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

Computational Investigation and Histopathological Validation of Interaction Between Stent Graft and Aorta in Retrograde Type A Dissection After TEVAR in Canine Models

PURPOSE

Retrograde type A dissection (RTAD) after thoracic endovascular aortic repair (TEVAR) has been a major drawback of endovascular treatment. To our knowledge, no studies have simulated and validated aortic injuries caused by stent grafts (SGs) in animal models. Therefore, the aim of this study was to evaluate and quantify the SG-aorta interaction through computational simulations and to investigate the underlying mechanism through histopathological examinations.

METHODS

Two custom-made Fabulous^® (DiNovA Meditech, Hang Zhou, China) SGs were implanted in 2 canine aortas with a 5-mm difference in the distance in landing locations. The aortic geometries were extracted from RTAD and non-RTAD cases. A computational SG model was assembled based on the implanted SG using the software Pro-ENGINEER Wildfire 5.0 (PTC Corporation, Needham, Mass). TEVAR simulations were performed 7 times for each canine model using Abaqus software (Providence, RI, USA), and the maximum aortic stress (MAS) was calculated and compared among the groups. Three months after SG implantation, the canine aortas were harvested, and were examined using hematoxylin and eosin staining and Elastica Van Gieson (EVG) staining to evaluate histopathological changes.

RESULTS

In the computational models for both canines, MAS was observed at the proximal bare stent (PBS) at aortic greater curve. The PBS generated higher stress toward the aortic wall than other SG parts did. Moreover, the MAS was significantly higher in canine No.1 than in canine No.2 (0.415±0.210 versus 0.200±0.160 MPa) (p<0.01). Notably, in canine No.1, an RTAD developed at the MAS segment, and histopathological examinations of the segment showed an intimal flap, a false lumen, elastin changes, and medial necrosis. RTAD was not observed in canine No.2. In both SG-covered aortas, medial necrosis, elastic fiber stretching, and inflammatory infiltration were seen.

CONCLUSION

The characteristic MAS distribution remained at the location where the apex of the PBS interacted with the aortic wall at greater curve. RTAD histopathological examinations showed intimal damage and medial necrosis at the proximal landing zone, at the same MAS location in computational simulations. The in vivo results were consistent with the computational simulations, suggesting the MAS at greater curve may cause RTAD, and the potential application of computational simulation in the mechanism study of RTAD.

Endo-Bentall for proximal aortic dissection: from conception to application

The endovascular treatment of pathologies of the ascending aorta has not been incorporated into routine clinical practice. The aim of this article is to provide an overview of the endovascular treatment of pathologies of the ascending aorta, particularly type A aortic dissection. A thorough analysis and discussion of anatomical, physiological, clinical and technical challenges, and obstacles is performed. Conventional straight stent-grafts alone are not capable of fixing the entire complex underlying problem in the vast majority of patients with acute type A aortic dissection. An endovascular valve-carrying conduit consisting of a proximal transcatheter aortic valve connected to a covered stent-graft would be able to close a primary entry tear in the ascending aorta, ensure coronary perfusion, initiate true lumen expansion, treat malperfusion, treat aortic regurgitation, drain any pericardial effusion through a transapical approach, and possibly stabilize the distal aorta. Two thirds of all patients with acute aortic dissection are potential candidates for endovascular treatment, and the concept may help to significantly improve survival in patients with acute aortic dissection.

Impact of Thoracic Endovascular Aortic Repair on Pulsatile Circumferential and Longitudinal Strain in Patients With Aneurysm

Purpose: To quantify both pulsatile longitudinal and circumferential aortic strains before and after thoracic endovascular aortic repair (TEVAR), potentially clarifying TEVAR-related complications. Methods: This retrospective study assessed the impact of TEVAR on pulsatile aortic strains through custom developed software and cardiac-gated computed tomography imaging of 8 thoracic aneurysm patients (mean age 71.0±8.2 years; 6 men) performed before TEVAR and during follow-up (median 0.1 months, interquartile range 0.1–5.8). Lengths of the ascending aorta, the aortic arch, and the descending aorta were measured. Diameters and areas were computed at the sinotubular junction, brachiocephalic trunk, left subclavian artery, and the celiac trunk. Pulsatile longitudinal and circumferential strains were quantified as systolic increments of length and circumference divided by the corresponding diastolic values. Results: Average pulsatile longitudinal strain ranged from 1.4% to 7.1%, was highest in the arch (p<0.001), and increased after TEVAR by 77% in the arch (7.1%±2.5% vs 12.5%±5.1%, p=0.04) and by 69% in the ascending aorta (5.6±2.3% vs 9.4±4.4%, p=0.06). Average pulsatile circumferential strain ranged from 3.6% to 5.0% before TEVAR and did not differ significantly throughout the thoracic aorta; there was a nonsignificant increase after TEVAR at the unstented sinotubular junction (5.0%±1.4% vs 6.3%±1.0%, p=0.18), with a significant increase at the celiac trunk (3.6%±1.8% vs 6.2%±1.8%, p=0.02). Pulsatile circumferential strains within stented segments were deemed unreliable due to image artifacts. Conclusion: TEVAR was associated with an increase of pulsatile longitudinal strains (in the arch) and circumferential strains (at the celiac trunk) in unstented aortic segments. These observations suggest increased pulsatile wall stress after TEVAR in segments adjacent to the device, which may contribute to the understanding of stent-graft–related complications such as retrograde dissection, aneurysm formation, and rupture.

Patient demographics and cardiovascular risk factors differentially influence geometric remodeling of the aorta compared with the peripheral arteries

BACKGROUND

Detailed knowledge of the dimensions and shape of the main arteries of the body and how they change with age and disease is important for understanding arterial pathophysiology and improving minimally invasive devices to treat arterial diseases. Our goal was to describe and compare geometric remodeling of the aorta and peripheral arteries in the context of patient demographics and cardiovascular risk factors.

METHODS

Three-dimensional reconstructions of computed tomography angiography scans were performed in 122 subjects 5-93 years of age (mean 47 ± 24 years, 64 M/58 F). Best-fit arterial diameters, lengths, and tortuosity for the principle named arteries in the chest, abdomen, pelvis, and upper thigh were measured, and multiple linear regression analysis was performed to examine how these morphologic parameters associate with patient demographics and risk factors.

RESULTS

Large elastic arteries increased their diameter, length, and tortuosity with age, whereas muscular arteries primarily became more tortuous. Demographics and risk factors explained >70% of the variation in diameters of the abdominal aorta, paravisceral aorta, and the aortic arch; and >75% of variation in tortuosity from the profunda femoris to the brachiocephalic artery. Male sex, larger body mass index, and hypertension contributed to larger diameters, whereas the presence of diabetes was associated with somewhat-straighter arteries. Overall, the effects of cardiovascular risk factors on geometric remodeling were small compared with those of demographics.

CONCLUSION

The geometry of the vascular tree is greatly affected by aging, demographics, and some risk factors. Elastic and muscular arteries remodel differently, possibly as the result of differences in their microstructure.