Title: The development of an algorithm to calculate in individual patients with abdominal aortic aneurysm (AAA) when repair is indicated to improve survival
Funder: Department of Health (England)

Abstract: Design:This proposal combines a literature review of patient risk factors influencing perioperative mortality with an analysis of data on risk factors for open AAA surgery in over 3600 patients in the VGNW programme. An algorithm predicting mortality risk in AAA surgery will be developed and validated against data on over 4900 AAA repairs in the National Vascular Database (NVD). The data from this algorithm (incorporating long term follow up for VGNW patients) will then be combined with data from the algorithm on risk of AAA rupture developed in the Cambridge Biostatistics Unit. We will then be in a position to calculate for individual patients with AAA when repair optimises health-adjusted life expectancy using Markov modelling.Search and Review Strategy:A systematic review will be carried out to calculate health costs to the NHS and a literature review to identify any important risk factors not included in VGNW. These will be done using an extensive electronic search supplemented by hand searches and reference to all relevant databases. Identified papers will be independently screened by two reviewers using a written protocol and supervised by Prof Davies.Setting:The algorithm on perioperative mortality in AAA repair will be developed in the Biostatistics Dept in Manchester using VGNW data. To facilitate the previously commissioned NIHR HTA research in Cambridge additional data on 1210 patients undergoing AAA surveillance for up to 11 years will be provided by the Aneurysm Surveillance Clinic at UHSM.Health Technologies being assessed:The new health technology is AAA surveillance with an algorithm to optimize the timing of AAA repair. This will be compared with existing standard care: AAA surveillance with AAA repair at >5.5cms in men.Measurement of cost and outcomes: A detailed methodology for measuring QALY’s and NHS costs is in Appendix B.Sample size: The data on 3600 AAA repairs in VGNW is sufficient to ‘train’ an algorithm predicting perioperative risk. This will be validated against a’ test set’ of 4900 AAA repairs in the NVD (after deducting VGNW data). Confidence intervals around predicted mortality risk will be calculated.Expected output of research: 1) An algorithm describing the expected rate of growth and risk of rupture for asymptomatic small AAAs. 2) An algorithmpredicting perioperative and long term mortality risk in elective open AAA surgery. 3) A final algorithm incorporating algorithms 1 and 2 to calculate health-adjusted life expectancy for each individual patient. Patients and clinicians will benefit from reliable information on the risk of rupture and surgery allowing informed choice.Project timetable: The MRC Biostatistics Unit in Cambridge anticipate completing algorithms on AAA growth rates and risk of rupture by November 2010. Preparation in Manchester starts as soon as this grant is awarded: Start date 3/01/2011. The literature review and data validation for 1210 AAA surveillance patients will be completed by June 2011. The VGNW data (incorporating risk factors from the literature review) will be completed and validated allowing the training of our risk prediction algorithm by December 2011. This will then be validated against NVD data in the spring of 2012. The systematic review of health costs will be commenced in January 2012. The final Markov algorithm incorporating health-adjusted life expectancy the Cambridge and Manchester algorithms and health costs will be developed May – October 2012. Reports to NIHR and manuscripts for publication will be completed November – December 2012.


Research activity codes: 6.4 SURGERY;8.4 RESEARCH DESIGN AND METHODOLOGIES (HEALTH SERVICES)
Health categories: CARDIOVASCULAR