Impact of hospital annual mitral procedural volume on mitral valve repair rates and mortality

Abstract

Background and aim of the study: The aim of this investigation was to examine the impact of hospital annual mitral volume on mitral valve (MV) repair rates and mortality.

Methods: The 2005-2008 Nationwide Inpatient Sample (NIS) database was searched to identify patients who had undergone either MV repair (ICD-9-CM code 35.12) or MV replacement (ICD-9-CM codes 35.23 and 35.24). The hospitals were stratified into five categories based on the annual volume of all mitral procedures (< 10, 10-20, 21-40, 41-79, and > or = 80 cases/year). The relationship between hospital annual mitral procedure volume and MV repair rates, as well as hospital mortality for MV repair, was then examined for patients undergoing isolated MV surgery (excluding those aged < 30 years and those with congenital heart disease, concomitant coronary revascularization, ventricular aneurysm excision, heart transplant and other valvular interventions, except tricuspid). Chi-square tests of independence were used to test for differences between the mitral volume categories, and Cochran-Armitage tests to check for trends across the years.

Results: The sample included a total of 12,857 patients from 603 hospitals. Mitral repair rates increased as a function of hospital mitral volume, ranging from 34% for hospitals with < 10 mitral cases/year to 53% for hospitals with > or = 80 mitral cases/year. Follow up comparisons revealed that an annual mitral volume of > 40 cases/year was associated with a significantly higher rate of MV repair (p < 0.005). There was a significant trend of increasing MV repair rates over time for hospitals with annual mitral volumes of 20-40 and 41-79 cases/year (p = 0.0001). The MV repair mortality ranged from 1.33% to 2.29%, and did not differ among hospitals as a function of the annual mitral volume (p = 0.2982).

Conclusion: Mortality after MV repair was low, and independent of the hospital annual mitral volume. A hospital annual mitral volume of fewer than 40 cases per year was associated with a lower rate of MV repair. Addressing the factors responsible for this finding constitutes an important area for future improvement in the care of patients with MV disease.