Validation of a Simple Score to Determine Risk of Hospital Mortality After the Norwood Procedure

Abstract

The ability to quantify patient-specific hospital mortality risk before the Norwood procedure remains elusive. This study aimed to develop an accurate and clinically feasible score to assess the risk of hospital mortality in neonates undergoing the Norwood procedure. All patients (n = 549) in the publically available Pediatric Heart Network Single Ventricle Reconstruction trial database were included in the analysis. Patients were randomly divided into a derivation (75%) and validation (25%) cohort. Preoperative factors found to be associated with mortality upon univariable analysis (P < 0.2) were included in the logistic regression model. The score was derived by including variables independently associated with mortality (P < 0.05). A 20-point score using 6 variables (birth weight, clinical syndrome or abnormal karyotype, surgeon Norwood volume or year, anatomic subtype, ascending aorta size, and obstructed pulmonary venous return) was developed using relative magnitudes of the covariates׳ odds ratio. The score was then tested in the validation cohort. In weighted regression analysis, model predicted risk of mortality correlated closely with actual rates of mortality in the derivation (R2 = 0.87, P < 0.01) and validation cohorts (R2 = 0.82, P < 0.01). Patients were classified as low (score: 0-5), medium (6-10), or high risk (>10). Mortality differed significantly between risk groups in both the derivation (6% vs 22% vs 77%, P < 0.01) and validation (4% vs 30% vs 53%, P < 0.01) cohorts. This mortality score is accurate in determining risk of hospital mortality in neonates undergoing planned Norwood operations. The score has the potential to be used in clinical practice to aid in risk assessment before surgery. Clinical trial registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT00115934.

Keywords: Mortality; Norwood; Score; pediatric; single ventricle.

Copyright © 2016 Elsevier Inc. All rights reserved.

Figures

Figure 1

Weighted calibration plots demonstrating the association between predicted mortality rates based on the derivation cohort and observed mortality rates for each risk score in the derivation cohort (top) and validation cohort (bottom). The dashed line represents perfect calibration. The sizes of the bubbles demonstrate the relative weights assigned based on the number of patients with that particular mortality risk score.

Figure 2

Mortality Risk by Score Group

Figure 2

Mortality Risk by Score Group