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Ann Thorac Surg 2006;81:1800-1801
© 2006 The Society of Thoracic Surgeons
Division of Cardiovascular Surgery, The Hospital for Sick Children, 555 University Ave, Suite 1525, Toronto, ON, Canada M5G 1X8
(Email: glen.vanarsdell{at}sickkids.ca).
Dr Sinzobahamvya and colleagues [1] have rightly identified the need to quantify surgical outcomes based on anatomic and physiologic risk factors. In their analysis, a comprehensive Aristotle score of 20 or greater was associated with a significantly higher early and late mortality.
Present understanding of risk for various congenital heart lesions is derived from cohort studies where analysis of risk is made by observation of diagnosis, specific anatomy, operative factors, and physiologic risk. These elements are subjected to multivariable analysis to determine independent measures of risk. One such report from 2003 is a Congenital Heart Surgeons Society (CHSS) analysis of 710 Norwood operations [2], which revealed incremental risk factors for death to be patient related (lower birth weight, older age, and smaller ascending aortic size), surgical (longer circulatory arrest time and shunt arising from the neoaorta), and institutional.
A synthesis of known risk has been created into expert consensus based models. The two models most commonly utilized are RACHS-1 (Risk Adjustment for Congenital Heart Surgery) [3] and the comprehensive Aristotle model [4]. The RACHS-1 classification is a diagnosis, age, and other anomaly based risk stratification that has six categories of increasing risk; a Norwood is in risk category 5. The comprehensive Aristotle score accounts for diagnosis with its potential for mortality, morbidity, and procedural risk as well as providing additional risk scoring for patient specific factors. The Norwood procedure has a basic numeric risk of 14.5/15 (ASD = 3, TOF with a transannular patch = 8 and a biventricular repair for hypoplastic left heart complex = 15). The comprehensive Aristotle score adds 7 weighted Norwood specific variables and a potential 98 other weighted procedure independent variables (see Tables 1 and 2 in the manuscript). An Aristotle score above 20 implies multiple anatomic and or physiological risk factors.
Scientific validation of the consensus models is ongoing. A snapshot comparison of measured risk versus expert consensus raises points of interest. In the CHSS paper, risk was identified as being incremental. As examples, for each drop in weight of 1 kg there was a doubling of mortality. In contrast, the comprehensive Aristotle system deals with weight by adding a score of 2 points for a weight <2.5 kg, or a 14% increase. In the CHSS study, each week of older age increased risk by 10%, and in the Aristotle scoring system you add 3 points if the baby is over 1 month of age. The CHSS regression approach provides an incremental risk. The comprehensive Aristotle score provides a weighted risk.
To understand the predictability of the consensus models, our group examined over 11,000 patient records and evaluated the RACHS-1 and the basic Aristotle score for correlation with observed surgical outcome [5]. Both scoring systems were better than chance but fell below expectations as a measuring tool for accurate prediction of outcome. Data were not available to test the comprehensive Aristotle score.
The authors of the present manuscript have measured the utility of the comprehensive Aristotle score for predicting survival. Before we as a scientific community accept validity of such analysis for institutional comparison (with all the potential implications), a correlation of present known odds ratios for risks in individual patients needs to be evaluated against the individual comprehensive Aristotle score and the RACHS-1 classification. One would anticipate that testing consensus based scoring systems against regression based scientific data would allow a rationale for calibration of the consensus. With ongoing testing and calibration, it is conceivable that sensitivity and specificity of a consensus based system could correlate highly with outcomes predicted by measured incremental risk. Until then we must be cautious in our interpretation of consensus based scoring systems.
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  J. Li, G. Zhang, H. Holtby, S. Cai, M. Walsh, C. A. Caldarone, and G. S. Van Arsdell Significant correlation of comprehensive Aristotle score with total cardiac output during the early postoperative period after the Norwood procedure J. Thorac. Cardiovasc. Surg., July 1, 2008; 136(1): 123 - 128. [Abstract] [Full Text] [PDF]
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