Treatment Options for Abdominal Aortic Aneurysm

Surgical Intervention for Abdominal Aortic Aneurysm

Elective surgical treatment of an abdominal aortic aneurysm (AAA) is considered when:

  • Aneurysm is expanding slowly and can be followed through imaging at regular intervals
  • Aneurysm is symptomatic
  • Fusiform aneurysm (tubular shaped) where the circumference of the aorta is distended up to 5 cm. in diameter
  • Saccular aneurysm (outpouching from one section of the aorta) that is up to twice the diameter of the unaffected section of the abdominal aortic aneurysm

In the general population, the best predictor of life expectancy in the presence of an abdominal aortic aneurysm is age and presence of other medical conditions. These considerations are part of the decision analysis of whether to undergo surgical repair of an abdominal aortic aneurysm and if so, which procedure is most appropriate. Because the risks associated with surgery are considerable, surgery may be delayed until the aneurysm has grown to 5.5 cm. or, possibly, when the risk of complications exceeds the risk of surgery. The goal, however, is to repair high-risk aneurysms before complications develop.

There are several factors that an individual with an abdominal aortic aneurysm should consider and discuss with their health-care provider before making a decision of whether or not to undergo elective surgery for AAA repair. These factors include:

  • Risk of rupture
  • Risk of mortality during the elective surgery
  • Life expectancy following surgery

  • Comorbid (co-existing) medical conditions

    • coronary artery disease (e.g., atherosclerosis)
    • other cardiac diseases (e.g., arrhythmias, congestive heart failure)
    • peripheral vascular disease
    • hypertension (high blood pressure)
    • pulmonary disease (e.g., COPD)
    • impaired kidney function
    • morbid obesity

  • Patient preference

Patients with coronary artery disease pose a special surgical challenge for elective repair of abdominal aortic aneurysms because myocardial infarction (heart attack) is a major risk factor for perioperative mortality (up to 30 days post surgery) in these patients. Some doctors estimate that 50% to 60% of cases of perioperative mortality are due to cardiovascular or cardiac related events and, therefore, the following factors should be evaluated prior to undergoing elective AAA repair surgery:

  • Electrocardiogram (EKG)
  • History of cardiovascular disease
  • Cardiac stress test

If uncontrolled hypertension is present, it must be treated at the earliest opportunity since high blood pressure increases the risk of potential rupture of an abdominal aortic aneurysm. In some circumstances, corrective cardiac surgery may be performed before repair of the abdominal aortic aneurysm which reduces postoperative mortality rate due to cardiac complications.

One of the most important criteria for deciding which surgical procedure to undergo for elective surgical repair of an abdominal aortic aneurysm (AAA) is the experience of the surgeon performing the repair as well as the experience and training of the hospital staff in assisting and treating patients undergoing each type of surgery. The aspect of surgical experience is highly associated with morbidity and mortality rates and warrants careful attention by the patient before making any decisions.

There are two surgical options available for the repair of abdominal aortic aneurysms:

Open Repair

This is an invasive surgical procedure in which an incision is made through the abdomen to expose the abdominal aorta and gain access to the aneurysm. A prosthetic tube-like graft (stent-graft), usually composed of a synthetic material (e.g., Dacron) is surgically sewn into place in order to repair the aneurysm. Following surgery, the individual is in the intensive care unit usually for up to 3 days and remains in the hospital on the average of 5-10 days. Recovery time on the average is 2-3 months depending on age and other factors.

Each individual considering open surgical repair must be evaluated carefully to determine if they have a high risk profile for mortality, including:

  • Cardiovascular disease
  • Abnormal electrocardiogram
  • Chronic Obstructive Pulmonary Disease (COPD) or other pulmonary involvement
  • Elevated creatinine levels (indicative of renal impairment)
  • Older age
  • Gender - estimates are that women may be at 1.5 times greater risk of perioperative mortality than men

  • Anatomical features of the aneurysm and aorta are important since they can effect several technical issues, including:

    • the implantation of the stent-graft (e.g., sealing, risk of slippage)
    • if the aneurysm is close to the renal arteries, more clamping of those arteries may be required during surgery potentially elevating the time of renal ischemia (lack of oxygen) and stress on the vascular system
    • clot formation or calcification can effect clamping as well as placement of stent
    • if the aneurysm is stuck to adjacent structures (e.g., veins, ureters, or bowel) this can increase the level of risk for surgical complications.
Surgical Approaches

There are two surgical approaches with which the surgeon can expose the aorta for repair:

  • Transperitoneal approach which involves gaining access to the AAA via a midline abdominal incision.

  • Left retroperitoneal approach where the incision to gain access to the AAA is towards the left side of the abdomen. This type of incision has gained acceptance due to several advantages, including:

    • improved pulmonary function
    • less post-operative pain
    • fewer gastrointestinal complications
    • shorter postoperative time in the intensive care unit
    • shorter hospital stay

The left retroperitoneal incision is also beneficial for people with underlying medical conditions, including:

  • Prior abdominal or pelvic radiation
  • Dialysis
  • Obesity
  • Aneurysms close to the renal arteries
Advantages of Open Surgical Repair

Advantages of open repair of abdominal aortic aneurysm include:

  • Low rate of surgical reintervention (second operation required to correct a problem arising from the initial surgery).
  • Low rate of complications due to endoleaks or other graft related problems. An "endoleak" is persistent blood flow into the aneurysm. There are several types of endoleaks, but the most common include a leak resulting from an incomplete seal of the stent-graft to the aortic wall or resulting from opposing blood flow from collateral vessels.
  • Long-term success rates
Risks of Open Surgical Repair

Postoperative complications of open repair for abdominal aortic aneurysm include:

  • Cardiac events - More than one half of complications that occur postoperatively are cardiac in nature and they account for up to 60% of postoperative deaths, the majority due to heart attack.

  • Hemorrhage - This is the second most common complication and is often due to technical difficulties or errors.

  • Pulmonary insufficiency - Since abdominal aortic aneurysms are so closely associated with smoking and chronic obstructive pulmonary disease (COPD), pulmonary insufficiency is a common complication for those patients. This risk factor can be somewhat reduced if patients stop smoking several weeks prior to surgery. Individuals who are at high risk for developing this complication include:

    • smokers
    • patients with COPD
    • patients over the age of 70
    • obese patients

  • Renal (kidney) failure - Although renal failure may occur in up to 8% of patients who undergo open repair, only a small percentage requires dialysis. Renal failure is related primarily to procedures during surgery (e.g., clamping of the renal arteries during surgery, use of radiographic contrast dyes).

  • Gastrointestinal ischemia and/or dysfunction - Temporary dysfunction or paralysis of the small or large intestines often due to manipulation of the intestines during surgery or fluid retention.

  • Erectile Dysfunction - Open abdominal aortic aneurysm repair has been reported to be associated with impairment of sexual function in men, most likely because of autonomic nerve injury and pelvic blood flow changes

  • Graft infection - This may occur months to years following surgery and is associated with significant morbidity and mortality. Prophylactic use of antibiotics prior to surgery is helpful in reducing the risk of this complication.

Estimates of mortality during or following open repair for abdominal aortic aneurysm is related to experience of the surgeon and ranges from 4% mortality for surgeons who have performed a high volume of open repair to 8% for those with a low volume of experience with open repair.

Endovascular Aneurysm Repair (EVAR)

Endovascular aneurysm repair (EVAR) is usually reserved for a limited selection of patients, including:

  • Individuals with AAA who cannot tolerate open surgery due to concurrent medical conditions
  • Individuals who are elderly

Endovascular aneurysm repair is a newer and less invasive surgical technique as compared with open AAA repair and is usually done under regional (spinal) or local anesthesia. Using this technique, the surgeon creates an incision in the groin area and a catheter containing the prosthetic graft within a metal (mesh) stent is advanced through the femoral artery under radiological guidance (ultrasound or X-ray) up to the area of the aneurysm. When the stent-graft is correctly inflated and anchored into place, the aneurysm is shielded from blood flow and may even shrink over time. This procedure is followed by a temporary period in the intensive care unit and hospitalization of approximately one week.

The stent-graft provides an alternative pathway for blood to flow through the aorta without filling the aneurysm, which reduces pressure on the aneurysm and reduces the risk of bursting. The proximal end of the graft (end closer to the heart) is placed just below the lower of the two renal arteries and the distal ends usually extend into the two iliac arteries in each leg (bifurcated stent). The Food and Drug Administration (FDA) to date has approved two stents to be used for endovascular repair of AAA - the Guidant Ancure stent-graft and the Medtronic AneuRx stent graft. They differ in the materials from which they are made and how they attach to the arterial walls.

Factors that are taken into consideration to determine if patients with an abdominal aortic aneurysm may be eligible candidates for EVAR include:

  • The presence of other underlying medical (comorbid) conditions
  • Anatomy of the blood vessels (e.g., if they are unusually positioned or very curved)
  • Experience of the surgeon
  • Experience of the hospital staff participating in this procedure
  • Patient's life expectancy following surgery
  • Level of risk if open surgery was performed
  • Presence of debris (e.g., calcifications or fatty deposits) in the segment of the aorta immediately above the aneurysm
  • If the individual meets the specific criteria for inclusion determined by the manufacturer of the EVAR equipment
  • If the individual is prepared to assume the burden of continued regular surveillance for the rest of his or her life

In addition to other diagnostic tests, patients undergoing EVAR undergo abdominal aortic and pelvic angiograms with a marking catheter to enhance the precision of the previous tests (e.g., ultrasound). Precise measurements are crucial component of the decision to proceed with EVAR.

Although EVAR does allow treatment inclusion for individuals who may have other underlying medical conditions, there is continued debate regarding the inclusion of elderly people with comorbid conditions. These patients are considered at a higher risk for complications and their survival rate at three years following surgery is 58%. It is estimated that up to 10% of all EVAR surgeries undergo conversion to open repair because of unexpected technical difficulties or complications during the procedure

Studies indicate that EVAR limits the expansion of AAAs in up to 90% of cases and prevents rupture of the aneurysm in up to 98% of individuals undergoing the procedure. The rate of rupture for aneurysms repaired with EVAR is approximately 0.5% at 3 to 4 years post surgery. As more years pass since the initiation of the procedure, longer term results will become available.

FDA Public Health Notification about Endovascular Grafts

In March 2008, the U.S. Food and Drug Administration (FDA) issued a public health notification to re-emphasize the need for continued surveillance of patients treated with endovascular grafts and provided updated information on the mortality risks associated with the use of the AneuRx Stent Graft System to prevent AAA rupture. The FDA's public health notification focused on the AneuRx Stent Graft System because it is the only currently marketed device with a significant number of patients with long-term clinical follow-up at five years.

The FDA had issued two previous public health notifications (2001 and 2003) identifying several serious adverse events, including aneurysm rupture, in patients treated with the AneuRx Stent Graft. Previously, the FDA reported that late aneurysm-related mortality among AneuRx graft patients was about 0.4% per year. More recent longer-term data suggests that aneurysm-related mortality continues to increase after 3 years post-implant, reaching 1.3% by year 4 and 1.5% by year 5. These rates are substantially higher than the mortality rate for open surgical repair of AAA, which averages 0.18% per year (range = 0% to 0.3% per year).

Based on these findings, the FDA recommended that the AneuRx Stent Graft System be used only in select patients who meet the appropriate risk-benefit profile. In determining the risk-benefit profile for patients with AAA disease and the appropriate treatment option, factors that need to be considered include:

  • The risk of long-term AAA-related mortality, especially due to AAA rupture - Based on more complete follow-up data, the latest information available suggests that the average risk of late AAA-related mortality associated with AneuRx exceeds that associated with open surgery.

  • The experience of the institution or the surgeon - If open surgery or endovascular repair is performed in institutions or by surgeons with little experience with these surgical procedures, the mortality rate may be considerably higher than average for that procedure.

  • Surgical risk factors for the individual patient - Patients who have substantial surgical risk factors such as older age and co-morbidities (e.g., heart, kidney, or lung diseases) may experience a higher than average mortality rate for open surgical repair of AAA. For a 70-year old patient, for example, the mortality rate could range from 2% with no risk factors to over 40% with multiple co-morbidities.

  • The patient's willingness to comply with the follow-up schedule for continued surveillance of the endovascular graft.

Advantages of Endovascular Aneurysm Repair

Advantages of endovascular AAA repair include:

  • Lower perioperative risk because it is less invasive surgery
  • Shorter hospitalization
  • Shorter recovery time
  • Fewer adverse events, particularly cardiac, renal, and pulmonary than for open surgery (estimates range from 30-70% reduction of these complications)
  • Lower incidence of erectile dysfunction than open surgery
  • Enables individuals who otherwise could not tolerate open surgery with general anesthesia to benefit from elective AAA repair
Complications of Endovascular Aneurysm Repair

The disadvantages of EVAR include:

  • Late complications
  • High rate of reintervention
  • There is no indication of improved survival over open AAA repair
  • Population considered eligible is very limited
  • Burden on the patient to undergo continual surveillance is very high

Complications that may occur either during or after endovascular repair for abdominal aortic aneurysm include:

  • Endoleaks - This is characterized by persistent leakage of blood from fabric tears or from the joints connecting each part of the stent-graft. The blood leaks into the aneurismal sac between the graft and the arterial wall but not into the abdominal cavity. This complication occurs in 10-20% of AAA repairs. There are four types of endoleaks - types I and III are associated with continued expansion and rupture while types II and IV rarely causes adverse effects and may seal themselves.
  • Problems with durability of stent-graft
  • Later secondary reintervention and/or open repair
  • Injury to arteries due to insertion of catheter
  • Occlusion of renal or hypogastric arteries due to improper placement of graft
  • Injury to kidneys due to toxicity of contrast dyes
  • Post-implant syndrome - a syndrome characterized by back pain and fever but without other evidence of infection
  • Blood clot formation
  • Rupture of aneurysm

If in the course of surgery, the surgeon finds that the anatomy of the patient is more complex than originally anticipated, the surgeon will convert EVAR over to open surgery.

It is important for the individual undergoing elective surgery for abdominal aortic aneurysm to consider carefully the risks and benefits of each type of surgical procedure (open repair or EVAR) as well as to consult closely with their physicians regarding individual risk factors for aspects of both procedures.