Introduction | Statistics | Standard Repair
 
Introduction
"Abdominal aortic aneurysm" isn't a condition you hear about everyday. Yet two Mayo Clinic studies document a three-fold increase over the past 40 years. The increase may be partly due to the upsurge in smoking since World War II. Also, as more people live longer, this type of aneurysm occurs more frequently. About 15,000 Americans die each year from ruptured abdominal aortic aneurysms. Compared with the half million who die annually of heart attacks, the number of deaths due to aneurysms is small. But it's scary that an abdominal aneurysm may rupture and cause sudden death. If detected early, however, surgery eliminates this silent danger 95 percent of the time.

A Weakened Artery
An aneurysm is a bulging or ballooning of an artery wall. It usually occurs when the arterial wall becomes weak or damaged by accumulation of cholesterol-containing fatty deposits (atherosclerosis).

Other factors that contribute to weakening of the arterial wall are:

• High blood pressure
• Smoking
• Male gender
• Age 55 or older
• Family history of abdominal aortic aneurysm.

Once elasticity is reduced, the force of the heartbeat can cause an artery to slowly stretch and bulge.

An abdominal aortic aneurysm occurs in your body's largest artery, the aorta. Usually, this aneurysm develops beyond where the aorta branches to supply blood to your kidneys and above where it divides to supply blood to your pelvis and legs.

The abdominal aorta's diameter normally ranges from 3/4 to 1 inch. Small aneurysms--less than 2 inches (5 centimeters)--rarely rupture. As they grow bigger than this, however, the risk of rupture increases by 5 percent each year.

As with any aneurysm, the danger is that an abdominal aortic aneurysm will leak or burst, causing life-threatening bleeding. A few people may feel pain in their backs as an aneurysm enlarges. But most abdominal aortic aneurysms are "silent "--they enlarge slowly with no symptoms.

If you're at high risk
A careful physical examination can detect 70 to 80 percent of abdominal aortic aneurysms. By placing a stethoscope on your abdomen, your doctor can pick up sounds of turbulent blood flow over the aorta's roughened surface. Gentle pressure on your abdomen can help determine whether you have a pulsating mass. Being overweight, however, reduces accuracy. And, usually, further evaluation is needed. For a more accurate test, your doctor may use ultrasound. Routine screening for an aortic aneurysm using computed tomography (CT) or magnetic resonance imaging (MRI) scans isn't usually necessary or cost-effective.

When do you need surgery?
Surgery is almost always needed when the diameter of an aneurysm enlarges to at least 2 inches. The operation involves an incision into your abdomen to open the aorta and remove cholesterol and fatty buildup. The surgeon implants a flexible tube (graft) to replace the enlarged artery. Recovery from elective surgery takes about six weeks, including a one-week hospital stay. Emergency repair of a ruptured aortic aneurysm is less successful--62 percent of people die before they reach the hospital. Of those who have surgery, 50 percent live. As an alternative to abdominal surgery, Mayo Clinic is one of several medical centers investigating a new procedure called endovascular surgery. It involves passing a collapsed graft up the femoral artery in your leg into the weakened aorta, then securing the graft with metallic stints. Similar to balloon angioplasty, the graft is then inflated to restore normal blood flow. Endovascular surgery may become a safer and easier alternative to traditional surgery, especially for people at high surgical risk. Find out sooner, not later. Prevention and early detection are the keys to avoiding death from an abdominal aortic aneurysm. If you're at least 55 years old, know your risks and what steps you can take to protect yourself.

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Statistics
JAMA 1992 Nov 18; 268(19):2678-86 Katz DA;
Littenberg B; Cronenwett JL
(93059913 NLM)

OBJECTIVES: To compare two clinical strategies for the management of small abdominal aortic aneurysms (AAAs) less than 5 cm in diameter: early surgery (repair small AAAs when diagnosed) and watchful waiting (measure AAA size every 6 months and repair when the diameter reaches 5 cm).

DATA SOURCES: We reviewed data from an earlier longitudinal study of patients with small AAAs to estimate incidence rates of rupture or acute expansion. Estimates for other parameters in the model were obtained by searching the medical literature (MEDLINE, 1966 to present).

DATA SYNTHESIS--We constructed a Markov decision tree to compare early surgery with watchful waiting in patients with asymptomatic AAAs less than 5 cm in diameter, with respect to long-term survival in quality-adjusted life years. The average annual rates of rupture or acute expansion for AAAs with a maximal transverse diameter of less than 4.0, 4.0 to 4.9, and at least 5.0 cm, are 0, 3.3, and 14.4 events per 100 patient-years of observation, respectively. At an average rupture rate of 3.3 events per 100 patient-years and an average operative risk for elective surgery (4.6%, 30-day mortality), our model predicts that early surgery improves survival in patients who present with a 4-cm AAA. The benefit of early surgery decreases with increased age at presentation. If the average rupture rate for AAAs less than 5 cm is assumed to be low (eg, 0.4 event per 100 patient-years), watchful waiting if favored, particularly as operative risk increases. The decision in this subgroup, however, is sensitive to possible future increases in operative risk.

CONCLUSIONS In the majority of scenarios that we examined, earlysurgery is preferred to watchful waiting for patients with AAAs lessthan 5 cm in diameter. Watchful waiting is generally favored, however,for patients with a low risk of AAA rupture or acute expansion,including those patients who present with very small AAAs (eg, <4cm). More accurate data concerning the rupture risk of AAAs less than 5cm would improve clinical decision making.

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Standard Repair
The current standard operation for abdominal aortic aneurysms was developed in the mid 1950s and consists of replacement of the weakened, dilated portion of the aorta with an artificial graft manufactured from a polyester material (Dacron).

The abdomen is opened to expose the aorta which is then temporarily clamped above and below the aneurysm. It is usually possible to place the upper clamp just below the origins of the branches to the kidneys so that the kidneys continue to receive blood flow throughout the operation. Blood flow to the legs is interrupted while the aorta is clamped but this is not usually a problem, particularly if heparin is administered to prevent any static blood from clotting.

The aneurysm itself is then incised, opened throughout its length and any contained blood clot and debris is removed. The graft is inserted by sewing it to the normal calibre aorta above and below the opened aneurysm so that it lies within what was the inside of the aneurysm. Many aneurysms can be repaired with a simple, straight tubular graft although if the aneurysm extends further downwards, a "trouser" shaped graft can be used to replace the main arteries to the pelvis and legs (iliac arteries) as well.

When the clamps have been removed and blood flow is re-established through the graft, the wall of the aneurysm is closed over the graft, largely to protect it from becoming adherent to loops of intestine. Most patients will be monitored in an Intensive Care Unit or High Dependency Unit for the first 24 to 48 hours after operation and will be fit for discharge home after 7 to 10 days. Full convalescence from any major operation of this type may be expected to take up to 4 weeks. Any major abdominal operation under a general anaesthetic carries the risk of major complications and death. Respiratory complications can occur after any painful abdominal operation which discourages deep breathing and coughing, particularly when the patients are likely to be elderly and to have smoked in the past. These risks can be minimized by intensive post-operative chest physiotherapy and the use of epidural anesthesia to reduce post-operative pain.

Bleeding is clearly a risk in an operation which involves major blood vessels and great care is taken during aneurysm surgery to ensure, as far as possible, that suture lines at the ends of the graft are fully sealed and blood-tight. Blood loss during a routine operation typically averages 500 to 1000 mls and may be much greater in technically difficult and prolonged operations. Most patients will require blood transfusion during or after the operation. The use of "bank" blood (with its associated small risks of transmission of infections and adverse reactions) can be reduced or even eliminated completely by the "pre-donation" of patient's own blood in the 2 to 3 weeks before operation, by the temporary removal of 500 to 1000 mls of the patient's own blood at the beginning of surgery to be returned as the procedure finishes and by the use of blood salvage machines which retrieve blood lost during the operation and prepare it for retransfusion.

The single greatest source of post-operative complications in aneurysm surgery is the heart. Most patients undergoing aneurysm repair will be at least 65 years old, many will have some degree of coronary artery disease and many will have a history of previous heart attack, angina or hypertension. Careful preoperative investigation is needed to identify and, where possible, treat these pre-existing problems. Skilled anesthesia is required during the procedure to minimize strain on the heart caused by blood loss and the major changes in blood flow which occur with clamping and unclamping the aorta. Careful post-operative monitoring in ITU can help to ensure optimum heart and lung function in the important first 24 hours.

Overall, elective aneurysm repair carries a risk of death of approximately 4% - 5% in hospitals which perform a reasonable number of these operations. This risk should, however, be compared to the risk of death from sudden rupture of an aortic aneurysm which exceeds 80%. 95% of patients will make a good recovery from elective aneurysm surgery and will have returned fully to their pre-operative level of health and activity within a month or two. Long term complications after successful aneurysm repair are comparatively rare and it is unusual for there to be later problems with the graft or with further aneurysm formation. Interference with sexual function in men can occur after aneurysm surgery and it is often wise to discuss this possibility with patients in whom this may be important. Impotence or failure of erection can occur if the blood vessels in the pelvis which supply the penis are involved in the aneurysm process. A more common complication is failure of ejaculation, which is produced by the almost unavoidable damage to nerve fibers which surround the lower end of the aorta.

Patients who have undergone successful aneurysm repair have an average life expectancy afterwards which is almost identical to that of the normal population of the same age.