Endovascular aneurysm repair

Endovascular aneurysm repair (EVAR) was first pioneered in the early 1990s. Since then technology of the devices has rapidly progressed and EVAR is now widely used as treatment of thoracic and abdominal aortic aneurysms (AAA).

The advantages of endovascular repair over open repair is that they are less invasive than open surgery, have a lower surgical morbidity and mortality rate, and they reduce the length of post-operative stay in hospital. One disadvantage is the need for life-long follow-up imaging, and the long-term durability of graft material is yet to be proven.

Indications

EVAR is performed in patients undergoing elective aneurysm repair as well as patients undergoing emergency repair (e.g. traumatic aortic injury and ruptured AAA).

Contraindications

Relative contraindications include:

• narrow iliac arteries, e.g. ~8 mm
• sharply angulated iliac arteries
• short aneurysmal neck
• tapering aneurysmal neck
• highly likelihood of graft occluding a visceral vessel once deployed

Procedure

EVAR is performed by inserting a stent-graft into the lumen of the aneurysmal portion of the aorta. The stent-graft consists of a graft that provides a conduit for blood flow and a stent that anchors the graft to the aorta and provides structural support for the graft material. The aim is to divert blood flow into the graft, thereby bypassing the aneurysm.

Pre-procedure evaluation

The key to successful EVAR is proper pre-procedural planning. Not all aneurysms are suitable for EVAR, depending on the anatomy of the aneurysm and iliac vessels. For those deemed suitable, careful aneurysm measurements (usually with CTA) will ensure the graft is the correct length and diameter. If the graft is too short the aneurysm will not be excluded from the circulation; if it is too long important branch vessels may be inadvertently occluded; and if it is too narrow in diameter there will not be an adequate seal against the aortic wall which may result in an endoleak.

The pre-EVAR CTA also needs assess the access vessels (ie the CFA, EIA and CIAs)  to document any atherosclerotic disease as well as the diameters of these vessels (for passage of the device delivery systems).

Equipment

Stent-grafts are made in a number of configurations. In AAA repair, the most common configuration is a bifurcated graft extending from the aorta into the common iliac or external iliac arteries. This typically requires access via both common femoral arteries. The grafts are modular in construction, that is they are assembled in the patient in stages. The main body is deployed first, followed by the iliac limbs. The materials used in the stent-graft vary with each manufacturer but most grafts are made of expanded polytetrafluoroethylene (ePTFE) or woven polyester, and most stents are made of nitinol or stainless steel.

Technique

Depending on the institution, EVAR is performed by interventional radiologists, vascular surgeons or both together. The patient typically requires a general anaesthetic.

A stent-graft is inserted via the common femoral artery and deployed once it is confirmed in adequate position under the image intensifier, similar to other types of stent insertion. However, the diameter of the stent-graft and its delivery device are large (usual delivery device size ranges between 18 and 24 French), thus the procedure typically requires surgical exposure and closure of the common femoral artery, although percutaneous arterial access methods are also available.

Adjunctive procedures

Adjunctive procedures are sometimes required to improve the technical success of EVAR just prior to or during endovascular repair. These include angioplasty of stenoses before device delivery, angioplasty of stenosis in the graft, embolisation of branch vessels to prevent endoleak, and stent reinforcement of endograft limb.

Complications

Recognised complications include:

• endoleak: occurs in 30-40%
• continued enlargement of the aneurysm sac without endoleak: 2-40% ⁸
• delayed aneurysm rupture
• graft migration
• branch vessel occlusion with end-organ ischaemia/infarction
• infection
• stent-graft structural breakdown
• groin complications

Patients require life-long imaging surveillance to monitor for endoleak, aneurysm expansion and graft integrity. This is most commonly performed via CTA. MRA is an alternative but stainless steel stents cause major susceptibility artefact that limits its usefulness in such cases.

Different CT techniques have been advocated:

• single phase CTA
• dual phase CTA: non contrast and arterial phase, or arterial and delayed phase
• triple phase CTA: non contrast, arterial phase and delayed phase

The need for non-contrast and delayed phase images is controversial, particularly in light of the cumulative radiation dose the patient will receive over the rest of their life. However, delayed imaging is felt to be important in order to detect slow endoleaks that do not show in the arterial phase.

Outcomes

For elective AAAs compared to open repair, EVAR shows improved 30-day operative mortality but this is not sustained by five years. There are also higher rates of delayed complications and re-intervention in EVAR ^5,6. However, for ruptured AAAs EVAR may demonstrate reduced peri-operative and longer-term (four year) mortality compared to open repair ⁷.