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Screening for Abdominal Aortic Aneurysms

Screening for abdominal aortic aneurysms is required for patients who are known to have an existing aneurysm.  However, Australian guidelines are not so clear regarding screening of high risk, asymptomatic individuals who have normal clinical examinations. In particular, overseas guidelines (but not Australian ones) are specific about the indications for screening men whose first degree relatives have a history of abdominal aortic aneurysms.

Risk factors for abdominal aortic aneurysms include male gender, a history of smoking, age over 50 years (the majority of individuals with abdominal aortic aneurysms are aged over 60 years), hypertension, hypercholesterolaemia, atherosclerosis, connective tissue diseases such as Marfan’s syndrome or autoimmune vasculitis and uncommonly, infection (classically syphilis) or abdominal trauma.

The UK and USA both have screening programmes in the form of ultrasound for abdominal aortic aneurysms for men at age 65 years, and this has been proven cost-effective. Australian studies suggest that such screening in this country will also reduce mortality and is also cost-effective. A one-off screening in Australia has been proposed for men between the ages of 65 and 75 years; however, this recommendation has not actually been implemented.1 Despite the lack of Australian guidelines, GPs should be aware of possible indications for screening of men, based on not just multiple risk factors for abdominal aortic aneurysms, but also because of the presence of a family history of this despite the absence of significant risk factors.

Because women have one fifth the risk of aortic aneurysm compared with men, routine screening has not been recommended for women (although women have a worse outcome if they develop an aortic aneurysm).2  The obvious compromise here is to be alert to the family history of abdominal aneurysms in female patients too. Intermittent clinical examination for aneurysms in the abdomen (pulsatile masses, bruits, poor peripheral pulses) in both men and women with such a family history or multiple risk factors should also prompt further investigation.

Patients suspected of having an abdominal aortic aneurysm require an urgent CT scan of the chest and abdomen with contrast. Contrast should only be used if the renal function has been normal in the recent past and there is no history of contrast allergy (if there is any doubt a non-contrast scan should be arranged instead). Patients with possible symptomatic abdominal aortic aneuryms should be sent to the Emergency room of the nearest appropriate level hospital by ambulance for management.

Patients with known abdominal aortic aneurysms require screening. This is usually performed for every six months, in the absence of new symptoms. The risk of rupture begins to outweigh the risk of conservative management (in most cases) if the aneurysm is showing signs of complications (e.g. possible dissection or rupture, embolisation, renal or aortic valve involvement, pressure damage of adjacent structures); if it is extensive (e.g. thoracoabdominal aortic aneurysms); if it is rapidly enlarging in between investigations; or if it is over 5.5 cm in diameter for men (or 5.0 cm for women).

Individuals with existing abdominal aortic aneurysms require a full physical examination and periodic investigation of cardiovascular risk factors (blood pressure, full blood count, fasting lipids, blood glucose, C-reactive protein, liver and renal function, urinary albumin creatinine ratio).  An ECG, carotid dopplers and a chest x-ray should be arranged to assess occult vascular disease and relevant co-morbidities.  A referral to a cardiologist for investigation of asymptomatic ischaemic heart disease should be considered, especially if surgical intervention for the aneurysm is a possibility at some stage in the future.

In high risk patients and those who already have an aneurysm, active management of cardiovascular risk factors is required. In particular, the fasting cholesterol should be under 4.0mmol/L, the HDL over 1.0 mmol/L, the LDL under 2.0mmol/L and triglycerides under 1.2mmol/L. These levels are very difficult to achieve in many patients without the use of statins or other cholesterol therapies. Blood pressure should ideally be reduced to 120/80 mmg/Hg and patients with diabetes require excellent glycaemic control.

 

1. Mundy L, Hiller J. Targeted screening for abdominal aortic aneurysm. Australia and New Zealand Horizon Scanning Network, Adelaide Health Technology Assessment, Commonwealth of Australia), 2008.
http://www.horizonscanning.gov.au/internet/horizon/publishing.nsf/Content/BB580B674729F620CA2575AD0080F351/$File/_Aug_2008_Targetted%20screening%20for%20abdominal%20aortic%20aneurysm.pdf

2. Cardiovascular Health Network, Abdominal aortic aneurysm model of care, Department of Health, Western Australia, 2008. http://www.healthnetworks.health.wa.gov.au/modelsofcare/docs/AAA_Model_of_Care.pdf