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Ann Thorac Surg 2007;83:1635-1639
© 2007 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Endovascular Stent-Graft Placement of Aneurysms Involving the Descending Aorta Originating From Chronic Type B Dissections

Departments of Cardiothoracic Surgery and Interventional Radiology, University of Vienna Medical School, Vienna, Austria

Accepted for publication December 18, 2006.

^_* Address correspondence to Dr Czerny, Waehringer Guertel 18-20, Vienna A-1090, Austria (Email: martin.czerny{at}meduniwien.ac.at).

	Abstract

Top Abstract Introduction Patients and Methods Results Comment References

 
Background: The performance of endovascular stent-graft placement in patients suffering from aneurysms involving the descending aorta originating from chronic type B dissections is unclear.

Methods: Within a 2-year period, we treated 6 patients with this pathology. Four patients required extension of the proximal landing zone (autologous double transposition, n = 2; subclavian-to-carotid artery transposition, n = 2) before stent-graft placement.

Results: Supra-aortic rerouting procedures and endovascular stent-graft placement were performed successfully in all patients. Closure of the primary entry tear, full expansion of the stent-graft, and eventually, thrombosis of the false lumen was achieved in 5 patients. In 1 patient with a short proximal landing zone, a persisting type Ia endoleak was observed. In all patients with successful primary entry closure, a reduction in aneurysm diameter occurred. Mean follow-up is 16 months (range, 4 to 25).

Conclusions: Endovascular stent-graft placement of aneurysms involving the descending aorta originating from chronic type B dissections may serve as a valuable treatment option in this complex pathology. The chronic dissection membrane can be successfully compressed against large areas of the native aortic wall. A sufficient proximal landing zone is mandatory for early and late success.

	Introduction

Top Abstract Introduction Patients and Methods Results Comment References

 
Endovascular stent-graft placement has developed as a safe and effective treatment for various acute and chronic diseases of the thoracic aorta [1–6]. Whereas feasibility and effectiveness of this procedure are proven for acute type B dissections, little information is available regarding patients with late aneurysm formation on the basis of a chronic type B dissection [7–9]. It is not clear whether the self-expanding capacity of the stent-graft can compress the fibrous, potentially rigid, chronic dissecting membrane against the native aortic wall. A further concern is whether reperfusion of the false lumen through distal reentry sites may occur beneath the covered length of the dissected aorta.

The aim of this study was to evaluate the performance of endovascular stent-graft placement of aneurysms involving the descending aorta originating from chronic type B dissections.

	Patients and Methods

Top Abstract Introduction Patients and Methods Results Comment References

 
Between September 2004 and June 2006, 6 patients suffering from aneurysms involving the descending aorta originating from chronic type B dissections were treated at our department. There were 4 men and 2 women with a mean age of 63 years (range, 50 to 75). Three patients had already undergone previous cardiovascular procedures (ascending and hemiarch replacement due to acute dissection, n = 2; coronary artery bypass graft surgery, n = 1). Mean aneurysm diameter was 6.3 cm (range, 5.5 to 10.0 cm). Besides maximum diameter, the rapidity of expansion is basic to our decision making. We regard expansion of 6 mm or more within 6 months as rapid and will recommend these patients for treatment although they have not reached the generally accepted 6 cm maximum diameter. Mean numeric EuroSCORE (European System for Cardiac Operative Risk Evaluation) was 8.8 (range, 5 to 13) and mean logistic EuroSCORE was 17.1 (range, 5.2 to 39.4). Therefore, conventional surgical repair was deemed high risk. The Ethics Committee approved this study and waived the need for patient consent.

Preoperative Evaluation and Surgical Approach
Preoperative evaluation was by multisclice computed tomography scans to exclude major occlusive disease of the supra-aortic branches and of the aortoiliac axis. These studies assured later arterial access for stent-graft placement and the presence of a sufficient proximal neck of at least 1.5 cm. In 4 patients, supra-aortic rerouting procedures were necessary to create a sufficient proximal landing zone (autologous double transposition, n = 2; subclavian-to-carotid artery transposition, n = 2).

Autologous Double Transposition
The original method has been described in detail [10]. Through an upper hemisternotomy, the left common carotid artery is clamped, transversely dissected at its origin, and an end-to-side anastomosis is made between the left common carotid artery and the brachiocephalic trunk. An analogous procedure is carried out between the left subclavian artery and the transposed left common carotid artery.

Subclavian-to-Carotid Artery Transposition
Access is gained through a supraclavicular incision. The lateral insertion of the sternocleidomastoid muscle is transsected. After identification of the left vertebral artery, the subclavian artery is clamped and dissected at its origin, and an end-to-side anastomosis between the subclavian and left carotid artery is performed.

Stent-Graft Systems Used
Three different commercially available stent-graft systems were used. The Excluder (and later TAG) stent-graft (WL Gore, Flagstaff, Arizona) was used in 4 patients. The Talent endovascular stent-graft (Medtronic, Santa Rosa, California) was used in 1 patient. The Relay stent-graft (Bolton Medical, Sunrise, Florida) was used in another patient. For all systems, the diameter of the stent-graft was calculated from the largest diameter of the proximal or distal neck, and an oversizing factor of 10% to 20% was added.

Stent-Graft Placement
Stent-graft placement was performed during general anesthesia. In all patients, a common femoral artery access was chosen. Initially, a 5F pigtail catheter was advanced through the right brachial artery into the aortic arch to reconfirm the morphology and extent of the lesion. After systemic treatment with heparin 80 IU/kg bodyweight, an arteriotomy was made and the system was advanced under fluoroscopic guidance. Afterward, stent-grafts were deployed during systemic hypotension with a systolic pressure of 60 mm Hg.

	Results

Top Abstract Introduction Patients and Methods Results Comment References

 
Time Intervals and Supra-Aortic Rerouting Procedures
An exact description of all relevant variables of these patients is provided in Table 1. Mean interval between acute type B dissection and treatment of late aneurysm was 26 months (range, 4 to 84). All patients recovered uneventfully without any signs of transient or permanent neurologic injury after rerouting the supra-aortic branches. Furthermore, no adverse events with regard to spinal cord perfusion were observed.

Follow-Up Period
The mean follow-up period is 16 months (range, 4 to 25). Patients were readmitted for completion computed tomography scans after 3 months and biannually thereafter. In the 5, primarily successful, cases, full expansion of the stent-graft and thrombosis of the false lumen was achieved. In these patients, a reduction in aneurysm diameter was observed.

Figures 1, 2, and 3 show the course of a patient 6 years after acute type B dissection. After placement, the stent-graft is substantially compressed by the rigid chronic dissecting membrane. However, after 4 months, the stent-graft fully expanded, the true lumen enlarged, and the false lumen completely thrombosed in the thoracic aorta.

View larger version (133K): [in this window] [in a new window]   Fig 1. Aneurysm involving the descending aorta originating from a chronic type B dissection.

View larger version (136K): [in this window] [in a new window]   Fig 2. Computed tomography scan after endovascular stent-graft placement.

View larger version (112K): [in this window] [in a new window]   Fig 3. Computed tomography scan after 4 months, showing complete expansion of the stent-graft.

View larger version (118K): [in this window] [in a new window]   Fig 4. Computed tomography scan before stent-graft placement.

View larger version (147K): [in this window] [in a new window]   Fig 5. Computed tomography scan after stent-graft placement.

View larger version (119K): [in this window] [in a new window]   Fig 6. Computed tomography scan after 12 months, showing complete regression of the aneurysm.

	Comment

Top Abstract Introduction Patients and Methods Results Comment References

Conventional surgical therapy for aneurysms involving the descending aorta originating from chronic type B dissections remains very invasive despite substantial improvements in extracorporeal and anesthesiologic algorithms [11]. Endovascular stent-graft placement has proven its effectiveness in acute, particularly complicated, type B dissections [7–9]. However, little information is available for patients with late aneurysm formation on the basis of a chronic type B dissection, although the feasibility of endostenting has been demonstrated in individual cases [12, 13].

In this study, we focused on patients at high risk for conventional surgical repair. Three patients had already undergone previous cardiovascular procedures. Furthermore, owing to distal arch involvement and to the size of the aneurysm, proximal application of a clamp to initiate left heart bypass would not have been feasible. Thus, repair would have required deep hypothermic circulatory arrest and an open distal arch anastomosis.

As reported previously, early and late success of endovascular stent-graft placement directly correlates with the length of the proximal landing zone [5]. Therefore, we applied rerouting procedures in 4 patients to create a sufficient proximal neck [10]. This concept turned out to be successful in the majority of patients.

The distal landing zone is far more complex, and two different hypotheses have some rationale. One hypothesis regards the pathology of a chronic type B dissecting aneurysm as that of an atherosclerotic aneurysm. This interpretation requires the distal landing zone to be at least 1.5 cm to obviate subsequent reintervention.

The other hypothesis regards the pathology of a chronic type B dissection to be that of a dissection. If so, the length of the distal landing zone is unimportant because blood flow is redirected into the true lumen by closing the primary entry tear, and the true lumen is decompressed. That closes the false lumen, and thrombosis occurs over time. The timeframe for thrombosis within the false lumen is not predictable as is the situation in acute type B dissections. As in acute type B dissections, however, thrombosis is expected, and in fact observed, opposite the stent-graft. Furthermore, because of the nature of the disease and the potential coverage, the threat posed by a type Ib endoleak is difficult to determine and is probably not the same as in an atherosclerotic aneurysm; thus there is no need for immediate therapy.

Presumably, both hypotheses are applicable to a variable degree according to each individual case. Without doubt, our proposed method performs best for an isolated distal arch aneurysm originating from a chronic type B dissection with a short dissection membrane and a regular diameter in the middle third of the descending aorta. In a complex thoracoabdominal aneurysm originating from a chronic type B dissection, however, our proposed method is doomed to failure.

The covered length of the dissected aorta also should be discussed. It is not possible to cover the entire length of the dissection as the majority extend to the iliac bifurcation. Coverage slightly caudal to the distal extent of the aneurysm may be sufficient, and this raises the question of patient selection. In our experience, distal arch aneurysms are most suitable for this approach. The more distally the aneurysm is located, the length of coverage, intercostal arterial supply, and effectiveness of mid- and long-term aneurysmal exclusion become more problematic.

With chronic dissections, one cannot expect to retain perfusion in the abdominal aortic segment and also to appose the dissection membrane against the aortic wall as occurs with acute dissections. Once the primary tear has been covered, however, blood flow is redirected into the true lumen and its branches, and thrombosis is encouraged in the false lumen. This goal does not define success of atherosclerotic aneurysms, but is consistent with the definition of success in dissections. It is self-explaining, however, that primarily proximal aortic pathologies should be treated by this approach at the very beginning of the experience of the scientific community unless the proof of principle is supplied by other centers.

In 1 patient, a persisting type Ia endoleak was found. This patient had already undergone two sternotomies because of ascending and hemiarch replacement due to an acute type A dissection and secondary rupture of the arch anastomosis. He had a common origin of the brachiocephalic trunk and the left common carotid artery. Therefore, merely subclavian-to-carotid artery transposition could be performed from an extrathoracic approach. A third sternotomy was deemed, for various reasons, too risky in this particular situation. This result underlines the importance of not compromising the length of the landing zone. Several other questions in addition to landing zones arise, when offering an endovascular treatment option to this particular subgroup of patients. Another concern is whether the self-expanding stent-graft is able to appose the fibrous, potentially rigid, chronic dissecting membrane against the native aortic wall. In this series, this effect was observed in all patients with successful initial closure of the primary entry tear. This effect evolves over time, however, and may take several months to fully expand the stent-graft.

Limitations of the Study
The number of patients is terribly small. We believe that current knowledge and experience are far too limited to provide percentages of effectiveness and timeframes to achieve complete apposition of the dissecting membrane to the aortic wall. These patients represent a subgroup of patients with aortic pathologies that were not thought suitable for an endovascular approach owing to lack of knowledge and lack of adequate devices. The issue deserves much attention in the future, and the experience of other groups involved in the field will either confirm our approach or will bring it into question.

Summarizing, endovascular stent-graft placement of aneurysms involving the descending aorta originating from chronic type B dissections may serve as a valuable treatment option in patients with complex pathology. The chronic dissection membrane can be successfully apposed to large areas of the native aortic wall. A sufficient proximal landing zone is mandatory for early and late success.

	References

Top Abstract Introduction Patients and Methods Results Comment References

 

1. Dake MD, Kato N, Mitchell RS, et al. Endovascular stent-graft placement for the treatment of acute aortic dissection N Engl J Med 1999;340:1546-1552.[Abstract/Free Full Text]
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7. Hutschala D, Fleck T, Czerny M, et al. Endoluminal stent-graft placement in patients with acute aortic dissection type B Eur J Cardiothorac Surg 2002;21:964-969.[Abstract/Free Full Text]
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11. Coselli JS, LeMaire SA, Conklin LD, Adams GJ. Left heart bypass during descending thoracic aortic aneurysm repair does not reduce the incidence of paraplegia Ann Thorac Surg 2004;77:1298-1303.[Abstract/Free Full Text]
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