Modular Stent Research Articles

Functional Evaluation of Embedded Modular Single-Branched Stent Graft: Application to Type B Aortic Dissection With Aberrant Right Subclavian Artery.

BackgroundEndovascular repair of type B aortic dissection (TBAD) with aberrant right subclavian artery (ARSA) is challenging due to anatomical complexity. The embedded modular single-branched stent graft (EMSBSG) could solve this problem. However, the hemodynamic efficacy of this innovative technique has not been fully assessed. This study aimed to propose morphometric and functional indicators to quantify the outcomes of EMSBSG in treating TBAD with ARSA.Material and MethodsA patient who had TBAD with ARSA underwent EMSBSG implantation was admitted. Computational fluid dynamics (CFD) and three-dimensional structural analyses were conducted based on CTA datasets before the operation (Pre-1) and at 4 and 25 days after EMSBSG implantation (Post-1 and Post-2). Quantitative and qualitative functional analyses were conducted via pressure-, velocity- and wall shear stress (WSS) -based parameters, such as the luminal pressure difference (LPD), total energy loss, and flow distribution ratio. By precisely registering the aortas at the three time points, parameter variations in the EMSBSG region were also computed to investigate the prognostic improvement after EMSBSG implantation.ResultsThe first balance point of LPD distally shifted to the abdominal aorta in Post-1 by a distance of 20.172 cm, and shifted out of the dissected region in Post-2, indicating positive pressure recovery post EMSBSG. The flow distribution ratios of all aortic arch branches increased after EMSBSG implantation. A positive normal deformation index in the EMSBSG region confirmed true lumen expansion; dominant ARN (area ratio of negative value) of pressure and WSS-based parameters indicated an improved prognosis from Post-1 to Post-2.ConclusionsThe short-term results of EMSBSG in treating TBAD with ARSA proved to be promising, especially in EMSBSG region. Comprehensive evaluation could provide new insight into the therapy of TBAD with ARSA. Thus, it might guide the further management of complex aortic arch lesions.

Optimal design of vascular stents using a network of 1D slender curved rods

In this manuscript we present a mathematical theory and a computational algorithm to study optimal design of mesh-like structures such as metallic stents by changing the stent strut thickness and width to optimize the overall stent compliance. The mathematical constrained optimization problem is to minimize the “compliance functional” over a closed and bounded set of constraints. The compliance functional is the stent’s overall elastic energy. The constraints are the minimal and maximal strut thickness, and a given fixed volume of the stent material. We prove the existence of a minimizer, thereby proving that the constrained optimization problem has a solution. A numerical scheme based on an iteration procedure is introduced, and implemented within a Finite Element Method framework. Optimal design of three different stent prototypes is considered: (1) a single zig-zag ring, which can be found in many complex stent designs on the US market as a basic cell in the modular stent design, (2) a Palmaz–Schatz type stent consisting of 6 zig-zag rings, and (3) a Cypher(TM) type stent consisting of zig-zag rings with sinusoidal connectors. Several interesting optimization solutions are found, some of which have already been implemented in the design of the currently available stents on the US market. The resulting computational algorithm is compared to a Genetic Algorithm, and it is shown that our computational approach outperforms the Genetic Algorithm in the following three key aspects: (1) computation time, (2) accuracy, and (3) maintaining the symmetry of the solution.

One-year results from the DETOUR I trial of the PQ Bypass DETOUR System for percutaneous femoropopliteal bypass

ObjectiveThe objective of this study was to evaluate the 1-year safety and effectiveness outcomes associated with the PQ Bypass DETOUR System (PQ Bypass, Milpitas, Calif) for the percutaneous bypass of long-segment femoropopliteal occlusive disease. MethodsThis prospective, single-arm, multicenter trial enrolled patients with long-segment femoropopliteal arterial disease. The DETOUR System percutaneously deploys modular stent grafts to bypass femoropopliteal lesions through a transvenous route. Eligible patients included those with TransAtlantic Inter-Society Consensus C and D lesions >100 mm in length. The primary safety end point was the major adverse event (MAE) rate through 1 month, defined as the composite of death, clinically driven target vessel revascularization (CD-TVR), or major amputation. The primary effectiveness end point was stent graft patency through 6 months, defined as freedom from stenosis ≥50%, occlusion, or CD-TVR. ResultsDuring a 24-month period, 78 patients (82 limbs) were enrolled. The average core laboratory-measured lesion length was 371 ± 55 mm; 79 of 82 lesions (96%) were chronic total occlusions, and 55 of 82 lesions (67%) had severe calcification. The rates of technical and procedural success measured during the index procedure were both 96%, with satisfactory delivery and deployment of the device without MAEs in 79 of 82 limbs. Through 1 month, there were no deaths or amputations; CD-TVRs occurred in 2 of 81 limbs (3%), and freedom from MAEs was 98% (79/81). The 1-year Kaplan-Meier primary, assisted primary, and secondary patency rates were 81% ± 4%, 82% ± 4%, and 90% ± 3%, respectively. The ankle-brachial index increased an average of 0.25 ± 0.27 between baseline and 1 year (P < .001). Through 1 year, the Kaplan-Meier estimates of freedom from stent graft thrombosis, CD-TVR, and MAE were 84% ± 4%, 85% ± 4%, and 84% ± 4%, respectively. At 1 year, the Rutherford class improved in 77 of 80 limbs (96%), and 65 of 80 (81%) were asymptomatic. Deep venous thrombosis developed in 2 of 79 target limbs (3%) through 1 year, both at the femoropopliteal vein level. There were no instances of pulmonary embolism. ConclusionsThe 1-year results from the DETOUR I trial show that the PQ Bypass DETOUR System is a safe and effective percutaneous treatment option for patients with longer, severely calcified, above-knee femoropopliteal lesions.

Multilayered Parallel Endografting for Urgent Endovascular Repair of a Severely Angulated Thoracoabdominal Aortic Aneurysm

Total endovascular repair of TAAA using branched, fenestrated stent grafts have been performed with promising midterm results. However, severe angulation of the aorta as well as close proximity of the visceral and renal artery ostia pose a significant technical challenge in designing and implanting branched, fenestrated stent grafts. Parallel grafting offers an alternative technique, allowing an urgent, or emergent total endovascular repair of symptomatic, or ruptured TAAA. We describe a technique of 4-vessel incorporation in a total endovascular repair of TAAA, using multilayered parallel endografting via bilateral femoral and unilateral brachial access. A 76-year-old male with severe chronic obstructive pulmonary disease and coronary artery disease presented with a symptomatic 9cm extent IV thoracoabdominal aortic aneurysm. The thoracic, and paravisceral segments of his aorta, as well as the iliac arteries were severely angulated, whereas the superior mesenteric and the celiac arteries had a common origin. An urgent total endovascular aortic repair was performed. The aorta and the iliac arteries were straightened by placing stiff wires from bilateral femoral arteries in a "buddy" fashion. In addition, a brachiofemoral "body-floss" wire was established. Over this body-floss wire, thoracic stent grafts were deployed in multiple layers, alternating with parallel branch stents into visceral and renal arteries. Distally, a bifurcated modular stent graft was deployed down to the common iliacs, achieving complete aneurysm exclusion. Patient recovered well without complications and was discharged home in 5days. Postoperative computed tomography scan showed patent visceral and renal stents and complete exclusion of the aneurysm without evidence of endoleak.

Analysis of the Influence of Endograft Geometry on Blood Hemodynamics in Abdominal Aortic Aneurysm by Computational Fluid Dynamics

Objectives: Endovascular Aneurysm Repair (EVAR) is considered the treatment of choice for Abdominal Aortic Aneurysm (AAA). However, thrombotic deposits found incidentally in abdominal aortic endografts are common and the deposition of thrombus is reported to be influenced by the geometry of the aortic stent graft. We used computational fluid dynamic techniques to analyze the biomechanical factors associated with different stent graft morphologies Methods and models: Computational fluid dynamic models were constructed to investigate the biomechanical factors affecting both tuburlent flow and the drag force in modular AAA stent grafts. The resultant flow separation and drag force as a net change of fluid momentum were calculated on the basis of varying three-dimensional geometry. Modular AAA stent grafts with four different lengths of graft mani body were compared. Computational fluid dynamic simulations were then performed on each stent graft model according to its geometric parameters to determine the flow separation and the actual change in drag force experienced by the stent graft. Results: In all these simulations, the blood flow created as adverse pressure gradient when blood flow decelerated. Flow separation occurred when the boundary layer velocity gradient dropped almost to zero causing recirculation and vortices to be formed downstream of the main graft body and leading to intraprosthetic thrombosis and endograft limb obstruction. With a shorter length graft main body, it was possible to avoid flow separation, reducing the probability of occurrences of the flow recirculation and vortices. The drag force causing device migration was higher with elevated blood pressure and unchanged with the main body length. Conclusion: Flow separation in modular AAA stent grafts is common and occurs more often in endografts with a longer main body. The shorter main body design of the endograft can be applied without the expense of increasing drag force.

Comparison of outcomes following endovascular repair of abdominal aortic aneurysms based on size threshold

Size threshold for operative repair of abdominal aortic aneurysms (AAAs) has been determined based on risks and outcomes of open repair vs surveillance. The influence of endovascular aneurysm repair (EVAR) on this threshold is less established. The purpose of this study is to determine whether long-term outcomes following EVAR are affected by maximum diameter at the time of treatment. Patients undergoing EVAR with modular stent grafts from 2000 to 2011 were identified from a prospectively maintained database and stratified by maximum aortic diameter at the time of repair: small (4.0-4.9cm), medium (5.0-5.9cm), and large (≥6.0cm). Comparisons of demographics, indications for repair, perioperative complications, and long-term outcomes were made using analysis of variance, χ(2), and Kaplan-Meier plots. Seven hundred forty patients were identified: 157 (21.2%) small, 374 (50.5%) medium, and 209 (28.2%) large. Patients differed by mean age (69.3± 8.09, 71.7± 8.55, and 73.6± 8.77years for small, medium, and large, respectively; P< .001), coronary artery disease (42% small, 57% medium, 51.2% large; P= .01), prior coronary angioplasty (14.6% small, 18.2% medium, 9.6% large; P= .02), congestive heart failure (5.7% small, 15.2% medium, 19.6% large; P= .01), prior vascular surgery (7% small, 15.8% medium, 10% large; P= .016), and chronic obstructive pulmonary disease (21% small, 27% medium, 33% large; P= .038). Small AAAs were more frequently symptomatic (19.7% small, 7.5% medium, 8.1% large; P< .001). There was no difference in perioperative complication rates (P=.399), expansion ≥5mm (2.6% small, 5.6% medium, 7.2% large; P= .148), or all-type endoleak (40.8% small, 41.7% medium, 44.5% large; P= .73). Small AAAs developed fewer type I endoleaks (5.1% vs 6.95% medium and 14.8% large; P= .001). Compared with small AAAs, both medium (P= .39) and large (P< .001) required secondary intervention more frequently, with hazard ratios of 2.32 (95% confidence interval, 1.045-5.156) and 4.74 (95% confidence interval, 2.115-10.637), respectively. Ten-year survival was 72%, 63.1%, and 49.8% in the small, medium, and large groups, respectively (P< .001) with one rupture-related death after EVAR in the large group. All-cause mortality differed among the 75- to 84-year-old patients (30.4% small, 51.6% medium, 55.7% large; P= .017). EVAR for small AAAs shows improved long-term outcomes than for age-matched patients with larger aneurysms.

Computational Fluid Dynamics Evaluation of the Cross-Limb Stent Graft Configuration for Endovascular Aneurysm Repair

The technique of crossing the limbs of bifurcated modular stent grafts for endovascular aneurysm repair (EVAR) is often employed in the face of splayed aortic bifurcations to facilitate cannulation and prevent device kinking. However, little has been reported about the implications of cross-limb EVAR, especially in comparison to conventional EVAR. Previous computational fluid dynamics studies of conventional EVAR grafts have mostly utilized simplified planar stent graft geometries. We herein examined the differences between conventional and cross-limb EVAR by comparing their hemodynamic flow fields (i.e., in the "direct" and "cross" configurations, respectively). We also added a "planar" configuration, which is commonly found in the literature, to identify how well this configuration compares to out-of-plane stent graft configurations from a hemodynamic perspective. A representative patient's cross-limb stent graft geometry was segmented using computed tomography imaging in Mimics software. The cross-limb graft geometry was used to build its direct and planar counterparts in SolidWorks. Physiologic velocity and mass flow boundary conditions and blood properties were implemented for steady-state and pulsatile transient simulations in ANSYS CFX. Displacement forces, wall shear stress (WSS), and oscillatory shear index (OSI) were all comparable between the direct and cross configurations, whereas the planar geometry yielded very different predictions of hemodynamics compared to the out-of-plane stent graft configurations, particularly for displacement forces. This single-patient study suggests that the short-term hemodynamics involved in crossing the limbs is as safe as conventional EVAR. Higher helicity and improved WSS distribution of the cross-limb configuration suggest improved flow-related thrombosis resistance in the short term. However, there may be long-term fatigue implications to stent graft use in the cross configuration when compared to the direct configuration.

Comparison of Long-term Outcomes Following Endovascular Repair of Abdominal Aortic Aneurysms Based on Size Threshold

Size threshold for operative repair of abdominal aortic aneurysms (AAA) has been determined based on risks and outcomes of open repair vs surveillance. The influence of endovascular repair (EVAR) on this threshold is less established. The purpose of this study is to determine whether long-term outcomes of EVAR are affected by maximum diameter at time of treatment. All patients who underwent EVAR with modular stent grafts between January 2000 and December 2011 at a single academic institution were identified from a prospectively maintained database. Patients were stratified based on maximum aortic diameter at time of repair: small (4.0-4.9 cm), medium (5.0-5.9 cm), and large (6.0 cm). Comparisons of demographics, indications for repair, and perioperative complications were made among the groups. Long-term follow-up was reviewed for expansion of the native aneurysm sac 5 mm, secondary intervention involving the native aneurysm or stent graft, and all-cause mortality. Statistical analyses were made using analysis of variance, χ2, and Kaplan-Meier plots. During the study period, 740 patients underwent EVAR with modular stent grafts: 157 small (21.2%), 374 medium (50.5%), and 209 large (28.2%). Preoperative patient characteristics were similar among the groups with exception to mean age (69.3 ± 8.09, 71.7 ± 8.55, and 73.6 ± 8.77 years for small, medium, and large, respectively; P < .001), history of coronary artery disease (42% small, 57% medium, 51.2% large; P = .01), prior coronary angioplasty (14.6% small, 18.2% medium, 9.6% large; P = .02), congestive heart failure (5.7% small, 15.2% medium, 19.6% large; P = .01), prior vascular surgery (7% small, 15.8% medium, 10% large; P = .016), and chronic obstructive pulmonary disease (21% small, 27% medium, 33% large; P = .038). Clinical classification differed significantly as a larger percentage of small AAAs were symptomatic (19.7% small, 7.5% medium, 8.1% large; P < .001). No difference in perioperative complication rates (P = .399) or all-type endoleak at any surveillance visit (40.8% small, 41.7% medium, 44.5% large; P = .73) was observed among the groups. However, the small AAA group developed fewer type I endoleaks (5.1% vs 6.95% medium and 14.8% large; P = .001). Aneurysm sac expansion of 5 mm was observed in 2.6% of small, 5.6% of medium, and 7.2% of large AAAs during the follow-up period but did not achieve a significant difference (P = .148). Secondary intervention rates differed significantly as 5.1% of small, 7.5% of medium, and 12.9% large AAAs required secondary intervention (P = .018). In direct comparison with small AAAs, medium (P = .39) and large (P < .001) groups both required secondary intervention more frequently, with hazard ratios of 2.32 (95% confidence interval, 1.045-5.156) and 4.74 (95% confidence interval, 2.115-10.637), respectively. Overall 10-year survival was 72% in the small, 63.1% in the medium, and 49.8% in the large group (P < .001) with no known AAA-related deaths. Age-adjusted all-cause mortality differed significantly among the group aged 75 to 84 years (30.4% small, 51.6% medium, 55.7% large; P = .017). EVAR for small AAAs demonstrates improved long-term outcomes when compared with EVAR for medium and large AAAs. These data suggest that EVAR for AAAs ranging from 4 to 5 cm may have better outcomes than EVAR for age-matched patients with larger aneurysms.

The Future of Abdominal Aortic Aneurysm Treatment and the Role of Totally Percutaneous Endografting

Endovascular abdominal aortic aneurysm repair (EVAR) has experienced a continuous spread worldwide as a result of the constant drive to develop innovative methods and devices that enable physicians to achieve therapeutic aims while reducing procedural risks and patient discomfort. Randomised controlled studies have demonstrated clear early benefits over open repair in terms of mortality and morbidity, but a high reintervention rate jeopardised the EVAR outcome. Complications in EVAR, such as endoleaks, separation of modular components, stent or hook fractures and distal migration of the endograft, can lead to aneurysm enlargement and thus to the native risk of aneurysm rupture. In order to prevent such complications and minimise potential re-interventions, new-generation stent grafts, low-profile delivery systems and new percutaneous closing devices have been developed and adopted, making a totally percutaneous approach possible and desirable. Nevertheless, operators must be aware and trained to face every complication that could possibly develop during and after the procedure. Given these circumstances, EVAR is under consideration as the first line of treatment for abdominal aortic aneurysms.

Current Tips for Ensuring Successful Transfemoral Short Limb Cannulation in Modular Aortic Endografts: A New Method for Incorporation in Practice

One of the most crucial steps in endovascular infrarenal abdominal aortic aneurysm repair is the short limb catheterization of the modular device and the confirmation of the intrastent position of the guidewire. Failed connection of the contralateral iliac limb to the main body because of malposition of the catheterizing guidewire may lead to serious complications. A new method confirming successful passage of the guidewire in the short leg of the main body of the modular stent graft, thus ensuring that the extension will be accurately docked within the short limb, is described in detail. Furthermore, current tips for ensuring successful short limb cannulation are also described in brief.

Commentary on "Current Tips for Ensuring Successful Transfemoral Short Limb Cannulation in Modular Aortic Endografts: A New Method for Incorporation in Practice"

One of the most crucial steps in endovascular infrarenal abdominal aortic aneurysm repair is the short limb catheterization of the modular device and the confirmation of the intrastent position of the guidewire. Failed connection of the contralateral iliac limb to the main body because of malposition of the catheterizing guidewire may lead to serious complications. A new method confirming successful passage of the guidewire in the short leg of the main body of the modular stent graft, thus ensuring that the extension will be accurately docked within the short limb, is described in detail. Furthermore, current tips for ensuring successful short limb cannulation are also described in brief.

Commentary on "Current Tips for Ensuring Successful Transfemoral Short Limb Cannulation in Modular Aortic Endografts: A New Method for Incorporation in Practice"

One of the most crucial steps in endovascular infrarenal abdominal aortic aneurysm repair is the short limb catheterization of the modular device and the confirmation of the intrastent position of the guidewire. Failed connection of the contralateral iliac limb to the main body because of malposition of the catheterizing guidewire may lead to serious complications. A new method confirming successful passage of the guidewire in the short leg of the main body of the modular stent graft, thus ensuring that the extension will be accurately docked within the short limb, is described in detail. Furthermore, current tips for ensuring successful short limb cannulation are also described in brief.

A New Modular Stent Graft to Reconstruct Aortic Arch

Endovascular repair by stent graft has been developed as a safe and less-invasive treatment for descending thoracic and abdominal aortic diseases. In case of involvement of the aortic arch, the challenge in endovascular repair is to maintain blood flow to the brain and upper extremities. Several studies have been done trying to repair this difficult part of the aorta with different stent grafts, and we have developed a new stent-graft device for aortic arch reconstitution. We implanted the new device in canine models to test its feasibility. The new stent graft was composed of three components: parts I and II were both bifurcated, one with long, narrow limb and the other short and wide, and part III was a tubular component. Ten adult hybrid dogs were operated with the new stent-graft procedure, and eight were successfully implanted with the stent grafts. The technical success rate was 80% (8 of 10). Five dogs survived for 3 months without obvious cerebral, visceral or limb ischaemia. Autopsies showed that the implanted stent grafts were patent and the vital side branches of aortic arch were well preserved. Our study demonstrates that it is possible to reconstruct aortic arch with the new branched stent grafts. The advantage of this device is that it is modular, more adaptable and surgical bypass could be possibly avoided.

DECISION TOOL FOR BIFURCATION STENTING BASED ON GEOMETRICAL ANALYSIS

The objective of this paper is to study the mechanical behaviors of angioplasty stents during and after implantation using a fluid–structure interaction computational technique. The deployment of a balloon expandable stent is simulated using immersed finite element method (IFEM), which was developed for solving complex fluid and deformable structure interaction problems. Using this method, we modelled a stainless steel stent in a blood vessel. A balloon is deployed to assist the expansion of the stent that is to be plastically deformed. The balloon is modelled as a thin hyperelastic material while the stent has the property of steel. The mechanical behaviors such as the expansion mechanism, stress distribution on the stent, and the surrounding fluid velocity profile during the implantation of the stent are studied. With appropriate applied internal pressure, the balloon inside the stent is deployed which linearly expands the diameter of a Medtronic AVE Modular Stent S7 until it reaches 1.7 times of its original diameter. The results will assist in the development of novel stent designs and stent deployment protocols to minimize vascular injury during stenting and reduce restenosis.

Transrenal Deployment of a Modular Stent Graft to Repair AAAs with Short Necks: Experiments in Dogs

Severely angulated (> 60 degrees ) or short (< 15 mm) proximal necks remain significant anatomical limitations for endovascular stent-graft repairs for abdominal aortic aneurysms. Ensuring proper proximal fixation of the stent-graft to the host artery without the short-or long-term risks of endoleak or migration represents a particular technical challenge for these anatomical circumstances. An innovative balloon expandable stent combined with a weft-knitted prosthesis was specifically designed for these situations by modelling the stent to the neck anatomy without overdistension or potential barotrauma allowing better incorporation of the device. The Latecba stent-graft consists of a 2 parts modular design. The first one, Module A, is deployed at the transrenal level and consists of a Palmaz type stent whose first half is bare and second half is sutured to a crimped weft-knitted polyester graft whose distal end holds a constriction. The second Module B is a non-crimped weft-knitted graft attached to 2 stainless steel stents. The first stent is entirely contained in the proximal textile tube, allowing fixation to module A. The second stent, which is left uncovered over the distal third, ensures proper fixation of the stent-graft distally. Following the creation of a prosthetic aneurysm in the infrarenal aorta in 32 dogs, 29 received the Latecba stent-graft for scheduled durations of 10 days, 1 month, 3 months and 6 months. Proper deployment of the stent-grafts was achieved without difficulty. All 29 animals survived and the devices were all patent at sacrifice. No device defects or migrations were observed and the stent-grafts proved to be efficient in this setting to exclude the aneurysm. Analyses of the explanted devices (gross observations, RX, CT scan, IVUS, angioscopy) confirmed the stability of this modular stent-graft. Further on-going clinical investigations are warranted to validate this concept before this stent-graft becomes commercially available without any restriction.

Specific Shortcomings of Endograft Design

Further to the rapid enlargement of an aneurysm to 5.6 cm in diameter after 3 years of surveillance, a 79-year-old patient was fitted with a Vanguard modular stent graft and monitored on a regular basis for 6 years. Two years later, the aneurysmal sac ruptured. The patient died 1 month after an open surgery. The device was devoid of any encapsulation and the ipsilateral limb was detached from the body. The Nitinol skeleton was mostly maintained, however, some polypropylene sutures were broken. The resulting motion of the sharp-angled Nitinol wires caused abrasion and resulted in a few localized holes that were sufficient to permit blood to percolate through the textile wall. Some polyester yarns in the warp direction were ruptured. The Nitinol wire used in this device was shown to be corrosion resistant but the selection of the polypropylene suture was inappropriate. Because this technology is maturing rapidly, these weaknesses can be avoided in the future generations of endovascular devices. It is recommended that these Nitinol wires be sutured to the fabric and that polyester yarns stronger than 68 decitex in tubes 8 mm in diameter are selected.

An Alternative to Aorto-uni-iliac EVAR and Femoro-femoral Crossover in a Patient Having an Aorto-iliac Aneurysm with an Occluded External Iliac Artery

An endovascular procedure for excluding an aorto-iliac aneurysm whilst simultaneously preserving one internal iliac artery is described in a patient with complex iliac pathology. The procedure involved the use of Advanta V12 covered stents to bridge the gap between the contralateral limb of the main body of a custom-made Zenith stent graft and the internal iliac artery on the side of an external iliac artery occlusion. Minimal modifications to the standard design of modular stent grafts make it possible to treat high risk patient with complex pathology with minimal morbidity.

Stent modeling using immersed finite element method

The objective of this paper is to study the mechanical behaviors of angioplasty stents during and after implantation using a fluid–structure interaction computational technique. The deployment of a balloon expandable stent is simulated using immersed finite element method (IFEM), which was developed for solving complex fluid and deformable structure interaction problems. Using this method, we modelled a stainless steel stent in a blood vessel. A balloon is deployed to assist the expansion of the stent that is to be plastically deformed. The balloon is modelled as a thin hyperelastic material while the stent has the property of steel. The mechanical behaviors such as the expansion mechanism, stress distribution on the stent, and the surrounding fluid velocity profile during the implantation of the stent are studied. With appropriate applied internal pressure, the balloon inside the stent is deployed which linearly expands the diameter of a Medtronic AVE Modular Stent S7 until it reaches 1.7 times of its original diameter. The results will assist in the development of novel stent designs and stent deployment protocols to minimize vascular injury during stenting and reduce restenosis.

Modular branched stent graft for endovascular repair of aortic arch aneurysm and dissection.

We describe a modular stent graft for use in endovascular repair of aneurysms of the aortic arch. Carotid-carotid and left carotid-subclavian bypass grafts are created surgically. Two large, fully stented grafts are inserted endoluminally. The proximal component is bifurcated, with a wide proximal trunk and two distal limbs, one long and narrow, the other short and wide. This component is inserted through the carotid artery and deployed with the trunk and short wide limb in the ascending thoracic aorta; the long narrow limb opens into the innominate artery. After delivery system removal and carotid artery repair, a distal component is inserted through a femoral approach to bridge the gap between the short, wide distal limb of the proximal component and the nondilated descending thoracic aorta. The result is a branched stent graft, implanted proximally into the ascending aorta and distally into the innominate artery and descending thoracic aorta. The system has been used successfully to treat a large wide-necked pseudoaneurysm of the aortic arch.

Changes in the Proximal Neck of Abdominal Aortic Aneurysms Early after Endovascular Treatment

Long-term success of endovascular treatment of infrarenal abdominal aortic aneurysms (AAA) depends on secure "attachment" of the stent to the proximal and distal necks of the aneurysm. The purpose of this retrospective study was to detect changes in the proximal neck early after endovascular treatment of infrarenal AAA. Between November 1997 and December 1998, we performed endovascular treatment of infrarenal AAA in 43 patients. A bifurcated modular stent (AneuRx by Medtronic) was used in all patients. An oversized stent with a diameter 10% greater than the preoperative diameter of the proximal neck of the AAA was used in all cases. Follow-up examinations were carried out at 1, 6, and 12 months using plain roentgenography, color Doppler ultrasound, and CT scan with contrast injection. Statistical analysis was performed using the Student's t-test. Deterioration of the aortic neck is the result of a variety of mechanisms. The natural history of the infrarenal neck of AAA following endovascular repair (as well as conventional open repair) is progressive enlargement. Stenting could be an added risk factor for expansion. Strict follow-up is essential for early detection of this complication.