Commercial Stent Grafts Research Articles

Outcomes of hand-made versus commercial stent grafts in frozen elephant trunk.

The frozen elephant trunk (FET) technique is effective for treating extended aortic arch aneurysms. This study compares hand-made and factory-made devices in this context. A retrospective case-control study was conducted on 68 patients who underwent FET for distal aortic arch aneurysm at our institution. We used two different types of devices: hand-made stent graft in group Z (17 cases, 25.0%) and a commercialized stent graft in group J (51 cases, 75.0%). The study compared demographic characteristics and the outcomes between the two groups. In-hospital mortality was equivalent in both groups (5.9%). Spinal cord injury rates were 5.9% in group Z and 3.9% in group J. Group Z had a higher rate of aortic events (55.9% vs 96.9%, p < 0.001) and more frequent stent migration. The number of cases with aneurysm diameter shrinkage was lower in group Z. The landing zone angle at insertion influenced aneurysm changes, being 17.6 degrees in shrink cases and 26.7 degrees in unchanged or enlarged cases (p = 0.045). FROZENIX device notably reduced incidences of postoperative complications compared to hand-made prostheses. Factors such as insertion angle and stent size, rather than changes in the landing zone angle, appeared to influence aneurysm shrinkage. The use of FROZENIX in TARFET procedures has shown benefits in reducing complications and improving long-term prognosis, taking into account the landing zone angle.

Outcomes of thoracic endovascular aortic repair using fenestrated stent grafts in patients with thoracic aortic distal arch aneurysms.

Thoracic endovascular aortic repair (TEVAR) for aortic arch aneurysms is challenging because of anatomical restrictions and the presence of cervical branches. Revascularization of the cervical branch is required when conventional commercial stent grafts are used. TEVAR using fenestrated stent grafts (FSG) often does not require additional procedures to revascularize cervical branches. This study aimed to evaluate the features and initial and midterm outcomes of TEVAR using fenestrated stent grafts. From April 2007 to December 2016, 101 consecutive patients underwent TEVAR using fenestrated stent grafts for distal aortic arch aneurysms at a single centre. Technical success, complications, freedom from aneurysm-related death, secondary intervention and aneurysm progression were retrospectively investigated. All the patients underwent TEVAR using fenestrated stent grafts. The 30-day mortality rate was zero. Cerebral infarction, access route problems and spinal cord injury occurred in 4, 3 and 2 patients, respectively. Each type of endoleak was observed in 38 of the 101 patients during the course of the study; 20/38 patients had minor type 1 endoleaks at the time of discharge. The endoleak disappeared in 2 patients and showed no significant change in 8 patients; however, the aneurysm expanded over time in 10 patients. Additional treatment was performed in 8 of the 10 patients with type 1 endoleaks and dilatation of the aneurysm. The rate of freedom from aneurysm-related death during the observation period was 98%. TEVAR with FSG is a simple procedure, with few complications. Additional treatment has been observed to reduce aneurysm-related deaths, even in patients with endoleaks and enlarged aneurysms. Based on this study, the outcomes of endovascular repair of aortic arch aneurysms using a fenestrated stent graft seem acceptable.

Computational Comparison of the Mechanical Behavior of Aortic Stent-Grafts Derived from Auxetic Unit Cells

PurposeInappropriate stent-graft (SG) flexibility has been frequently associated with endovascular aortic repair (EVAR) complications such as endoleaks, kinks, and SG migration, especially in tortuous arteries. Stents derived from auxetic unit cells have shown some potential to address these issues as they offer an optimum trade-off between radial stiffness and bending flexibility.MethodsIn this study, we utilized an established finite element (FE)-based approach to replicate the mechanical response of a SG iliac limb derived from auxetic unit cells in a virtual tortuous iliac aneurysm using a combination of a 180° U-bend and intraluminal pressurization. This study aimed to compare the mechanical performance (flexibility and durability) of SG limbs derived from auxetic unit cells and two commercial SG limbs (Z-stented SG and circular-stented SG models) in a virtual tortuous iliac aneurysm. Maximal graft strain and maximum stress in stents were employed as criteria to estimate the durability of SGs, whereas the maximal luminal reduction rate and the bending stiffness were used to assess the flexibility of the SGs.ResultsSG limbs derived from auxetic unit cells demonstrated low luminal reduction (range 4–12%) with no kink, in contrast to Z-stented SG, which had a kink in its central area alongside a high luminal reduction (44%).ConclusionsSG limbs derived from auxetic unit cells show great promise for EVAR applications even at high angulations such as 180°, with acceptable levels of durability and flexibility.

Endovascular repair in type A aortic dissection: Anatomic candidacy for currently manufactured stentgrafts and conceptual valve-carrying devices for an Endo-Bentall procedure.

Endovascular treatment has been suggested as alternative for open surgery as treatment for type A aortic dissection, but current devices have severe anatomic limitations. This study assesses computed-tomography-based anatomic suitability of currently manufactured stent grafts as well as two embodiments of valve-carrying devices. In a retrospective single-center cohort of 200 consecutive ascending/arch operations between 2009 and 2018, 112 type A aortic dissection patients were identified and evaluated for endovascular candidacy based on locations of entries, landing zone diameters/lengths and supra-aortic vessel origins according to the anatomical instructions for use criteria of 6 commercially available, (tubular, branched or fenestrated) stentgrafts. Two suggested valve-carrying devices with inner branches or fenestrations for the coronary arteries and branches for the supra-aortic vessels were also evaluated. The anatomic feasibility for commercial stentgrafts ranged from 4% to 21%. The main limitations was proximal landing zone diameter (considering oversizing <15%) and length due to dilatation and an entry too close to the sinotubular junction. For the valve-carrying conduits, anatomical feasibility was between 31% and 80%. with the main limiting factors the diameter of the aortic annulus and its distance to the coronary arteries. Anatomic applicability of currently manufactured stentgrafts for the treatment of type A aortic dissection is mainly limited by the absence of a suitable proximal landing zone in the ascending aorta and might substantially be improved by anchoring in the aortic annulus using a valve-carrying device which employs either fenestrations or branches for the coronary arteries.

The Technological Advancement to Engineer Next-Generation Stent-Grafts: Design, Material, and Fabrication Techniques.

Endovascular treatment of aortic disorders has gained wide acceptance due to reduced physiological burden to the patient compared to open surgery, and ongoing stent-graft evolution has made aortic repair an option for patients with more complex anatomies. To date, commercial stent-grafts are typically developed from established production techniques with simple design structures and limited material ranges. Despite the numerous updated versions of stent-grafts by manufacturers, the reoccurrence of device-related complications raises questions about whether the current manfacturing methods are technically able to eliminate these problems. The technology trend to produce efficient medical devices, including stent-grafts and all similar implants, should eventually change direction to advanced manufacturing techniques. It is expected that through recent advancements, especially the emergence of 4D-printing and smart materials, unprecedented features can be defined for cardiovascular medical implants, like shape change and remote battery-free self-monitoring. 4D-printing technology promises adaptive functionality, a highly desirable feature enabling printed cardiovascular implants to physically transform with time to perform a programmed task. This review provides a thorough assessment of the established technologies for existing stent-grafts and provides technical commentaries on known failure modes. They then discuss the future of advanced technologies and the efforts needed to produce next-generation endovascular implants.

Acute Complex Endovascular Aortic Repair - Off-the-shelf vs. Surgeon-modified Stent Grafts

Treatment of complex abdominal and thoracoabdominal aortic aneurysms is challenging. Open surgical repair is a high-risk operation, especially in emergency cases. Endovascular aneurysm repair with a patient-specific custom-made stent graft in patients with symptomatic or ruptured complex aortic aneurysms is not possible, due to the manufacturing time required. In such cases, alternative endovascular techniques can be used. The "off-the-shelf" and "surgeon-modified" stent grafts are valid options for the endovascular treatment of complex aneurysms in urgent and emergent patients. The former are standardised commercially manufactured fenestrated or branched stent grafts, which are available off-the-shelf with an anatomical feasibility in 50 - 80% of the patients. The "surgeon-modified" stent grafts refer to a technique, in which a commercially available stent graft is modified by the surgeon under sterile conditions directly before the implantation, in order to add the required fenestrations, scallops and/or branches. The modification takes approximately 60 - 120 min and haemodynamic stability of the patient is mandatory. Because of the off-label use of the commercial stent graft, detailed patient consent about the modification complications and risks should be performed whenever possible. A comparison of results on mortality and morbidity between "off-the-shelf" and "surgeon-modified" stent grafts has been published, although a direct comparison would be unfair for several reasons (different design, lack of extensive outcomes reports, long learning curve and different modification techniques). The "surgeon-modified" and "off-the-shelf" fenestrated/branched stent grafts are used in the treatment of high-risk patients with symptomatic or contained ruptured complex aneurysms. The outcomes of the two techniques are good, although the long-term durability of the former should be further investigated.

IFT15. Improved Outcomes of Thoracic Endovascular Aortic Repair Using Fenestrated Stent Graft from Zone 0 for Challenging Distal Aortic Arch Aneurysms

Thoracic endovascular aortic repair (TEVAR) using debranching or chimney techniques for distal aortic arch aneurysms cannot avoid surgical manipulation of the left common carotid artery (LCCA), which Results in a prolonged operation time with an increasing risk of stroke. Zone 0 TEVAR using a fenestrated stent graft (SG) is simple, but has a risk of endoleaks via a fenestration. We report the modified zone 0 fenestrated TEVAR. From 2007 to 2018, we have performed zone 0 TEVAR using a fenestrated SG for 74 patients with mainly degenerative distal aortic arch aneurysms located less than 15 mm away from LCCA, which is the subjects of this study. Until 2014, semi-custom-made fenestrated SG (Najuta prototype; Fig) designed to preserve blood flow into the brachiocephalic artery and LCCA had been placed from zone 0 (the control group). Since 2015, commercial SG with proximal bare stent (Valiant, Medtronic, Dublin, Ireland) has been additionally placed from zone 2 following zone 0 TEVAR using Najuta (the modified group). The left subclavian artery has been surgically reconstructed if necessary. There was no difference between the control (n = 37) and the modified group (n = 37) with ages of 78.2 and 80.0 years, aneurysms size of 60.4 and 58.4 mm, and proximal neck lengths between the LCCA and aortic aneurysm of 11.1 and 12.0 mm (Table). Early mortality rate was 0% in the both groups. The contrast-enhanced computed tomography scans at 7 days after TEVAR showed that high incident rate of type I endoleaks, from 32.4% in the control group to 5.4% in the modified group (P = .003) without increasing perioperative stroke rates (5.4%). During the follow-up period of 3 years after TEVAR, enlargement of more than 5 mm of aneurysm size was found in 9 nine (24.3%) in the control group and zero of the modified group (P = .001). There was one case of aorta-related late death in the control group. Nine aorta-related events including secondary intervention or enlargement of aneurysm occurred only in the control group. Zone 0 TEVAR using fenestrated SG (Najuta) combined with zone 2 TEVAR using Valiant with a proximal bare stent, provided significantly reduced incident of type I endoleaks via a fenestration. Zone 0 fenestrated TEVAR is a viable treatment for challenging distal aortic arch aneurysms.TableControl group (n = 37)Modified group (n = 37)P valueType I endoleaks at 7 days12 (32.4%)2 (5.4%).003Perioperative stroke2 (5.4%)2 (5.4%)1.000Survival rate at 3 years75.6 ± 7.1%91.7 ± 5.6%.304Aorta-related event-free rate at 3 years72.7 ± 7.8%100%.010 Open table in a new tab

Selection of Stents by Calculation of Arterial Cross-sectional Area in Modified Sandwich Technique for Complex Aortoiliac Arterial Lesions

We prospectively evaluated the modified sandwich technique for treatment of complex aortoiliac arterial lesions using commercial stent grafts selected according to the arterial cross-sectional area. The primary outcomes were technical feasibility and mid-term follow-up results. We prospectively enrolled 13 patients (mean age 63.85±6.12years) with aortoiliac arterial lesions (5 infrarenal abdominal aortic dissections, 1 lower abdominal aortic occlusion, 5 iliac artery aneurysms, 1 external iliac arterial pseudoaneurysm, and 1 type IB endoleak following endovascular aneurysm repair) for endovascular repair with the modified sandwich technique. All lesions were complex and unsuitable for routine endovascular treatment. The bifurcated stent-graft diameters were determined by calculating the arterial cross-sectional area. Success and complication rates were recorded. Patients were followed for 20.69±6.51 (range 6-31) months and stent patency determined by contrast-enhanced ultrasound and computed tomography 1, 3, and 6months post-operatively and every 12months thereafter. The initial technical success rate was 100%, and no surgical complications occurred. The primary patency of the stent grafts was 100% during follow-up. Post-procedural type I "gutter" endoleaks occurred in 4 patients (30.8%) after 1month. At 3months, the endoleaks in 3 of the 4 patients had disappeared without treatment, and the remaining endoleak resolved after coil embolization. The sandwich technique is a safe and effective therapy for complex aortoiliac arterial lesions. Stent-graft sizes based on the arterial cross-sectional area can ensure technical success and reduce the rate of "gutter" endoleaks.

Endovascular Aneurysm Repair in Patients with Conical Neck Anatomy.

PurposeCone shape neck is regarded as non-instruction for use (IFU) in most commercial stent graft. However, in real practice, liberal application of endovascular aneurysm repair (EVAR) for outside of IFU happens. We investigate non-adherence to conical neck anatomy in terms of early aneurysmal exclusion results.Materials and MethodsFrom January 2010 to December 2013, 105 patients with abdominal aortic aneurysm (AAA) underwent EVAR in Daegu Catholic University Medical Center. Among them, 38 patients (36.2%) had AAA with conical neck. We investigated the clinical characteristics of patients and the details of conical neck. We also analyzed the clinical results, such as endoleak, migration, procedure failure, perioperative mortality, and admission duration between conical neck and non-conical neck.ResultsThe maximum diameter of AAA was larger (60.95 mm vs. 52.68 mm, P=0.016) and the infrarenal neck length was shorter (25.07 mm vs. 38.13 mm, P=0.000) in conical neck group. During the procedure, type Ia endoleak occurred more in conical neck group (23.7% vs. 6.0%, P=0.013) and it could be successfully solved with additional adjunctive treatments, such as balloon or Palmaz stent. Although there was no statistical significance, mortality was higher and admission duration was longer in the conical neck (15.8% vs. 6.0%, 16.62±13.12 days vs. 13.03±13.13 days). Mean follow-up duration was 319.2±366.45 days. Successful aneurysmal exclusion was achieved.ConclusionThe presence of conical neck may not be a contraindication for EVAR. However, conical neck requires careful observation for additional adjunctive treatments because it increases the risk of type Ia endoleak.

Endovascular anatomic reconstruction of the iliac bifurcation with covered stentgrafts in sandwich-technique for the treatment of complex aorto-iliac aneurysms

ObjectiveEndovascular anatomic reconstruction of iliac artery bifurcation in aorto-iliac aneurysms using commercial stentgrafts in sandwich-technique by bilateral transfemoral approach. Methods24 patients (mean 73.8±standard deviation 6.8years) with complex aorto-iliac aneurysms (AAA): n=17; diameter 64±15 [48–100]mm; common-iliac-artery (CIA): n=27; 43±15 [30–87]mm; internal-iliac-artery (IIA): n=14; 28±8 [15–43]mm) were prospectively enrolled for EVAR with preservation of the IIA (n=31; bi-lateral n=7).Maintenance of antegrade flow to IIA by iliac reconstruction was performed in sandwich-technique prior to EVAR.Follow-up of 15.0±10.8 [1–40]months included contrast-enhanced ultrasound and computed-tomography after 1week, 3, 6 and every 12months. ResultsInitial technical success for anatomic reconstruction of the iliac arteries in 31 instances was 100%. Primary patency of iliac neo-bifurcations was 90.9% (20/22) at 6months and 84.2% (16/19) at 1year. Postprocedural gutter-endoleaks type 1b were obvious in 6.5% (2/31) of cases, which disappeared 3months later. Aortic/iliac aneurysm-size after 1year decreased (>5mm) in 61.5% of patients. No aneurysm-size increase or late rupture occurred. ConclusionsEndovascular reconstruction of the iliac bifurcation with commercial standard stentgrafts is safe and effective. Transfemoral approach allows extension of distal landing zone for EVAR while preserving the internal iliac artery blood-flow, even in unfavorable iliac anatomy.

A multi-institutional survey of interventional radiology for type II endoleaks after endovascular aortic repair: questionnaire results from the Japanese Society of Endoluminal Metallic Stents and Grafts in Japan.

To investigate the current status of interventional radiology (IR) procedures for a type II endoleak (T2EL) in Japan, and to identify the technical aspects that affect treatment results. A retrospective survey was conducted by distributing questionnaires to 25 institutions. The eligibility criteria were endovascular aortic repair (EVAR) performed using commercial stent grafts and IR performed for T2EL between January 2007 and December 2013. Technical success was defined as disappearance of the EL on digital subtraction angiography immediately after embolization, and imaging success was defined as no EL on contrast-enhanced computed tomography within 6months. Statistical comparisons of the number of involved branches, embolization level, embolic material, and changes in aneurysm size were made between the imaging success and imaging failure groups. The technical and imaging success rates were also compared between the initial therapy and repeat groups. A total of 166 cases were investigated. Initial therapy was performed in 147 cases (88.6%), with repeat therapy in 19 cases (11.4%). Transcatheter arterial embolization (TAE) was used most frequently, in 161 cases (97%), with direct puncture (DP) used in 5 cases (3%). Both coil embolization for the branches and NBCA embolization for the sac were frequently chosen. The technical success rate was 83.2% (TAE group), and the imaging success rate was 46.5% (TAE+DP groups). Branch+sac embolization was performed more frequently in the imaging success group. There was no significant difference in the number of involved branches or embolic material between the imaging success and imaging failure groups. Enlargement of the aneurysm was more frequently seen in the imaging failure group. There were no significant differences in the technical success and imaging success rates between the initial therapy and repeat groups. This is the first report of a multi-institutional questionnaire survey of IR procedures for T2EL after EVAR in Japan that was conducted to determine the current status. Enlargement of aneurysm size after embolization was more frequently seen in the imaging failure group. It is important to embolize both branch and sac to achieve imaging success, regardless of embolic material. Long-term outcomes need to be investigated.

In Vitro and Pilot In Vivo Evaluation of a Bioactive Coating for Stent Grafts Based on Chondroitin Sulfate and Epidermal Growth Factor

PurposeTo evaluate the potential of a bioactive coating based on chondroitin sulfate (CS) and tethered epidermal growth factor (EGF) for improvement of healing around stent grafts (SGs). Materials and MethodsThe impact of the bioactive coating on cell survival was tested in vitro on human vascular cells using polyethylene terephthalate films (PET) as a substrate. After being transferred onto a more “realistic” material (expanded polytetrafluoroethylene [ePTFE]), the durability and mechanical behavior of the coating and cell survival were studied. Preliminary in vivo testing was performed in a canine iliac aneurysm model reproducing type I endoleaks (three animals with one control and one bioactive SG for each). ResultsCS and EGF coatings significantly increased survival of human smooth muscle cells and fibroblasts compared with bare PET or ePTFE (P < .05). The coating also displayed good durability over 30 days according to enzyme-linked immunosorbent assay and cell survival tests. The coating did not affect mechanical properties of ePTFE and was successfully transferred onto commercial SGs for in vivo testing. No difference was observed on computed tomography and macroscopic examinations in endoleak persistence at 3 months, but the bioactive coating deposited on the abluminal surface of the SG (exposed to the vessel wall) increased the percentage of healed tissue in the aneurysm. No adverse effect, such as neointima formation or thrombosis, was observed. ConclusionsThe bioactive coating promoted in vitro cell survival, displayed good durability, and was successfully transferred onto a commercial SG. Preliminary in vivo results suggest improved healing around bioactive SGs.

Apparatus for Comparison of Pullout Forces for Various Thoracic Stent Grafts at Varying Neck Angulations and Oversizes

The purpose of this study is to provide an apparatus for comparison of pullout forces for various thoracic stent grafts at varying neck angulations and oversizes. An invitro platform capable of performing pullout tests was used on stent grafts in angulated silicone tubes designed for this study (0°, 45°, 90°, and 135° with a 32-mm inner diameter) in a temperature-controlled chamber (37±2°C). Three commercial stent grafts with sizes commonly used in Taiwan (Valiant: 34, 36, 38, and 40mm; Zenith TX2: 34, 36, 38, and 40mm; and TAG: 34, 37, and 40mm) were used, and each size was tested 8 times for each angulation condition. The mean dislodgement forces (DFs) at 0° angulation within 10-20% oversize were approximately 22.7, 9.6, and 9.0N for the Valiant, Zenith TX2, and TAG devices, respectively, whereas the mean DFs decreased by 46%, 38%, and 50% to 12.3, 5.9, and 4.5N when the angulation reached 135°. Regression analysis shows that neck angulation was a significant factor for the Valiant and Zenith TX2 devices (P<0.0001 and P<0.0001, respectively) but not for the TAG device (P=0.483). In addition, oversize and interactions between variables (angulation × oversize) exhibited significant effects on the DFs for all devices (P<0.0001). We successfully built up an apparatus for comparison of pullout forces for various thoracic stent grafts at varying neck angulations and oversizes. With the empirical comparative data of different brand stent grafts under various conditions shown and compared, our findings suggest that aortic neck angulation has a negative correlation with stent-graft fixation. To have better stent-graft fixation and seal in the aortic arch for thoracic endovascular aortic repair, a longer landing zone with cautiously selected oversize is a more suitable selection.

Clinical practice and thinking on chimney technique for endovascular aortic repair

Chimney technique is an assistive technology of endovascular aortic repair, which is used to reconstruct the vital branch vessel invaded by aortic pathology. In chimney technique, most of the commercial aortic stent-graft can be used, and covered branch stent-graft is recommended to decrease the risk of type I a endoleak. The suggested oversizing for aortic stent-graft and branch stent-graft is 15% and 5% respectively, and the length of overlapping between stent-grafts should be more than 2 cm. Type I a endoleak is the main concentration, appropriated oversizing and overlapping are important precautions theoretically. Anticoagulation therapy post-operation is crucial in preventing restenosis of the chimney stent-graft.

In House Enhanced 3D Printing of Complex AAA for EVAR Treatment Planning and Preoperative Simulation

Three dimensional printing (3D printing) is becoming a common useful technology in many areas in medicine. This technology allows better appreciation of complex anatomical and pathologic conditions. In vascular medicine and surgery 3d modeling may become of help in Endovascular Aortic Repair (EVAR) treatment planning, especially in cases of complex angulations and branching at the aneurysm neck. Accurate and rapid solid 3d models were prepared in house using common and freely available software programs, and an accurate 3D printer. These solid models allowed palpation and manual handling and visual inspection for a better appreciation of complex AAA necks. Color enhancement of these models added another dimension of comprehension, even for experienced surgeons and invasive radiologists. A full sized model may allow more accurate measurements of branch distances and angles in space when tortuosity is severe. Fenestrations and “Chimney” branches may be easily envisioned preoperatively. In addition, 3D hollow outer shells were constructed to obtain a workable AAA arterial wall-like model for rehearsal and preoperative stent graft deployment simulation. Various commercial stent grafts from several manufacturers were deployed under fluoroscopy to evaluate feasibility of the planned procedure. In simple AAA cases device deployment simulation was always successful, but in one AAA case with a severely angulated neck all devices failed. We conclude that 3D printing and modeling and outer shell fabrication for preoperative simulation are helpful in EVAR planning of complex AAA.

A biomimetic approach for designing stent-graft structures: Caterpillar cuticle as design model

Stent-graft (SG) induced biomechanical mismatch at the aortic repair site forms the major reason behind postoperative hemodynamic complications. These complications arise from mismatched radial compliance and stiffness property of repair device relative to native aortic mechanics. The inability of an exoskeleton SG design (an externally stented rigid polyester graft) to achieve optimum balance between structural robustness and flexibility constrains its biomechanical performance limits. Therefore, a new SG design capable of dynamically controlling its stiffness and flexibility has been proposed in this study. The new design is adopted from the segmented hydroskeleton structure of a caterpillar cuticle and comprises of high performance polymeric filaments constructed in a segmented knit architecture. Initially, conceptual design models of caterpillar and SG were developed and later translated into an experimental SG prototype. The in-vitro biomechanical evaluation (compliance, bending moment, migration intensity, and viscoelasticity) revealed significantly better performance of hydroskeleton structure than a commercial SG device (Zenith™ Flex SG) and woven Dacron® graft-prosthesis. Structural segmentation improved the biomechanical behaviour of new SG by inducing a three dimensional volumetric expansion property when the SG was subjected to hoop stresses. Interestingly, this behaviour matches the orthotropic elastic property of native aorta and hence proposes segmented hydroskeleton structures as promising design approach for future aortic repair devices.

Stent graft performance in the treatment of abdominal aortic aneurysms: The influence of compliance and geometry

The long-term success of the endovascular procedure for the treatment of Abdominal Aortic Aneurysms (AAAs ) depends on the secure fixation of the proximal end and the geometry of the stent–graft (SG) device. Variations in SG types can affect proximal fixation and SG hemodynamics. Such hemodynamic variations can have a catastrophic effect on the vascular system and may result from a SG/arterial wall compliance mismatch and the sudden decrease in cross-sectional area at the bifurcation, which may result in decreased distal perfusion, increased pressure wave reflection and increased stress at the interface between the stented and non-stented portion of the vessel. To examine this compliance mismatch, a commercial SG device was tested experimentally under a physiological pressure condition in a silicone AAA model based on computed tomography scans. There was a considerable reduction in compliance of 54% and an increase in the pulse wave velocity of 21%, with a significant amount of the forward pressure wave being reflected. To examine the SG geometrical effects, a commercial bifurcated geometry was compared computationally and experimentally with a geometrical taper in the form of a blended section, which provided a smooth transition from the proximal end to both iliac legs. The sudden contraction of commercial SG at the bifurcation region causes flow separation within the iliac legs, which is known to cause SG occlusion and increased proximal pressure. The blended section along the bifurcation region promotes a greater uniformity of the fluid flow field within the distal legs, especially, during the deceleration phase with reduced boundary layer reversal. In order to reduce the foregoing losses, abrupt changes of cross-section should be avoided. Geometrical tapers could lead to improved clinical outcomes for AAA SGs.

The Education System to Master Endovascular Aortic Repair in Japan – The Japanese Committee for Stentgraft Management

Objective The Japanese Committee for Stentgraft Management (JACSM) was established with the aim of ensuring the safe and proper reach of commercial stent grafts following their regulatory approval. This study examines the validity of the practice standards developed by JACSM. Methods JACSM comprises 10 associations related to endovascular treatment. Based on the practice standards developed by JACSM, the status of practising institutions, practising surgeons, supervising surgeons and the results of follow-up surveys were analysed. Results In the 2.5 years following the establishment of JACSM, 298 institutions have fulfilled the practice standards. The number of practising surgeons reached 493, and the number of supervising surgeons reached 177. There were 3089 registered cases up to June 2009. The present study analysed 1570 cases registered in the 2 years from July 2006 to June 2008. The hospital mortality rate was low (0.4%) in the follow-up surveys. Conclusions Early results following the introduction of stent grafts were generally good. The procedure spread safely without the learning curve seen in the initial stages following introduction of new medical materials, indicating that the practice standards were appropriate.

Hybrid Procedures for Thoracoabdominal Aneurysms

(1) Observation. This option is usually tendered if the aneurysm is not large enough to be considered an immediate threat to the patient’s life or if the patient is too old or sick to benefit from intervention. Lifestyle improvements (i.e., weight loss, exercise, and smoking cessation) and optimization of medical therapy (i.e., an antiplatelet regimen, antihypertensive agents, statins, diabetes control, and physiotherapy) are crucial to improving life expectancy and quality of life in these patients; however, regrettably, they are often underutilized. (2) Open surgery. This is still considered the gold standard of treatment for TAAA. If patients are wisely selected and operated at a qualified institution, the life expectancy of surgically treated TAAA patients improves dramatically, achieving satisfactory postoperative functional status. There are, however, several drawbacks to this option. For one, mortality for more extensive TAAAs (i.e., type II) is not negligible. In survivors, the operation may be burdened by paraplegia, possibly one of the most catastrophic complications that may occur, and other cerebrovascular events. Cardiac events, as well as end-stage renal insufficiency requiring dialysis or respiratory insufficiency requiring prolonged mechanical ventilation, are other feared complications. (3) Endovascular procedure. This is clearly a less invasive and hugely appealing approach; however, it has many restrictions that limit its use to a very few centers worldwide. First, several anatomical requirements need to be met. Second, the required branched stentgrafts, which are custom-made by a single manufacturer, are expensive and typically take more than 8 weeks to produce. Lastly, top-level endovascular experience, technical expertise, and radiological equipment are required to accomplish these procedures. (4) Hybrid procedures. This approach consists of an open surgical procedure to debranch and reroute the renal and/or splanchnic vessels followed by endovascular deployment of an off-the-shelf commercial stent-graft for aneurysm exclusion. The open surgery is usually limited to the abdomen, which is particularly advantageous in patients with severe respiratory insufficiency or previous thoracotomy.

Analysis of blood flow behaviour in custom stent grafts

Endovascular aneurysm repair (EVAR) is an attractive alternative to open surgery for treating abdominal aortic aneurysms (AAAs). However, the implantation of stent grafts into AAAs can result in post-operative complications such as stent graft migration, rupture or endoleak. EVAR has therefore been carried out only on selected patients. Stent grafts are usually standard commercial stent grafts (CSGs); however, custom made stent grafts (cmSGs) of various shapes and sizes are sometimes used to fit patients’ anatomies. In the present study, the cmSGs were specially designed and fabricated by the surgeons at the Pitié-Salpétriére hospital in Paris. Two patients carrying cmSGs with unfavourable geometries showing tortuous shapes, angulation, widening, narrowing, curvature and kinking and one patient with a cmSG with a more favourable geometry resembling a straight tube were examined. These three clinical cases were investigated using three-dimensional numerical simulations, and the results showed that even when the cmSG geometries are unfavourable, the drag forces to which they are subjected are of a similar magnitude to those exerted on CSGs, or even smaller. The hemodynamic analysis carried out on the two unfavourable cmSGs showed the occurrence of low velocity values in the main trunk of the cmSGs, high velocities linked to recirculation areas downstream from kinking and strong distal narrowing. These flow patterns are liable to induce thrombus. However, since cmSG implantation can save the lives of patients for whom neither classical stent grafts nor open surgery are indicated, it can be concluded that these devices are useful in some cases.