Original Article
Congenital heart surgery outcome analysis: Indian experience
Asian Cardiovascular & Thoracic Annals 21(6) 675–682 ß The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0218492312466751 aan.sagepub.com
Sumit Vasdev1, Sandeep Chauhan1, Madhur Malik1, Sachin Talwar2, Devagourou Velayoudham2 and Usha Kiran1
Abstract Background: The study aimed to analyze the outcome of congenital heart surgery in a subset of Indian patients, using the Aristotle Basic Complexity score, the Risk Adjustment for Congenital Heart Surgery categories, and the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality categories. Patients and methods: 1312 patients 120 min), morbidity (intensive care unit stay >7 days), and mortality. Results: The overall mortality was 6.85%, with mean a Aristotle Basic Complexity score, Risk Adjustment for Congenital Heart Surgery category, and Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality category of 7.17 2.04, 2.28 0.78, and 2.24 1.06, respectively. The mortality predictive capacity of the Risk Adjustment for Congenital Heart Surgery category (c ¼ 0.76) was similar to that of the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality category (c ¼ 0.75); both were better compared to the Aristotle Basic Complexity score (c ¼ 0.66). The Risk Adjustment for Congenital Heart Surgery category and Aristotle Basic Complexity score correlated with morbidity and difficulty outcomes. Conclusion: The study shows that the Aristotle Basic Complexity score, the Risk Adjustment for Congenital Heart Surgery category, and the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality category are tools of case mix stratification to analyze congenital heart surgery outcomes in a subset of the Indian population.
Keywords Aristotle score, heart defects, congenital, risk adjustment
Introduction Modern-day medical practice importantly encompasses evaluation of the quality of care. One of the important measures to assess quality of care is an analysis of the outcomes of the care provided. In the setting of pediatric congenital heart surgery, outcome analysis purely on the basis of mortality and morbidity may be misleading due to the large number of surgical procedures that vary in complexity. Presently, the Aristotle Basic Complexity (ABC) score, Aristotle Comprehensive Complexity (ACC) score, Risk Adjustment for Congenital Heart Surgery (RACHS-1) categories, and the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality
score (STS-EACTS MS) have been developed for analyzing congenital heart surgery outcomes.1–3 The ABC score was developed by a consensus of experts from 50 centers in 23 countries. For 145 operative procedures, scores were given for potential 1 Department of Cardiac Anesthesia, All India Institute of Medical Sciences, New Delhi, India 2 Department of Cardiothoracic and Vascular Surgery, All India Institute of Medical Sciences, New Delhi, India
Corresponding author: Sumit Vasdev, MD, Department of Cardiac Anesthesia, All India Institute of Medical Sciences, VIIth Floor, CN Centre, New Delhi 110029, India. Email: [email protected]
676 mortality, morbidity, and technical difficulty, ranging from 0.5–5, and cumulating in a score range of 1.5–15. The score further allows grouping procedures as: level 1 (score 1.5–5.9), level 2 (score 6–7.9), level 3 (score 8–9.9), and level 4 (score 10–15).4–6 A validation study of the ABC score has been conducted from the Society of Thoracic Surgeons (STS) Congenital Heart Surgery Database and the European Association for Cardiothoracic Surgery (EACTS) Congenital Heart Surgery Database.7 The ACC score is the sum of the basic score and patient-adjusted complexity score (0–10 points). This includes procedure-dependent factors (0–5 points) and procedure-independent factors (general, clinical, extracardiac and surgical: 0–5 points). The ACC score recognizes 6 levels of complexity, from the less complex level 1 with 1.5–5.9 points to the most complex level 6 with 20.1–25 points.1 The RACHS-1 system is also a consensus-based categorization developed by an 11-member panel of experts. The RACHS-1 system categorizes congenital cardiac operations into 6 categories with increasing risk of mortality. The RACHS-1 system has been validated in the Danish and the German populations.8,9 In contrast to the Aristotle and RACHS-1 systems which are subjectively derived, the STS-EACTS MS has been proposed as an objective empirically based categorization of 148 procedures into 5 categories termed the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality categories (STS-EACTS MC). The system also gives a difficulty ranking to the surgical procedures. The STS-EACTS MC was developed using the STS-EACTS dataset for the years 2002– 2007, and the same has been validated in the dataset for 2007–2008.3 These scoring systems have not yet been studied in Indian patients. This study was conducted to analyze the outcomes of congenital heart surgery according to the ABC score, RACHS-1, and STS-EACTS categories, and to evaluate the predictability of mortality by the 3 systems in a subset of Indian patients.
Patients and methods During the period from February 2010 to August 2011, 1359 patients below the age of 18 years undergoing elective cardiac surgery were studied prospectively. Excluded from the study was surgical closure of patent ductus arteriosus in premature newborns, primary extracorporeal membrane oxygenation, and cardiac pacemaker implantation.7 The data were obtained for age, sex, weight, height, procedure, duration of surgery, cardiopulmonary bypass (CPB) time, intensive care unit (ICU) stay, hospital stay, and mortality. Mortality was defined as death during the same hospitalization regardless of cause. The procedures were
Asian Cardiovascular & Thoracic Annals 21(6) assigned an ABC score, RACHS-1 category, and the STS-EACTS mortality score, category and difficulty ranking. For children undergoing more than one procedure during the same hospital stay, the primary procedure was scored, and in cases of combined procedures, the procedure with the highest score, category, and ranking was considered. For each class of the ABC, RACHS-1, and STS-EACTS scoring systems, the 3 outcome indices were calculated on the basis of the total patients in the level or category: the mortality index was the percentage of patients who died, the morbidity index was the percentage of patients who had ICU stay >7 days, and the difficulty index was the percentage of patients having duration of surgery (offpump) or CPB time >120 min. The overall strength of the association between the 3 scores and each outcome index was assessed graphically by plotting the observed outcome indices as a function of each class of the 3 scoring systems. For analysis of the difficulty index in the STSEACTS system, the difficulty ranks were arbitrarily divided into 4 classes: class 1 (difficulty rank 1–37), class 2 (difficulty rank 38–74), class 3 (difficulty rank 75–111), and class 4 (difficulty rank 112–148), which were different to the mortality categories used for mortality and morbidity index analysis. The receiver operating characteristic curve for the 3 systems was used to assess the predictability of mortality by measuring the c-index, that is the area under the curve. The c-index represents the probability that a randomly selected patient who had the studied outcome (mortality) had a higher predicted risk of the outcome compared to a randomly selected patient who did not experience the outcome (discharged). The c-index varies from 0.5–1, with 0.5 representing chance, and 1 representing maximum probability of the predicted outcome. The Pearson correlation coefficient (r), corresponding p value, and the coefficient of association (r2) were determined among the 3 outcome indices and the scoring systems. The odds ratio analysis was performed to determine the differentiation between the different levels and categories of the 3 scoring systems for the mortality, morbidity, and difficulty outcome indices. The odds ratio evaluates whether the odds of a certain event or outcome is the same for 2 groups. The odds ratio of 1 is the true neutral value, indicating equal odds for both outcomes in the 2 groups.10
Results Of the 1359 children studied, 1312 (96.5%) could be scored using both the ABC and STS-EACTS MC scores, whereas 1300 (95.6%) could to be scored by the RACHS-1 system. The distribution of the children in different levels and categories of the scoring systems
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Figure 1. Percentage distribution of patients in different classes of the scoring systems. ABC: Aristotle Basic Complexity Score; RACHS-1¼Risk Adjustment for Congenital Heart Surgery system, STS-EACTS MC: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories; STS-EACTS DR: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery difficulty ranking.
is shown in Figure 1. None of the children belonged to category 5 or 6 of the RACHS-1 system, or category 5 of the STS-EACTS system. The mean age of the children studied was 40.199 43.155 months (ranging from 2 days to 17 years) and the overall mortality was 6.85% with a mean ABC score of 7.17 2.04, RACHS-1 category of 2.28 0.78, STS-EACTS mortality category of 2.24 1.06, and STS-EACTS difficulty rank of 62.39 37.74 (Table 1). The graphical plots of mortality (Figure 2(a)), morbidity (Figure 2(b)), and difficulty (Figure 2(c)) outcome indices showed correlation of the increase in ABC levels and RACHS-1 categories. The STS-EACTS mortality categories showed an increase in mortality with higher categories (Figure 2(a)), but the morbidity index decreased from category 3 to 4 (Figure 2(b)). The difficulty index correlated well with the arbitrary classes of STS-EACTS difficulty rank (Figure 2(c)). The receiver operating characteristic curves showed the predictability of mortality by the ABC (Figure 3(a)), RACHS-1 (Figure 3(b)), and STS-EACTS MC (Figure 3(c)) systems. The RACHS1 (c-index ¼ 0.7654) and STS-EACTS MC (cindex ¼ 0.7556) showed greater predictability for mortality than the ABC system (c-index ¼ 0.6676). The p values for the differences in c-index showed a significant difference when comparing ABC with RACHS-1 and STS-EACTS MC (Table 2). Both the ABC and RACHS-1 system correlated significantly with the mortality, morbidity, and difficulty outcome indices (Table 3). In the STS-EACTS system, the correlation was statistically significant for mortality index with the mortality categories, and for difficulty index with the
arbitrary difficulty ranking classes (Table 3). The odds ratio analysis within the different categories of RACHS-1 showed significant differentiation for mortality, morbidity, and the difficulty outcome indices (Table 4). The ABC levels also differentiated well in odds ratio analysis, apart from the mortality between level 2 and 3, and the morbidity index between level 1 and 2 (Table 5). The STS-EACTS mortality categories differentiated significantly the mortality outcome index, and the difficulty ranks had significant odds ratio differentiation for the difficulty outcome (Table 6).
Discussion The ABC score and the RACHS-1 system were developed as tools for assessing the outcomes in congenital heart surgery, with the idea to negate the confounding effect of a case mix of diverse complexity. Both scoring systems, based on subjective probabilities, stratified the congenital heart surgery procedures into categories of increasing mortality. STS-EACTS MC is an objective empirically based model derived from the STS-EACTS database between the years 2002 and 2007. In the present study, the 3 systems were used to assess the predictability of mortality, in essence as a model for outcome analysis, in a subset of the Indian population. All 3 systems showed the ability to predict mortality, which was higher for RACHS-1 and STS-EACTS MC compared to the ABC scoring system. The results were similar to the earlier studies on the STS-EACTS database (year 2007–2008) which determined the c-index of STS-EACTS MC as 0.778, RACHS-1 as 0.745, and
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Table 1. Patient and procedure characteristics. Variable
No. of patients
*
40.199 43.155
Age (months) Age distribution 1 year Body surface area (m2) Operation on CPB CPB time (min) [range] Operation without CPB Non-CPB operative time (min) [range] ICU stay (days) [range] Hospital stay (days) [range] Mortality Cause of mortality Low cardiac output Sepsis Pulmonary hypertensive crises Sudden cardiac arrest ABC score ABC level RACHS-1 category STS-EACTS MS STS-EACTS MC STS-EACTS DR
16 (1.21%) 44 (3.35%) 400 (30.48%) 852 (64.93%) 0.485 0.236 1084 81.14 39.61 [10–295] 228 79.78 23.33 [44–180] 3.58 4.08 [1–53] 7.04 4.24 [2–57] 90 (6.85%) 44 (48.8%) 23 (25.5%) 15 (16.6%) 8 (8.8%) 7.17 2.04 2.49 0.85 2.28 0.78 0.67 0.52 2.24 1.06 62.39 37.74
ABC: Aristotle Basic Complexity score; CPB: cardiopulmonary bypass; ICU: intensive care unit; RACHS-1: Risk Adjustment for Congenital Heart Surgery system; STS-EACTS DR: Society of Thoracic Surgeons, European Association for Cardiothoracic Surgery Congenital Heart Surgery difficulty ranking; STS-EACTS MC: Society of Thoracic Surgeons, European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories; STS-EACTS MS: Society of Thoracic Surgeons, European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality score.
ABC as 0.687.3 However, another study of a small population sample from Thailand has reported STSEACTS MC to have a lower c-index of 0.66, this difference was account for by only a small number of patients in category 4.11 The STS-EACTS, in addition to being objective, further differs from the ABC as a differentiator of mortality from that of difficulty levels. The ABC score takes into account a potential difficulty along with morbidity and mortality. While STS-EACTS is purely based on procedure-specific mortality rates and allots a technically less difficult case such as pulmonary artery banding to the higher category of 4, despite having a lower difficulty rank of 21. In the present study, the STS-EACTS
difficulty ranks were shown to significantly correlate with the difficulty outcome index. The difference in the c-index of RACHS-1 and ABC in the present study was also close to the earlier reported studies of Al-Radi and colleagues12 and O’Brein and colleagues.7 Kang and colleagues13 also reported the RACHS-1 categories to have a larger logistic regression Wald statistic of 17.7 vs. 4.8 of the ABC score. Apart from mortality, the complete assessment of quality of care involves morbidity as an important outcome in analysis. With mortality decreasing as a result of the improvements in congenital cardiac surgery, anesthesia, perfusion techniques, and postoperative intensive care, morbidity is emphasized as the quality of outcome for survivors. Our study demonstrated a significant correlation of morbidity index with that of ABC (r ¼ 0.9529) and RACHS-1 (r ¼ 0.9866) compared to the nonsignificant correlation of morbidity index with STS-EACTS (r ¼ 0.8411). However, we used the morbidity surrogate of ICU stay for this analysis. Morbidity should ideally be based on observed postoperative complications weighed according to their severity. Clarke and colleagues14 proposed that morbidity score be constituted with the following 4 components: postoperative hospital length of stay, postoperative time on the ventilator, postoperative extracorporeal membrane oxygenation and/or ventricular-assist device time, and major complications (reoperation, permanent pacemaker for atrioventricular block, nerve palsy, neurological disorders, and dialysis). Sata and colleagues15 have also recently proposed an objective morbidity score based on the observed postoperative complications, and compared it to the ABC morbidity score. A large series analysis of the proposed objective morbidity score is yet to be performed. Another dimension of the outcome analysis scores is the evaluation of performance which can allow interinstitute comparisons and gauge improvement over the years. RACHS-1 was used to demonstrate an improvement in congenital heart surgery (from 1997 to 2004) in Guatemala, and it has been used for comparing interinstitute outcomes.16,17 The Aristotle Committee1 has defined operative performance using the equation: operative performance ¼ complexity score hospital survival. Arenz and colleagues18 have used the ABC and ACC scores to analyze the evolution of performance in congenital heart surgery over the years 2006 to 2009. STS-EACTS mortality categories have also been proposed as a tool to compare mortality outcome across institutions with different case mixes.3 The present study represents the outcome performance in a subset of Indian patients using consensus-based and empirically derived outcome tools of the STS and EACTS databases. The study has the potential for
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Figure 2. Relationship between the three scoring systems and the (a) mortality, (b) morbidity and the (c) operative difficulty indices. ABC: Aristotle Basic Complexity Score; RACHS-1 ¼ Risk Adjustment for Congenital Heart Surgery system, STS-EACTS MC: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories; STS-EACTS DR: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery difficulty ranking.
Figure 3. Receiver operating characteristic (ROC) curve as a predictor of mortality for (a) Aristotle Basic Complexity Score (ABC), (b) Risk Adjustment for Congenital Heart Surgery system (RACHS-1), and (c) Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories (STS-EACTS MC).
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Asian Cardiovascular & Thoracic Annals 21(6) Table 2. c-index for the 3 systems and p values for differences between them. System
c-index
Comparison
p value
STS-EACTS MC ABC RACHS-1
0.7556 0.6676 0.7654
STS-EACTS MC vs. ABC STS-EACTS MC vs. RACHS-1 RACHS-1 vs. ABC
0.04 0.81 0.02
p40.05 is significant. ABC: Aristotle Basic Complexity score; RACHS-1: Risk Adjustment for Congenital Heart Surgery system; STS-EACTS MC: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories.
Table 3. Coefficient of correlation of various scores to the mortality, morbidity, and difficulty indices. Scores ABC
RACHS-1
STS-EACTS MC* &STS-EACTS DRy
r (r2) p r (r2) p r (r2) p
Mortality index
Morbidity index (ICU stay >7 days)
Difficulty index (CPB >120 min)
0.9844 (0.969) 0.015* 0.9672 (0.9355) 0.032 0.9781 (0.9567) 0.021
0.9529 (0.908) 0.04 0.9866 (0.9734) 0.013 0.8411 (0.7074) 0.15
0.9661 (0.9333) 0.033 0.957 (0.917) 0.042 0.957 (0.9166) 0.042
r ¼ Pearson correlation coefficient, r2 ¼ coefficient of determination, p40.05 is significant. *STS-EACTS MC used for mortality and morbidity index correlation. ySTS-EACTS DR used for difficulty index correlation. ABC: Aristotle Basic Complexity score; CPB: cardiopulmonary bypass; ICU: intensive care unit; RACHS-1: Risk Adjustment for Congenital Heart Surgery system; STSEACTS DR: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery difficulty ranking; STS-EACTS MC: Society of Thoracic Surgeons, European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories.
Table 4. Odds ratio comparison between different categories of RACHS-1 for mortality, morbidity, and difficulty indices. Mortality index
Morbidity index (ICU stay >7 days)
Difficulty index (CPB>120 min)
RACHS-1
Odds ratio
p value
Odds ratio
p value
Odds ratio
p value
1 1 1 2 3 2
0.0996 0.0183 0.0079 0.0783 0.4341 0.18
0.1082 0.005 0.0008
Congenital heart surgery outcome analysis: Indian experience
Asian Cardiovascular & Thoracic Annals 21(6) 675–682 ß The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0218492312466751 aan.sagepub.com
Sumit Vasdev1, Sandeep Chauhan1, Madhur Malik1, Sachin Talwar2, Devagourou Velayoudham2 and Usha Kiran1
Abstract Background: The study aimed to analyze the outcome of congenital heart surgery in a subset of Indian patients, using the Aristotle Basic Complexity score, the Risk Adjustment for Congenital Heart Surgery categories, and the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality categories. Patients and methods: 1312 patients 120 min), morbidity (intensive care unit stay >7 days), and mortality. Results: The overall mortality was 6.85%, with mean a Aristotle Basic Complexity score, Risk Adjustment for Congenital Heart Surgery category, and Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality category of 7.17 2.04, 2.28 0.78, and 2.24 1.06, respectively. The mortality predictive capacity of the Risk Adjustment for Congenital Heart Surgery category (c ¼ 0.76) was similar to that of the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality category (c ¼ 0.75); both were better compared to the Aristotle Basic Complexity score (c ¼ 0.66). The Risk Adjustment for Congenital Heart Surgery category and Aristotle Basic Complexity score correlated with morbidity and difficulty outcomes. Conclusion: The study shows that the Aristotle Basic Complexity score, the Risk Adjustment for Congenital Heart Surgery category, and the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality category are tools of case mix stratification to analyze congenital heart surgery outcomes in a subset of the Indian population.
Keywords Aristotle score, heart defects, congenital, risk adjustment
Introduction Modern-day medical practice importantly encompasses evaluation of the quality of care. One of the important measures to assess quality of care is an analysis of the outcomes of the care provided. In the setting of pediatric congenital heart surgery, outcome analysis purely on the basis of mortality and morbidity may be misleading due to the large number of surgical procedures that vary in complexity. Presently, the Aristotle Basic Complexity (ABC) score, Aristotle Comprehensive Complexity (ACC) score, Risk Adjustment for Congenital Heart Surgery (RACHS-1) categories, and the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality
score (STS-EACTS MS) have been developed for analyzing congenital heart surgery outcomes.1–3 The ABC score was developed by a consensus of experts from 50 centers in 23 countries. For 145 operative procedures, scores were given for potential 1 Department of Cardiac Anesthesia, All India Institute of Medical Sciences, New Delhi, India 2 Department of Cardiothoracic and Vascular Surgery, All India Institute of Medical Sciences, New Delhi, India
Corresponding author: Sumit Vasdev, MD, Department of Cardiac Anesthesia, All India Institute of Medical Sciences, VIIth Floor, CN Centre, New Delhi 110029, India. Email: [email protected]
676 mortality, morbidity, and technical difficulty, ranging from 0.5–5, and cumulating in a score range of 1.5–15. The score further allows grouping procedures as: level 1 (score 1.5–5.9), level 2 (score 6–7.9), level 3 (score 8–9.9), and level 4 (score 10–15).4–6 A validation study of the ABC score has been conducted from the Society of Thoracic Surgeons (STS) Congenital Heart Surgery Database and the European Association for Cardiothoracic Surgery (EACTS) Congenital Heart Surgery Database.7 The ACC score is the sum of the basic score and patient-adjusted complexity score (0–10 points). This includes procedure-dependent factors (0–5 points) and procedure-independent factors (general, clinical, extracardiac and surgical: 0–5 points). The ACC score recognizes 6 levels of complexity, from the less complex level 1 with 1.5–5.9 points to the most complex level 6 with 20.1–25 points.1 The RACHS-1 system is also a consensus-based categorization developed by an 11-member panel of experts. The RACHS-1 system categorizes congenital cardiac operations into 6 categories with increasing risk of mortality. The RACHS-1 system has been validated in the Danish and the German populations.8,9 In contrast to the Aristotle and RACHS-1 systems which are subjectively derived, the STS-EACTS MS has been proposed as an objective empirically based categorization of 148 procedures into 5 categories termed the Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery mortality categories (STS-EACTS MC). The system also gives a difficulty ranking to the surgical procedures. The STS-EACTS MC was developed using the STS-EACTS dataset for the years 2002– 2007, and the same has been validated in the dataset for 2007–2008.3 These scoring systems have not yet been studied in Indian patients. This study was conducted to analyze the outcomes of congenital heart surgery according to the ABC score, RACHS-1, and STS-EACTS categories, and to evaluate the predictability of mortality by the 3 systems in a subset of Indian patients.
Patients and methods During the period from February 2010 to August 2011, 1359 patients below the age of 18 years undergoing elective cardiac surgery were studied prospectively. Excluded from the study was surgical closure of patent ductus arteriosus in premature newborns, primary extracorporeal membrane oxygenation, and cardiac pacemaker implantation.7 The data were obtained for age, sex, weight, height, procedure, duration of surgery, cardiopulmonary bypass (CPB) time, intensive care unit (ICU) stay, hospital stay, and mortality. Mortality was defined as death during the same hospitalization regardless of cause. The procedures were
Asian Cardiovascular & Thoracic Annals 21(6) assigned an ABC score, RACHS-1 category, and the STS-EACTS mortality score, category and difficulty ranking. For children undergoing more than one procedure during the same hospital stay, the primary procedure was scored, and in cases of combined procedures, the procedure with the highest score, category, and ranking was considered. For each class of the ABC, RACHS-1, and STS-EACTS scoring systems, the 3 outcome indices were calculated on the basis of the total patients in the level or category: the mortality index was the percentage of patients who died, the morbidity index was the percentage of patients who had ICU stay >7 days, and the difficulty index was the percentage of patients having duration of surgery (offpump) or CPB time >120 min. The overall strength of the association between the 3 scores and each outcome index was assessed graphically by plotting the observed outcome indices as a function of each class of the 3 scoring systems. For analysis of the difficulty index in the STSEACTS system, the difficulty ranks were arbitrarily divided into 4 classes: class 1 (difficulty rank 1–37), class 2 (difficulty rank 38–74), class 3 (difficulty rank 75–111), and class 4 (difficulty rank 112–148), which were different to the mortality categories used for mortality and morbidity index analysis. The receiver operating characteristic curve for the 3 systems was used to assess the predictability of mortality by measuring the c-index, that is the area under the curve. The c-index represents the probability that a randomly selected patient who had the studied outcome (mortality) had a higher predicted risk of the outcome compared to a randomly selected patient who did not experience the outcome (discharged). The c-index varies from 0.5–1, with 0.5 representing chance, and 1 representing maximum probability of the predicted outcome. The Pearson correlation coefficient (r), corresponding p value, and the coefficient of association (r2) were determined among the 3 outcome indices and the scoring systems. The odds ratio analysis was performed to determine the differentiation between the different levels and categories of the 3 scoring systems for the mortality, morbidity, and difficulty outcome indices. The odds ratio evaluates whether the odds of a certain event or outcome is the same for 2 groups. The odds ratio of 1 is the true neutral value, indicating equal odds for both outcomes in the 2 groups.10
Results Of the 1359 children studied, 1312 (96.5%) could be scored using both the ABC and STS-EACTS MC scores, whereas 1300 (95.6%) could to be scored by the RACHS-1 system. The distribution of the children in different levels and categories of the scoring systems
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Figure 1. Percentage distribution of patients in different classes of the scoring systems. ABC: Aristotle Basic Complexity Score; RACHS-1¼Risk Adjustment for Congenital Heart Surgery system, STS-EACTS MC: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories; STS-EACTS DR: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery difficulty ranking.
is shown in Figure 1. None of the children belonged to category 5 or 6 of the RACHS-1 system, or category 5 of the STS-EACTS system. The mean age of the children studied was 40.199 43.155 months (ranging from 2 days to 17 years) and the overall mortality was 6.85% with a mean ABC score of 7.17 2.04, RACHS-1 category of 2.28 0.78, STS-EACTS mortality category of 2.24 1.06, and STS-EACTS difficulty rank of 62.39 37.74 (Table 1). The graphical plots of mortality (Figure 2(a)), morbidity (Figure 2(b)), and difficulty (Figure 2(c)) outcome indices showed correlation of the increase in ABC levels and RACHS-1 categories. The STS-EACTS mortality categories showed an increase in mortality with higher categories (Figure 2(a)), but the morbidity index decreased from category 3 to 4 (Figure 2(b)). The difficulty index correlated well with the arbitrary classes of STS-EACTS difficulty rank (Figure 2(c)). The receiver operating characteristic curves showed the predictability of mortality by the ABC (Figure 3(a)), RACHS-1 (Figure 3(b)), and STS-EACTS MC (Figure 3(c)) systems. The RACHS1 (c-index ¼ 0.7654) and STS-EACTS MC (cindex ¼ 0.7556) showed greater predictability for mortality than the ABC system (c-index ¼ 0.6676). The p values for the differences in c-index showed a significant difference when comparing ABC with RACHS-1 and STS-EACTS MC (Table 2). Both the ABC and RACHS-1 system correlated significantly with the mortality, morbidity, and difficulty outcome indices (Table 3). In the STS-EACTS system, the correlation was statistically significant for mortality index with the mortality categories, and for difficulty index with the
arbitrary difficulty ranking classes (Table 3). The odds ratio analysis within the different categories of RACHS-1 showed significant differentiation for mortality, morbidity, and the difficulty outcome indices (Table 4). The ABC levels also differentiated well in odds ratio analysis, apart from the mortality between level 2 and 3, and the morbidity index between level 1 and 2 (Table 5). The STS-EACTS mortality categories differentiated significantly the mortality outcome index, and the difficulty ranks had significant odds ratio differentiation for the difficulty outcome (Table 6).
Discussion The ABC score and the RACHS-1 system were developed as tools for assessing the outcomes in congenital heart surgery, with the idea to negate the confounding effect of a case mix of diverse complexity. Both scoring systems, based on subjective probabilities, stratified the congenital heart surgery procedures into categories of increasing mortality. STS-EACTS MC is an objective empirically based model derived from the STS-EACTS database between the years 2002 and 2007. In the present study, the 3 systems were used to assess the predictability of mortality, in essence as a model for outcome analysis, in a subset of the Indian population. All 3 systems showed the ability to predict mortality, which was higher for RACHS-1 and STS-EACTS MC compared to the ABC scoring system. The results were similar to the earlier studies on the STS-EACTS database (year 2007–2008) which determined the c-index of STS-EACTS MC as 0.778, RACHS-1 as 0.745, and
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Table 1. Patient and procedure characteristics. Variable
No. of patients
*
40.199 43.155
Age (months) Age distribution 1 year Body surface area (m2) Operation on CPB CPB time (min) [range] Operation without CPB Non-CPB operative time (min) [range] ICU stay (days) [range] Hospital stay (days) [range] Mortality Cause of mortality Low cardiac output Sepsis Pulmonary hypertensive crises Sudden cardiac arrest ABC score ABC level RACHS-1 category STS-EACTS MS STS-EACTS MC STS-EACTS DR
16 (1.21%) 44 (3.35%) 400 (30.48%) 852 (64.93%) 0.485 0.236 1084 81.14 39.61 [10–295] 228 79.78 23.33 [44–180] 3.58 4.08 [1–53] 7.04 4.24 [2–57] 90 (6.85%) 44 (48.8%) 23 (25.5%) 15 (16.6%) 8 (8.8%) 7.17 2.04 2.49 0.85 2.28 0.78 0.67 0.52 2.24 1.06 62.39 37.74
ABC: Aristotle Basic Complexity score; CPB: cardiopulmonary bypass; ICU: intensive care unit; RACHS-1: Risk Adjustment for Congenital Heart Surgery system; STS-EACTS DR: Society of Thoracic Surgeons, European Association for Cardiothoracic Surgery Congenital Heart Surgery difficulty ranking; STS-EACTS MC: Society of Thoracic Surgeons, European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories; STS-EACTS MS: Society of Thoracic Surgeons, European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality score.
ABC as 0.687.3 However, another study of a small population sample from Thailand has reported STSEACTS MC to have a lower c-index of 0.66, this difference was account for by only a small number of patients in category 4.11 The STS-EACTS, in addition to being objective, further differs from the ABC as a differentiator of mortality from that of difficulty levels. The ABC score takes into account a potential difficulty along with morbidity and mortality. While STS-EACTS is purely based on procedure-specific mortality rates and allots a technically less difficult case such as pulmonary artery banding to the higher category of 4, despite having a lower difficulty rank of 21. In the present study, the STS-EACTS
difficulty ranks were shown to significantly correlate with the difficulty outcome index. The difference in the c-index of RACHS-1 and ABC in the present study was also close to the earlier reported studies of Al-Radi and colleagues12 and O’Brein and colleagues.7 Kang and colleagues13 also reported the RACHS-1 categories to have a larger logistic regression Wald statistic of 17.7 vs. 4.8 of the ABC score. Apart from mortality, the complete assessment of quality of care involves morbidity as an important outcome in analysis. With mortality decreasing as a result of the improvements in congenital cardiac surgery, anesthesia, perfusion techniques, and postoperative intensive care, morbidity is emphasized as the quality of outcome for survivors. Our study demonstrated a significant correlation of morbidity index with that of ABC (r ¼ 0.9529) and RACHS-1 (r ¼ 0.9866) compared to the nonsignificant correlation of morbidity index with STS-EACTS (r ¼ 0.8411). However, we used the morbidity surrogate of ICU stay for this analysis. Morbidity should ideally be based on observed postoperative complications weighed according to their severity. Clarke and colleagues14 proposed that morbidity score be constituted with the following 4 components: postoperative hospital length of stay, postoperative time on the ventilator, postoperative extracorporeal membrane oxygenation and/or ventricular-assist device time, and major complications (reoperation, permanent pacemaker for atrioventricular block, nerve palsy, neurological disorders, and dialysis). Sata and colleagues15 have also recently proposed an objective morbidity score based on the observed postoperative complications, and compared it to the ABC morbidity score. A large series analysis of the proposed objective morbidity score is yet to be performed. Another dimension of the outcome analysis scores is the evaluation of performance which can allow interinstitute comparisons and gauge improvement over the years. RACHS-1 was used to demonstrate an improvement in congenital heart surgery (from 1997 to 2004) in Guatemala, and it has been used for comparing interinstitute outcomes.16,17 The Aristotle Committee1 has defined operative performance using the equation: operative performance ¼ complexity score hospital survival. Arenz and colleagues18 have used the ABC and ACC scores to analyze the evolution of performance in congenital heart surgery over the years 2006 to 2009. STS-EACTS mortality categories have also been proposed as a tool to compare mortality outcome across institutions with different case mixes.3 The present study represents the outcome performance in a subset of Indian patients using consensus-based and empirically derived outcome tools of the STS and EACTS databases. The study has the potential for
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Figure 2. Relationship between the three scoring systems and the (a) mortality, (b) morbidity and the (c) operative difficulty indices. ABC: Aristotle Basic Complexity Score; RACHS-1 ¼ Risk Adjustment for Congenital Heart Surgery system, STS-EACTS MC: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories; STS-EACTS DR: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery difficulty ranking.
Figure 3. Receiver operating characteristic (ROC) curve as a predictor of mortality for (a) Aristotle Basic Complexity Score (ABC), (b) Risk Adjustment for Congenital Heart Surgery system (RACHS-1), and (c) Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories (STS-EACTS MC).
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Asian Cardiovascular & Thoracic Annals 21(6) Table 2. c-index for the 3 systems and p values for differences between them. System
c-index
Comparison
p value
STS-EACTS MC ABC RACHS-1
0.7556 0.6676 0.7654
STS-EACTS MC vs. ABC STS-EACTS MC vs. RACHS-1 RACHS-1 vs. ABC
0.04 0.81 0.02
p40.05 is significant. ABC: Aristotle Basic Complexity score; RACHS-1: Risk Adjustment for Congenital Heart Surgery system; STS-EACTS MC: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories.
Table 3. Coefficient of correlation of various scores to the mortality, morbidity, and difficulty indices. Scores ABC
RACHS-1
STS-EACTS MC* &STS-EACTS DRy
r (r2) p r (r2) p r (r2) p
Mortality index
Morbidity index (ICU stay >7 days)
Difficulty index (CPB >120 min)
0.9844 (0.969) 0.015* 0.9672 (0.9355) 0.032 0.9781 (0.9567) 0.021
0.9529 (0.908) 0.04 0.9866 (0.9734) 0.013 0.8411 (0.7074) 0.15
0.9661 (0.9333) 0.033 0.957 (0.917) 0.042 0.957 (0.9166) 0.042
r ¼ Pearson correlation coefficient, r2 ¼ coefficient of determination, p40.05 is significant. *STS-EACTS MC used for mortality and morbidity index correlation. ySTS-EACTS DR used for difficulty index correlation. ABC: Aristotle Basic Complexity score; CPB: cardiopulmonary bypass; ICU: intensive care unit; RACHS-1: Risk Adjustment for Congenital Heart Surgery system; STSEACTS DR: Society of Thoracic Surgeons and European Association for Cardiothoracic Surgery Congenital Heart Surgery difficulty ranking; STS-EACTS MC: Society of Thoracic Surgeons, European Association for Cardiothoracic Surgery Congenital Heart Surgery mortality categories.
Table 4. Odds ratio comparison between different categories of RACHS-1 for mortality, morbidity, and difficulty indices. Mortality index
Morbidity index (ICU stay >7 days)
Difficulty index (CPB>120 min)
RACHS-1
Odds ratio
p value
Odds ratio
p value
Odds ratio
p value
1 1 1 2 3 2
0.0996 0.0183 0.0079 0.0783 0.4341 0.18
0.1082 0.005 0.0008
