- The strongest predictor of AAA formation overall is family history
- Women are less likely to develop an AAA than men of a similar age, though if they do they have:
- An increased risk of rupture
- A higher mortality rate
- There is increased prevalence in Caucasians compared to Black and Asian ethnic groups
- Smoking is the most important modifiable risk factor in the formation, progression and rupture-risk of AAA
AAA; Pathophysiology
AAA; Pathophysiology
Resources
- Anaesthesia for endovascular repair of ruptured abdominal aortic aneurysms (BJA Education, 2022)
- Anaesthesia for elective open abdominal aortic aneurysm repair (BJA Education, 2013)
- Anaesthesia for endovascular aortic aneurysm repair (WFSA, 2014)
- Anaesthesia for ruptured abdominal aortic aneurysm (BJA Education, 2008)
- An aortic aneurysm is a permanent, >3cm dilatation anywhere along the path of the aorta
- Abdominal aortic aneurysms (AAA) can be classified according to their relationship to the renal arteries:
- In order of increasing badness:
- Infra-renal
- Juxta-renal
- Para-renal
- Supra-renal
- The overall incidence is 4.9 - 9.9% of the population
- Within the aneurysmal segment of the aorta there's a reduced number of collagen and elastic fibres
- The fibres which are present suffer from poor quality cross-links
- The vascular wall strength is further compromised by:
- Increased elastase activity leading to elastin resorption
- Increased protease activity
- Localised inflammatory changes
- Arterial wall mural thrombus and plasminogen activation
Rupture
- An AAA will expand with time and, eventually, rupture
- The strongest predictors of rupture are:
- Maximum diameter
- Annual expansion rate, which bizzarely appears to be slower if you have diabetes
- The risk of rupture becomes clinically significant once >5cm
- Between 4 - 5.5cm, the annual rupture rate is 1%
- Once 5.5cm in diameter, the annual risk of rupture is 12% (men) - 18% (women)
Screening
- Screening in the UK is for men >65yrs old
- It is neither cost-effective nor suitably mortality-reducing to screen other patient groups
- Abdominal ultrasound is the first-line imaging tool for diagnosis and surveillance, with sensitivity and specificity near 100%
Pharmacological interventions
- Smoking cessation can slow aneurysmal growth 15 - 20%
- Naturally there are a whole plethora of other benefits, including reduced perioperative morbidity relating to wound dehiscence and cardiorespiratory complications
- Statins may alter aneurysmal growth, and also minimise perioperative myocardial ischaemia
- Low-dose aspirin prescribed once AAA is diagnosed for prevention of coronary events in patients with significant vascular disease
- Both ACE-I and β-blockers should be considered in such patients given their high risk of cardiovascular disease
Surveillance
- Regular surveillance takes place to monitor size and expansion rate
- There is no long-term survival benefit to early surgery for patients with AAAs of 4.0 - 5.5cm diameter according to the UK-SAT (1998) and ADAM-US (2000) studies
- If either >5.5cm or symptomatic, urgent referral to a vascular unit is indicated
- The Multicentre Aneurysm Screening Study (2002) demonstrated a 53% reduction in mortality in UK men aged 65-74 years who:
- Attended for regular screening ultrasound and
- Underwent elective surgery when the aneurysm diameter reached 5.5 cm