Risk factors and modelling the risk of abdominal aortic aneurysm rupture and repair

Abdominal aortic aneurysm (AAA) rupture is estimated to cause 170,000 deaths worldwide each year. Most AAAs are asymptomatic until rupture, but incidental imaging and screening programs identify many small aneurysms which have a low risk of rupture. The only current treatment for AAA is repair by endovascular or open surgery, but current guidelines recommend that elective repair is only considered when the aneurysm diameter is 50mm or greater in women and 55mm or greater in men. Smaller AAAs are monitored by repeat imaging until they reach surgical threshold, but some small AAAs rupture during the surveillance period. More comprehensive way of predicting which small AAAs will subsequently rupture or require elective repair would enable more personalised selection for elective repair. This article describes the risk factors and attempts to develop comprehensive models to predict AAA rupture and repair. Female gender, higher mean arterial and pulse pressure, and current smoking are associated with a higher risk of small AAA rupture. A range of imaging findings, including large volume of intra-luminal thrombus, greater tortuosity of the infra-renal aorta and higher peak wall stress, have been associated with higher risk of AAA rupture in some studies. Furthermore, high plasma matrix metalloproteinase-12, desmosine, angiopoietin-2 and aggregan have been associated with greater risk of requiring AAA repair. Ultimately models which incoporate a range of the clinical, imaging and blood risk factors would appear to likely be optimal for best prediction of event risk but currently validated models incorporating these risk factors have not been developed.