Screening for Vascular Disease in a Former Smoker

As part of his preparation for retirement, a 66-year-old executive undergoes a complete physical examination. He is in good health and has no symptoms to report. Along with other age-appropriate screening studies, you discuss testing for vascular disease with him.

HISTORY
The patient has had mild hypertension for about 10 years; it is currently well controlled with a low-dose angiotensin-converting enzyme inhibitor. He consumes 1 or 2 drinks daily. He does not smoke but was a half-pack to pack-a-day smoker when he was younger.

PHYSICAL EXAMINATION
His weight is normal for his age and body habitus. Physical findings, including blood pressure, are all within normal limits.

LABORATORY AND IMAGING RESULTS
A hemogram, blood chemistry results, ECG, and chest radiograph are all normal.

Which of the following statements is correct?
A. A one-time screening for abdominal aortic aneurysm (AAA) by CT scanning is indicated now.
B. AAA screening has been effectively performed by your careful abdominal examination in this non-obese man.
C. A one-time screening for AAA by ultrasonography is indicated now.
D. If an AAA is detected, he will require surgery for repair.
 

CORRECT ANSWER: C

AAA, defined as a dilatation of 3.0 cm or more in the wall of the abdominal aorta, is common in patients older than 65 years. AAAs are found in 6% of men aged 65 years, and their incidence increases by 6% per decade. "Clinically relevant" AAAs (those larger than 4.0 cm in diameter) occur in 1% of men aged 65 years, and their incidence increases by 2% to 4% per decade.¹

The chief clinical relevance of AAA is the risk for the catastrophic complication of rupture, which, according to rough estimates, occurs in about one-third of cases. Once rupture occurs, the prognosis is extremely grim: most patients do not make it to the hospital, and of those who do, half do not survive the emergency surgery. Total survivorship of AAA rupture is about 10% to 15%.²Natural history of AAAs. The time line of events in AAA has been documented by excellent natural history studies.^1,3 Rupture is extremely unlikely as long as the diameter is less than 5.5 cm. However, AAAs expand inexorably over time, and the expansion accelerates in an exponential manner as the diameter increases. Modification of risk factors (diabetes, hypertension, and hyperlipidemia) probably can slow the rate of expansion somewhat, but this alone does not seem to be adequate therapy. Smoking cessation significantly slows the expansion rate in AAA. Ultimately, however, if a patient lives long enough, questions of whether, when, and how to prevent rupture of the AAA by surgery will have to be addressed.

Risk factors. Risk factors for AAA have been well defined.¹ Age and family history are the strongest nonreversible risk factors; age 65 years marks the onset of increased frequency of AAA. Other important acquired risk factors include hypertension (present in this patient), chronic obstructive pulmonary disease, and atherosclerotic disease elsewhere in the vascular system.1

The strongest independent acquired risk factor is smoking, which has a relative risk of 7.6. Although duration of smoking increases risk, the number of cigarettes smoked per day apparently does not. As few as 100 cigarettes can significantly increase risk. This patient, despite his having stopped smoking, has this risk factor.

Screening. The US Preventive Services Task Force (USPSTF) has recently recommended one-time screening for AAA in men aged 65 to 75 years who have ever smoked.² This patient fulfills these criteria. The USPSTF analysis revealed that such screening will result in one AAA death prevented for every 500 patients screened. For nonsmokers and women, however, many more screenings are required to prevent an AAA death, which makes screening in these groups inappropriate both on clinical grounds and in terms of cost-effectiveness.²

Recent follow-up studies from a multicenter aneurysm screening study have confirmed that the early mortality benefit of screening ultrasonography is maintained in the longer term.³ In addition, all-cause mortality is reduced in screened patients. Thus, the cost-effectiveness of screening improves over time.^3,4

Methods of detection include physical examination and a variety of imaging studies. Physical examination is convenient and inexpensive. However, it misses 20% even of large aneurysms (greater than 5.0 cm). Physical examination is still less accurate with smaller lesions. Thus, as a screening technique it is far too insensitive, and choice B is not correct.

Ultrasonography (choice C) has a sensitivity approaching 100%, is noninvasive, and is relatively inexpensive. CT with contrast (choice A) is probably as accurate, but it is far more expensive and would expose screened patients to contrast with nephrotoxicity and allergic potential, as well as to significant radiation. Thus, it is not the preferred method at this time.

Treatment. Usually, an AAA can be serially monitored until a critical size is reached-typically greater than 5.5 cm.^5,6 Thus, choice D is incorrect. Once an AAA grows beyond 5.5 cm, the risk for rupture begins to increase exponentially and surgery is indicated. Current techniques include open surgical repair and endovascular stent grafting; these were discussed in a previous "What's The 'Take Home'?" case.⁵ .

Outcome of this case. Ultrasonography revealed a 3-cm intrarenal AAA. The patient will have regular surveillance with repeated ultrasonographic screenings at 6- to 12-month intervals.

 

References:

REFERENCES:

1. Almahameed A, Latif AA, Graham LM. Managing abdominal aortic aneurysms: treat the aneurysm and the risk factors. Cleve Clin J Med. 2005;72:877-888.
2. US Preventive Services Task Force. Screening for abdominal aortic aneurysm: recommendation statement. Ann Intern Med. 2005;142:198-202.
3. Kim LG, P Scott RA, Ashton HA, et al. A sustained mortality benefit from screening for abdominal aortic aneurysm. Ann Intern Med. 2007;146:699-706.
4. Birkmeyer JD, Upchurch GR Jr. Evidence-based screening and management of abdominal aortic aneurysm. Ann Intern Med. 2007;146:749-750.
5. Rubin RN. Pulsatile abdominal mass in an elderly man. Consultant. 2005;45:95-98.
6. Powell JT, Greenhalgh RM. Clinical practice. Small abdominal aortic aneurysms. N Engl J Med. 2003;348:1895-1901.