Screening for Abdominal Aortic Aneurysm

Peter D. Newcomer, MD

Disclaimer No financial support for this talk

was given.

Objectives Review abdominal aortic aneurysm

risks, natural history and treatment. Review the USPSTF and Canadian

recommendations regarding screening. Determine whether and how we should

screen for abdominal aortic aneurysm. Understand which patients would be

best targeted by screening if we do.

Case Presentation A 72 y.o. nonsmoking woman with a

history of hypertension, anxiety disorder, and GERD asks your opinion of a screening test being offered in her senior apartment complex. This test is supposed to measure “my carotids and aorta and a third thing I can’t remember”. She has no known history of vascular disease, diabetes, or coronary disease. She is currently asymptomatic and her blood pressure has been historically well controlled.

Case Presentation Exam is benign. There is no

abdominal mass or bruit noted. Normal cardiovascular exam with good pulses.

The patient has Medicare insurance. She would like you to order the tests

that would have been in the local screening test so she doesn’t have to pay for it herself.

The Vascular Health Screen First, what are the three tests that

patient is referring to? 1) Carotid Ultrasound 2) Abdominal Aortic Ultrasound 3) Peripheral Arterial Doppler Cost (around $55 each or $100 for all

three, varies)

Objectives Review abdominal aortic aneurysm

risks, natural history and treatment.

Review the USPSTF and Canadian recommendations regarding screening.

Determine whether and how we should screen for abdominal aortic aneurysm.

Understand which patients would be best targeted by screening if we do.

Definition Abdominal aortic aneurysm (AAA)

is defined as an aortic diameter of greater than 3 cm and its incidence increases with age.

Risk Factors for AAA(OR)(Odds Ratios From Aneurysm Detection and Management (ADAM) Veterans Affairs Cooperative Study Group, Ann Inter Med 3/97)

Smoking (odds ratio 5.57) Male sex (4.56) Positive family history (1.95) White versus black race (2) Atherosclerosis (1.5) Hypertension (1.2) (Diabetes) (0.54) Age, height, hyperlipidemia also associated

but smoking-related risk explained 78% of all AAA found in this study of 73,451 patients.

Figure 1. Prevalence of abdominal aortic aneurysm 4.0 cm or larger in men by age and smoking history. Data adapted from Lederle et al. (28).

Prevalence

Lederle, F. A. Ann Intern Med 2003;139:516-522

Prevalence of Abdominal Aortic Aneurysms 3.0 cm or Larger in Veterans 50 to 79 Years of Age

Natural History:Risk of Rupture Very low in aneurysms less than 4.0 cm in diameter.

5 percent for those 4.0 to 4.9 cm in diameter.

25 percent for those 5.0 to 5.9 cm in diameter.

35 percent for those 6.0 to 6.9 cm in diameter.

75 percent for those 7.0 cm in diameter.

Natural History:Rate of Increase 0.19 cm per year for aneurysms 2.8 to 3.9 cm

in baseline diameter. 0.27 cm per year for those 4.0 to 4.5 cm in

baseline diameter. 0.35 cm per year for those 4.6 to 8.5 cm in

baseline diameter.

Rate of increase is more rapid in smokers. (Estimates of 20-25% increase in rate).

Natural History: Surgical Intervention Elective repair is considered for

aneurysms that are: Bigger than 5.5cm Increasing by >0.5cm in 6months Symptomatic

Objectives Review abdominal aortic aneurysm

risks, natural history and treatment. Review the USPSTF and Canadian

recommendations regarding screening.

Determine whether and how we should screen for abdominal aortic aneurysm.

Understand which patients would be best targeted by screening if we do.

USPSTF Recommendation (1996) “There is insufficient evidence to

recommend for or against routine screening of asymptomatic adults for abdominal aortic aneurysm with abdominal palpation or ultrasound.”

Thanks a lot.

Canadian Task Force on the Periodic Health Exam (1994) “While there is insufficient evidence

to recommend for or against screening with physical examination or ultrasound, the prudent physician may choose to include a targeted physical examination for aneurysm in males over 60 in the periodic health examination.”

Other USPSTF Recommendations Carotid U/S: There is insufficient

evidence to recommend for or against screening asymptomatic persons for carotid artery stenosis using the physical examination or carotid ultrasound.

PAD: Routine screening for PAD in asymptomatic persons is not recommended.

Objectives Review abdominal aortic aneurysm

risks, natural history and treatment. Review the USPSTF and Canadian

recommendations regarding screening. Determine whether and how we

should screen for abdominal aortic aneurysm.

Understand which patients would be best targeted by screening if we do.

Why Screen for AAA at All?

It’s estimated that only 18% of patients with ruptured AAA reach a hospital and survive surgery.

Why Screen for AAA at All? An AAA usually enlarges over time

and once 5 cm in diameter the risk of rupture is 25-41% over 5 years.

It is the tenth most common cause of death for an individual over 55. (About 9000 deaths/yr in the US).

Mortality With AAA Repair

Elective repair of AAA is performed with mortality rates averaging less than 5%.

In the presence of a ruptured AAA the surgical mortality is 50-80%.

Screening Tests Palpation Abdominal ultrasound CT MRI

Palpation Varying results but one study (Annals March 01)

showed: Sensitivity of 68% Specificity of 75%

Sensitivity increases with size of aneurysm (82% for 5 cm or more)

Sensitivity decreases with obesity. (in 12 out of 99 patients with AAA who had waist of less than 40 inches and AAA > 5cm the sensitivity was 100%)

ABDOMINAL AORTIC ANEURYSM THE EXAM

METHOD

THE PATIENT’S ABDOMEN SHOULD BE RELAXED WITH THE KNEES FLEXED.

THE EXAMINER FEELS CEPHALAD OF THE UMBILICUS FOR THE AORTIC PULSATION.

PLACE BOTH HANDS ON THE ABDOMEN WITH THE INDEX FINGER ON EITHER SIDE OF THE PULSATING AORTA. ESTIMATE THE WIDTH ( NL <2.5CM IN WIDTH).

JAMA 1999;281:77-81

BATES 8TH ED, 2003

Ultrasound Screening Simple and Safe No radiation exposure Sensitivity and specificity are

nearly 100% Cost-Effective

Effectiveness of Screening

Four randomized trials of AAA screening done since the last USPSTF recommendation, including more than 125,000 men, have now reported results of up to 5 years of follow-up.

Deaths related to AAA were reduced by 28 to 68%.

Largest of the four was the Multicentre aneurysm screening study (MASS).

These trials are reviewed in depth in Annals Sept 2003 article.

MultiCentre Aneurysm Screening Study (MASS) (Nov. 2002)

Objective: to assess the cost effectiveness of ultrasound screening for AAA.

67,800 men age 65-74 in the UK. Death due to AAA was reduced 42% in the

screening group. (elective repair if > 5.5cm)

Over 4 years the cost was about 45,000$ /year gained. This is expected to go down with time.

Cost Effectiveness Before the 4 trial reports noted above 6

cost effectiveness analyses were done showing costs per life-year saved ranging from $2000 to $41550.

These assumed AAAs larger than 4 or 5 cm would be repaired. The current literature would support repair at 5.5 cm and would be at least as effective and less costly.

If a quick screen for AAA was adopted the cost could be decreased significantly.

Repeated Screening Several screening programs have

addressed this. (Annals Sept. 2003).

The yield is very low (0.1% in one study of 2622 veterans).

Repeat screening is not recommended based on the results of these studies.

Screening in Women A randomized trial of 9342 women

(Br J Surg 2002) has shown the incidence of rupture at 5 and 10 years was the same for the screened and control groups of women.

There has been no evidence that screening in women is effective.

Current Practice Remember that the USPSTF

recommendations were made before the 4 randomized trials of AAA screening.

The USPSTF is now reconsidering AAA screening in light of the recent trials.

What Should We Do Now? Offer targeted screening for AAA.

Screen the highest risk group. Men over 60 with history of smoking and vascular disease. (Or multiple other risk factors).

Discuss alternative ways to pay for screen. (Not covered by Medicare or any local HMO’s… yet.) Consider encouraging commercial screening.

Perform one time abdominal ultrasound. Find ways to lower costs of screening

ultrasound. Consider screening during a preventative exam.

Future Directions If USPSTF recommends AAA

screening, health plans will probably follow with coverage.

Primary care specialists could start using personal ultrasound imagers to screen during the preventative exam.

AAA Screening by Internists If we should be screening for AAA

then we should be proactive about getting that screening for our patients.

We can afford an ultrasound imager for limited exams in our clinics.

We can learn to use it easily. We can be ahead of the curve, when

screening is recommended.

AAA Screening by Internists A study in J Gen intern med (Dec

2001) showed that primary care residents were able to achieve an abdominal aortic ultrasound-independent competence level after an average of 3.4 proctored exams.

Personal Ultrasound Imager These devices have been

compared to standard imaging. (July 2000, J of the Am Soc of Echocardiography).

The amount of time to use is around 5 minutes.

The negative predictive value (compared to standard echocardiography) was 99%.

Selected Bibliography Lederle “Ultrasonographic Screening for

Abdominal Aortic Aneurysms” Annals of Int Med 2003;139(6)

Ashton, et al., The Multicentre Aneurysm Screening Study (MASS) in to the effect of abdominal aortic aneurysm screening on mortality in men: a randomized controlled trial. Lancet 2002;360:1531-9