What is the recommended surveillance protocol for patients with an infrarenal abdominal aortic aneurysm (AAA)?

Surveillance Protocol for Infrarenal Abdominal Aortic Aneurysm

For patients with infrarenal abdominal aortic aneurysm (AAA), surveillance frequency should be determined by aneurysm size, with duplex ultrasound (DUS) recommended as the primary imaging modality for most surveillance intervals.

Surveillance Intervals Based on AAA Size

Small AAA (25-29 mm)

• DUS surveillance should be performed every 4 years in patients with aortic diameter ≥25 mm and <30 mm who have a life expectancy >2 years 1
• This extended interval is appropriate as these patients have low risk of developing large AAA within 10 years 1

AAA 30-39 mm

• DUS surveillance should be performed every 3 years 1
• This interval has been shown to be safe and cost-effective for aneurysms of this size 1, 2

AAA 40-44 mm

• Annual DUS surveillance is recommended for men with AAA of 40-49 mm and women with AAA of 40-44 mm 1
• More frequent monitoring is necessary due to higher growth rates at this size range 1, 2

AAA 45-49 mm

• For women with AAA of 45-49 mm, DUS surveillance should be performed every 6 months 1
• For men with AAA of 45-49 mm, annual DUS surveillance should continue 1
• Women require more frequent monitoring due to their four-fold higher rupture risk compared to men with similar-sized aneurysms 1, 3

AAA 50-55 mm

• For men with AAA of 50-55 mm, DUS surveillance should be performed every 6 months 1
• For women with AAA of 50 mm or larger, intervention should be considered as they have reached the threshold for repair 1
• More frequent surveillance is needed as these aneurysms approach the intervention threshold and have higher growth potential 1

Imaging Modalities

Primary Surveillance

• DUS is recommended as the first-line imaging modality for AAA surveillance 1
• Benefits include non-invasive nature, lack of radiation exposure, and cost-effectiveness 4

Alternative Imaging

• CT or MRI is recommended if DUS does not allow adequate measurement of AAA diameter 1
• CT provides superior visualization of the abdominal aorta and its branches 1
• MRI is a reasonable alternative to CT in selected patients (particularly young patients and women) when long-term follow-up is anticipated, to reduce cumulative radiation exposure 1

Pre-intervention Imaging

• CT is recommended for preoperative planning when an AAA meets criteria for repair 1
• This allows detailed assessment of aortic anatomy and branch vessels 1

Special Considerations

Rapid Growth

• Consider shorter surveillance intervals for AAAs showing rapid growth (≥10 mm per year or ≥5 mm per 6 months) 1
• Intervention may be considered in these cases regardless of absolute diameter 1

Risk Factors for Growth

• Smoking increases aneurysm growth rate by approximately 0.35 mm/year 3
• Diabetes may decrease growth rate by approximately 0.51 mm/year 3
• Consider more frequent surveillance in smokers 1, 5

Gender Differences

• Women have similar AAA growth rates to men but a four-fold higher rupture risk 1, 3
• This justifies more frequent monitoring and earlier intervention thresholds for women 1, 3

Clinical Pearls and Pitfalls

• AAAs are typically asymptomatic until rupture, which carries a mortality rate of 75-90% 4, 5
• The risk of rupture increases with aneurysm size, female gender, smoking, and hypertension 4, 5
• Ensure patients maintain scheduled surveillance as AAAs can expand unpredictably 4
• Optimal cardiovascular risk management is recommended for all patients with AAA to reduce major adverse cardiovascular events 1
• Fluoroquinolones should generally be avoided in patients with AAA unless there is a compelling clinical indication and no reasonable alternative 1