Aortic Aneurysm Expansion Index (AAEI): Explanation and Clinical Context The Aortic Aneurysm Expansion Index (AAEI) quantifies the annual relative increase in aortic diameter, expressed as a percentage per year. It is calculated using the formula: (Follow-up Diameter - Baseline Diameter) / (Baseline Diameter × Time Interval) × 100%.
AAEI helps clinicians identify patients at risk of rapid aneurysm growth and potential rupture. Generally, an expansion rate greater than 10% per year is considered high risk and may warrant surgical or endovascular intervention, whereas rates below 5% per year are considered low risk and may be monitored with routine imaging.
AAEI is particularly useful for both thoracic and abdominal aortic aneurysms and can guide follow-up intervals and timing of intervention. Factors influencing expansion include baseline aneurysm size, hypertension, smoking, connective tissue disorders, and age.
Reference:
Davies RR, et al. "Natural history of thoracic aortic aneurysms: Growth rates and risk of rupture." Circulation. 2002;106:197-202. doi:10.1161/01.CIR.0000026572.79383.8D
Vorp DA. "Biomechanics of abdominal aortic aneurysm." J Biomech. 2007;40:1887-1902. doi:10.1016/j.jbiomech.2006.10.018