Thoracic endovascular stent grafting inhibits aortic growth: an experimental study

Assessment of Large Animal Vascular Dimensions for Intra-Aortic Device Research and Development: A Systematic Review

Animal studies are often required to evaluate new cardiovascular medical devices before they reach the market. Moreover, first-generation novel devices including aortic endovascular prostheses and circulatory support devices are often larger than later iterations or tested in a limited range of sizes. One of the challenges in evaluating these devices is finding a model that is both accessible and anatomically similar to humans, as there is a paucity of data on vascular dimensions in large animals. We set out to complete a comprehensive review of available reports on vascular dimensions in swine, ovine, and bovine models, with a particular focus on the descending aorta and ilio-femoral arteries. We searched Embase and MEDLINE databases for reports of descending aorta and peripheral vascular dimension in large animal models. Data from swine, ovine, and bovine models were separated by weight into 3 categories: 40 to 60 kg, 61 to 80 kg, and >80 kg. We also incorporate our computed tomography angiography data from 4 large sheep and 9 calves into this review. Swine, sheep, and calf >80 kg may serve as the best models to maximize aortic diameter resemblance to humans. If device implantation can be achieved in aortas of smaller dimensions, care should be taken to ensure access site suitability such as the common femoral artery in these smaller animals.

Can a self-expanding pediatric stent expand with an artery? Relationship of stent design to vascular biology

OBJECTIVES

A large-diameter, intravascular, self-expanding stent system capable of continued expansion during somatic and vascular growth was modeled with finite element analysis (FEA), manufactured and tested in an animal model.

BACKGROUND

Children can quickly outgrow intravascular stents. If a stent could expand after implantation in arteries this would be ideal for use in pediatric patients.

METHODS

Computer-aided design and FEA were used to design and manufacture large-diameter, self-expanding nitinol stents with both high and low chronic outward force (COF). Four distinct stents with similar designs but with variable lengths and strut thicknesses were manufactured. Fourteen of these stents were implanted in the abdominal aortas or iliac arteries of four juvenile swine.

RESULTS

All animals survived without complication to their designated time points of harvest (90 or 180-days), and all stents expanded to greater diameters than the adjacent non-stented artery. Luminal diameter growth was 34-49% and 20-23% for stented and non-stented segments, respectively. Histologic examination revealed variable degrees of the internal elastic lamina and/or medial disruption with a mean injury score ranging from 0.70 ± 0.56 to 1.23 ± 0.21 and low COF stents implanted in smaller arteries having a larger injury score. Inflammatory responses and stenosis formation were minimal and ranged from 0.50 ± 0.71 to 3.00 ± 0.00 and 5.52 ± 1.05% to 14.68 ± 9.12%, respectively. The stent's COF did not correlate with vessel expansion or vascular injury.

CONCLUSIONS

Self-expanding stents can mirror and even exceed somatic growth. Although longer-term testing is needed, it may be possible to custom tailor self-expanding stents to expand after arterial implantation in pediatric patients.

Open Conversion for Recurrent Endograft Occlusion after Endovascular Treatment of Blunt Traumatic Aortic Injury: A Peculiar Case Report

BACKGROUND

We report a rare case of delayed, symptomatic thoracic endograft thrombosis after the initial thoracic endovascular aortic repair (TEVAR) for blunt thoracic aortic injury which was successfully retreated with a redo TEVAR, followed by open conversion due to recurrent partial occlusion of the distal edge of the endografts.

METHODS

Two years ago, a 22-year-old man had undergone an emergency TEVAR for blunt thoracic aortic injury. A Zenith Cook 22 × 100 mm (Cook Incorporated, Bloomington, IN) endograft was used. Six months later, he underwent an emergency endovascular relining of the endograft using the same type of device. The multiorgan perfusion was completely restored except for the spinal cord injury. After 8 months, a recurrent partial occlusion of the distal edge of the second graft was documented. The thoracic aorta was replaced with a 22-mm silver-coated graft (Maquet Spain, SLU).

RESULTS

Histology examination showed a neointimal formation and thickening and fibrosis of the inner 1/3 of the media with loss of smooth muscle cells and increase of the elastic fibers.

CONCLUSIONS

The need for secondary interventions or open conversion because of potential complications after TEVAR for traumatic aortic injury is an additional consideration when weighing the risks and benefits of endovascular repair and subsequent surveillance strategies.

The Evaluation of Aortic Diameter Changes During Long-Term Follow-Up After Endovascular Treatment of Acute Blunt Traumatic Thoracic Aortic Injuries

Purpose:

To evaluate the variations in aortic diameters and long-term results in patients who underwent thoracic endovascular aortic repair (TEVAR) for acute blunt traumatic thoracic aortic injuries (BTTAIs).

Materials and Methods:

We retrospectively evaluated 23 patients with a mean age of 39 years (range: 17-74 years) who underwent TEVAR for BTTAI between October 2000 and November 2014. All of the patients underwent computed tomography angiography (CTA) before hospital discharge as a baseline imaging for the subsequent follow-up examinations. The technical success, overall survival, and complications were evaluated. Furthermore, the aortic diameters outside of the stent-graft (1 cm proximal and 1 cm distal to the stent-graft) and the aortic diameters within the stent-graft (2 cm distal to the proximal end and 2 cm proximal to the distal end) were assessed. The diameters at baseline on CTA were compared with those of the latest available follow-up examination.

Results:

Technical success was 100% with a mean follow-up of 65.4 months (range: 12-171 months). No death was registered, and 2 (8.7%) of 23 endograft-related complications (1 stent-graft distal infolding and 1 endoleak 2 and 4 months after the procedure, respectively) were observed. An increase in aortic diameter either proximal or distal to the stent-graft (mean value 0.7 and 0.5 mm, respectively) or within the stent-graft (mean value of 0.5 mm for both proximal and distal diameters) was registered (mean follow-up at 65.4 months, range: 12-171 months).

Conclusion:

Aortic dilatation following TEVAR for BTTAI is minimal during long-term follow-up. Endovascular treatment represents a durable and safe option in acute BTTAIs.

Delayed presentation of aortoesophageal fistula after endovascular repair

The incidence of aortoesophageal fistula after thoracic endovascular aortic repair has increased following an increase in thoracic endovascular aortic procedures. A 68-year-old man was diagnosed with aortoesophageal fistula 6 years after thoracic endovascular aortic repair of a descending aortic aneurysm. Due to massive hematemesis and instability, he underwent a left thoracotomy, graft repair of the aorta with stent removal, gastrostomy, and proximal esophagostomy. Unfortunately, he died 1 week later due to sepsis. Aortoesophageal fistula may present long after thoracic endovascular aortic repair, and clinicians treating such cases should always be aware of this complication.

Early histological changes in the porcine aortic media after thoracic stent-graft implantation

PURPOSE

To describe the histological findings in the aortic wall 5 days after thoracic endovascular aortic repair (TEVAR) in a porcine model.

METHODS

Two overlapping stent-grafts were implanted in each of 6 juvenile pigs, covering the entire descending thoracic aorta (DTA). On the 5(th) postoperative day, tissue samples were taken from the DTA in each animal. Medial thickness and medial necrosis were quantified and compared to measurements from the aortas of 6 control animals.

RESULTS

Significant medial thinning was observed in stent-covered regions in the test animals. At the proximal landing zone, aortic wall thickness changed from 1387±68 to 782±74 µm within the covered aortic segment (p = 0.028); at the distal landing site, the wall thickness was 365±67 µm within the stent and 501±57 µm distally (p = 0.028). In the overlap zone, the aortic wall measured 524±122 vs. 1053±77 µm in native controls (p = 0.004). Aortic thickness proximal to the graft did not differ from the proximal region of native aortas (1468±96 vs. 1513±80 µm, p = 0.423), but the aorta was significantly thinner distal to the stent (707±38 vs. 815±52 µm, p = 0.004). Laminar necrosis constituted 38%±7% of the media in the proximal landing zone, 54%±4% in the overlap zone, and 46%±13% in the distal landing zone.

CONCLUSION

In this porcine model, significant medial thinning and necrosis of the stented aorta was observed. The findings suggest an early phase of vulnerability of the aortic wall, before scarring and adaptive changes have strengthened the residual aorta.

Potential long-term complications of endovascular stent grafting for blunt thoracic aortic injury

Blunt thoracic aortic injury (BTAI) is a rare, but lethal, consequence of rapid deceleration events. Most victims of BTAI die at the scene of the accident. Of those who arrive to the hospital alive, expedient aortic intervention significantly improves survival. Thoracic endovascular aortic repair (TEVAR) has been accepted as the standard of care for BTAI at many centers, primarily due to the convincing evidence of lower mortality and morbidity in comparison to open surgery. However, less attention has been given to potential long-term complications of TEVAR for BTAI. This paper focuses on these complications, which include progressive aortic expansion with aging, inadequate stent graft characteristics, device durability concerns, long-term radiation exposure concerns from follow-up computed tomography scans, and the potential for (Victims of Modern Imaging Technology) VOMIT.

Extra-anatomic bypass for recurrent abdominal aortic and renal in-stent stenoses following radiotherapy for neuroblastoma

We describe the case of an 11-year-old girl with an abdominal neuroblastoma which was operated and intraoperatively irradiated nine years ago. After six years, she developed stenoses of the infrarenal abdominal aorta and both renal arteries. Initial treatment of the stenosed vessels comprised endovascular balloon dilatations and repeated stent-graft implantations, including drug eluting stents. However, severe in-stent stenoses occurred during follow-up and the girl developed acute renal failure. Open surgery was performed with two extra-anatomic bypasses, a thoracic-to-abdominal aortic bypass and a left iliac-to-renal bypass, on an urgent basis. The postoperative course was uneventful and the patient was discharged home two weeks after the operation with full recovery of renal function. We conclude that endovascular stent-graft placement in children can only be a palliative treatment due to outgrowing of the stent-graft and the potential risk of re-stenosis, especially after a history of irradiation. Vascular surgery with placement of extra-anatomic bypasses will provide a definite treatment.