Key Facts

AAA is a common and potentially fatal condition. The NHS screening programme has reduced AAA-related mortality. Understanding the indications for surveillance and repair is essential.

Epidemiology

~6,500 new AAA diagnoses/year in UK. Rupture accounts for ~4,000 deaths/year. Prevalence decreasing due to declining smoking rates. The NHS AAA screening programme (since 2013) has reduced AAA-related mortality in screened populations.

Aetiology

• Atherosclerosis: Degenerative process in aortic wall — most common cause
• Smoking: Strongest modifiable risk factor (~5× increased risk)
• Genetic: Family history (first-degree relative = 4× risk); connective tissue disorders (Marfan, Ehlers-Danlos type IV)
• Inflammatory: Mycotic (infected) aneurysm — rare but important
• Other risk factors: Male sex, age >65, hypertension, COPD, hyperlipidaemia

Pathophysiology

• Chronic inflammation of aortic wall → destruction of elastin and collagen in media and adventitia
• Matrix metalloproteinase (MMP) activity breaks down structural proteins
• Wall tension increases with diameter (Laplace's law: Wall tension = Pressure × Radius)
• Risk of rupture increases exponentially with size: <5.5cm ~1%/year; 5.5-6cm ~10%/year; >7cm ~30%/year
• Most AAAs are infrarenal (~95%); may extend to involve iliac arteries

Asymptomatic (Most Common)

• Incidental finding on screening USS or imaging for other indications
• Pulsatile, expansile abdominal mass above umbilicus

Symptomatic (Unruptured)

• Abdominal or back pain (expansion or inflammation)
• Peripheral embolisation (blue toe syndrome, trash foot)
• Compression of adjacent structures

Ruptured AAA (Surgical Emergency)

• Classic triad: Sudden-onset abdominal/back pain + haemodynamic instability + pulsatile abdominal mass
• Only ~50% present with all three features
• May present with syncope, flank pain mimicking renal colic, groin pain
• Retroperitoneal rupture (more common): Tamponaded; patient may initially be stable
• Intraperitoneal rupture: Rapidly fatal — free blood in peritoneum

Red Flags

• Sudden abdominal/back pain + known AAA = ruptured until proven otherwise
• Hypotension in patient >50 with abdominal pain — consider ruptured AAA
• Do NOT delay transfer to theatre for CT if patient is haemodynamically unstable

Screening/Surveillance

• USS abdomen: Measure AP diameter (accurate ± 2mm)
• Surveillance intervals: 3-4.4cm → annual; 4.5-5.4cm → 3-monthly

Elective Pre-operative

• CT angiography: Gold standard for surgical planning — anatomy, size, relation to renals, iliac involvement
• Cardiac assessment: CPET (cardiopulmonary exercise testing) to assess fitness
• Renal function: U&Es (contrast nephropathy risk)
• FBC, G&S/crossmatch: Pre-operative

Emergency (Suspected Rupture)

• CT aortogram: If haemodynamically STABLE → confirms diagnosis, guides management
• If UNSTABLE: Direct to theatre — do NOT delay for imaging
• Crossmatch 6-10 units: Major haemorrhage protocol

Surveillance (Small AAA)

• <5.5cm: Conservative management with surveillance USS
• Optimise cardiovascular risk factors: Smoking cessation (most important), statin, antihypertensive, antiplatelet
• No evidence that beta-blockers slow AAA growth

Elective Repair (≥5.5cm or Symptomatic or Growing >1cm/year)

EVAR (Endovascular Aneurysm Repair):

• Stent graft deployed via femoral arteries under fluoroscopic guidance
• Lower 30-day mortality (~1.5% vs ~4.5% open)
• Requires suitable anatomy (adequate neck length/angulation, iliac access)
• Requires lifelong CT surveillance for endoleaks
• No long-term survival advantage over open repair (EVAR-1 trial)

Open Surgical Repair:

• Laparotomy, cross-clamp aorta, synthetic graft (Dacron)
• Higher initial mortality but more durable — fewer re-interventions
• No need for lifelong surveillance CT

Emergency Repair (Ruptured AAA)

• Permissive hypotension: Target systolic ~80-100 mmHg (prevents further bleeding)
• Major haemorrhage protocol: O-negative blood initially, then crossmatched
• EVAR (if anatomy suitable and expertise available) or open repair
• Even with emergency surgery, mortality ~50%

Referral Criteria

• AAA ≥5.5cm — vascular surgery MDT
• Rapid growth (>1cm/year) — vascular surgery
• Symptomatic AAA — urgent vascular referral
• Suspected rupture — 999, immediate vascular surgery

• Elective EVAR: 30-day mortality ~1.5%
• Elective open: 30-day mortality ~4-5%
• Ruptured AAA: Overall mortality ~80%; ~50% reach hospital alive; operative mortality ~50%
• EVAR-1 trial: Lower early mortality but no difference in long-term survival; higher re-intervention rate for EVAR
• Screening: Reduces AAA-related mortality by ~45% (MASS trial)
• Small AAA (<5.5cm): Annual rupture risk <1%; surveillance is safe

AAA Surveillance Programme

Key Trials