 mm. Thus, the proposed method is able to rapidly and accurately measure the stent circumferential deflection angle, which is highly complex and cannot be measured using traditional methods. CONCLUSIONS: The proposed method can significantly reduce the statistical observation time and information processing cost compared to the traditional morphological observation methods. Moreover, when new morphological parameters are required, one can quickly and accurately obtain the target parameters by new "combinatorial functions." Iterative modification of the data set itself is avoided.

Endovascular repair of de novo post-stenotic aortic coarctation aneurysms with complex collateral supply: two cases with long and medium term follow-up.

PURPOSE: To report the technical details and outcomes of the endovascular repair of two cases of de novo post-stenotic aortic coarctation aneurysms complicated by complex collateral supply. CASE PRESENTATIONS: Two patients with thoracic aortic aneurysms complicated by complex aneurysm sac collaterals distal to a previously untreated thoracic aortic coarctation have been treated at our institution. Open surgical intervention was deemed to carry a high risk of haemorrhage due to the degree and complexity of arterial collateralisation. In the first case, selective embolisation of collateral vasculature was performed prior to successful exclusion of the aneurysm with a thoracic endovascular stent-graft and then balloon-expandable stent dilatation of the coarctation stenosis. In the second case, the additional technique of using a jailed sheath within the aneurysm sac allowed for selective embolisation of previously inconspicuous collaterals after deployment of the stent-graft and stent combination. RESULTS: Technical success was achieved in both patients with successful occlusion of the aneurysm, with no recorded complications or aneurysm sac perfusion in the long and medium term follow up periods respectively. CONCLUSION: De novo post stenotic aortic coarctation aneurysms are rare. Endovascular repair is a safe and durable technique that provides a less invasive alternative to open surgical repair. The use of a jailed sheath allows for complete selective embolisation of complex collaterals avoiding a type II aneurysm endoleak.

Numerical Simulation on Support Performance of NiTi Alloy Thoracic Aortic Stent / 医用生物力学

Objective To study the influence of different support heights, support numbers and cross-sectional dimensions on support performance of NiTi thoracic aortic stents. Methods Twenty-seven scaffold models with different parameters were established by using AutoCAD 2016 and SoildWorks 2014 software. HyperMesh 14.0 was used for tetrahedral mesh division, and ABAQUS 2017 was used for support performance simulation analysis. Results With the decrease of support height, the support stiffness would increase; a larger cross-section size would lead to a larger support stiffness; with the increase of support numbers, the support stiffness would increase. Among the influencing factors of support performance, the order of influence degree was support height＞section size＞support numbers. Conclusions The research findings have certain guiding significance for the development and research of thoracic aortic stents, and provide theoretical basis for the selection and optimization of clinical stents.

Spinal ischaemia after thoracic endovascular aortic repair with left subclavian artery sacrifice: is there a critical stent graft length?

OBJECTIVES: Thoracic endovascular aortic repair (TEVAR) is used for treatment of thoracic aortic pathologies, but the covered stent graft can induce spinal ischaemia depending on the length used. The left subclavian artery contributes to spinal cord collateralization and is frequently occluded by the stent graft. Our objective was to investigate the impact of covered stent graft length on the risk of spinal ischaemia in the setting of left subclavian artery sacrifice. METHODS: Twenty-six pigs (German country race, mean body weight 36 ± 4 kg) underwent simulated descending aortic TEVAR via left lateral thoracotomy, with left subclavian artery and thoracic segmental artery occlusion in normothermia. Animals were assigned to treatment groups according to simulated stent graft length: TEVAR to T8 (n = 4), TEVAR to T9 (n = 4), TEVAR to T10 (n = 4), TEVAR to T11 (n = 7) and TEVAR to T12 (n = 1) and a sham group (n = 6). End points included spinal cord perfusion pressure, cerebrospinal fluid pressure and spinal cord blood flow using fluorescent microspheres. RESULTS: There were no group differences in spinal cord perfusion pressure drop or in spinal cord perfusion pressure regeneration potential at 3 h after the procedure: from a baseline average of 75 mmHg (95% confidence interval 71-83 mmHg) to 73 mmHg (67-75 mmHg) at 3 h in Group T10 versus from a baseline average of 67 mmHg (95% CI 50-81 mmHg) to 65 mmHg (95% confidence interval 48-81 mmHg) in Group T8. There were no differences in the spinal cord blood flow courses over time in the different groups nor was there any difference in cerebrospinal fluid pressure levels and cerebrospinal fluid pressure dynamics between groups. However, we did observe local blood flow distribution to the spinal cord that was inhomogeneous depending on the distance between the simulated stent graft end and the first thoracic anterior radiculomedullary artery. CONCLUSIONS: The risk of spinal ischaemia after serial segmental artery occlusion does not depend on the distal extent of the aortic repair alone. Future attempts to allow patient risk stratification for spinal ischaemia need to focus on anterior radiculomedullary artery anatomy together with the extent of planned aortic repair.

Endovascular stent for iatrogenic penetrating injury of the thoracic aorta.

PURPOSE: This is a report of the endovascular management of an iatrogenic descending thoracic aortic injury with long-term follow-up. CASE REPORT: A 74-year-old medically complex female underwent the inadvertent percutaneous placement of a 6F sheath directly into the descending thoracic aorta during an attempted pericardiocentesis at an outside hospital. Upon transfer, the patient underwent endovascular placement of a thoracic stent graft to cover the entry site and recovered without incidence. The patient has remained free of complications for nearly 8 years of follow-up care. CONCLUSIONS: Endovascular stent graft utilization of the thoracic aorta has increased the treatment scope for the management of emergent and elective aortic pathology. This is particularly useful in clinical scenarios deemed too high an open surgical risk secondary to significant comorbidities.

Late complications and distal growth rates of Marfan aortas after proximal aortic repair.

OBJECTIVES: Conflicting results have been reported on late aortic growth and complication rates of the descending thoracic aorta in patients with Marfan syndrome (MFS) after proximal aortic surgery. METHODS: Of 198 Marfan patients followed up regularly, 121 (43% David-I, 7% David-II, 11% supracoronary replacement, 52% mechanical conduit, 8% arch replacement) were analysed after proximal aortic surgery retrospectively. 97% had MFS1, 3% MFS2 (Loeys-Dietz-Syndrome); 56% were male and the mean age was 35 ± 13 years. 65% were initially operated on for root/ascending aortic aneurysm and 35% for aortic dissections. Using automated computed tomography angiography and magnetic resonance angiography cross-sectional analyses, the mean diameters of the distal arch, mid-descending and distal supradiaphragmatic descending thoracic aorta were measured at early and late follow-up (mean 6.3 years for aneurysms and 4.7 years for dissections). The mean duration of clinical follow-up was 7.6 years and the cumulative clinical follow-up comprised 894 patient-years. RESULTS: At 20 years, overall freedom from distal aortic complications and/or reintervention was 76% (51-86%) for aneurysms and 52% (28-71%) for dissections (P = 0.03). In non-dissected aortas, distal aortic growth was significant, but minimal: arches grew from 25.2 ± 0.6 to 26.3 ± 0.8 mm (P = 0.01), mid-descending aortas from 22.2 ± 0.5 to 24.9 ± 1.2 mm (P = 0.05) and distal descending aortas from 22.1 ± 0.7 to 24.2 ± 1.4 (P = 0.02, 0.58 mm/year ± 0.5 mm). Dissected distal aortas increased by a mean of 0.3 ± 0.5 mm/year. Dissection (P < 0.001), urgent procedure (P = 0.02) and hypertension (0.052) were associated with larger distal aortic diameters at late follow-up and more significant aortic growth over time. CONCLUSIONS: Late distal complication rates are low for patients initially presenting with aneurysms. The risk of late distal reoperation is dictated by the initial pathology and by the presence of an initial dissection and not by faster distal aortic growth. Strategies to completely restore a non-dissected anatomy might improve late surgical outcome in Marfan's syndrome.