POP-STAR: The Prospective Data Collection on Patients With Abdominal Aortic Aneurysms at the Stockholm Aneurysm Research Group (STAR)

Abdominal aortic aneurysms (AAA, ICD10 I71.4) are asymptomatic dilatations of the infrarenal aorta (≥3cm) with potential to rupture. This multifactorial disease is known to be caused by the progressive degradation of the aortic wall. AAAs have life-threatening consequences in the event of rupture (rAAA): the mortality is 100% if left untreated. The risk of rupture is closely related to the size of the AAA. When a patient is diagnosed with an AAA, life-long surveillance is initiated with regular ultrasound or computed tomography (CT) scans performed at vascular services. Prophylactic surgery is performed when the risk of rupture exceeds the risk of treatment: according to international guidelines, surgical evaluation and repair is indicated at a threshold of 55 mm (50 mm in women) to avoid rupture and subsequent death.

The mortality after planned, elective AAA repair is estimated at 1.5%. By contrast, the mortality after emergency surgery for rAAA reaches 30%. As such, there is much to be gained by early identification of AAAs to enable timely intervention and reduce aneurysm-related morbidity and mortality in the population. The important non-modifiable risk factors for developing the disease include male sex, smoking, high age and family history of AAA. Since 2006, one-time ultrasound screening for AAAs among elderly men has been gradually introduced in Sweden - the programme reached nationwide coverage in 2015. A prevalence of 1.4-2.0% has been recorded in the screened population and an overall reduction of 40% in aneurysm-related death has been demonstrated (annual decline in aneurysm-related mortality of 4%). It is not, however, cost-efficient to screen the female population due to low prevalence and high age at onset of disease.

Previous investigations have indicated that 10-25% of all patients admitted for rupture were already known by the health care system but were subsequently lost to follow-up. Importantly, some large aneurysms never rupture while some small aneurysms (<55 mm) unpredictably do so - in the randomized controlled trial of UKSAT, an annual rupture risk of 1% was documented for small AAAs.

Despite these shortcomings at a patient-specific level, there is still only one verified measure, the diameter, for evaluating growth, risk of rupture and indication for surgery. Consequently, the current follow-up protocol for AAA patients is generalized and fails to consider factors such as age, female sex, smoking, aneurysm morphology and lung function impairment. The major challenge within the field is risk assessment with high precision in order to provide treatment for the right patient and the right time.

The standard surveillance entails repeated diameter measurements: the larger the aneurysm, the shorter the control intervals. The POP-STAR project explores new methods of AAA surveillance by prospective data collection comprising of patient demographics, radiological properties and follow-up information on patients diagnosed with AAAs. All patients will be subjected to standard care flow - POP-STAR adds patient risk profiling and scheduled imaging follow-up. The goal is to be able to characterize the radiological and biomechanical profiles of AAAs for accurate risk stratification, ultimately aiming at individualized AAA patient care.