Use of a balloon-expandable intravascular graft in the management of type B aortic dissection in an animal model

Mechanisms of aortic dissection: From pathological changes to experimental and in silico models

Aortic dissection continues to be responsible for significant morbidity and mortality, although recent advances in medical data assimilation and in experimental and in silico models have improved our understanding of the initiation and progression of the accumulation of blood within the aortic wall. Hence, there remains a pressing necessity for innovative and enhanced models to more accurately characterize the associated pathological changes. Early on, experimental models were employed to uncover mechanisms in aortic dissection, such as hemodynamic changes and alterations in wall microstructure, and to assess the efficacy of medical implants. While experimental models were once the only option available, more recently they are also being used to validate in silico models. Based on an improved understanding of the deteriorated microstructure of the aortic wall, numerous multiscale material models have been proposed in recent decades to study the state of stress in dissected aortas, including the changes associated with damage and failure. Furthermore, when integrated with accessible patient-derived medical data, in silico models prove to be an invaluable tool for identifying correlations between hemodynamics, wall stresses, or thrombus formation in the deteriorated aortic wall. They are also advantageous for model-guided design of medical implants with the aim of evaluating the deployment and migration of implants in patients. Nonetheless, the utility of in silico models depends largely on patient-derived medical data, such as chosen boundary conditions or tissue properties. In this review article, our objective is to provide a thorough summary of medical data elucidating the pathological alterations associated with this disease. Concurrently, we aim to assess experimental models, as well as multiscale material and patient data-informed in silico models, that investigate various aspects of aortic dissection. In conclusion, we present a discourse on future perspectives, encompassing aspects of disease modeling, numerical challenges, and clinical applications, with a particular focus on aortic dissection. The aspiration is to inspire future studies, deepen our comprehension of the disease, and ultimately shape clinical care and treatment decisions.

Review of Current Advances in the Mechanical Description and Quantification of Aortic Dissection Mechanisms

Aortic dissection is a life-threatening event associated with a very poor outcome. A number of complex phenomena are involved in the initiation and propagation of the disease. Advances in the comprehension of the mechanisms leading to dissection have been made these last decades, thanks to improvements in imaging and experimental techniques. However, the micro-mechanics involved in triggering such rupture events remains poorly described and understood. It constitutes the primary focus of the present review. Towards the goal of detailing the dissection phenomenon, different experimental and modeling methods were used to investigate aortic dissection, and to understand the underlying phenomena involved. In the last ten years, research has tended to focus on the influence of microstructure on initiation and propagation of the dissection, leading to a number of multiscale models being developed. This review brings together all these materials in an attempt to identify main advances and remaining questions.

Biomechanical Changes After Thoracic Endovascular Aortic Repair in Type B Dissection

Thoracic endovascular aortic repair (TEVAR) has evolved into an established treatment option for type B aortic dissection (TBAD) since it was first introduced 2 decades ago. Morbidity and mortality have decreased due to the minimally invasive character of TEVAR, with adequate stabilization of the dissection, restoration of true lumen perfusion, and subsequent positive aortic remodeling. However, several studies have reported severe setbacks of this technique. Indeed, little is known about the biomechanical behavior of implanted thoracic stent-grafts and the impact on the vascular system. This study sought to systematically review the performance and behavior of implanted thoracic stent-grafts and related biomechanical aortic changes in TBAD patients in order to update current knowledge and future perspectives.

Human ex-vivo model of Stanford type B aortic dissection

OBJECTIVE

To report a new human ex vivo model of type B aortic dissection (TBAD) and to assess if the locations of the primary entry tear determine the patterns of dissection propagation.

METHODS

Twenty fresh human aortas were harvested. TBADs were surgically initiated 2 cm below the left subclavian artery at four different locations (lateral, n = 5; medial, n = 5; anterior, n = 5; posterior, n = 5). Aortas were thereafter connected to a bench-top pulsatile flow model to induce antegrade propagation of the dissection.

RESULTS

Antegrade propagation of the dissection was achieved and reached at least the celiac trunk (CT) in all the cases. Dissection was propagated to the renal aorta in 16 (80%) and infrarenal aorta in seven cases (35%). Left renal artery with or without the CT originated more often from the false channel when primary entry tear was lateral. Right renal artery and the CT most often originated from the false channel when primary entry tear was medial. When the CT was the only one originating from the false channel, primary entry tear was more often anterior, whereas when it originated from the true channel, it was more often posterior.

CONCLUSIONS

This human ex vivo model of TBAD is reproducible, since, in all the aortas, extended dissection was achieved and provides the first model of human aortic dissection with infrarenal aorta extension allowing future assessment of endovascular devices developed for human use. Furthermore, it allows clarification of the patterns of aortic dissection propagation and visceral and renal artery involvement according to the site of the primary entry tear.

An experimental model of Stanford type B aortic dissection

PURPOSE

To create an experimental model of aortic dissection with a long-lasting patent false lumen as a proper animal model for development of less-invasive treatment for aortic dissection.

MATERIALS AND METHODS

Fifteen adult beagle dogs (weight, 10-12 kg) were used. The descending aorta was exposed by a left thoracotomy at the sixth intercostal space. The entry for the aortic dissection was created surgically just distal to the origin of the left innominate artery and the reentry was 5 cm distal to the entry point. Normal saline solution was injected into the aortic wall (ie, media) between these two points to create the dissection. The dogs were followed up at 1 day, 3 months, 1 year, and 2 years.

RESULTS

All 12 surviving dogs had completely patent true and false lumina without any thrombi. Microscopic examination showed that the dissection was created in the tunica media layer, making it identical to aortic dissection in humans. Color Doppler imaging confirmed the patency of the true and false lumina and the relatively narrowed true lumen.

CONCLUSION

In this canine model of aortic dissection, the false lumen has excellent long-term patency and the dissection plane is histologically similar to that in human aortic dissection. This model may contribute to the development of new treatments for Stanford type B aortic dissection.

Dissection of the abdominal aorta in blunt trauma: endovascular or conventional surgical management?

BACKGROUND

Dissection of the abdominal aorta caused by blunt trauma is a rare injury, often complicated by thrombosis within the true and false lumens and sometimes aortic rupture. The mortality rate with conservative medical management is approximately 75%, whereas it ranges from 18% to 37% with surgical treatment.

METHODS

At our institution, 7 of the 87 patients admitted because of blunt aortic trauma, between January 1995 and January 2002, had abdominal aortic dissection.

RESULTS

Four patients were treated using endovascular techniques by percutaneous stent placement. The indications for endovascular management were lower limb ischemia in one case and extension of the dissection in two; one patient was asymptomatic. Aortic dissection was complicated by ischemic paraplegia in two patients, and both were treated by conventional operative repair. One patient was managed medically because of a minimal intimal disruption. No deaths were related to the aortic dissection or its treatment. Angiographic and computed tomographic (CT) studies showed thrombosis of the false lumen and complete obliteration of the dissection in the endovascular group. The neurologic condition of the two paraplegic patients either cleared completely or partially improved.

CONCLUSION

In the absence of ischemic paraplegia or other injuries that require emergency surgery, endovascular treatment is a safe and efficient method for treating traumatic infrarenal aortic dissection.

Intraluminal rotatory device: a hypothesized new approach for the treatment of type B aortic dissections

Acute dissection is the most common and frequently fatal catastrophic event to effect the aorta. Current treatments are unsatisfactory, particularly for Type B dissections where the mortality is excessive (approaching 33%) yet the late complication rate is high. It is hypothesized that an alternative approach would be to introduce an intraluminal freely rotating device via the femoral artery to lie adjacent to the site of the initial intimal tear. As a result it is predicted that the local shear stress would become zero, effectively arresting the dissection process. At the same time, the centrifugal force developed by the device would oppose the layers of the dissection, increasing the likelihood of false lumen obliteration. Such an approach may result in less short-term mortality and a lower long-term complication rate than current treatments.

Development of a symmetric canine abdominal aortic aneurysm model with clinical relevance for endovascular graft studies

This study was designed to develop a large-animal model to study and validate transluminally placed endovascular grafts and related techniques for treating abdominal aortic aneurysms with minimal trauma. In four dogs, a segment of infrarenal abdominal aorta was dissected and an endarterectomy was performed through an aortotomy to remove the entire intima of this controlled aortic segment. The opening was patched with chemically processed bovine pericardium, and an identical patch was applied after aortotomy of the opposite side of the aorta. Aortic diameter and flow were measured before and after the procedure. Angiograms were obtained just before retrieval. All dogs recovered quickly with no complications. Aortic diameter increased approximately 2.7-fold. Aneurysm size and shape remained stable until the end of the experiments at 4 or 8 weeks. Gross and histologic studies for 4- and 8-week specimens were similar. Factor VIII/von Willebrand factor staining showed complete reendothelialization of the endarterectomized wall, with a moderate degree of intimal hyperplasia. The patch material retained its acellular nature and its surface was covered with thrombus or fibrinous material mixed with blood cells and inflammatory cells. Thus, this model is feasible and suitable for endovascular graft healing studies.

Treatment of Stanford type B aortic dissection with stent-grafts: preliminary results

PURPOSE

To evaluate the feasibility and safety of endovascular stent-graft placement in treating Stanford type B aortic dissection.

MATERIALS AND METHODS

Seven patients underwent endovascular stent-graft placement for type B aortic dissection. Five patients had acute and two had chronic dissection. In five patients, the proximal entry tear was within 2 cm of the origin of the left subclavian artery, and in two patients it was beyond this site. In three patients, the noncovered proximal portion of the stent-graft was placed across the origin of the left subclavian artery. The efficacy of the procedure was assessed at follow-up studies 3, 6, 12, and 24 months after intervention.

RESULTS

The procedure was technically and clinically successful in six patients (86%). The left subclavian artery remained patent in all patients. In two patients with involvement of aortic branches, endovascular stent-graft placement restored adequate blood flow to the compromised branches. One patient was readmitted 1 month later because the dissection extended into the ascending aorta. In all but this patient, closure of the entry tear and thrombosis of the false lumen along the stent-graft were achieved. All false lumina shrank considerably. The mean follow-up time was 14 months (range, 1-25 months).

CONCLUSION

Type B aortic dissections within and beyond 2 cm of the origin of the left subclavian artery can be treated safely and effectively by means of endovascular stent-graft placement.

Endovascular management of traumatic infrarenal abdominal aortic dissection

Dissection is a recognized finding after blunt trauma to the abdominal aorta. Immediate and long-term prognosis is poor without surgical treatment especially since most patients present severe associated injuries. On the basis of encouraging results using endovascular techniques to treat experimental dissection of the descending thoracic aorta, we treated three patients with traumatic infrarenal abdominal aortic dissection by percutaneous stent placement. There were two men 34 and 41 years of age and one 89-year-old woman. In all patients, dissection began in the infrarenal portion of the aorta and extended into the iliac arteries. All patients had multiple associated injuries. The main symptoms were acute abdominal pain (two patients) and ischemia of the lower extremities (two patients). Diagnosis was missed in one patient despite exploratory laparotomy for an associated injury. Two patients were treated in the acute phase by placement of a self-expanding endovascular prosthesis at the aortoiliac level. The third patient was treated in the chronic phase by placement of a balloon-expandable endovascular stent. All procedures were performed uneventfully by femoral route. Success of treatment was confirmed by arteriography and computed tomography (CT) scan demonstrating obliteration of the dissection. Upon late follow-up examination, all patients were in satisfactory condition, with normal Doppler ultrasound findings. These findings confirm experimental studies using endovascular treatment for dissection of the descending thoracic aorta and are promising for future clinical management.

Noncoronary vascular stenting

The aim of this report is to review the current state of the art with respect to noncoronary vascular stenting. A review of the literature was performed, examining the historical aspects of stent design and usage, as well as the currently available designs and their respective functions. When appropriate, we note our personal experience with stent placement in each anatomic site. Currently available stents take many forms: balloon-expandable, self-expanding, and shape-memory alloy. Varied design modifications have been made to maximize the open area, to limit the surface area of the prosthesis, to increase (or decrease) flexibility, and to increase (or decrease) stent plasticity and elasticity. Modifications to minimize thrombogenicity are also underway. The clinical uses of the currently available stents in multiple anatomic locations will be discussed. Intravascular stents are an addition to the arsenal available for prolonging blood vessel patency.

Aortic dissection: percutaneous management of ischemic complications with endovascular stents and balloon fenestration

PURPOSE

The purpose of this study was to evaluate endovascular stenting (EVS) and balloon fenestration (BF) of intimal flaps for the management of lower extremity, renal, and visceral ischemia in acute or chronic aortic dissection.

METHODS

Twenty-two patients (16 male, 6 female) with a median age of 53 years (range 35 to 77 years) underwent percutaneous treatment for peripheral ischemic complications of 12 type A (five acute, seven chronic) and 10 type B (nine acute, one chronic) aortic dissections.

RESULTS

Ten patients had leg ischemia, 13 had renal ischemia, and 6 had visceral ischemia. Sixteen patients were treated with EVS including 11 with renal, 6 with lower extremity, 2 with superior mesenteric artery, and 2 with aortic stents. Three patients had BF of the intimal flap, and three had BF in combination with EVS. Revascularization with clinical success was achieved in all 22 patients. Two patients died 3 days and 13.4 months after the procedure was performed, respectively. Of the remaining 20 patients, 1 is lost to follow-up, and 19 have persistent relief of clinical symptoms. Mean follow-up time is 13.7 months (range 1.1 to 46.5 months). One case was complicated by guidewire-induced perinephric hematoma.

CONCLUSION

EVS and BF provide a safe and effective percutaneous method for managing peripheral ischemic complications of aortic dissection.