Abdominal aortic aneurysm : gender aspects on risk factors and treatment

Abstract

Abdominal Aortic Aneurysm (AAA) is a common condition in the Western world and an important cause of sudden death. Recent research emphasizes that although women are inherently less likely to develop AAA, those who do develop AAA seem to have a more unfavorable aneurysm disease than men with higher rupture risk and also exhibit higher standardized mortality ratio after intervention. Despite previous efforts to elucidate gender differences in patients suffering from AAA it is obvious that further research is necessary. This thesis is based on four studies focusing on different gender aspects of patients with AAA.

The first study is a population-based investigation of temporal trends in number of interventions performed for AAA and outcome in Sweden 1990-2005. The study included 14369 patients. Interventions for non ruptured, but not for ruptured AAA increased over time. Among patients treated for non ruptured AAA an expected rapid increase of endovascular repair was observed. The male to female ratio did not change during the study period. We did not find any gender differences in postoperative mortality after adjustment for age.

In the second study the risk of AAA associated with positive family history was assessed. This is the first population-based case-control study within this field. 3183 AAA cases and 15943 age, gender, and region matched controls were included. We were able to demonstrate that the relative risk associated with a positive family history of AAA was approximately doubled (odds ratio 1.9; 95% confidence interval 1.6-2.2). We did not find any influence of gender.

In the third study the prevalence of thoracic aortic aneurysm (TAA) in patients diagnosed with AAA was investigated. AAA patients attending the out-patient clinic at Karolinska University Hospital who had been examined with an abdominal and thoracic computer tomography (CT), were included (n=354). We found that approximately one quarter had a concurrent TAA, using gender specific criteria. Women were particularly affected, 48% compared to 23% in men (p<0.0001).

The fourth study attempted to widen the understanding of the higher rupture risk in women with AAA compared to men by investigating this difference from a biomechanical perspective. Several studies have shown that Peak Wall Stress (PWS) and Peak Wall Rupture Risk (PWRR), predicted by a Finite Element (FE) analysis of AAA derived from CT, is a better predictor of rupture than AAA diameter. PWS and PWRR were estimated for 15 men and 15 women with AAA. Women were analyzed with female wall properties and with male wall properties . PWS was similar, whereas PWRR was slightly higher among women. When female patients received male wall properties , no difference in mean PWRR between women and men was found. The results suggest that geometrical properties alone do not explain the previously reported higher rupture risk for female AAA patients, more likely differences in biomechanical properties could contribute.

Although obvious gender differences in AAA patients exist, this thesis also reveals several similarities. The studies point out the need of future research in order to optimize the care of AAA patients.