Patient Selection Criteria for Endovascular Aortic Aneurysm Repair: Optimizing Outcomes

Abstract

Endovascular aortic aneurysm repair (EVAR) has become the preferred treatment for abdominal aortic aneurysms, offering a minimally invasive alternative to open surgery. However, successful outcomes depend on meticulous patient selection. This review explores the key criteria for patient eligibility, including aneurysm size, morphology, and the quality of the proximal and distal aneurysm necks. Additionally, imaging assessment and various device variables, including anatomical suitability, are examined to emphasize their influence on procedural success. As EVAR technology evolves, understanding the nuances of patient selection remains crucial for maximizing technical success and clinical outcomes, while minimizing complications including endoleaks and migration, and extending the benefits of the procedure to a broader range of patients.

It has been over 30 years since Parodi ¹ and Volodos ² first individually reported the endovascular repair of an aortic aneurysm (EVAR) using a covered stent. Since that time, there has been significant growth in the treatment of aortic aneurysms using endovascularly positioned stent grafts to exclude aneurysmal aortic segments. Unfortunately, the long-term durability of these repairs has always been a question. Even with continued iterations in devices and techniques, data on long-term aneurysm-related mortality and the need for additional secondary procedures in patients who have undergone EVAR have raised concerns about the procedure's role, particularly in younger surgical candidates. ^{3 4 5 6 7 8} The selection of patients and appropriate endovascular aortic devices has proven critical in minimizing the risk of aneurysm-related mortality and improving the durability of EVAR.

Technical Success

Technical success is defined as the exclusion of the aortic aneurysm during the endograft placement procedure. The proper selection of patients based on their vascular anatomy and comorbidities, as well as the selection of the appropriate endograft configuration, has led to nearly 100% technical success in the treatment of abdominal aortic aneurysm (AAA). Long-term success, or durability, of the endovascular repair is defined by the continued exclusion of the aortic aneurysm over time preventing aneurysm-related mortality.

Patient Selection

The patient's comorbidity profile and life expectancy must be weighed against the patient's rupture risk when deciding upon the decision to proceed with aneurysm repair. Open surgical options must be considered along with endovascular options, especially in young patients with favorable comorbidity profiles. The most significant factors for survival post–AAA repair have been reported as advanced age, cardiac disease, oxygen-dependent chronic obstructive pulmonary disease, and renal dysfunction. ⁹ Once the decision is made to proceed with endovascular repair, several factors need to be considered ( Table 1 ).

Table 1. Selection factors that define the aortic neck in abdominal aortic aneurysm.

Critical factor	Description
Neck length	Short neck (≤ 10 mm) may result in maximal seal failure and disease progression
Neck diameter	Diameter of > 28 mm suggests disease involvement; reverse taper indicated by > 2 mm dilatation within 1 cm
Neck angulation	Angulation > 60 degrees minimizes the ability to achieve optimal stent coverage of healthy aorta
Morphology of the neck	Presence of thrombus or calcium can compromise sealing and fixation

The morphology of the aneurysm is the first selection criteria. If the aneurysm is saccular or irregular in configuration, the aneurysm may require more urgent treatment. The saccular aneurysms affect one wall more than others increasing the risk of rupture. Some etiologies and anatomy may prompt open surgical repair such as in patients with infections or mycotic aneurysms. ¹⁰ Saccular aortic aneurysms may be associated with pain and the decision to treat these aneurysms should not rely purely on aneurysm size ( Fig. 1 ). In contrast, traditional aneurysms are fusiform, and the aneurysmal diameter is directly related to rupture risk ( Figs. 2 and 3 ). Guidelines have been established to aid in patient selection for fusiform aortic repair based on diameter. The Society for Vascular Surgery recommends elective repair in patients with low or acceptable surgical risk who have a fusiform AAA equal to or greater than 5.5 cm. ¹¹ This recommendation carries a grade 1 (strong) recommendation with high-quality evidence. Women with AAAs between 5 and 5.4 cm may also be considered for treatment; however, the strength of the recommendation is weaker, and the quality of evidence is only moderate. The European Society for Vascular Surgery reiterates similar guidelines, recommending the repair of asymptomatic AAAs greater than 5.5 cm in men and 5 cm in women, mostly related to their smaller vessel size. ¹² Additionally, aortic diameter growth greater than 0.5 cm per year is considered rapid growth and prompts aortic repair. Once the decision is made to treat a patient, it is important to assess whether they are a suitable candidate for open surgical repair, endovascular repair, or surveillance. Recent guidelines have recommended that those with aortic aneurysms should be treated at high-volume centers. ^{11 12}

Fig. 1.

A 77-year-old male with a fusiform 6-cm abdominal aortic aneurysm on CTA.

Fig. 2.

A 70-year-old male with a saccular abdominal aortic aneurysm. Distal irregularity at the level of the distal aorta (red arrow).

Fig. 3.

An 80-year-old male with a 6-cm abdominal aortic aneurysm with an angled proximal neck. Image highlighting the angled neck ( a ). Image with endograft positioning in the neck to maximize the seal ( b ). Final angiogram with maximal seal ( c ).

There are several anatomical factors to assess the candidacy of patients for endovascular aortic repair. The assessment of the proximal and distal aortic neck is of primary anatomic importance. The length of the neck and the quality of the aortic neck are critical to predict the proper seal (or apposition) of the graft to the aortic wall. The length of the aortic seal is related to the aortic diameter over the length of the aortic neck. The durability of the seal is dependent on the proper fixation of the graft to the wall of the aortic neck to maintain the seal. The fixation is maximized using hooks and barbs on the endografts to help the graft maintain their seal over time.

Additionally, the morphology of the aortic neck is important to predict the durability of maintaining an endograft at the aortic neck. If there is a thrombus or calcification within the circumference of the neck of the aneurysm, the seal and fixation of the aortic graft to the aortic neck will be compromised. Neck morphology is usually assessed by evaluating the extent of the neck circumference affected by thrombus or calcification. When up to 90 degrees of the neck circumference (25%) is involved, this is considered minimal. However, when more than 180 degrees of the circumference (>50%) of the aortic proximal neck is involved by thrombus or calcification, the ability for proper neck fixation and the long-term durability of the aortic repair will be impaired. Furthermore, if the aorta at the level of the neck is dilated (over 28 mm in the abdominal aorta), the risk of further aneurysm progression is present, making the length of the aortic neck even more imperative for ensuring the durability of the repair. Similarly, the term “reversed tapered neck” represents involvement of the aneurysm neck making early future dilatation much more probable. The length and quality of the proximal and distal aortic neck have driven aortic aneurysm therapy to maximize aortic neck length. Traditionally, aortic endografts have required a proximal neck of at least 2 cm in the thoracic aorta and 1 to 1.5 cm in the abdominal aorta.

The angulation of the aortic neck can reduce the length and amount of vessel contact between the aortic graft and the neck, thereby limiting the effectiveness of the seal and fixation. Traditionally, aortic neck angulation greater than 45 degrees is considered significant ( Fig. 3 ). However, several devices have been designed to accommodate a certain degree of angulation by allowing for long seal zones, even with an angled neck. With more conformable devices, the aortic graft in the aorta can be angled during deployment to maximize the seal in the infrarenal aorta by matching the angle of the infrarenal neck.

When evaluating a proximal neck, it is important to assess its length, diameter, and morphology, as previously mentioned. Multiple studies have shown that infrarenal aortic repairs with a challenged proximal neck carry a greater risk of Type IA endoleak around the proximal aspect of the neck. These patients also face a higher risk of aneurysm-related mortality. ^{4 13 14} Unfortunately, studies have shown that the use of endografts for AAAs outside of the instructions for use is associated with a higher risk of type 1A endoleak and aneurysm-related mortality. ¹⁵

The use of fenestrated endografts, off-the-shelf branched grafts, and physician-modified devices has served to increase the length of seal and fixation in the aorta. These devices allow for the incorporation of branch vessels and extend the proximal neck length to above the celiac trunk in abdominal aneurysms. Similarly, branched thoracic grafts facilitate the use of the distal aortic arch and the proximal descending thoracic aorta, maximizing the length of the proximal aortic neck. ^{16 17 18 19} These advancements enable longer and more secure proximal neck sealing, thereby increasing the durability of the repair. When selecting possible treatments for aortic aneurysms, we must consider not only traditional devices but also branch and fenestrated devices as well as open surgical options for all patients. The use of fenestrated devices and physician-modified endovascular grafts (PMEGs) has enabled operators to maximize the proximal seal zone, expanding it beyond the traditional 15-mm axial zones to 3- to 4-cm extended zones ( Fig. 4 ). Multicenter data of over 1,200 PMEGS from 19 international centers demonstrate encouraging results in these patients. This included thoracic, thoracoabdominal, and abdominal PMEGs with a high technical success rate of approximately 95% and impressive freedom from aneurysm-related mortality near 90% at 5 years. ¹⁶

Fig. 4.

A 75-year-old female with an enlarging juxtarenal abdominal aortic aneurysm (AAA). CT imaging demonstrates the extensive juxtarenal AAA. ( a ) Angiogram demonstrates the location of visceral vessels with physician-modified grafts fenestrations aligned ( b ). Spot image demonstrating the partial deployment of endograft in the abdominal aorta ( c ). Angiogram demonstrates branch stents in each of the four visceral vessels ( d ).

Imaging

The selection of anatomical criteria for endovascular aortic repair is based on imaging, which allows us to define the size of the aneurysm as well as assess the angulation, length, and diameter of the proximal and distal neck. This evaluation helps us determine the extent of the aneurysm and plan potential treatment options. CT angiography (CTA) is the standard technique for assessing and selecting patients for endovascular aortic repair. CTA is typically performed consistently across centers and provides isotropic images, meaning the images can be reconstructed in any plane while maintaining spatial integrity. CTA also enables precise measurement of the aortic diameter at the neck, helping to exclude patients with large or tapered necks, as these are associated with a higher risk of aneurysm progression.

In the thoracic aorta, it is essential to assess the angulation, the location of the great vessels, and the aortic diameter, as well as any anatomical variations. The development of thoracic branch endografts has expanded the use of endovascular repair for the thoracic aorta. When selecting patients, it is important to evaluate the status of the ascending aorta, aortic arch, and proximal descending aorta to optimize the length of the proximal neck. In the thoracic aorta, the goal is to achieve at least a 2-cm seal zone, which is crucial due to the natural angulation of the arch and the inherently larger diameter of the aorta. Thoracic branch endografts can be used in conjunction with carotid-to-carotid or carotid-to-subclavian bypasses to preserve blood flow to the great vessels during thoracic repair.

Data

In 2020, a study examined the durability of Excluder and Endurant stent grafts. ²⁰ The study included a cohort of 275 devices. At 7 years, the overall clinical success rate for both types of devices was ∼60%. A key finding was the relationship between proximal neck dilation and the size of the originally placed stent graft. When devices with a 32-mm diameter were placed, approximately 12% proximal neck dilation occurred over the 7-year period, with a significant number of patients experiencing greater than 10% dilation. Conversely, patients with smaller aortic devices (26 mm) also demonstrated neck dilation, but at a much slower rate. This highlights that larger aortic diameters are more prone to dilation, necessitating longer necks and close monitoring of these patients after repair.

The issue of aneurysm-related mortality remains a critical challenge in AAA repair. The notable UK-COMPASS AAA Trial, ²¹ which included over 2,200 patients in England, compared outcomes of open repair, EVAR, and fenestrated repair. At the 3-year follow-up, patients who underwent open repair had the highest survival rate, with ∼80% survival for both fenestrated and EVAR procedures. These results underscore the importance of careful consideration of repair methods in complex cases.

As we reassess patient selection for endovascular aortic repair, we must consider procedural and long-term success, especially with the reduction of aneurysm-related mortality. The aim of aortic aneurysm repair should be to extend survival while preventing aortic-related mortality. As we evaluate this technology, it is crucial to consider whether it is an alternative to conventional open surgical repair or an option reserved for patients who are not candidates for traditional surgical approaches. Over the past 35 years, since the pioneering work of Dr. Parodi and others, the use of stent grafts has evolved significantly in the treatment of aortic aneurysms, but the importance of careful patient and graft selection is still critically important.

Conclusion

Optimizing outcomes for endovascular aortic repair relies heavily on careful patient selection. Aside from the patient's medical comorbidities, key anatomical criteria, such as aneurysm size, morphology, and the condition of the proximal and distal landing zones, are essential for achieving long-term success. Additionally, considering patient-specific factors such as comorbidities, life expectancy, and anatomical suitability ensures a personalized approach that balances procedural risk and benefits. As advances in technology continue to expand the eligibility for EVAR, an understanding of selection criteria will improve long-term outcomes.