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(December 17, 2007). doi:10.1510/mmcts.2007.002824 Copyright © 2007 European Association for Cardio-thoracic Surgery Procedure Degenerative aneurysm of the descending aorta. Endovascular treatmentCardiothoracovascular Department, Cardiovascular Radiology Unit, University Hospital S. Orsola, Padiglione 21-Via Massarenti 9, 40138 Bologna, Italy * Corresponding author: * Tel.: +39-051-6364747; fax: +39-051-6364747 rossella.fattori{at}unibo.it
The incidence of thoracic aortic aneurysms has a rate of occurrence of 10.9 cases per 100,000 person/year, with an estimated 5-year risk of rupture ranging from 16% (diameter between 4 and 5.9 cm) to 31% (6 cm or more). Despite increasing awareness of the important role of early diagnosis in treatment options, guidelines about therapeutic strategies are actually lacking, as well as definite evidence of pharmacological treatment able to resolve or delay the disease progression. Endovascular treatment proposed as alternative to surgery has been considered a therapeutic innovation, especially because of low invasiveness, which allows to treat even high surgical risk patients. The procedure is performed under general anesthesia, mechanical ventilation and blood pressure invasive monitoring (right radial artery cannulation). The common femoral artery or external iliac artery are used for access after surgical exposure. After exposition of the artery, a 6F sheath is inserted and 5000 UI of heparin administered. Angiography is then performed to identify the lesion, landing zones and its relation to side branches. Endovascular stent-graft is thus loaded on an extra-stiff guidewire and delivered, with induced hypotension, under fluoroscopic and transesophageal echo control. Post procedural angiography and echocardiography control are performed to reveal the final result.
Key Words: Endovascular treatment • Thoracic aortic aneurysm
In the past decades the incidence of thoracic aortic aneurysms (TAAs) was estimated to be 3.5 cases per 100,000 person/year. Recently, a population-based study of thoracic and thoraco-abdominal aortic aneurysm reported an incidence of 10.9 cases per 100,000 person/year, revealing an increased rate of occurrence of the disease [1]. Although many studies have identified risk factors related to the formation and progression of aortic aneurysms, none has fully explained the etiology of the disorder. Atherosclerosis could be considered a concomitant process and not a direct cause of aneurysm formation and growth. Recently, the role of inflammation has also been investigated in promoting aneurysm growth and rupture. Aortic medial degeneration has been demonstrated in most aneurysms, regardless of their cause and location. The overall survival of patients with TAAs has improved significantly in the past few years. The estimated 5-year risk of rupture of a TAA with a diameter between 4 and 5.9 cm is 16%, but it rises to 31% for aneurysms of 6 cm or more. Thoracic aortic diseases historically represent a challenge for surgeons, due to procedural complexity and clinical problems related to surgical access and anesthetic techniques. Atherosclerosis being the major leading cause, affected people are mostly aged, often with co-morbidities such as ischemic heart disease, hypertension, COPD or diabetes, which negatively influence surgical risk and patient outcome. The surgical access, consisting in thoracotomy with often associated phreno-laparotomy, is particularly invasive and carries substantial risks of serious cardiovascular and respiratory dysfunctions. Hemorrhage, coagulative disorders, medullar ischemia, cerebrovascular accident and renal failure could complicate surgery and postoperative outcome and, therefore, patient prognosis. Mortality and morbidity range from 5 to 15% in elective cases and up to 50% in emergency situations [2, 3]. Endovascular treatment (EVT), proposed as alternative to surgery, has been considered a therapeutic innovation, especially because of low invasiveness, which allows to treat even at-risk patients.
The technique is described in the following text and highlighted by schematics and intraoperative angiographic photos and videos. Preoperative and postprocedural multidetector CT scans of the entire aorta are also shown. Images and videos belong to a 55-year-old man with a large (55 mm) degenerative aneurysm of the middle portion of the thoracic descending aorta (Photo 1 and Video 1), undergoing endovascular treatment.
Endovascular stent-graft placement procedure is performed through femoral or external iliac approach, usually under general anesthesia and mechanical ventilation, and must be done in a standard operating room equipped with an angiographic set and transesophageal echocardiography (TEE). Blood pressure is monitored by right radial artery cannulation. When femoral arteries are too small, vascular access may be achieved through the common iliac artery or the abdominal aorta using a temporary conduit to provide vascular access. All the procedures should be performed under fluoroscopy and, if available, TEE which can provide additional information, such as the optimal landing zone or, after stent-graft delivery, the presence of perigraft leakage or kinking. After the percutaneous (Seldinger technique) insertion of a 5F introducer, a 5F sheath with distal radio opaque markers (e.g. Cordis/Johnson & Johnson – MMCTSLink 157) is placed via the left brachial artery to identify the left subclavian artery ostium and allow angiography during the procedure. This marker is crucial for optimal stent placement in aneurysms with a short proximal neck. In more distal lesions, a catheter may be placed inside the celiac trunk through contralateral femoral artery approach to mark its origin. After exposition of the femoral artery (a schematic is available at http://www.medscape.com/content/2004/00/46/66/466607/art-466607.fig1.jpg) a 6F introducer (Photo 2A) and a 6F sheath (Photo 2B) are inserted, a guidewire is positioned in the ascending aorta and 5000 UI bolus of heparin administered.
Thus, angiography is performed to identify the lesion, its relation to side branches and optimal landing zone (Photo 3 and Video 2).
The stent-graft delivery system is then loaded over a 260–300-cm long extra-stiff guidewire (e.g. Back-Up Meier/Boston Scientific or Lunderquist/Cook – MMCTSLink 158) through the transverse arteriotomy of the common femoral artery and advanced under fluoroscopy (Photos 2C and 4).
When the optimal landing zone is reached, the endoprosthesis is delivered under fluoroscopic control (Photo 5, Schematic 1 and Video 3), with induced hypotension (systolic pressure <70 mmHg) to prevent inadvertent downstream displacement of the stent-graft during delivery.
After deployment, TEE control (Photo 6) and angiography (Video 4) are performed to reveal the final result and in case of perigraft leakage (Photo 7) or graft kinking, a latex balloon is then introduced and inflated to mould the stent-graft and obtain its complete expansion (Photos 2D and 8). After TEE control, a final aortogram is then performed to verify proper stent-graft positioning and complete aneurysm exclusion (Photo 9 and Video 5).
Finally, the delivery sheath is removed and the arteriotomy is sutured. TEE is fundamental during endovascular procedure [4, 5, 6, 7]. With this technique it is possible to visualize the correct position of guide, catheters and stent-graft system. Furthermore, TEE provides a real-time evaluation of aortic wall condition at the neck sites, constituting a simple fluoroscopic marker of proximal or distal landing zone. After stent-graft delivery, TEE with color-Doppler is able to identify blood flow inside the aneurysm sac (endoleak) or initial thrombosis (echo-contrast effect) as an indicator of the efficacy of the procedure [7]. When balloon inflation for stent remodeling is necessary, TEE could establish the correct grade of balloon distension and the contact with aortic wall, avoiding the risk of overinflation and aortic wall damage. TEE, therefore, is useful in all phases of endovascular procedure allowing to reduce the use of angiography and, thus, radiations and contrast media, reducing potential risk of complications.
Results of literature international registries and a single-center series are summarized in Table 1.
The Stanford Clinical Trial, the first performed with thoracic stent-graft [8, 9, 10], with a large population (103 patients) and 10 years of follow-up, showed a perioperative mortality rate of 9%, and a survival rate of 82%, 49% and 27%, respectively, after 1, 5 and 8 years. However, most of the deaths (57/65, 87.7%) arose from nonaortic causes such as cancer, cerebrovascular accident, acute myocardial infarction or heart failure and many others. Freedom from aortic rupture was, indeed, 99%, 94% and 91% at 1, 5 and 8 years. Results about endovascular treatment of TAAs with ‘second generation’ stent-grafts, arise from multicenter international registries such as EUROSTAR, GORE-TAG and TTR [11, 12, 13]. In the EUROSTAR (European collaborators on stent/graft techniques for thoracic aortic aneurysm and dissection repair) [11] registry, 249 of 443 patients had a degenerative thoracic aneurysm. Primary technical success was obtained in 87%; device-related complications occurred intraoperatively in 16% of patients, and arterial injuries in 2.4% of patients. Neurologic events consisted of paraplegia/paraparesis (4.0%) or stroke (2.8%). Perioperative mortality rates ranged from 5.3% in elective procedures and 28% in emergency repair. Late survival after one-year follow-up was 80% with 2.1% of aneurysm-related deaths. In the GORE-TAG registry [12], 139 of 142 patients (98%) had a successful implantation of endovascular device with a perioperative mortality rate of 1.5%. Major complications included stroke (4%), paraplegia-paraparesis (3%) and vascular trauma (14%). Device-related complication such as migration, components disconnection or wire fractures has been reported in 10–14% of cases during the 2 years of follow-up period. Overall, 2-year survival rate was 75% with an aneurysm-related mortality of 2%. The TTR (Talent Thoracic Retrospective) [13] registry collected data from 457 patients (344 elective and 113 emergency): 137 of them had a degenerative aortic aneurysm. Perioperative overall mortality rate was 5% with in-hospital complication rate of 3.7% for stroke, 1.7% for paraplegia-paraparesis and 3.3% for vascular injuries. Device-related complication has been reported in 2.4% of cases. Survival rates at 1, 3 and 5 years were 91%, 85% and 77.5%, respectively, with an aneurysm-related mortality of 2.6%. The most frequently reported complications in EVT were stroke and paraplegia, ranging respectively from 2.8 to 3.7% and from 1.7 to 14% [11, 12, 13]. Our personal experience is based on 224 patients treated with stent-graft for different thoracic aortic diseases (aortic dissection, penetrating atherosclerotic ulcer, intramural hematoma and aneurysm): 45 of them were affected by TAA. Forty-two procedures have been elective while three patients underwent stent-graft repair under emergency conditions. Technical success rate was 97%, with no in-hospital mortality. Major complications consisted of paraparesis in two patients and paraplegia in one patient. Stent related mortality (aortic rupture and aorto-esophageal fistula) occurred in two patients during follow-up. Aorto-esophageal fistula has been frequently reported after TAA endovascular treatment, representing one of the most dreadful complications of EVT of large atherosclerotic aneurysms. The close contact of a large aneurysm sac with the esophagus, along with inflammatory response of the aneurysm wall to a foreign body may ultimately lead to adventitial erosion and fistulization.
Even if innovative and less invasive, EVT is not feasible in all of TAAs, due to anatomic features: vascular imaging is crucial for patient selection, endoprosthesis choice and planning of the treatment.
Anatomic conditions Efficacy of EVT is based on radial forces of endoprosthesis due to nitinol core, a bind of nickel and titanium characterized by elastic proprieties together with thermic memory and strength. An oversizing of the prosthesis caliber ranging from 10 to 20% if compared to aortic neck diameter, is generally able to ensure a good attachment and, therefore, an exclusion of the aneurysm sac from blood flow. An accurate measurement of aortic diameters is thus mandatory in EVT planning (Photo 10).
The diameter of stent-graft releasing systems ranges from 22 to 27 French (7 to 9 mm) and the femoro-iliac access must be dimensionally adequate, especially in the presence of atherosclerosis, calcifications and tortuosity (Photo 11).
Aortic wall assessment at the level of landing zone is a crucial step in the feasibility assessment. An atheromasic, thrombotic or heavy calcified wall could cause failure of aneurysm sealing. It is generally accepted that the length of neck (a portion of normal aortic wall between the origin of left subclavian artery/celiac trunk and proximal/distal extremities of the aneurysm) should be at least 1–1.5 cm. If the aortic neck is shorter than 1 cm it could be unable to exclude aneurysm from blood flow, with a high risk of device migration in the long-term. Extension of the anatomic coverage of the proximal neck is possible by intentional occlusion of the left subclavian artery with or without previous left subclavian artery revascularization by extra anatomic bypass of supra-aortic vessels. Controversy exists regarding the need of left subclavian artery revascularization before stent-graft occlusion. Steinberg et al. [14] reported an incidence of 5.4% of ischemic complications in intentional occlusion of the vertebral artery. A recent meta-analysis on endovascular repair of proximal descending aorta [15] reports 28% of complications in patients in which occlusion of the left subclavian artery is not protected by previous revascularization, with respect to 3% of complications in patients previously submitted to preventive revascularization. Left subclavian artery bypass or transposition could be performed with a supra-clavear surgical approach: this technique is minimally invasive and could preserve from potential complications like cerebellar infarction (vertebral artery occlusion) and subclavian-vertebral steal syndrome [15]. Furthermore, reperfusion of the aneurismatic sac from subclavian artery (type II endoleak) could be avoided.
Postoperative follow-up A close imaging follow-up is recommended during the first year (1, 3, 6 and 12 months) after the procedure [16, 17] (Photo 12 and Video 6).
The most important morphologic parameters that should be evaluated are the presence/absence of blood flow inside the aneurysm sac (endoleak), aortic dimension, morphology of prosthesis (position and structural integrity), diameter and morphology of proximal and distal neck and aortic wall abnormalities. The presence of blood flow inside the aneurysm sac (endoleak) is an indicator of procedural failure and has an important clinical impact in thoracic aortic disease, with a potential risk of aortic rupture. According to current nomenclature, five types of endoleak have been identified [18, 19, 20] (Schematic 2).
Endoleak is defined type I when blood flow originates from proximal or distal extremities of the graft, with reperfusion of aneurysm sac; type II endoleak is caused by a retrograde blood flow arising from a tributary artery of excluded portion (left subclavian artery, intercostal arteries). Type III endoleak originates from a prosthetic material defect (holes, laceration) or from segment disconnection; type IV endoleak is caused by stent macroporosity and generally resolves spontaneously, while type V (endotension) derives from a pressure rise inside excluded sac without evidence of blood flow. Endoleaks may occur early or late during follow-up: the former appear often at the end of EV procedure, the latter during follow-up examinations. Type I and type III endoleaks need immediate surgical (conversion to open surgery) or endovascular procedure (proximal or distal graft extension) because they usually lead to aneurysm sac expansion and rupture. Treatment of type II endoleaks is dependent by aneurysm expansion during follow-up; however, most of type II endoleaks evolve to spontaneous sealing [13]. Migration of the stent-graft is rarely reported in thoracic series. Migration of a thoracic stent-graft may cause aortic branches occlusion such as celiac trunk and other splanchnic vessels with severe ischemic consequences. Early and mid-term results of thoracic atherosclerotic aneurysm EVT are encouraging. However, long-term outcome data results are necessary to definitively assess reliability of stent-graft materials and improvement in patient survival.
In conclusion, in the choice between surgical or endovascular repair of TAAs, many factors must be considered, including clinical conditions, co-morbidities, anatomic situation, materials' efficacy and last, but not less important, experience of the center.
The authors acknowledge the department of Radiology and the SCOM, CHU Rangueil, Toulouse, France for Schematic 2.
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