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J Thorac Cardiovasc Surg 2009;137:1133-1140
© 2009 The American Association for Thoracic Surgery

Congenital Heart Disease

The complex relationship between pediatric cardiac surgical case volumes and mortality rates in a national clinical database

^a Division of Cardiothoracic Surgery, Oregon Health and Science University, Portland, Ore
^b Outcomes Research and Assessment Group, Duke Clinical Research Institute, Durham, NC
^c Division of Pediatric Cardiothoracic Surgery, Department of Surgery, Case Western Reserve University, Cleveland, Ohio
^d Drexel University College of Medicine, Philadelphia, Pa
^e Congenital Heart Institute of Florida, Saint Petersburg and Tampa, Fla

Received for publication May 9, 2008; revisions received November 19, 2008; accepted for publication December 19, 2008.

^_* Address for reprints: Karl F. Welke, MD, Division of Cardiothoracic Surgery L353, Oregon Health and Science University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97239-3098. (Email: welkek{at}ohsu.edu).

Objective: We sought to determine the association between pediatric cardiac surgical volume and mortality using sophisticated case-mix adjustment and a national clinical database.

Methods: Patients 18 years of age or less who had a cardiac operation between 2002 and 2006 were identified in the Society of Thoracic Surgeons Congenital Heart Surgery Database (32,413 patients from 48 programs). Programs were grouped by yearly pediatric cardiac surgical volume (small, <150; medium, 150–249; large, 250–349; and very large, 350 cases per year). Logistic regression was used to adjust mortality rates for volume, surgical case mix (Aristotle Basic Complexity and Risk Adjustment for Congenital Heart Surgery, Version 1 categories), patient risk factors, and year of operation.

Results: With adjustment for patient-level risk factors and surgical case mix, there was an inverse relationship between overall surgical volume as a continuous variable and mortality (P = .002). When the data were displayed graphically, there appeared to be an inflection point between 200 and 300 cases per year. When volume was analyzed as a categorical variable, the relationship was most apparent for difficult operations (Aristotle technical difficulty component score, >3.0), for which mortality decreased from 14.8% (60/406) at small programs to 8.4% (157/1858) at very large programs (P = .02). The same was true for the subgroup of patients who underwent Norwood procedures (36.5% [23/63] vs 16.9% [81/479], P < .0001). After risk adjustment, all groups performed similarly for low-difficulty operations. Conversely, for difficult procedures, small programs performed significantly worse. For Norwood procedures, very large programs outperformed all other groups.

Conclusion: There was an inverse association between pediatric cardiac surgical volume and mortality that became increasingly important as case complexity increased. Although volume was not associated with mortality for low-complexity cases, lower-volume programs underperformed larger programs as case complexity increased.