Ann Thorac Surg 2006;81:1794-1800
© 2006 The Society of Thoracic Surgeons
Original article: Cardiovascular
Comprehensive Aristotle Score: Implications for the Norwood Procedure
Nicodème Sinzobahamvya, MD
*
,
Joachim Photiadis, MD,
Daiva Kumpikaite, MD,
Christoph Fink, MD,
Hedwig C. Blaschczok, MD,
Anne Marie Brecher, MD,
Boulos Asfour, MD, PhD
Department of Pediatric Thoracic and Cardiovascular Surgery, German Pediatric Heart Center, Sankt Augustin, Germany
Accepted for publication December 2, 2005.
* Address correspondence to Dr Sinzobahamvya, Deutsches Kinderherzzentrum Sankt Augustin, Arnold Janssen-Strasse 29, 53757 Sankt Augustin, Germany (Email: sinzo.md{at}dkhz.de).
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Abstract
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BACKGROUND: Aristotle score is emerging as a reliable tool to measure surgical performance. We estimated the comprehensive Aristotle score for the Norwood procedure, correlated it with survival, and considered its impact on surgical management of hypoplastic left heart syndrome.
METHODS: Comprehensive Aristotle score was retrospectively calculated for 39 consecutive Norwood procedures performed from 2001 to 2004. Survival was estimated by the Kaplan-Meier method.
RESULTS: The Aristotle scores ranged from 14.5 to 23.5 (mean, 19.12 ± 2.52; median, 19.5). The score was 20 or greater in 44% (17 of 39) of cases. The most frequent patient-adjusted factors were aortic atresia (n = 16), interrupted aortic arch (n = 9), mechanical ventilation to treat cardiorespiratory failure (n = 19) and shock resolved at time of surgery (n = 13). Hospital mortality was 58.8% (10 of 17) in case of score of 20 or more and 9.1% (2 of 22) for score less than 20 (p = 0.0014). From 2003 on, all patients with a score less than 20 survived. Actuarial estimate of survival at 1 year is 56.2% ± 7.9% and there have been no late deaths after 1 year. One-year survival is much lower (p = 0.001) for patients with scores of 20 or greater (29.4% ± 11.05%) compared with those whose scores were less than 20 (77.3% ± 8.9%).
CONCLUSIONS: This study shows significant correlation of comprehensive Aristotle score with hospital mortality and late survival after Norwood palliation. It suggests that operative survival on the order of 90% may be achieved in patients with comprehensive complexity scores of less than 20. Efforts should be devoted to improve survival of high-risk patients (score 
20).
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Introduction
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The newly introduced complexity Aristotle score [1, 2] is the sum of potentials for early mortality, morbidity (intensive care unit length of stay), and anticipated surgical technique difficulty (each, 0.5 to 5 points). Although still under validation, it is emerging as a useful tool to measure surgical performance, and as such, can be applied to quality improvement efforts. The comprehensive Aristotle score adds to the basic score (procedure complexity: 1.5 to 15 points) patient-adjusted complexity score (0 to 10 points). This comprises procedure-dependent factors (0 to 5 points) and procedure-independent factors (general, clinical, extracardiac, surgical; 0 to 5 points). With a basic score of 14.5, the Norwood procedure is actually recognized as the most complex surgical intervention with the highest risk in congenital heart disease, except for hypoplastic left heart syndrome (HLHS) biventricular repair (15 points).
Preliminary results show that hospital mortality significantly correlates with the highest Aristotle score with a very low survival when the score reaches 20 to 25 [3, 4]. This level is often attained for Norwood procedures.
This work estimates the comprehensive Aristotle score for the Norwood procedures performed in the last 4 years, correlates it with survival, and discusses its possible impact on surgical practice.
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Patients and Methods
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Patients
All 39 patients who underwent Norwood procedure from January 2001 to December 2004 were included. No patient was denied surgery in the period because of preoperative poor condition. Our unit does not offer heart transplantation as treatment option for hypoplastic left heart syndrome (HLHS). Males predominated (n = 31; 79.5%) . The age at operation ranged from 4 days to 275 days (median, 9); and the weight was 3.3 kg ± 0.49 kg (range, 1.6 to 4.3 kg). Indication was classic HLHS for 26 neonates and functional single ventricle with systemic outflow tract obstruction in the other 13 patients. Two newborns with hypoplastic left heart complex [5] were switched, during the same operating time, to univentricular palliation after failure of biventricular repair attempt.
Management
A multidisciplinary protocol was followed as described in a recent report [6]. Surgery included aortic arch augmentation using pulmonary homograft material, atrial septectomy, and placement of a polytetrafluoroethylene shunt either from the innominate artery (n = 33, diameter 3.5 to 5 mm) or from the right ventricle (n = 6, diameter 5 or 6 mm) to the pulmonary artery. The aortic arch was reconstructed with continuous antegrade cerebral perfusion in 35 patients and the entire procedure was performed on a beating heart in 13 patients as previously described [7]. Modified ultrafiltration was always applied. From October 2002 on, oximetric catheters (4F [Edwards Life Sciences, Irvine, California]) were placed through the right atrium into the superior vena cava to allow continuous monitoring of systemic venous oxygen saturation (SvO2) and to estimate Qp/Qs. An additional line was placed in the common atrium for pressures monitoring and infusion of inotropic drugs. These included usually dopamin 3 to 6 µg · kg-1
· min-1 and milrinone 0.5 to 0.9 µg · kg-1
· min-1. Norepinephrine or epinephrine was added if supplementary inotropic support became necessary. Infusion of milrinone or phentolamine (2 to 8 µg · kg-1
· min-1), or both, was adapted in case of low SvO2, acidosis, increasing lactate levels or low urinary output, to reduce systemic afterload. In all but 1 patient, the sternum was left open for 3 days (median duration), to achieve hemodynamic stabilization. Extracorporeal membrane oxygenation (ECMO), used selectively after 2003, was instituted in 2 neonates. Survivors were treated with aspirin 2 mg/kg daily and usually with digoxin, carvedilol, or captopril until second-stage palliation, 3 to 6 months after Norwood I, bidirectional cavopulmonary (Glenn) anastomosis. The Fontan circulation by means of extracardiac total cavopulmonary connection (TCPC) was completed 1 to 2 years later.
Data Collection and Statistical Analysis
Preoperative and perioperative data to estimate comprehensive Aristotle score were collected retrospectively. The "Aristotle score final nov 30 2004" version (Aristotle Institute, Denver, Colorado; available at: http://www.aristotleinstitute.org/) was used. Inquiry for follow-up and late survival took place in September 2005. Kaplan-Meier curves for actuarial survival were calculated using the GraphPad Prism (San Diego, California). The log-rank test assessed the statistical differences between two groups. Fisher's exact test was used to analyze univariate risk factors for hospital mortality after Norwood procedure. This analysis was limited to factors per variables affecting at least 4 patients. Differences were considered statistically different at a p value of 0.05 or less.
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Results
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Comprehensive Aristotle Score
Patient-adjusted dependent factors for the 39 Norwood procedures are shown in Table 1. Aortic atresia (n = 16) and interrupted aortic arch (n = 9) predominated. Independent general, clinical, and extracardiac factors are displayed in Table 2. Preoperative clinical condition was often characterized by mechanical ventilation to treat cardiorespiratory failure (n = 19) and shock (n = 13). Myocardial (n = 4) and renal dysfunction (n = 4) were seen in 10% of cases. Details about the definition of these factors are found in Appendixes B3 and B4 of Lacour-Gayet and colleagues [1]. The comprehensive Aristotle scores ranged from 14.5 to 23.5 (mean, 19.12 ± 2.52; median, 19.5). The score was 20 or greater in 44% of cases (17 of 39).
Comprehensive Aristotle Score and Discharge or 30-Day Mortality
Twelve patients died early after Norwood palliation, for an overall mortality of 30.8% (95% confidence interval: 17.0% to 47.6%). Most deaths occurred either perioperatively (n = 2, failure of biventricular repair attempt) or in the first 48 postoperative hours (n = 6, hypoxemia and low cardiac output). Extracorporeal membrane oxygenation had to be discontinued in 2 neonates because of cerebral hemorrhage. The remaining 2 deaths were a consequence of multiorgan failure.
Mortality was 58.8% (10 of 17) in case of Aristotle score at least 20, and 9.1% (2 of 22) when the score was less than 20 (p = 0.0014). Figure 1
displays the successive comprehensive Aristotle scores over time and corresponding early deaths. It is noteworthy that from 2003 on, there was no early mortality for patients with a score below 20. Univariate analysis of dependent and independent factors, as well as other surgical technique factors showed the sole "obstructed pulmonary venous return" (restrictive left atrial outflow) to be significantly (p = 0.024) associated with early death. In particular, there was no statistical difference between the 2001 to 2002 and the 2003 to 2004 periods (p = 0.29). However there was tendency for higher mortality in case of "shock–resolved at time of surgery" (p = 0.16), absence of SvO2 monitoring (p = 0.15) and for nonbeating-heart surgery (p = 0.27). When Norwood was performed on beating heart and SvO2 monitoring was applied (n = 8) there was no mortality (p = 0.04). Association of mechanical ventilation and previous shock reached almost statistical significance (p = 0.06) as incremental risk for early mortality.
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Fig 1. Comprehensive Aristotle scores in 39 consecutive patients over years 2001 (n = 10), 2002 (n = 7), 2003 (n = 15), and 2004 (n = 7). Each dot represents a Norwood procedure. Crossed dots represent Norwood procedures that were followed by hospital (early) deaths. The horizontal line delineates two groups of patients: low-risk patients (n = 22) with scores less than 20 and high-risk patients (n = 17) with scores of 20 or more.
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Details of factors, management variables, and outcome for the 17 patients with Aristotle scores of 20 or greater and those for the 22 patients with scores less than 20 are given, respectively, in Table 3
and Table 4. Mean duration of postoperative ventilation and intubation for early survivors (n = 27) was 188 ± 105 hours (range, 48 to 478); there was no difference (p = 0.99) whether Aristotle score was below 20 (n = 20) or at least 20 (n = 7).
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Table 3. Factors, Management for Patients With Comprehensive Aristotle Score of 20 or Greater (n = 17) and Outcome After Norwood Procedure
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Table 4. Factors, Management for Patients With Comprehensive Aristotle Score Less Than 20 (n = 22) and Outcome After Norwood Procedure
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Survival
Actuarial survival for all 39 patients is 56.2% ± 7.9% from 1 year on (Fig 2), with highest mortality during the first 6 months. One-year survival is much lower (p = 0.001) for patients with Aristotle score of 20 or more (29.4% ± 11.05%) than for those with a score less than 20 (77.3% ± 8.9%; Fig 3).
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Fig 2. Kaplan-Meier estimate of survival after Norwood procedure for all 39 patients. Vertical bars represent standard error of the mean (SEM). Actuarial estimate of survival at 1 year is 56.2% ± 7.9%, and there have been no late deaths after 1 year.
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Fig 3. Kaplan-Meier estimate of survival after Norwood procedure for patients with comprehensive Aristotle score less than 20 (n = 22) and for patients with score of 20 or more (n = 17). The numbers indicate patients at risk at the time of estimate. Vertical bars represent standard error of the mean (SEM). The difference in survival between the two groups is highly significant: p = 0.001 (log-rank test).
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Overall outcome is displayed in Figure 4. Seven patients achieved TCPC palliation. Two interstage deaths were due to shunt thrombosis; autopsy in the third interstage death revealed neither shunt thrombosis nor obstruction.
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Comment
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The Aristotle score is an expert consensus-based risk stratification model that is still under validation. It includes risk factors for the Norwood procedure (dependent and independent factors) that have been validated in the literature by multi-institutional studies [8]. Determination of detrimental factors for early survival in this series is hampered by small numbers of patients so that some differences do not become statistically significant. Adoption of Aristotle scoring enabled global analysis of individual risk factors displayed in Tables 3 and 4.
Retrospective evaluation of dependent factors for the Norwood procedure is straightforward. But estimation of independent factors may be incomplete. We restricted this study to the last 4 years to limit the probability of missing patient-adjusted factors. Nevertheless, figures of comprehensive Aristotle score given here might be low. Patients of the year 2005 were excluded to allow an accurate estimation of 1-year survival. The score of 20 was chosen as a cut-off because 19.5 was the calculated median for comprehensive Aristotle scores in this series, and also because preliminary results of Aristotle scoring show that survival is low when the score reaches the level of 20 to 25 [3, 4]. The relative high number (44%) of cases with a score of 20 or more reflects our policy to not deny surgery because of preoperative poor condition.
This study confirms the utility of the comprehensive Aristotle score as instrument to measure case complexity within a single surgical procedural group. Indeed, when Aristotle score reached or exceeded 20, the chance to survive the Norwood procedure was only 40%. In a recent published multi-institutional series [4], hospital mortality after Norwood procedure has been reported to be 31.4% (95 of 303; 95% confidence interval: 26.1% to 36.9%), which corresponds well with our own 30.8% (12 of 39; 95% confidence interval: 17.0% to 47.6%). Application of Aristotle score allows a fair performance comparison according to case mix complexity. In this series, by selecting cases with a score under 20, our early survival rate would be slightly above 90%. Tweddell and colleagues [9] reported a 93% survival for the group of 81 patients operated upon from July 1996 through August 2001. Aristotle scoring would permit outcome comparison and addresses the issue of patient selection. Checchia and colleagues [10] use a scoring system that embraces some factors (ventricular function, tricuspid regurgitation, ascending arch size, atrial septal defect characteristics, and age at surgery) that are somewhat comparable to some dependent and independent factors of Aristotle score. They report 80% survival rates at 30 days among patients considered lower risk. It is to be noted that, in our experience, as of year 2003 no patient with a score under 20 died early after first-stage palliation. The results of this study first imply that the comprehensive Aristotle score should be estimated before operation. The operative risk can thus be classified as low (score < 20) or high (score 20), and afterward parents can be accordingly counseled. Secondly, our experience suggests that, in actual surgical practice, a Norwood procedure with a comprehensive Aristotle score below 20 should be encumbered with an early mortality of less than 10%.
Last of all, efforts should be devoted to improve survival of high-risk patients with a score of 20 or more. Little can be done to reduce the impact of dependent factors, except the age at operation, which should be kept under 1 month—ideally under 14 days according to Checchia and associates [10]. There may be the possibility of positively influencing general and clinical independent factors before intervention. Ideally, HLHS neonates should be referred to specialized centers before clinical deterioration. That is confirmed by the finding that preoperative mechanical ventilation and shock reached almost statistical significance (p = 0.06) as incremental risk for early mortality in this relative small series. Early referral would include, in our setting, prenatal diagnosis and referral on the day of birth or the day after. That would increase the chance to present to surgery in better condition and thus to survive surgery, as shown by Tworetzky and associates [11], even if Mahle and associates [12] have reported that despite improvement of preoperative condition and reduction of neurologic injury, prenatal diagnosis was not associated with reduced hospital mortality. A multidisciplinary protocol plays a vital role in stabilizing the patient before intervention. Recent modifications of surgical technique bear additional potential for outcome improvement. They should be considered for application for these high-risk patients, namely, aortic arch reconstruction under continuous antegrade cerebral perfusion and on beating heart as recently reported by us [7], use of larger shunts [13], and postoperative continuous monitoring of SvO2; and not to forget, the threshold to start ECMO support should be lowered [14].
Notwithstanding cardiac transplantation, it is not yet clear which place the alternative method of surgical or interventional bilateral pulmonary banding and ductus arteriosus stenting might take for high-risk patients. Indications, results, and issues about off-pump HLHS palliation are well discussed by Pizarro and Murdison [15], who actually apply this strategy to neonates with poor preoperative condition (severe organ dysfunction, shock, contraindications to anticoagulation, very low weight, and so forth).
As for other complex congenital heart lesions, survival after surgery tends to stabilize after 1 year. Late survival rate is heavily influenced by early mortality. The 1-year survival rate of 56.2% ± 7.9% in this series is similar to the 60% in the multi-institutional study reported by Ashburn and associates [8]. Grouping according to Aristotle score gives a more accurate prognosis, confirming the poor outcome in case of a score of 20 or more, with less than 30% 1-year survival, but an encouraging almost 80% for a score less than 20.
In conclusion, this study shows a correlation of the comprehensive Aristotle score with early death and late survival after the Norwood procedure, helping to analyze mortality in a nonselected patient cohort. Routine preoperative estimation of Aristotle score will emphasize the importance of additional management endeavors to improve the outcome of HLHS neonates.
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Acknowledgments
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In honor of Andreas E. Urban, MD, FETCS, head of Department and director of the Heart Center, for his 65th anniversary.
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References
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Abstract
Introduction
