Predicting risk of rupture and rupture-preventing re-intervention utilising repeated measures on aneurysm sac diameter following endovascular abdominal aortic aneurysm repair

Background: Clinical and imaging surveillance practices following endovascular aneurysm repair (EVAR) for intact abdominal aortic aneurysm (AAA) vary considerably and compliance with recommended lifelong surveillance is poor. This study developed a dynamic prognostic model to enable stratification of patients at risk of future secondary rupture or rupture preventing re-intervention (RPR) to enable the development of personalised surveillance intervals. Method: Baseline data and repeat measurements of post-operative aneurysm sac diameter from the EVAR-1 and EVAR-2 trials were used to develop the model with external validation in a cohort from Helsinki. Longitudinal mixed-effects models were fitted to trajectories of sac diameter and model-predicted sac diameter and rate of growth were used in prognostic Cox proportional hazards models. Results: 785 patients from the EVAR trials were included of which 155 (20%) suffered at least one rupture or RPR during follow-up. An increased risk was associated with pre-operative AAA size, rate of sac growth, and the number of previously detected complications. A prognostic model using only predicted sac growth had good discrimination at 2-years (C-index = 0.68), 3- years (C-index= 0.72) and 5-years (C-index= 0.75) post-operation and had excellent external validation (C-indices 0.76 to 0.79). After 5-years post-operation, growth rates above 1mm/year had a sensitivity of over 80% and specificity over 50% in identifying events occurring within 2 years. Conclusion: Secondary sac growth is an important predictor of rupture or RPR. A dynamic prognostic model has the potential to tailorsurveillance by identifying a large proportion of patients who may require less intensive follow-up.