Endovascular aneurysm repair (EVAR) is a type of minimally-invasive endovascular surgery used to treat pathology of the aorta, most commonly an abdominal aortic aneurysm (AAA). When used to treat thoracic aortic disease, the procedure is then specifically termed TEVAR for "thoracic endovascular aortic/aneurysm repair." EVAR involves the placement of an expandable stent graft within the aorta to treat aortic disease without operating directly on the aorta. In 2003, EVAR surpassed open aortic surgery as the most common technique for repair of AAA, and in 2010, EVAR accounted for 78% of all intact AAA repair in the United States.
Medical uses Standard EVAR is appropriate for aneurysms that begin below the renal arteries, where there exists an adequate length of normal aorta (the "proximal aortic neck") for reliable attachment of the endograft without leakage of blood around the device ("endoleak"). If the proximal aortic neck is also involved with the aneurysm, the patient may be a candidate for complex visceral EVAR with a fenestrated or branched EVAR.
Patients with aneurysms require elective repair of their aneurysm when it reaches a diameter large enough (typically greater than 5.5 cm) such that the risk of rupture is greater than the risk of surgery. Repair is also warranted for aneurysms that rapidly enlarge or those that have been the source of emboli (debris from the aneurysm that dislodges and travel into other arteries). Lastly, the repair is also indicated for aneurysms that are the source of pain and tenderness, which may indicate impending rupture. The options for repair include traditional open aortic surgery or endovascular repair.
Endovascular procedures aim to reduce the morbidity and mortality of treating arterial disease in a patient population that is increasingly older and less fit than when major open repairs were developed and popularized. Even in the early days, significant risks were accepted in the understanding that the large open operation was the only option. That is not the case in most patients today.
Studies that assign aneurysm patients to treatment with EVAR or traditional open surgery have demonstrated fewer early complications with the minimally invasive approach. Some studies have also observed a lower mortality rate with EVAR. The reduction in death, however, does not persist long-term. After a few years, the survival after repair is similar to EVAR or open surgery. This observation may be the result of durability problems with early endograft, with a corresponding need for additional procedures to repair endoleaks and other device-related issues. Newer, improved technology may reduce the need for such secondary procedures. If so, the results of EVAR may improve to the point where long-term survival benefit becomes evident.
EVAR is also used for rupture of the abdominal and descending thoracic aorta, and in rare cases used to treat pathology of the ascending aorta.
Aortic dissection Endografts have been used in patients with aortic dissection, noting the extremely complex nature of open surgical repair in these patients. In uncomplicated aortic dissections, no benefit has been demonstrated over medical management alone. In uncomplicated type B aortic dissection, TEVAR does not seem either to improve or compromise 2-year survival and adverse event rates. Its use in complicated aortic dissection is under investigation. In the Clinical Practice Guidelines of the European Society for Vascular Surgery, it is recommended that in patients with complicated acute type B aortic dissection, endovascular repair with thoracic endografting should be the first line intervention.
Before people are deemed to be suitable candidates for this treatment, they have to go through a rigorous set of tests. These include a CT scan of the complete thorax/abdomen/pelvis and blood tests. The CT scan gives precise measurements of the aneurysm and the surrounding anatomy. In particular, the calibre/tortuosity of the iliac arteries and the relationship of the neck of the aneurysm to the renal arteries are important determinants of whether the aneurysm is amenable to endoluminal repair. In certain occasions where the renal arteries are too close to the aneurysm, the custom-made fenestrated graft stent is now an accepted alternative to doing open surgery.
Relative contraindications A patient's anatomy can be unsuitable for EVAR in several ways. Most commonly, in an infrarenal aneurysm, a potential EVAR candidate lacks adequate length of the normal-diameter aorta between the aneurysm and the takeoff of the renal arteries, the "infra-renal neck". Another relative contraindications include prohibitively small iliac arteries, aneurysmal iliac arteries, prohibitively small femoral arteries, or circumferential calcification of the femoral or iliac arteries.
In addition to a short proximal aortic neck, the neck may be angulated, large in diameter, or shaped like a funnel (conical) where the neck diameter at the top is larger than the neck diameter at the bottom. Along with a short proximal aortic neck, necks with any of these characteristics are called "hostile necks" and endovascular repair can be either contraindicated or associated with early-late complications of endoleak, or endograft migration, or both.
Many of the advances in EVAR technique aim to adapt EVAR for these situations, and advanced techniques allow EVAR to be employed in patients who previously were not candidates.
Technique
The procedure is carried out in a sterile environment under fluoroscopic guidance. It is usually carried out by a vascular surgeon, interventional radiologist or cardiac surgeon, and occasionally, general surgeon or interventional cardiologist. The procedure can be performed under general, regional (spinal or epidural) or even local anesthesia.
Access to the patient's femoral arteries can be with surgical incisions or percutaneously in the groin on both sides. Vascular sheaths are introduced into the patient's femoral arteries, through which guidewires, catheters, and the endograft are passed.
Diagnostic angiography images are captured of the aorta to determine the location of the patient's renal arteries, so the stent-graft can be deployed without blocking these. Failure to achieve this will cause kidney failure. With most devices, the "main body" of the endograft is placed first, followed by the "limbs" which join the main body and extend to the iliac arteries, effectively protecting the aneurysm sac from blood pressure.
The abdominal aneurysm extends down to the common iliac arteries in about 25%-30% of patients. In such cases, the iliac limbs can be extended into the external iliac artery to bypass a common iliac aneurysm. Alternatively, a specially designed endograft, (an iliac branch device) can be used to preserve flow to the internal iliac arteries. The preservation of the hypogastric (internal iliac) arteries is important to prevent buttock claudication and impotence, and every effort should be made to preserve flow to at least one hypogastric artery.
The endograft acts as an artificial lumen for blood to flow through, protecting the surrounding aneurysm sac. This reduces the pressure in the aneurysm, which itself will usually thrombose and shrink in size over time.
Staging such procedures is common, particularly to address aortic branch points near the diseased aortic segment. One example in the treatment of thoracic aortic disease is revascularization of the left common carotid artery and/or the left subclavian artery from the innominate artery or the right common carotid artery to allow treatment of a thoracic aortic aneurysm that encroaches proximally into the aortic arch. These "extra-anatomic bypasses" can be performed without an invasive thoracotomy. Another example in the abdominal aorta is the embolization of the internal iliac artery on one side prior to coverage by an iliac limb device. Continued improvement in stent-graft design, including branched endografts, will reduce but not eliminate multi-stage procedures.
Percutaneous EVAR Standard EVAR involves a surgical cut-down on either the femoral or iliac arteries, with the creation of a 4–6 cm incision. Like many surgical procedures, EVAR has advanced to a more minimally invasive technique, by accessing the femoral arteries percutaneously In percutaneous EVAR (PEVAR), small, sub-centimeter incisions are made over the femoral artery, and endovascular techniques are used to place the device over a wire. Percutaneous EVAR has been systematically compared to the standard EVAR cut-down femoral artery approach. Moderate quality evidence suggests that there are no differences in short-term mortality, aneurysm sealing, long and short-term complications, or infections at the wound site. Higher quality evidence suggests that there are no differences in post-repair bleeding complications or haematoma between the two approaches. The percutaneous approach may have reduced surgical time.
Fenestrated EVAR
Fenestrated endovascular aortic/aneurysm repair (FEVAR) is performed in the cases where the aneurysm extends near or involves the visceral vessels (such as juxta-renal, para-renal, thoraco-abdominal aortic aneurysms). A custom-made graft with fenestrations (holes on the graft body to maintain the patency of the visceral arteries) is used for the procedure. When the aneurysm involves the visceral arteries, standard EVAR is contraindicated due to the lack of suitable infra-aortic segment for the endograft attachment; FEVAR achieves seal between the stent graft and para-visceral segment and/or more proximal segment while preserving the flow of the visceral arteries. FEVAR has been in use in the United Kingdom for over a decade and early results were published in Jun 2012. British Society for Endovascular Therapy and the Global Collaborators on Advanced Stent-Graft Techniques for Aneurysm Repair (GLOBALSTAR) Registry. Early results of fenestrated endovascular repair of juxtarenal aortic aneurysms in the United Kingdom. Circulation: 2012 Jun 5;125(22):2707-15. doi: 10.1161/CIRCULATIONAHA.111.070334. Correspondence to S R Vallabhaneni.
Branched EVAR
Thoracoabdominal aortic aneurysms (TAAA) involve the aorta in the chest and abdomen. As such, major branch arteries to the head, arms, spinal cord, intestines, and kidneys may originate from the aneurysm. An endovascular repair of a TAAA is only possible if blood flow to these critical arteries is preserved. Hybrid procedures offer one option, but a more direct approach involves the use of a branched endograft. However, the complex anatomy associated with the supra-aortic vessels is particularly difficult to accommodate with branched endograft devices. Dr. Timothy Chuter pioneered this approach, with a completely endovascular solution. After partial deployment of the main body of an endograft, separate endograft limbs are deployed from the main body to each major aortic branch. This procedure is long, technically difficult, and currently only performed in a few centers.
When the aneurysm begins above the renal arteries, neither fenestrated endografts nor "EndoAnchoring" of an infrarenal endograft is useful (an open surgical repair may be necessary). Alternatively, a "branched" endograft may be used. A branched endograft has graft limbs that branch off of the main portion of the device to directly provide blood flow to the kidneys or the visceral arteries.
Hybrid procedures