Thoracic aortic parallel stent-graft behaviour when subjected to radial loading

Do Balloon Catheters have a Different Radial Force Along Their Longitudinal Axis?

PURPOSE

This experimental study was designed to compare radial forces between the central portion and both ends of balloon catheters when dilating stenosis.

MATERIALS AND METHODS

Three balloon catheters of 6 and 8 mm in diameter and of variable length were tested: Mustang, Conquest, and Genoss PTA. Cylindrical modules to position balloon catheters and install the measuring tip during radial force measurements were made using a 3D printer. The measuring tip created 20% stenosis at the inner lumen. Both ends and center of the balloon catheter were located at the measuring tip. The radial force was measured after inflating the balloon catheter to the rated burst pressure.

RESULTS

For the different diameters and lengths of balloon catheters and cylinder sizes, the median inccenter, the radial rease in radial force at the distal end compared to the center was 16.5% (range: 9.8-35.2%) for Mustang, 12.4% (range: 10.3-25.5%) for Genoss, and 7.4% (range: -0.3-13.1%) for Conquest balloon catheters. Similarly, compared to that at the force at the proximal end was 10.8% greater (range: -2.9-18.3%) for Mustang, 9.9% greater (range: 3.9-22.3%) for Genoss, and 7.3% greater (range: -1.3-12.4%) for Conquest catheters.

CONCLUSION

The radial force is greater at both ends of the balloon than at the central portion, especially at the distal end. Dilation using the distal end of the balloon catheter is a practical method that can be applied in clinical practice without additional devices when encountering resistant stenosis, especially with semi-compliant balloons.

In vitro quantification of stent-graft behaviour during chimney thoracic endovascular aortic repair

OBJECTIVE

To quantify dynamic gutter phenomena and endograft deformations during double chimney thoracic endovascular aortic repair (ch-TEVAR) in a physiological model of the thoracic aorta subjected to pulsatile haemodynamic conditions.

METHODS

Two in vitro procedures revascularizing the brachiocephalic trunk and left common carotid artery were performed representing both balloon-expandable (BE, Ankura-BeGraft) and self-expandable (SE, Ankura-Viabahn) double ch-TEVAR configurations. Retrospectively gated computed tomography (CT) was used to evaluate endograft behaviour. Device interactions were characterised according to gutter volume, gutter surface deviation, and endograft deformation (D-ratio) at end-diastolic and peak-systolic aortic pressure.

RESULTS

Use of BE chimney grafts resulted in three times total gutter volume compared to SE chimney grafts. Gutter volumes were observed to vary dynamically between the end-diastolic and peak-systolic phases of the cardiac cycle, with the most substantial change associated with the BE configuration. Chimney graft deformations were dependent on device type, with SE devices exhibiting up to twice the deformation as BE devices. When adjacent, SE chimney grafts were observed to support each other, and thus tended towards a more consistently circular shape.

CONCLUSION

Gutter and chimney graft behaviour were dependent on device type, and exhibited both spatial and temporal variability. This study emphasises notable differences between BE and SE double ch-TEVAR configurations which should be considered when evaluating risk of endoleak. The findings reported here also support the use of gated CT to better identify device-related complications with ch-TEVAR, and can be used in the design of next generation devices.

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

PURPOSE

Inappropriate 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.

METHODS

In 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.

RESULTS

SG 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%).

CONCLUSIONS

SG 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.

Midterm Outcomes of Multicenter Castor Single-Branch Stent Graft Use in the Treatment of Thoracic Aortic Diseases

PURPOSE

The aim of this study was to evaluate the midterm efficacy and safety of a single-branch Castor stent graft in the treatment of thoracic aortic disease.

MATERIALS AND METHODS

Clinical data of 106 patients with thoracic aortic disease treated with Castor single-branch stent graft at 3 centers were collected between May 2018 and June 2023. The indicators included technical success, stent-related complication, reintervention, retrograde dissection, endoleak, distal stent graft-induced entry (dSINE), branch patency, and mortality. The outcomes of the Castor stent graft for multibranch reconstruction above the arch was also analyzed.

RESULTS

The technical success was 98.1% (104/106), while the surgical success was 93.4% (99/106). The reintervention was 2.8% (3/106), consisting of a case of retrograde type A dissection, an endoleak, and a dSINE. The retrograde dissection was 1.9% (2/106), while type I endoleak was 1.9% (2/106). The new dSINE was 2.8% (3/106), and the branch patency rate was 100%. The mortality was 1.9% (2/106). The mean follow-up time was 29.1±17.7 months. The 2-year post-surgery cumulative survival rate was 91.0%±3.1%, while the cumulative branch patency rate was 96.2%±2.2%. In addition, the cumulative freedom from stent-related reintervention rate was 93.2%±2.8%. A comparison showed no significant difference in the stent-related complication, branch patency, endoleak, reintervention, and mortality when the proximal end of the Castor stent graft was anchored to zones 1 or 2 of the aorta.

CONCLUSION

Castor single-branch stent graft showed favorable early and midterm outcomes in the treatment of thoracic aortic disease. In addition, it was feasible to combine Castor stent graft with other advanced techniques for multibranch aortic arch reconstruction.

CLINICAL IMPACT

The Castor single-branch stent graft was approval by the Chinese Food and Drug Administration in 2017. However, there were few studies on the mid-term outcomes for thoracic aortic disease after launching, which mainly focused on small single-center retrospective study. In the study, we assessed the mid-term outcomes of Castor stent graft through multi-center cases, Castor stent graft combined with other advanced techniques (such as fenestration and hybrid) for multi-branch reconstruction of aortic arch were also conducted. We found Castor single-branch stent graft showed favorable early and mid-term outcomes in the treatment of thoracic aortic disease. Additionally, it was feasible to combine Castor stent graft with other advanced technique for multi-branch aortic arch reconstruction. As an off-the-shelf branched stent graft with a wide range of models, it could be also used in most emergent situation. The Castor stent graft was expected to become more widely used in the future.

Computational analysis of endovascular aortic repair proximal seal zone preservation with endoanchors: A case study in cylindrical neck anatomy

BACKGROUND

Endovascular aortic repair is the common approach for abdominal aortic aneurysms, but endoleaks remain a significant problem with long-term success. Endoanchors have been found to reduce the incidence of type 1A endoleaks and can treat intraoperative type 1a endoleaks. However, little is known about the optimal number and position of endoanchors to achieve the best outcome.

METHODS

Using image segmentation and a computational model derived from a reconstructed native patient abdominal aortic aneurysm geometry, the stability of the proximal seal zone was examined through finite element analysis in Abaqus (Dassault Systèmes, Providence, RI). The biomechanical parameter of contact area was compared for varying numbers (0, 2, 4, 8) and positions (proximal, medial, distal) of endoanchors under different adhesion strengths and physiologic pressure conditions.

RESULTS

In every simulation, an increase in adhesion strength is associated with maintenance of proximal seal. For biologically plausible adhesion strengths, under conditions of normal blood pressure (120 mm Hg), the addition of any number of endoanchors increases the stability of the endograft-wall interface at the proximal seal zone by approximately 10% compared with no endoanchors. At hypertensive pressures (200 mm Hg), endoanchors increase the stability of the interface by 20% to 60% compared with no endoanchors. The positioning of endoanchors within the proximal seal zone has a greater effect at hypertensive pressures, with proximal positioning increasing stability by 15% compared with medial and distal positioning and 30% compared with no endoanchors.

CONCLUSIONS

Endoanchors improve fixation within the proximal seal zone particularly under conditions of high peak systolic pressure. Seal zone stabilization provides a mechanism through which endoanchor addition may translate into lower rates of type 1a endoleaks for patients.