The Effect of Center Volume on In-Hospital Mortality After Aortic and Mitral Valve Surgical Procedures: A Population-Based Study

Abstract

We aimed to determine the relationship between hospital volume and use of dual aortic and mitral valve surgical procedures. Patients who underwent both aortic and mitral valve repair or replacement during the same hospital stay were identified from the Nationwide Inpatient Sample (NIS). We compared patients' characteristics and in-hospital outcomes by the average annual center volume for multiple-heart valve surgical procedures, grouped into tertiles of patients with low (1 to 8), medium (9 to 18), and high (19+) volume categories using χ(2) tests and adjusted hierarchical logistic regression models. From 1998 to 2011 an estimated total of 87,675 patients underwent combined aortic and mitral valve surgical procedures across the United States. Although most patients' characteristics were similar across volume groups, high-volume centers were more likely to treat older patients with coronary artery disease and to perform concomitant tricuspid valve operations. Low-volume centers replaced the aortic and mitral valves concomitantly more frequently with mechanical valves compared with high-volume centers (66.1% vs 45.5%), and this difference persisted across age groups. Compared with low-volume centers, the risk-adjusted odds ratios for in-hospital mortality at medium- and high-volume centers were 0.85 (95% confidence interval [CI]: 0.74 to 0.99) and 0.66 (95% CI: 0.55 to 0.80), respectively. No significant interaction was found between overall facility major cardiac surgery volume and multiple-valve procedure volume with respect to mortality (p = 0.143). Hospital volume remains an important factor influencing risk-adjusted mortality after combined aortic and mitral valve surgical procedures. Hospitals that perform more than eight combined aortic and mitral heart valve operations demonstrate a superior statistical hospital survival compared with those that perform less than eight multiple-heart valve operations a year. Further policy interventions aimed to lower hospital mortality in low-volume centers may offer possibilities for quality improvement in the field of valve surgery.