Abdominal aortic aneurysm (AAA) is a common vascular disease and associated with risk of rupture, but also with a high cardiovascular (CV) event rate. A key difficulty in AAA is predicting these life-threatening complications, highlighting the need to explore the potential of novel techniques. Both progression of AAA and CV events are strongly linked to vascular health. In 2013, the SMART risk score is developed to calculate the risk of the patients for recurrent vascular events based on clinical characteristics. Recently, a novel, easy to perform, non-invasive test of endothelial function (the carotid artery reactivity (CAR) test), reflecting target organ damage, has recently been introduced. The CAR is a simple, quick (5-min), non-invasive test that uses ultrasound to examine the carotid artery in response to sympathetic stimulation by placing one hand in cold water. This test shows strong agreement with both coronary and aortic responses to sympathetic stimulation and predicted CV events in patients with peripheral arterial disease.

The aim of this prospective 2-year follow-up study is to investigate the predictive capacity of the CAR-test in comparison to the SMART risk score for the development of cardiovascular events in patients with an abdominal aortic aneurysm who have not yet reached the treatment threshold. This could aid clinical decision making in the need for (surgical) intervention, but also alter (drug) treatment to reduce risk of cardiovascular events. Secondary objectives are to investigate the predictive capacity of the CAR-test for progression of the abdominal aortic aneurysm, and to evaluate QoL scores in patients under surveillance for AAA. The aim is to provide insight if these scores can help clinical decision making.

The investigators will include 167 patients under surveillance for AAA who are all currently under the threshold for repair (i.e. AAA diameter 40-50 mm for men and 35-45 mm for women). Participants will be recruited from all collaborating hospitals (Radboudumc, Rijnstate, CWZ) after providing written informed consent. Additionally, AAA-patients under surveillance of general practitioners are eligible (and will be contacted through the hospital-links), since the nature of the tests allow for performing all tests at the general practitioners' office.

In this observational, prospective study, a total of 167 patients under surveillance for an AAA, who are currently under threshold for repair (i.e. AAA diameter 40-50 mm for men and 35-44 mm for women), will be included. Baseline patient characteristics will be registered, including traditional risk factors and CV-history. In addition to regular care of measuring AAA diameter progression (in mm/year), the investigators will perform the CAR-test (10-min) and non-invasive arterial stiffness measures (PWA and PWV with the SphygmoCor device (10-min) one time as baseline. Furthermore, the investigators will ask patients to complete a questionnaire about the quality of their life (Appendix 1). A second questionnaire tries to clarify the disease experience of the patients and can be found in Appendix 2. Both questionnaires will be asked to be completed at the start and the end of the study. Subsequently, the investigators will record major adverse cardiovascular events (MACE) according to the International Classification of Disease-10. Registration of MACE will be performed using hospital-records and following international guidelines. Across a 2-year follow-up, by means of regular follow-up appointments, the investigators will examine AAA progression (in mm/year) and the ability of the CAR parameter and arterial stiffness parameters to predict CV-events.

Inclusion Criteria:

• Male or female at least 18 years old;
• Informed consent form understood and signed and patient agrees to follow- up visits;
• Has an abdominal aortic aneurysm (AAA), who is still under surveillance;

Exclusion Criteria:

• Life expectancy < 2 years;
• Psychiatric or other condition that may interfere with the study;
• Participating in another clinical study, interfering on outcomes;
• Increased risk for coronary spasms (score Rose-questionnaire ≥2; this questionnaire can be found in Appendix 3);
• Presence of Raynaud's phenomenon, chronic pain syndrome at upper extremity(s), presence of an AV fistula or shunt, open wounds to the upper extremity(s), and/or scleroderma associated with placing the hand in ice water;
• Recent (<3 months) presence of angina pectoris, myocardial infarction, cerebral infarction, and/or heart failure, or PAD treatment.

Patients under surveillance for an AAA, who are currently under threshold for repair (i.e. AAA diameter 40-50 mm men and 35-44 mm for women), will be included. AAA patients will be recruited from all collaborating hospitals (Radboudumc, Rijnstate, CWZ), who provide written informed consent. Additionally, also AAA-patients under surveillance of general practitioners are eligible (and will be contacted through the hospital-links), since the nature of the tests allow for performing all tests at the general practitioners' office.