The volume-outcome link has been proposed as a quality indicator in mitral valve surgery. It would be especially significant in the elderly due to the higher perioperative risk and load of comorbidities. From 2000 to 2009, a study comprised 1,239 facilities that performed mitral valve surgery on Medicare patients. Only 9% of institutions did more than 40 mitral surgeries per year, whereas 29% performed 5 or less, and 51% performed 10 or fewer. Mitral repair rates were low, with 22.7% of hospitals performing one or less, 65.1% performing five or fewer, and just 5.6% performing more than 20 mitral repairs per year in persons 65 and older. Repair rates increased as the number of mitral surgeries performed per year increased: 5 or fewer, 30.5%; 6 to 10, 32.9%; 11 to 20, 34.9 %; 21 to 40, 38.8%; and more than 40, 42.0% (P =.0001). Compared to hospitals conducting more than 40 cases per year, institutions with lower volume had considerably higher adjusted surgical mortality: If there are 5 or fewer cases per year, the odds ratio (OR) is 1.58 (95% confidence interval [CI], 1.40-1.78); if there are 6 to 10 cases per year, the OR is 1.29 (95% CI, 1.17-1.43); if there are 11 to 20 cases per year, the OR is 1.17 (95% CI, 1.07-1.28); and if there are 21 to 40 cases per year, the OR is 1.15 (95% CI (95% CI, 1.05-1.26).

In comparison to the top quartile, hospitals with lower mitral repair rates had a higher risk of operative mortality: lowest quartile, OR 1.31 (95% CI, 1.20-1.44); second quartile, OR 1.18 (95% CI, 1.09-1.29); and third quartile, OR 1.14. (95% CI, 1.05-1.24). In low-volume hospitals, long-term mortality was similarly higher: hazard ratio (HR) 1.11 (95% CI, 1.06-1.18); 6 to 10 cases per year, OR 1.06 (95% CI, 1.02-1.10) compared to institutions performing more than 40 cases per year. Most hospitals only perform a few mitral valve surgeries on older patients. Higher repair rates were linked to a higher amount of mitral operations. Both a higher volume of mitral surgeries and a higher rate of mitral repair were linked to lower mortality.