STENTING
Edmunds Endovascular Stent Management of Thoracic Aneurysms and Dissections
Endovascular Stent Grafting of Descending Thoracic Aortic Aneurysms
Endovascular Stent-Grafts For Thoracic Aneurysms And Dissections
Frozen Elephant Trunk Procedure
Endovascular Stent Repair of Abdominal Aortic Aneurysm
Endovascular Stent Grafting of Descending Thoracic Aortic Aneurysms
Endovascular stent grafting of the descending thoracic aorta is receiving increasing attention, as it is a promising, less-invasive alternative to open surgical repair. Aortic stent-grafts first were used to exclude abdominal and, later, thoracic aortic true and false aneurysms. These grafts have been increasingly used to treat aneurysms, dissections, and traumatic ruptures of the descending thoracic aorta with good early and mid-term outcomes. Annually, thoracic aortic aneurysms affect approximately 6 persons per 100,000 population, and the descending thoracic aorta is involved in about 40% of those cases. Thoracic aortic aneurysms typically occur in elderly patients who have hypertension, coronary artery disease, and obstructive pulmonary disease, and are heavy smokers. Most of these aneurysms are incidentally diagnosed and are usually asymptomatic. Untreated patients with large thoracic aortic aneurysms have a 2-year mortality rate of > 70%, with most deaths occurring due to aneurysm rupture. Surgery in the distal thoracic aorta is challenging due to the imminent risk of high morbidity, including paraplegia, renal failure, stroke and prolonged ventilatory dependence, and mortality.3 Continued refinement of the endovascular approaches has decreased the need for open thoracic aortic aneurysm repair, especially in patients who are at high risk when undergoing conventional surgery. Patients who were not candidates for repair because of medical comorbidity may now be relatively safely treated with endovascular repair. The following description of an index case draws attention to the intricate issue of this serious disease in a high-risk category, and demonstrates a new therapeutic modality for patients in whom the outcome would otherwise be futile.
Historical Perspectives
Since the first endoluminal approach was described
by Dotter and Judkins6 in 1964, significant advances have been made in the field of vascular disease. Parodi and associates7 in 1991 reported the first successful clinical endovascular graft repair of an aortic aneurysm (ie, the infrarenal abdominal aorta) in Argentina. Subsequently, endovascular grafts have been used to treat a variety of arterial pathologies, including abdominal aortic aneurysms, thoracic aortic aneurysms, iliac artery aneurysms, occlusive disease, and traumatic lesions, with promising short-term and mid-term results.8 Successful endovascular balloon fenestration of a dissecting descending aortic membrane also was performed to treat mesenteric ischemia.9 Endovascular stent-graft placement as a minimally invasive and potentially safer treatment for aneurysms of the descending aorta was introduced in 1992. In 1994, Dake and associates10 evaluated the feasibility of a transluminal stent-graft placement to treat descending thoracic aortic aneurysms, including two patients with dissections. The placement of stent-graft prostheses was successful in all 13 patients. Despite the less invasive nature of the procedure and the quicker recuperation of the patient, reports of stent-graft use to exclude descending thoracic aortic aneurysms have been limited to a few case series and to isolated cases.
Advantages and Feasibility
Endovascular stent-grafting carries certain advantages
and limitations (Table 1). For example, the avoidance of thoracotomy potentially reduces the incidence of pulmonary complications, and patients with severe pulmonary compromise may not tolerate the single-lung ventilation that is needed for the ideal exposure of the descending thoracic aorta for open repair. In addition, avoiding the cross-clamping of the aorta may reduce complications such as paraplegia, renal failure, myocardial infarction, heart failure, and downstream embolization. Spinal cord ischemia with resultant paraplegia is of significant concern to all surgeons treating descending thoracic aortic aneurysms, and the endovascular stent-graft holds the potential for reducing the risk in patients who are at high risk for spinal cord ischemia. The role of catheter-based intraluminal stentgrafting in patients with thoracic aortic disease is undergoing active clinical investigation, and the results of short-term follow-up of endografting of aortic aneurysm are encouraging.8 Experience with the endovascular treatment of various aortic aneurysms demonstrates the feasibility of this approach even in unstable patients.8 Another advantage of the endovascular repair of the ruptured thoracic aortic aneurysm is its potential to reduce blood loss. The value of diminished blood loss may be far greater in patients with ruptured aneurysms, because these patients might already have lost a significant amount of blood from the rupture and further blood loss could precipitate shock, which is a devastating complication particularly with an extensive thoracic aortic dissection. In addition, the main sources of blood loss during standard surgical repair such as backbleeding from branch arteries, from anastomotic sites, and from iatrogenic venous injuries can be eliminated during endovascular repair.8 Transfemoral endovascular repair of thoracic aortic aneurysms can be performed under local anesthesia, culminating in a very simple and fast-track procedure.11 A recent study12 demonstrated that in 96% of cases of descending thoracic aneurysms, the endovascular stent-grafts were deployed successfully. There was no operative mortality, and only in one patient did stent dislocation into the aneurysm require subsequent open surgical repair. The technical feasibility of the procedure could be enhanced by CT scanning. A three-dimensional model can be constructed from helical CT scan images of a thoracic aortic aneurysm to assist in stent-graft design and in successful endoluminal positioning. In one study,13 109 stentgrafts in 101 patients were designed by this method and were deployed well in all patients. The design time also has been reduced from 4 to 0.5 h with experience.13
Prerequisites to Endovascular Stent-Graft Placement
In addition to the physical condition of the patient,
anatomic, device-specific, and technical matters must be addressed before considering transluminal placement of endovascular stent-grafts for the treatment of thoracic aortic aneurysms. The physical condition of the patient should take into account the life expectancy of the patient and the potential risks of conventional open repair. The major anatomic prerequisites to be considered include the localization and morphology of the aneurysm, the distal vascular access of a sufficient size, and a limited tortuosity of the abdominal and thoracic aorta. The safe transfemoral, endoluminal deployment of an aortic device depends on the anatomy (ie, the configuration of the aneurysm and the relationships of the aneurysm neck with the nearby major aortic arterial branches, mainly the left subclavian artery and the celiac axis) and on the vascular accessibility (through the iliac arteries).10 Device-specific issues include the delivery system, the graft material, and the metal support frame. The ideal device components are detailed in Table 2. The major objectives for successful endovascular stenting include access to the target deployment site, secure endograft fixation, and creation of a hemostatic seal between the graft and the native vessel wall, and between the modular graft components.
Complications
Although the short-term results are encouraging,
severe complications, including paraplegia, cerebral strokes, and aortic rupture, have been encountered (Table 3). Mitchell et al14 reported on 44 patients who underwent thoracic aortic stent-grafting, and there were three early deaths (ie, in 30 days), two late deaths, and two instances of paraparesis or paraplegia. Deaths were attributable to graft failure, aneurysmal expansion, or aortic rupture. In another study,15 the reported occurrences of paraplegia, stroke, and early mortality were 3%, 7%, and 9%, respectively. Although the endovascular repair of a thoracic aortic aneurysm shows a promising reduction in operative morbidity, the risk of spinal cord ischemia exists but is lower than that seen with open surgical repair.16 Concomitant or previous abdominal aortic aneurysm repair and long-segment thoracic aortic exclusion appear to be important risk factors for spinal cord ischemia. Spinal cord protective measures, such as cerebrospinal fluid drainage, the use of steroids, and the prevention of hypotension, should be used for patients with the aforementioned risk factors who are undergoing endovascular thoracic aortic aneurysm repair. The occurrence of paraplegia seems to be related to extensive stent grafting but not with short stents (ie, those <15 cm) and in the consecutive approach instead of the single approach if longer segments have to be stented.17 Monitoring before stent deployment of the evoked spinal cord potential during placement of a retrievable stent graft in the descending thoracic aortic aneurysm (to temporarily interrupt the intercostal arteries) can be a predictor of spinal cord ischemia after permanent stent graft placement.18 Other procedure-related complications with aortic endovascular stent placement are bowel infarction, renal failure, lower extremity embolism, false-lumen rupture, and postimplantation syndrome (ie, transient elevations of body temperature and C-reactive protein levels, and mild leukocytosis) with the reported incidence of these complications ranging from 0 to 75%.1823 Possible late complications include stent-graft migration or prolapse into the aneurysm, kinking of the endograft and aorta, endovascular leakage, infection, and aortic rupture.15,2428 Dake et al15 reported late stent-graftrelated complications in 38% of descending thoracic aortic aneurysm patients with stent-graft placement, including stent-graft migration, endovascular leakage, aortic dissection, distal embolization, gut ischemia, and infection. Fatal complications occurred in 4% of patients, including rupture of the treated aneurysm, stent-graft erosion into the esophagus, arterial injury, and excessive hemorrhage. Only 53% of patients at 3.7 years of follow-up were free of treatment failure, which was defined as early death, late death related to complications from the treated aortic segment, endovascular leakage, or the need for subsequent intervention.15
Comparison With Open Surgical Repair
Given a choice, most patients would opt for a
simpler, less invasive, less painful procedure, but most vascular surgeons prefer a cure as opposed to palliation as endovascular stent-grafting does not provide freedom from rupture. However, in an older, sicker population, any lack of certainty about a long-term cure after endovascular stentgraft repair seems less relevant. Thus, the decision to recommend one type of thoracic aortic aneurysm treatment over another is quite subjective, varies among institutions, and is governed by anatomic factors, comorbid conditions, the technical skills of the operator, and the availability and accessibility of the resources. In properly selected patients, endovascular repair appears to be comparable to the conventional open repair,2831 particularly in high-risk patients. As the endovascular devices are constantly improving and changing, a prospective randomized trial that matches patients with similar risks and descending thoracic aortic morphology to compare the endovascular treatment with an open surgical repair is far from a reality.
Current Perspectives
Although the treatment of thoracic aortic aneurysms
remains challenging, several institutions have substantiated the safety and effectiveness of stent grafts in the repair of these aneurysms. Currently, custom-designed, off-the-shelf, and home-made aortic stent-grafts are being used, and no thoracic aortic stent-grafts are commercially available in the United States. However, several aortic stent-grafts are now commercially available outside the United States (Table 4), and, with time, more and more physicians will acquire the skills required for the endovascular treatment of vascular pathologies. At the present time, the long-term durability of the currently available stent-graft systems is a concern, but with further technical advances it may become the procedure of choice in a substantial number of patients with descending thoracic aortic aneurysms, especially those who are at high risk for surgical repair due to advanced age or comorbid conditions.
Conclusion
The placement of endoluminal stent-grafts to exclude the rupture sites of descending thoracic aortic aneurysms is a technically feasible and relatively safe procedure. It may improve the short-term outcomes of patients with dissecting thoracic aneurysms with or without rupture or dissection. Extended follow-up is necessary to determine the long-term outcome. At the present time, it seems to be an acceptable option in high-risk elderly patients and in patients for whom no other feasible therapy exists.
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