The impact of institutional case volume on the prognosis of ruptured aortic aneurysms: a Japanese nationwide study

OBJECTIVES: To improve outcome for ruptured aortic aneurysms (rAAs), centralization of treatment is potentially effective. However, there is no nationwide survey for the current managements and outcomes of rAA in Japan. The aim of this study was to assess the volume-outcome relationship for rAA treatment using the nationwide claim-based database. METHODS: Using the Japanese Registry of All cardiac and vascular Diseases-Diagnostic Procedure Combination database, we identified patients admitted to 564 certified teaching hospitals with rAA between 1 April 2012 and 31 March 2015. Institutional case volume (cardiovascular surgeries per year) was categorized into quartiles (lowest, low, high and highest), and the odds ratios (ORs) for in-hospital mortality and neurological status at discharge were analysed for each quartile. RESULTS: Of 7086 eligible patients, 3925 (55.4%) died in hospital. Mortality rates decreased from 69.4% in the lowest volume to 43.8% in the highest volume category (P < 0.001). The favourable impact of institutional case volume was sustained even after adjustment for covariates [low volume: OR 0.83, 95% confidence interval (CI) 0.65-1.07; P = 0.147; high volume: OR 0.69, 95% CI 0.54-0.89; P = 0.005; and highest volume: OR 0.55, 95% CI 0.42-0.72; P < 0.001 vs lowest volume]. Additionally, other 3 institutional parameters (increased aortic surgery volume, cardiovascular surgeons' volume and certified cardiologists' volume) were consistently associated with reduced in-hospital mortality. The rate of coma at discharge was the lowest in the highest volume group (P < 0.001). Increased institutional volume was associated with lower in-hospital mortality. CONCLUSION: Establishing regionally tailored systems to transfer patients to high-volume centres is needed to improve outcomes.