Endovascular stent-grafting for diseases of the descending thoracic aorta

Diseases of the descending thoracic aorta such as traumatic rupture, acute dissection, aneurysm and intramural haematoma (IMH) represent lifethreatening conditions. Aneurysms exceeding a maximum diameter of 6 cm are considered for surgery. Traumatic rupture is an indication for operation either immediately because of a free rupture with haemodynamic instability or later because of formation of a coarctation, a true or false aneurysm, a contained rupture or an expanding haematoma [1]. While the standard treatment of Stanford type B dissection is medical therapy, surgery can become necessary in patients with signs of impending rupture (persisting pain, uncontrollable hypertension, left sided haemothorax), visceral or leg ischaemia, renal failure, paraparesis or paraplegia [1]. Nonetheless, the current early mortality rate of type B dissection treated by medicaments/drugs remains high (20–40% mortality in the first year [2, 3]). Although substantial progress in the perioperative management of aortic surgery has been made in the past years, mortality (5–20%) and morbidity rates still remain high. The major postoperative complications include myocardial infarction, respiratory failure, renal failure, stroke and paraparesis or paraplegia [1, 4–7]. The technique of endoluminal aortic stentgraft placement in abdominal aneurysms is now an established procedure. Although long-term results Principles: Endoluminal stent-grafts are emerging as a less invasive alternative to conventional open surgery in the management of descending thoracic aortic dissections and aneurysms. We describe our experience with endovascular stent-grafting in the treatment of thoracic aorta pathology. Methods: 17 Patients were treated with 23 endovascular stents. The underlying pathology was an atherosclerotic aneurysm verum (n = 5), a type B dissection with contained rupture (n = 3), an intramural haematoma with contained rupture (n = 1) and a false aneurysm of unknown origin (n = 1). One patient had Marfan’s syndrome and six patients had a traumatic rupture of the descending aorta. Results: Overall 23 stent-grafts were implanted. In one patient, conversion to an open graft replacement of the descending aorta was necessary. One patient died. In four patients (23.5%) a left carotid-subclavia bypass or transposition was performed to achieve a sufficient neck for the proximal stent-graft landing zone. The postoperative control-CT scans revealed a total of six endoleaks (EL) (four type I, one type II and one type IV). Two patients needed a graft extension in a second operation (4 days and 18 month after the first operation), two EL (one type I and one type II) disappeared after 9 and 18 months, respectively and two EL are still under observation. One patient developed a paresis after conversion to open graft replacement. Conclusions: A variety of diseases of the descending aorta can be treated by endoluminal stent-grafting, which seems to be a valid alternative to open repair in well selected cases. Mortality and morbidity in our small series were low. Continuous follow-up is mandatory.

Diseases of the descending thoracic aorta such as traumatic rupture, acute dissection, aneurysm and intramural haematoma (IMH) represent lifethreatening conditions.
Aneurysms exceeding a maximum diameter of 6 cm are considered for surgery.Traumatic rupture is an indication for operation either immediately because of a free rupture with haemodynamic instability or later because of formation of a coarctation, a true or false aneurysm, a contained rupture or an expanding haematoma [1].
While the standard treatment of Stanford type B dissection is medical therapy, surgery can become necessary in patients with signs of impending rupture (persisting pain, uncontrollable hypertension, left sided haemothorax), visceral or leg ischaemia, renal failure, paraparesis or paraplegia [1].Nonetheless, the current early mortality rate of type B dissection treated by medicaments/drugs remains high (20-40% mortality in the first year [2,3]).
Although substantial progress in the perioperative management of aortic surgery has been made in the past years, mortality (5-20%) and morbidity rates still remain high.The major postoperative complications include myocardial infarction, respiratory failure, renal failure, stroke and paraparesis or paraplegia [1,[4][5][6][7].
The technique of endoluminal aortic stentgraft placement in abdominal aneurysms is now an established procedure.Although long-term results Principles: Endoluminal stent-grafts are emerging as a less invasive alternative to conventional open surgery in the management of descending thoracic aortic dissections and aneurysms.We describe our experience with endovascular stent-grafting in the treatment of thoracic aorta pathology.
Methods: 17 Patients were treated with 23 endovascular stents.The underlying pathology was an atherosclerotic aneurysm verum (n = 5), a type B dissection with contained rupture (n = 3), an intramural haematoma with contained rupture (n = 1) and a false aneurysm of unknown origin (n = 1).One patient had Marfan's syndrome and six patients had a traumatic rupture of the descending aorta.
Results: Overall 23 stent-grafts were implanted.In one patient, conversion to an open graft replacement of the descending aorta was necessary.One patient died.In four patients (23.5%) a left carotid-subclavia bypass or transposition was per-formed to achieve a sufficient neck for the proximal stent-graft landing zone.The postoperative control-CT scans revealed a total of six endoleaks (EL) (four type I, one type II and one type IV).Two patients needed a graft extension in a second operation (4 days and 18 month after the first operation), two EL (one type I and one type II) disappeared after 9 and 18 months, respectively and two EL are still under observation.One patient developed a paresis after conversion to open graft replacement.
Conclusions: A variety of diseases of the descending aorta can be treated by endoluminal stent-grafting, which seems to be a valid alternative to open repair in well selected cases.Mortality and morbidity in our small series were low.Continuous follow-up is mandatory.

Summary Introduction
have to validate the promising initial results, this method may become the new gold standard for selected patients and may be lifesaving in a contained rupture [8][9][10].
The use of endovascular stent-grafts in the thoracic aorta is less common than in AAA.The first series of 13 patients was published in 1994 [11], followed by further publications with encouraging results [12][13][14][15].The present report describes a single centre experience with endovascular stent-grafting in the treatment of descending thoracic aorta diseases.

Materials and methods
From 1/97 to 12/2001, 17 out of 72 patients (23.6%) presenting with a pathology limited to the descending aorta and who would require surgical treatment, were treated by endovascular stentgraft placement.
The underlying pathologies / patient data are summarised in table 1.
A total of 23 stents were used.11 patients were initially treated with one stent graft, four patients needed an immediate and two a delayed extension due to a proximal leak (type I EL), 4 and 15 month after the first intervention.In most cases we used a Talent ® stent graft (Medtronic Inc., USA), in one case a Vanguard ® stent graft (Boston Scientific Inc., USA), and in two cases a Thoracic Excluder ® (Gore Inc., USA) was used.
Cardiovascular Underlying pathologies and patient data.
arterial hypertension, four were smokers and three had elevated blood cholesterol.One patient had coronary heart disease.
Endovascular procedure 15 procedures were carried out under general anaesthesia (89.4%), one in peridural and one in local anaesthesia.The intervention was performed in the operating room by a team consisting of a cardiovascular surgeon, an interventional angiologist and / or an interventional radiologist.Femoral artery access was achieved in 15 patients (mainly the right femoral artery).In two patients the femoral artery was either too small or diseased.Iliac graft access was then achieved through a retroperitoneal approach.In patient #16 a second stent was in-serted four days later due to a type I endoleak, using the same access [16].
In 12 cases (70.5%) a supplementary diagnostic catheter was used for proper device positioning and delivery using intermittent contrast angiography.In 10 patients the catheter was introduced through the brachial artery (seven from the right side, three from the left side).In two patients the contralateral femoral artery was punctured.
In all patients 70 IE Heparin per kilogram body weight was administered intravenously.The stent-graft system was inserted through a transverse arteriotomy and positioning of the graft was achieved under fluoroscopy.Before releasing the device mean arterial pressure was lowered to 50-60 mm Hg using stepwise perlinganit [17].In four patients (23.5%) the origin of the left subclavian artery was overstented to achieve a sufficient neck for the proximal landing zone of the stent-graft.Therefore the subclavian revascularisation procedure was performed directly before endovascular stent deployment (two subclaviancarotid transpositions, two carotid-subclavian bypass using either a saphenous vein graft or 6 mm PTFE graft).
At the end of the procedure control angiography was performed.Routine surveillance included conventional radiographs in two projections and contrast-enhanced spiral CT scans prior to discharge and at 3, 6, 12, 18 and 24 month postoperatively and yearly thereafter.In patients, in whom placement of the stent was possible (16/17 = 94.1% with one conversion to open surgery), average operation time was 157 minutes (range from 60 to 350 minutes).Technical success, defined as a perfect stent graft delivery and no primary endoleak, was achieved in 13 patients (76%).Early mortality was 5.8% (one patient).The following problems were observed:  CT of acute type B dissection.

Figure 7
Successful stenting of the dissection.

Results
adequate treatment.Intraoperative TEE revealed a retrograde dissection into the aortic arch, which could not be sealed by two endovascular stents.Due to the poor general condition, medical treatment was discontinued and the patient died.
No persistent paraparesis / paraplegia, distal embolisation or other major complications occurred.One patient required neck revision due to a lymphatic fistula after subclavia-carotid bypass.One inguinal haematoma had to be evacuated and one inguinal infection had to be treated surgically.No renal failure was encountered and all patients were discharged with a serum creatinin corresponding to the preoperative value.The average ICU stay was 4.3 days (0-23 days), including the three patients with multiple other injuries due to accidents.The patients were discharged after a median stay of 11, 6 days (7-34 days).Ten patients were discharged home, three to a rehabilitation clinic and three to a regional hospital.

Endoleaks
Two out of 15 patients showed a type I endoleak in the control angiography.Postoperative CT scans revealed another four endoleaks.One type I endoleak was sealed by distal extension four days later and one disappeared after 18 months of surveillance.Of the four newly detected endoleaks, two were type I, one type II and one type IV.In a type I endoleak, a reduction of the size of the endoleak was observed in control CT scans postoperatively and is still under observation.In another patient the type I EL was treated 18 months after first stent implantation with a new stent-graft placement for distal extension.The diameter of the aneurysm sac had increased.One type II endoleak disappeared after 9 months of surveillance.In the patient with type IV endoleak the aneurysm remained stable in size four months postoperatively and is still under observation.All endoleaks were observed in elderly patients.No late rupture occurred.The median follow-up by CT scans was 13.2 months (range 0-36 months).The clinical follow up is 18.6 months range (0-43 months).

Discussion
In 1991 the first successful implantation of an endovascular stent graft in a patient with abdominal aneurysm was described by Parody et al. [18].This success encouraged surgeons all over the globe to investigate the feasibility of thoracic aortic repair with transluminally placed endovascular stents.The first report of a successful thoracic aortic repair with an endovascular stent originates from Dake et al. in 1994 [11].Recent publications reported encouraging results, but nevertheless some concerns and drawbacks remain [7,[12][13][14][15].
The selection of possible candidates for an endovascular treatment has to be made carefully.Three major factors have to be considered: 1) the location and morphology of the aortic lesion, 2) the suitability of the vascular access and 3) the procedure limiting tortuosity of the abdominal and thoracic aorta.
The results in the present series are promising, especially in younger patients with traumatic rupture of the descending aorta.In this group of patients the technical difficulties concerning the vascular access are negligible and endovascular aortic repair can be performed even in patients with multiple injuries, including brain injury or bleeding disorders.
Emergent or early endovascular stent grafting for traumatic rupture of the thoracic aorta showed promising results.Lachat et al. [8] reported a series of 12 patients with 11 survivors, despite various additional severe concomitant lesions.Even in patients with brain injury, or liver and kidney lacerations, which represent a contraindication for open surgical repair, were successfully treated with stent grafts and survived.Endovascular treatment of aortic lesions close to the aortic isthmus does not seem to have a larger risk of postoperative paraplegia, when compared to open surgical repair in acute thoracic aortic rupture [19].The reason for this is probably the frequent location of the lesion within the proximal descending thoracic aorta.
Another indication for endovascular repair may be an intramural haematoma (IMH) in the descending aorta with or without a penetrating atherosclerotic ulcer (PAU).The difficulty with this pathology resides in the fact that the exact origin of the intramural bleeding can not always be easily verified.Ganaha et al [20] recently claimed both symptoms and radiological findings, such as recurrent pain, pleural effusion and both size and depth of the ulcer-like projection to be predictive of disease progression and therefore of a risk to the patient.Von Kodolitsch and Nienaber described the natural course of patients with IMH in a metaanalysis [21,22].Typical IMH without PAU led to overt aortic dissection in 12% of descending IMH, ended in aortic rupture in 9% or in stabilisation in 76%.30-day mortality after open surgery was 18% with repair of proximal IMH and 33% with repair of distal IMH, compared with 60% and 8% in-hospital mortality with medical treatment of proximal and distal IMH, respectively.
Determination of the so-called "landing zones" for safe proximal and distal graft attachment is absolutely essential.A minimum of 1.5 cm to 2 cm of normal aorta is required to anchor the stent.If the lesion is close to the level of the left subclavian artery and if the stent has to be placed within the aortic arch, prior revascularisation of the left subclavian artery has to be considered.In case of intentional covering of the left subclavian artery origin to increase the proximal landing zone, either a carotid-subclavian bypass or a subclavian-carotid transposition was used to restore subclavian artery blood flow.In contrary to a recent publication by Goerich et al. [23] in which 78, 5% of 23 patients reported no postinterventional complaints and therefore revascularisation was not considered to be primarily necessary, we believe that by covering the origin of the subclavian artery we prevent at least type II endoleaks.Whether this can be achieved by merely inserting an endovascular on-plug stent graft instead of ligation of the LSA during the revascularisation procedure has yet to be proven.Increasing the landing zone into the aortic arch but leaving a large branch open as a potential type II EL source does not seem to make sense.
The role of stent grafts in acute type B dissections at this time is not clear.Several reports [24][25][26][27][28] have demonstrated the use of endovascular techniques the treatment of complication in aortic dissection.It seems to make sense that aortic wall and diameter behaviour would be more favourably influenced by early covering of the intimal entry tear leading to re-pressurisation of the true lumen.On the other hand, acute clotting of the false lumen may cause visceral and spinal cord ischaemia.However, prospective trials with endovascular stent grafting of the acute dissected descending aorta have to be awaited before any conclusions can be drawn.
To introduce the stent successfully a suitable access has to be available.The femoral artery served as access in 15 patients (88%).In two cases (both women) a lumbotomy was necessary to provide iliac graft access since the femoral artery diameter was too small [16].Careful preoperative investigations are required -either with ultrasound or angiography -to choose optimal access.Further miniaturisation of the stent delivery systems should allow the introduction of the stent through the femoral artery in most cases.
The use of a second angiography catheter can be very helpful, either to determine the origin of the subclavian artery exactly or to identify the true and the false lumen of a dissection.In type B dissection it is imperative to verify the entry tear near the subclavian artery very precisely to allow a perfect stent placing.Intravascular ultrasound (IVUS) and trans-oesophageal echocardiography (TEE) are helpful for accurate stent placement, although the TEE probe can interfere visually at the aortic arch.
Although described by some authors [29], we did not encounter paraplegia after successful stent implantation in our patients.The patient who had to be converted suffered from a transient paresis of one leg.The lack of the need for aortic crossclamping and circulatory arrest compared to open surgery are considered to be major advantages in preventing ischaemic paraplegia.
A well-known and so far unsolved problem is the appearance of endoleaks.In 6 of 15 patients endoleaks were detected, making the incidence a high 40%.Although two EL disappeared spontaneously (after 9 respectively 18 months), two needed a second intervention and two are still under surveillance.Since type I EL is a significant risk factor for late rupture in endovascular repair of AAA, the same must be assumed in thoracic aneurysms [30].Whereas completion angiography showed an EL in only two patients, postoperative CT scan detected four more ELs.As we are reluctant to take a patient back to the OR immediately for open conversion, we tend to keep the EL under surveillance and hope that it will disappear spontaneously.Interestingly in the follow-up CT scans no new endoleaks developed.
When choosing an endovascular stent-graft procedure, the problems and limitations of this treatment have to be considered.Results of successful treatment of traumatic aortic rupture or of leaking aneurysms have shown that stent-grafts can be life saving.Although the withdrawal of a commercially available stent-graft because of spine breakages in one single stent can be understood from the point of view of the company, from the point of view of the patient in an urgent, life threatening situation it is a pity.When treating patients on an elective basis for aneurysm or dissection, issues of material stability, increasing aortic diameter in the natural course and potential endoleak appearance have to be considered.

Conclusion
In conclusion, endovascular stent-grafting of the descending aorta is a promising alternative technique to open surgery in well selected patients.Older patients profit from a minimal invasive procedure and regional anaesthesia.In younger patients with a completely different pathology, the results are excellent.Both patient selection and the technical development of the stent graft system itself have to be optimized in order to improve clin-ical results in the future.However, studies with larger series of patients and longer follow-up periods are highly desirable to confirm these early positive results and evaluate this new technique in the treatment of diseases of the descending thoracic aorta.A defined, closely matched control of these patients has to be done.Until this is available, our approach will remain cautious.
Type I: Endoleak related to the stent graft device itself, mostly due to an insufficient sealing of the proximal or distal part of the stent.Type II: Retrograde flow from collateral branches (lumbar, inferior mesenteric).Type III: Endoleak due to fabric tears, graft wall defect, modular disconnection or disintegration Type IV: Flow through the graft presumed to be associated with graft wall "porosity", endotension.

Figure 1
Figure 1Angiography of the aneurysm.

Figure 2
Figure 2Angiography while placing the stent.

Figure 3
Figure 3Modelling of the stent by the balloon.

Figure 4
Figure 4Angiography of the excluded aneurysm.

Figure 5 MRI
Figure 5 MRI of the excluded aneurysm.

1 .
Patient #7 had to be converted to open graft replacement because of stent kinking during delivery and overstenting of the left subclavian artery.The stent was removed and the proximal third of the descending aorta was replaced.The operation was performed with partial left heart bypass in mild hypothermia (32 °C).Postoperatively the patient suffered from a transient paresis of the left leg and a persistent left recurrent nerve palsy.2. In patient #11 a type I endoleak could not be eliminated despite balloon re-modelling.The endoleak disappeared 18 months after the operation spontaneously.3.In patient #16 the leaking aneurysm was incompletely excluded.Another stent for distal extension was not available.In a second operation four days later distal extension was completed.Postoperative course was free of complications.4. Patient #9 with acute type B dissection developed acute visceral ischaemia.Fenestration of the infrarenal abdominal aorta, re-vascularisation of the coeliac trunk and the superior mesenterial artery, hemicolectomy and cholecystectomy were performed.The following day, the proximal descending aorta began to leak.As the patient was not suitable for surgery, a stent implantation was considered to be

Patient age / sex pathology localisation of the lesion stent graft * time of surgery special after trauma / admission
risk factors were mainly present in older patients.Eight patients suffered from

Table 1
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