What are the risk factors for Abdominal Aortic Aneurysm (AAA)?

Risk Factors for Abdominal Aortic Aneurysm (AAA)

The major risk factors for AAA include male sex, smoking history, age over 65 years, and family history of AAA, with smoking being the strongest modifiable risk factor associated with a 5-fold increased risk of developing AAA. 1

Primary Risk Factors

Demographic and Non-Modifiable Factors

• Age: Prevalence increases significantly with age, particularly in those over 65 years 1
  • Prevalence ranges from 1.9% in men aged 45-54 to 18.5% in men aged 75-84 1
• Sex: Males have 4-5 times higher risk than females 1
  • Prevalence is 9.1-22% in men vs. 2-6.2% in women over 65 years 1
• Race/Ethnicity:
  • Lower risk in Black individuals (OR 0.59) 1
  • Lower risk in Mediterranean-born individuals compared to Australian-born (OR 0.6) 1
• Family history: Significant risk factor (OR 1.9) 1
  • First-degree relatives of patients with AAA have 21-25% prevalence in males and 3-7% in females 1

Modifiable Risk Factors

• Smoking: Most powerful risk factor (OR 5.57) 2
  • Risk increases with years of smoking and decreases with years after quitting 2
  • Accounts for approximately 78% of all AAAs ≥4.0 cm 2
• Hypertension: Independent risk factor 1, 3
• Hypercholesterolemia: Associated with increased risk 1

Associated Conditions

• Atherosclerosis: Strong association with AAA 1, 2
  • Coronary artery disease (OR 1.6) 1
  • Peripheral arterial disease 1, 3
• Genetic/connective tissue disorders: Particularly important in young patients 4
  • Marfan syndrome
  • Loeys-Dietz syndrome
  • Vascular Ehlers-Danlos syndrome

Protective Factors

• Diabetes mellitus: Negative association (OR 0.54) 2, 1
• Female sex: Protective effect (OR 0.22) 2
• Regular vigorous exercise: Associated with lower risk 1

Risk Factors for AAA Expansion and Rupture

• Large aneurysm diameter: Strongest predictor of rupture 1
  • 1-year rupture rates: 9% for AAAs 5.5-5.9 cm, 10% for 6.0-6.9 cm, 33% for ≥7.0 cm 1
• Rapid growth rate: >0.5 cm/year indicates high risk 4
• Continued smoking: Accelerates expansion 1, 3
• Persistent hypertension: Increases rupture risk 3
• Female sex: Paradoxically, while women have lower prevalence, they have higher rupture risk 1
• History of cardiac or renal transplant 1
• Decreased forced expiratory volume 1

Clinical Implications

• Screening is recommended for men aged 65-75 years who have ever smoked 5
• One-time ultrasonography screening is sufficient for those with normal initial results 1
• Patients with family history of AAA should be considered for earlier screening 1
• Smoking cessation is the most important modifiable intervention to reduce AAA risk 2

Common Pitfalls in Risk Assessment

• Assuming all patients with atherosclerotic disease have similar AAA risk (diabetes is actually protective)
• Overlooking family history, which significantly increases risk even in the absence of other risk factors
• Failing to recognize that women, while at lower risk for developing AAA, have higher rupture risk when AAA is present
• Not appreciating that smoking cessation gradually reduces risk but former smokers remain at elevated risk compared to never-smokers

Understanding these risk factors helps clinicians identify patients who may benefit from screening and implement appropriate preventive strategies to reduce AAA-related morbidity and mortality.