Abdominal Aortic Aneurysms: New Screening Guidelines And Repair Options
ABSTRACT: Improved screening guidelines and operative options can significantly decrease morbidity and mortality from abdominal aortic aneurysms in carefully selected patients.
CME OBJECTIVE: Readers will have a heightened awareness of the need to screen patients at high risk for abdominal aortic aneurysm and the operative risk/benefit ratio for different procedures.
William D. Jordan, Jr, MD; Mark A. Patterson, MD; Gilberto C. Russo, MD, PhD; Steven M. Taylor, MD, no conflicts of interest
Abdominal aortic aneurysm (AAA), enlargement of the abdominal aorta to 150% of its original diameter, is a significant cause of morbidity and mortality among older adults. UAB's Section of Vascular Surgery emphasizes cutting-edge care for vascular conditions, including endovascular repair for carefully selected patients, Section Chief William D. Jordan, Jr, MD, says. UAB's vascular surgery team includes Jordan, Mark A. Patterson, MD, Gilberto C. Russo, MD, PhD, and Steven M. Taylor, MD.
Many AAAs can eventually rupture if left untreated. The likelihood of rupture increases with size; one study estimates 1-year rupture rates of 11% for AAAs 5.0 cm to 5.9 cm and 26% for aneurysms 6.0 cm to 6.9 cm (J Am Coll Surg. 2004;199:946-960). "The results of rupture are devastating; only 50% of patients who experience aneurysm rupture survive. Of those who reach the hospital, fewer than half live to hospital discharge — even with successful repair," Patterson says.
AAAs kill about 9000 Americans a year. An estimated 4% to 8% of older men and 0.5% to 1.5% of older women harbor AAAs, according to the United States Preventive Services Task Force (USPSTF), which recently offered AAA screening recommendations.
AAAs are often asymptomatic for years, but are easily detected with ultrasonography, Taylor says. "Physicians should be aware of the high mortality of rupture and consider more aggressive screening for high-risk patients."
New Screening Guidelines
Major risk factors for AAA include older age, smoking history, and male sex. Family history, hypercholesterolemia, coronary heart disease, and cerebrovascular disease also increase risk.
Based on meta-analysis of four population-based, randomized, controlled trials of AAA screening, USPSTF found good evidence one-time ultrasonographic screening of men aged 65 to 75 years who are current or past smokers decreases AAA-related mortality, preventing one death for every 500 men screened during a 5-year period (Ann Intern Med. 2005;142:198-202).
Ultrasound screening for AAAs is highly sensitive (95%), with specificity close to 100% in settings with good quality control. Physical examination has poor accuracy and is an unsuitable substitute for ultrasound, USPSTF reports.
Although screening leads to an increased number of repairs, and these procedures are associated with significant morbidity and mortality, USPSTF found for men aged 65 to 75 years, benefits outweigh risks. The group reported no benefit for repeated screening after negative ultrasound. Men in this age bracket had a low 10-year incidence of new AAAs (0% to 4%), and those that occurred were unlikely to rupture because of small size (<4 cm).
USPSTF does not recommend routine screening for women, who had a low incidence of AAAs — one sixth that of men.
"These are general guidelines," Taylor says. "Because AAA screening is noninvasive, most patients with risk factors should be screened. For example, a female smoker in her 60s with a family history of AAA should definitely be screened."
Patterson agrees, noting "Although AAAs are more common in men, women with aneurysms carry a similar risk of devastating rupture."
"Aneurysms less than 5.5 cm in men and 4.5 cm in women, the usual thresholds for surgical intervention, should be monitored with periodic ultrasound — annually for AAAs smaller than 4 cm and twice a year for larger aneurysms," Russo says.
Elective repair is indicated when risk of rupture outweighs risk of repair, Russo says. "Surgeons should repair most AAAs larger than 5 cm or those that grow more than 1 cm a year. If ultrasound reveals a AAA of any size, physicians should refer patients to a vascular surgeon for evaluation."
Depending on patient profile and risk factors, surgeons may treat some AAAs that fall outside general repair guidelines, Taylor says. "For example, a man with a 5 cm AAA whose aorta is normally 25 mm has an aorta twice its usual size, but a 4 cm AAA in a woman with a normal aortic diameter of 15 mm is relatively much larger, and repair should be considered for both."
Repair Options
Vascular surgeons can repair AAAs with an open surgical approach or an endovascular technique. "Open repair is a well-proven, durable procedure. But, it involves a large incision, prolonged hospital stay, and a long recovery," Russo says. "Some older individuals or those with significant comorbidities are not candidates open surgery."
Operative mortality for open surgical repair is highly dependent on medical center experience, ranging from 2% to 5%; centers such as UAB that perform a large volume of open aneurysm repairs fall at the low end of this range, Patterson says.
Endovascular repair was developed as a less-invasive alternative for patients at high risk for surgery. During the procedure, surgeons channel catheters, guidewires, and introducer systems through femoral arteries and use fluoroscopic guidance to assemble an endograft inside the AAA.
A recent study of 404 patients who had AAA repair at UAB found both high- and low-risk patients who underwent endovascular repair had lower rates of short-term systemic complications and shorter hospital stays than those who had open repair (Ann Surg. 2002;237:623-630).
"Appropriate patient selection is the key to long-term success with endovascular repair," Patterson says. "Not all patients are anatomically suited for endovascular repair," Russo adds. "Computed tomography scan reveals aneurysm size and the shape, length, and angle of the aortic neck." Generally, aneurysms must have a neck length of >1.5 cm and a diameter >28 mm to be suitable for endovascular repair. Aneurysm size and iliac artery anatomy also may rule out endovascular repair, although surgeons can often overcome these issues.
Patient availability for follow up is also crucial, Taylor says. "Endovascular repair carries less short-term morbidity than open repair, making it attractive to patients. But, individuals undergoing the less invasive procedure have a higher incidence of mid- and long-term complications, including endoleak, perforations, and graft migration. Many of these issues can be addressed with endovascular techniques, but potential complications make diligent, lifelong follow up a necessity."
Recent Trial Data
Early data from the Dutch Endovascular Aneurysm Management (DREAM) trial that randomized 351 patients with AAAs >5 cm to either open or endovascular repair showed significant reductions in 30-day postoperative mortality in the endovascular group, 1.2% versus 4.6% for open repair (N Engl J Med. 2004;351:1607-1618). Patients in the endovascular group also reported short-term improvements in quality of life, but by 6 months, these differences diminished.
Results mirrored those of the larger British Endovascular Aneurysm Repair (EVAR-1) trial that enrolled more than 1000 patients and reported substantial reductions in 30-day operative mortality; 4.7% for open surgery, compared with 1.7% for endovascular repair (Lancet. 2004;364:843-848).
Recent publication of longer-term data from DREAM, EVAR-1, and EVAR-2 evaluating mortality, severe complications, and reintervention rates show many endovascular repair benefits do not persist beyond the early postoperative period.
Two years after DREAM trial randomization, participants in the open surgery group had cumulative survival rates of 89.6% versus 89.7% in the endovascular group, not a statistically significant difference. Both groups had similar rates of severe complications, aneurysm rupture, and reintervention, however, patients who underwent endovascular repair had lower aneurysm-related mortality, 2.1% versus 5.7% for those randomized to open surgery (N Engl J Med. 2005;352:2398-2405).
At 4-year follow up, all-cause mortality among EVAR-1 participants did not differ between open and endovascular repair. The endovascular group had higher rates of late complications and reintervention, but lower aneurysm-related mortality, 4% versus 7% (Lancet. 2005;365:2179-2186).
The 388 patients enrolled in EVAR-2 had significant comorbidities that ruled out open surgery. Participants were randomized to either endovascular repair or nonintervention. After 4 years, investigators found no survival benefit for repair versus nonintervention (Lancet. 2005; 365:2187-2192).
"The absence of long-term survival benefit in these trials surprised many vascular surgeons. Studies investigating results with newer devices will provide more data," Patterson says. "As a section, we remain enthusiastic about endovascular repair, because many patients clearly benefit and the technique and technology have allowed therapy for individuals who otherwise would not have been candidates for any treatment."
For more information:
Dr. William Jordan
Dr. Mark Patterson
Dr. Gilberto Russo
Dr. Steve Taylor
1.800.UAB.MIST
mist@uabmc.edu
Published in UAB Insight, Fall 2005