Residency · Residency · Vascular Surgery

Endovascular Aneurysm Repair (EVAR): Principles and Device Selection

Overview

Endovascular aneurysm repair (EVAR) is a minimally invasive technique that involves placing an endograft, or stent graft, inside an aneurysm to exclude it from systemic arterial pressure. This procedure was first performed by Juan Parodi in 1991 and has since become the dominant method for elective abdominal aortic aneurysm (AAA) repair in the United States, accounting for over 75% of such cases. EVAR offers the advantage of lower perioperative morbidity and mortality compared to open surgical repair. However, this benefit comes with the trade-off of higher rates of reintervention and the need for long-term surveillance to monitor for complications.

Principles of EVAR

The fundamental principle of EVAR is that the endograft creates a new conduit for blood flow within the aorta, effectively excluding the aneurysm sac from circulation. This exclusion relies on secure seal zones both proximally, at the infrarenal aortic neck, and distally, within the iliac arteries. Fixation of the endograft is achieved through a combination of radial force exerted by the stent, barbs or hooks that anchor into the vessel wall, and friction against the aortic wall. When the seal is complete, the aneurysm sac is depressurized, leading to thrombosis within the sac and eventual shrinkage. Failure to achieve a complete seal results in an endoleak, which allows continued pressurization of the aneurysm sac and increases the risk of rupture.

Anatomic Suitability

Proximal Neck Criteria (Instructions for Use - IFU)

Successful EVAR depends heavily on the anatomy of the proximal aortic neck, which must meet specific criteria outlined in device Instructions for Use (IFU). The neck length should be at least 15 mm for most devices, although some newer devices accept lengths as short as 10 mm. The diameter of the neck typically ranges between 18 and 32 mm, varying by device. Angulation is critical; infrarenal neck angulation should be less than 60 degrees, and suprarenal angulation less than 45 degrees to ensure proper graft apposition. The shape of the neck ideally features parallel walls, as conical or reverse-tapered necks pose challenges for sealing. Additionally, the presence of circumferential thrombus or calcification involving more than 50% of the neck circumference significantly increases the risk of seal failure.

Iliac Criteria

The iliac arteries serve as both access vessels and distal landing zones for the endograft limbs. Their diameter must range between 7 and 25 mm to accommodate the delivery system and provide an adequate distal seal. The iliac arteries must be navigable despite tortuosity to allow device passage. The common iliac artery diameter should be sufficient for distal sealing, with diameters greater than 20 mm potentially requiring specialized devices such as iliac branch devices or bell-bottom configurations. Furthermore, the iliac length must provide an adequate landing zone, generally at least 10 mm in the common iliac artery.

Access Vessels

Access vessels, typically the external iliac artery or common femoral artery (CFA), must be large enough to accommodate the delivery system, which usually ranges from 14 to 22 French in size. When these vessels are heavily calcified, narrow, or tortuous, alternative strategies may be necessary. Options include creating an iliac conduit by sewing a retroperitoneal Dacron graft to the iliac artery, using an endoconduit with a covered stent to dilate stenotic iliac arteries, or employing other alternative access routes.

Outside IFU Use

Despite the importance of adhering to IFU criteria, up to 40-60% of AAAs treated with EVAR are outside the manufacturer’s IFU. Such outside-IFU use is associated with higher rates of type Ia endoleak and increased need for reintervention. Nonetheless, experienced centers may selectively treat patients outside IFU with acceptable outcomes, provided there is a thorough risk-benefit discussion.

<image>Diagram of the infrarenal aortic neck anatomy relevant to EVAR planning, showing measurements of neck length, diameter, angulation (both infrarenal and suprarenal), thrombus distribution, and the relationship to the lowest renal artery, with ideal versus hostile neck characteristics compared side by side</image>

Current Device Platforms

Bifurcated Modular Endografts

Modern EVAR devices are modular, consisting of a main body with an ipsilateral limb and a contralateral limb deployed separately. This modular design allows for flexibility in accommodating various anatomies.

The Gore Excluder device features a low-profile delivery system (18 French), is flexible, constructed from expanded polytetrafluoroethylene (ePTFE), and uses active fixation with anchors. Medtronic’s Endurant II and IIs devices are made of polyester, provide suprarenal fixation with barbs, and come in a wide range of sizes. The Cook Zenith Alpha also uses polyester with suprarenal barbed fixation and incorporates Z-stent technology for enhanced radial strength. Endologix offers the AFX2, which employs an anatomical fixation concept at the aortic bifurcation with a unique unibody design. The ALTO device, also from Endologix, has a low-profile delivery system and uses PTFE, similar to the Ovation platform. The Ovation iX device introduces a novel concept with polymer-filled sealing rings for proximal fixation.

Aortouniiliac (AUI) Devices

Aortouniiliac devices consist of a single limb endograft deployed to one iliac artery, with an occluder placed in the contralateral iliac artery. This configuration requires a femorofemoral bypass to maintain perfusion to the contralateral leg. AUI devices are indicated when one iliac artery has unsuitable anatomy, in emergency situations, or when the contralateral iliac artery is severely diseased.

Deployment Technique

Procedural Steps

The EVAR procedure begins with gaining access via bilateral femoral cutdown or percutaneous access using the pre-close technique with Perclose devices. Aortography is performed to delineate the positions of the renal arteries, the aortic neck, and iliac anatomy. A stiff guidewire is then positioned in the thoracic aorta to facilitate device delivery.

The main body of the endograft is advanced and deployed just below the lowest renal artery, using fluoroscopic landmarks such as the renal arteries and radiopaque markers on the device for precise positioning. Controlled hypotension may be induced during deployment to prevent distal migration of the graft, a phenomenon known as "wind-socking." Next, the contralateral limb is catheterized from the opposite femoral artery and deployed. Ballooning with a compliant balloon is performed to mold the seal zones proximally, distally, and at overlap sites. Completion angiography assesses for endoleaks, limb patency, and renal artery perfusion.

Imaging During EVAR

Fluoroscopy combined with digital subtraction angiography (DSA) is essential for visualization during EVAR. Road-mapping techniques overlay angiographic images onto live fluoroscopy to guide device placement. Intravascular ultrasound (IVUS) is emerging as a valuable tool for sizing, positioning, and detecting endoleaks. Advanced centers may use fusion imaging, which overlays preoperative computed tomography (CT) scans onto live fluoroscopy for enhanced accuracy.

Anesthesia Options

General anesthesia is most commonly used, especially for complex cases. Regional anesthesia, such as spinal or epidural, is suitable for straightforward procedures. Local anesthesia with sedation can be employed for percutaneous EVAR in selected patients.

<image>Fluoroscopic image sequence showing EVAR deployment: (A) aortogram with renal artery identification, (B) main body deployment just below the renal arteries, (C) contralateral limb cannulation and deployment, (D) completion angiogram confirming aneurysm exclusion without endoleak</image>

Percutaneous EVAR (PEVAR)

Percutaneous EVAR utilizes a totally percutaneous approach with the "pre-close" technique, where Perclose ProGlide devices are deployed before introducing large sheaths. This method offers advantages such as faster recovery, fewer wound complications, and shorter hospital stays. However, it requires adequate common femoral artery size (greater than 7 mm) and minimal calcification at the access site. Contraindications include heavily calcified femoral arteries, previous groin surgery, and obesity that limits access.

Outcomes

Short-Term

In the short term, EVAR is associated with a perioperative mortality rate of 1-2%, significantly lower than the 4-5% seen with open repair. It also results in lower rates of myocardial infarction, pneumonia, renal failure, and intensive care unit stays. Hospital stays are shorter, typically 2-3 days compared to 7-10 days for open repair, and patients return to normal activities more quickly.

Long-Term (EVAR Trials)

Long-term data from major trials provide important insights. The EVAR-1 trial with 15-year follow-up showed that the perioperative mortality advantage of EVAR is lost by six months, with higher aneurysm-related mortality observed in the EVAR group during long-term follow-up. The reintervention rate for EVAR was approximately 12%. The OVER trial, with 14-year follow-up, found no difference in long-term survival between EVAR and open repair but noted more reinterventions and higher aneurysm-related death with EVAR. The DREAM trial reported similar findings, emphasizing the need for ongoing surveillance after EVAR.

Freedom from Reintervention

Freedom from reintervention after EVAR is about 70-80% at five years and 60-70% at ten years. In contrast, open repair has a freedom from reintervention rate exceeding 90% at ten years.

EVAR vs. Open Repair: Decision-Making

Decision-making between EVAR and open repair depends on multiple factors. EVAR is favored in older patients, typically over 80 years, those with multiple comorbidities or high operative risk, favorable neck and iliac anatomy, limited life expectancy where durability is less critical, patients able to comply with lifelong surveillance, and those with isolated AAA without concurrent pathology. Open repair is preferred in younger patients under 65 years, those fit for major surgery, patients with hostile neck anatomy or complex vascular anatomy, where long-term durability is critical due to longer life expectancy, patients unlikely to comply with surveillance, and those requiring concurrent renal or mesenteric repair.

Controversies

Several controversies surround EVAR. The use of EVAR in young patients raises concerns about long-term durability versus the benefit of lower perioperative risk. Treating patients outside IFU criteria remains debated, with some advocating for selective use in experienced centers and others discouraging it. Long-term data from EVAR-1 and OVER trials prompt discussion on whether they argue against EVAR or simply highlight the importance of rigorous surveillance. Management of type II endoleaks remains controversial regarding the aggressiveness of treatment. Additionally, EVAR in women presents challenges due to smaller access vessels, less favorable anatomy, and potentially worse outcomes.

Clinical Pearls

EVAR should not be considered a lesser procedure; it demands meticulous preoperative planning and lifelong surveillance. The aortic neck is the critical factor in EVAR success, requiring careful assessment of length, angulation, thrombus, and calcification. Percutaneous EVAR is becoming the standard approach, and the pre-close technique should be part of every vascular surgeon’s skill set. Surgeons must always have a backup plan, such as an iliac conduit if access fails or conversion to open repair if endograft deployment is unsuccessful. Coordination with anesthesia is important to achieve brief hypotension during deployment to prevent wind-socking. Completion angiography must confirm the absence of type I or III endoleaks, patency of both renal arteries, and patency of both limbs. Finally, patients undergoing EVAR require lifelong surveillance, and this necessity must be clearly communicated before the procedure.

References

• Parodi JC, et al. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Ann Vasc Surg. 1991;5(6):491-499.
• Patel R, et al. EVAR-1 trial: 15-year follow-up. Lancet. 2016;388:2366-2374.
• Lederle FA, et al. OVER trial long-term follow-up. N Engl J Med. 2019;380:2126-2135.
• Chaikof EL, et al. SVS practice guidelines on AAA. J Vasc Surg. 2018;67(1):2-77.
• Schermerhorn ML, et al. EVAR vs. open repair of AAA in Medicare beneficiaries. JAMA. 2015;313(11):1149-1158.

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