The management of abdominal aortic aneurysms

Abdominal Aortic Aneurysms

Metcalfe et al

The management of abdominal aortic aneurysms

David Metcalfe, Peter J.E. Holt, Matt M. Thompson 1. Department of Outcomes Research, St George’s Vascular Institute, Room 4.007, St George’s Healthcare NHS Trust, London, SW17 0QT Dr David Metcalfe BSc(Hons) MBChB Honorary Research Fellow Mr Peter J. E. Holt PhD FRCS Clinical Lecturer in Vascular Surgery and Outcomes Research Corresponding author Prof. Matt M. Thompson MD FRCS Professor of Vascular Surgery Guarantor Corresponding author: Mr PJE Holt, PhD FRCS St George’s Vascular Institute, STJ 4.007, St George’s Healthcare NHS Trust, Blackshaw Road, London, SW17 0QT UK [email protected] Tel: 0044 (0)20 8725 3205 Fax: 0044 (0)20 8725 3495 Contributor statement: DM conceived the review, extracted evidence, and drafted the manuscript. PJH co-authored the article including article direction, interpretation of the literature and editing the manuscript. MMT is sponsor and has approved the final manuscript. Licence: The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd and its licensees , to permit this article (if accepted) to be published in BMJ editions and any other BMJPG products and to exploit all subsidiary rights, as set out in our licence (http://resources.bmj.com/bmj/authors/checklists-forms/licence-for-publication). Statement of conflicts: The authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: they have no relationships that might have an interest in the submitted work in the previous 3 years; their spouses, partners, or children have no financial relationships that may be relevant to the submitted work; and the authors have no non-financial interests that may be relevant to the submitted work. Word count: 3,283 1


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Introduction An abdominal aortic aneurysm (AAA) is a permanent dilatation of the abdominal aorta >3cm in diameter (Fig. 1). The natural history is one of progressive enlargement, and maximum aortic diameter is the strongest predictor of aneurysm rupture.1-3 The reported incidence of AAA ranges from 4.9 to 9.9%4-6 and mortality following rupture exceeds 80%, accounting for 8000 deaths annually in the UK.7

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Elective surgical repair, by contrast, can be performed with an operative

mortality of 1-5% in the best centres8 9 and several countries have implemented population screening programmes to reduce aneurysm-related mortality.

This review considers the epidemiology of AAA and management strategies based on evidence from population studies, randomised controlled trials, meta-analyses, and published guidelines.

Who is at risk? The aetiology of AAA is complex with contributions from both familial susceptibility and degenerative components.10 A number of modifiable and non-modifiable risk factors are recognised, the most important of which are discussed below.10

1. Age Population studies demonstrated associations between age and AAA prevalence. One study of 4345 subjects found those aged 25-54 were significantly less likely (OR 0.15, 95% CI 0.07-0.32) to be diagnosed with an AAA than those aged over 75 (OR 7.73, 95% CI 1.89-31.73).11

2. Familial risk Patients with a positive family history have the highest risk of AAA formation. A Canadian survey of 2175 people with affected family members found an eight-fold increased risk of an ultrasound diagnosis of AAA among those who had an affected sibling.12 2


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3. Gender Females are less likely to develop an AAA with screening studies reporting a prevalence of 0.7-1.5%, significantly less than in age-matched males.13 14 However, one ultrasound screening study of women with multiple cardiovascular risk factors reported a prevalence of 6.4%, suggesting that high-risk subpopulations exist.13

Although less commonly affected, females with aneurysms are at increased risk of rupture (OR 1.49, 95% CI 1.16-1.91).1 15 16 For this reason, they may be referred with aneurysms of smaller diameter (e.g. >5cm) for consideration of operative intervention.17 Females also have a worse prognosis following aneurysm repair with one series of 8185 patients reporting women aged over 70 as being 40% more likely to die post-operatively than men (mortality ratio 1.40, 95% CI 0.16-1.70).18

4. Smoking The most important modifiable risk factor for aneurysm formation is smoking. A recent review showed that smokers were seven times more likely to develop aneurysmal dilatation than those who never smoked.10 Cohort studies have reported even higher risks (OR 13.72 (95% CI 6.12-30.78)), when comparing current smokers of ≥20 cigarettes day with never-smokers.11

Smoking is associated with increased growth rates and rupture risk. Data from the UK Small Aneurysm Trial suggested that current smoking was associated with more rapid aneurysm expansion (by 0.4mm/year) and higher risk of rupture after adjustment for baseline confounding factors.2 19

5. Hypertension The association between hypertension, aneurysm formation and accelerated growth is weak. One cohort study of 4345 people reported an association between hypertension and risk of AAA formation 3


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in women, 11 as did the Tromsø study which showed patients with hypertension were more likely than those without (OR 1.54, 95% CI 1.03-2.30) to be diagnosed with an AAA.20

The UK Small Aneurysm Trial demonstrated an association between hypertesion and risk of rupture with patients in the lowest blood pressure tertile (mean blood pressure 57-102mmHg) having a rupture rate of 2.0 per 100 person years compared with 3.1 among those in the highest tertile (117193mmHg).1

6. Ethnicity A retrospective study of 19,014 male screening programme participants reported an AAA prevalence of 4.69% (95% CI 4.4-5.0) in Caucasians and only 0.45% (95% CI 0.05-1.16) in men of Asian origin.21 Similarly, national data collected in the USA suggests the risk of AAA formation in black men aged >65 is half that experienced by their white counterparts.22

7. Diabetes Diabetes may protect against AAA formation and growth but increase risk of aneurysm rupture. A recent meta-analysis of seven retrospective and population-based studies found a reduced incidence of diabetes in patients with AAA (OR 0.65, 95% CI 0.60-0.70).23 Data from the Chichester screening trial suggested diabetes is associated with a 56% reduction in aneurysm growth rate.3

In summary, doctors should consider the diagnosis of AAA in younger patients as well as those targeted by screening programmes. The highest risk groups are white male smokers and those with a positive family history. AAA should also be considered in older women with cardiovascular risk factors.

How do patients present? 4


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Patients present along a spectrum from asymptomatic to overt signs of rupture (abdominal pain with hypotension and collapse)24. Consequently, both clinical suspicion and aneurysm screening are important in diagnosis. Symptomatic presentations include abdominal, loin, and/or lower back pain, all of which require urgent referral for investigation and management as they may indicate impending rupture.25 AAA may also cause distal embolisation. The authors of studies into delayed diagnosis and treatment of AAAs have concluded that, in patients presenting with a range of different complaints who have a moderate to high risk of cardiovascular disease (e.g. an older male with a history of smoking complaining of abdominal pain), AAA should be considered a likely diagnosis.24 26

How are AAAs diagnosed? Clinical signs The classical sign of an AAA is a pulsatile mass on abdominal palpation, which suggests aneurysmal dilation of the abdominal aorta. However, large variation exists in the reported sensitivity of palpation for detecting aneurysms, particularly in obese patients.24 27 One small prospective study found that the sensivitity of abdominal palpation by a doctor was 0.57 for detection of aneurysms 5cm. The specificity for excluding an AAA was 0.64.28

The detection of femoral or popliteal artery aneurysms should prompt abdominal examination and ultrasound as prospective case series suggest strong associations with AAAs of 85% and 62% respectively.29 30

First-line imaging As the clinical diagnosis of AAA is unreliable,24 26 clinicians should have a low threshold for arranging abdominal ultrasonography in at-risk patients. Ultrasound is a reliable, non-invasive and readily available means of establishing aortic diameter24 with sensitivity and specificity approaching 100%.31 32 5


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The role of population screening Ruptured AAA is associated with an 80% mortality rate. Of those reaching hospital, meta-analysis of 21,523 patients found an operative mortality of 48% (95% CI 46-50%).33 By contrast, in randomised trials, the elective repair of large aneurysms by open repair or endovascular stenting had a 30-day mortality of 4.6% (95% CI 2.0-8.9%) and 1.2% respectively (95% CI 0.1-4.2%).34 35 36 The aim of population screening is to identify aneurysms prior to rupture, allowing elective repair of large aneurysms or surveillance of patients with small aneurysms. Screening may also facilitate the medical optimisation of patients with AAA by making a positive diagnosis and driving aggressive risk factor management. Ultrasound is the preferred tool both for screening and surveillance.

There is strong evidence that population screening in men aged >65 is beneficial. A Cochrane review of four large randomised controlled trials4 14 37 38 found that screening was associated with a significant decrease in AAA rupture (OR 0.45, 95% CI 0.4-0.78) and aneurysm-related mortality (OR 0.60, 95% CI 0.21-0.99) for men aged 65-79, but not women (OR 1.07, 95% CI 0.93-1.21).32 A further meta-analysis of trials reporting long-term follow up (≥10 years) confirmed the finding of reduced aneurysm-related mortality (OR 0.55, 95% CI 0.36-0.86) and a trend towards reduced allcause mortality (OR 0.98, 95% CI 0.95-1.00), presumably due to risk factor management.39 There is currently insufficient evidence to justify screening in other at-risk populations (e.g. female smokers).32

Although the major trials screened over-65s, the optimum age at which screening should take place has not been determined. 9 40 However, 65 has been adopted by the UK National Health Service AAA Screening Programme (NAAASP) on a pragmatic basis; to balance the cost of requiring a second, interval screening exam whilst maximising the number of positive scans on a single test. The risk of developing a new AAA following a single negative screening ultrasound scan is small with one cohort study demonstrating that, of 2691 men aged 64-81 with aortic diameters 3cm dilatation of the aorta) are best referred to a regional vascular unit for surveillance or consideration of elective aneurysm repair.

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Prescribe an anti-platelet agent and statin for all newly diagnosed patients. Ensure that blood pressure is effectively controlled (