Congenital Heart Surgery Program Variable Case Mix: Risk Associated With Adjusted Mortality Rate

Background: Congenital heart operations are categorized into risk categories based on The Society of Thoracic Surgeons-European Association of Cardio-Thoracic Surgery Congenital Heart Surgery (STAT) Mortality Categories. The adjusted mortality rate should adjust for case mix.

Methods: The Society of Thoracic Surgeons Congenital Heart Surgery Public Reporting data were extracted for the top 50 U.S. News & World Report Cardiology and Heart Surgery Programs in 2021 (operations from January 2015 to December 2018). Variability in STAT 1 as a percentage of total operations and as a ratio to STAT 4+5 operations was evaluated.

Results: STAT 1 cases varied between centers from 18% to 37% of total. The ratio of STAT 1 to STAT 4+5 varied from 0.52 to 1.97. There was an inverse relationship between the STAT 1:STAT 4+5 ratio and adjusted mortality rate that did not reach statistical significance (P = .12). When programs (n = 12) in the quartiles with the highest vs lowest STAT 1:STAT 4+5 ratio were compared, a significant difference was found in the median adjusted mortality rate (2.2% vs 2.95%, P = .03).

Conclusions: There is a 4-fold difference in the ratio of STAT 1 to STAT 4+5 cases among congenital heart surgery programs, even when smaller programs are excluded, suggesting significant differences in the decision-making philosophy. Programs with the highest proportion of STAT 1 cases had lower adjusted mortality rate, suggesting that The Society of Thoracic Surgery Congenital Heart Surgery Database mortality risk model adjusts well but not completely for case-mix variability between programs.