Triple A:  Abdominal Aortic Aneurysms

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Our arteries represent the high-pressure side of the human blood circulatory system, veins, of course, being the low-pressure side. But when we say high pressure, what does that really mean? Blood pressure is measured in millimeters of mercury, or mm Hg. A blood pressure of 120 mm Hg, when converted to pounds per square inch, or psi, is only about 2.3 psi. This may seem to be a very low amount of pressure when you consider that normal household water pressure is 45 psi. But modern household water pipes are made of rigid materials like copper and plastic. Human blood pipes, if you will, are made of living tissue. Anything that weakens the walls of arteries over time, like prolonged hypertension and/or atherosclerosis, may cause the blood vessel wall to partially give way, creating a bulge in the wall of the vessel. This is called an aneurysm.

Abdominal aortic aneurysms (AAAs) are defined as having an aortic diameter or more than 3 cm, or about 1 1/8 inches. In the U.S., the estimated prevalence is 1.4% of people between 50 and 84 years of age, or 1.1 million adults. The prevalence is lower in women and lower among Black and Asian people than among White males. Risk factors for AAA include advanced age, family history, previous or current tobacco use, hypercholesterolemia, and hypertension.

Interestingly enough, diabetes is associated with a decreased risk. The primary risk of AAA is rupture and death from hemorrhage. As such, the goal of treatment is to discover and repair the aneurysm before it ruptures. The single most important predictor of rupture is the diameter of the aneurysm. Studies have shown that the risk of rupture in men is 1% per year for AAAs 5.0 to 5.9 cm in diameter, but 14% in men with AAAs 6 cm or more in diameter. The respective rates in women are 3.9% and 22.3% per year.

Studies have shown that the rate of survival with surgery vs. close monitoring is even up to 5.5 cm in diameter, but the survival rate rises with surgery once the AAA is over 5.5 cm. Therefore, current recommendations are monitoring AAAs measuring 3.0 to 3.9 cm with duplex sonography every three years, whereas aneurysms measuring 4.0 to 4.9 cm should be monitored annually, and those over 5.0 cm every six months.

Smoking cessation, treatment of high cholesterol, and treatment of hypertension are all recommended, but have not been shown to reduce growth of the aneurysm and should not be prescribed for that purpose. For AAAs large enough to warrant repair (usually > 5.5 cm), surgical options include open repair or endovascular aortic aneurysm repair (EVAR), which is done using arterial catheters. Basically, open repair requires clamping the arteries, removing the aneurysm, and using a graft sewn into the arterial wall to close it. EVAR uses stents that pass through the aneurysm, sealing it, but not removing it. Since the introduction of EVAR in 1991, more that 80% of AAA repairs are now performed using EVAR.

More information on AAAs and their repair can be found on the websites of the Society for Vascular Surgery (SVS), the European Society for Vascular Surgery (ESVS), or the U.S. Preventive Services Task Force (USPSTF).

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 By Peter Galvin, MG

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