Practical experience with databases for congenital heart disease: A registry versus an academic database

Practical Experience With Databases for Congenital Heart Disease: A Registry Versus an Academic Database William G. Williams and Brian W. McCrindle Increasingly, pooled data from multiple institutions are the source of published clinical results. A computerized database program is essential to compile and analyze clinical experience. The scope of data collection defines a database. Two types of databases, the registry and academic, are compared. In a registry database, some of the data are collected on all patients. The resources dedicated to data collection and entry are the practical limit to the extent of information in the database. The agreement on nomenclature for surgical diagnosis and procedure codes of congenital heart disease has paved the way for the development of a multi-institutional registry database. The registry database could provide a standard of care reference for early results after congenital heart surgery. The practical difficulty of data collection is obviated by limiting information to a basic minimum dataset. The academic database, in which all of the data are collected for a defined subset of patients, is designed to investigate a specific population of patients to generate new knowledge. It contains sufficient data to allow sophisticated statistical analysis to clarify the determinants of good and poor outcome, including early, mid- and long-term follow-up information. Multi-institutional pooling of detailed information derived from academic databases will be of increasing importance in generating new knowledge to foster improved therapy for patients with congenital heart disease. Copyright © 2002 by W.B. Saunders Company Key words: Database, congenital cardiac surgery, registry.

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ne of our responsibilities as physicians caring for patients with congenital heart disease is to know the results of the treatment that we recommend. Our patients and their families have a right to know the risks they will encounter, and what their long-term prognosis might be, with or without surgery. Knowing the results of our treatment may seem self-evident, but attaining this knowledge is a complex and time-consuming process. Traditionally, one learns of outcome results from textbooks and from journal publications or clinical experience. Published clinical results are usually from a single institution, but they are increasingly generated by pooling data from multiple institutions. How these available data relate to

From the Division of Cardiovascular Surgery, The Hospital for Sick Children, and the University of Toronto Faculty of Medicine, Toronto, Ontario, Canada. Address reprint requests to William G. Williams, MD, Cardiac Surgery, The Hospital for Sick Children, 555 University Ave, Toronto, Ontario, Canada M5G 1X8. Copyright © 2002 by W.B. Saunders Company 1092-9126/02/0501-0008$35.00/0 doi: 10.1053/pcsu.2002.31485

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our own experience obligates us to know the outcomes for the patients we have treated. Because outcomes of treatment usually change with time, although not invariably improving, our information must be easily and rapidly available. Comparisons of different sources of outcome results for any specific group of patients, including our own experience, is often complicated by variables that may change the prognosis: so-called “risk factors.” Given the complexity of human disease, a simple arithmetic comparison of outcomes may be invalid. Meaningful comparisons require inclusion of the known, and sometimes unknown, risk factors that affect outcome. Thus, the amount of data required for valid comparative analysis increases, and the only practical solution for maintaining the data collection and processing is a computerized database.

Database “A database is a structured collection of information. It need not necessarily be implemented on a computer system, but doing so offers many advantages.”1 A computerized database program is essential to compile and analyze clinical experience. There

Pediatric Cardiac Surgery Annual of the Seminars in Thoracic and Cardiovascular Surgery, Vol 5, 2002: pp 132-142

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Table 1. Scenarios for Possible Data Collection Database Content 1. 2. 3. 4.

Some of the data Some of the data All of the data for All of the data for

Descriptive Term

for all of the patients for some of the patients all of the patients a defined subset of patients

is tremendous interest in creating a congenital cardiac database on an international scale.2-6 The internet provides a platform to make this idea a reality. Recent agreement on surgical nomenclature codes (although not with pediatric cardiology) is one more major step in making an international database a possibility.7,8 The remaining challenge is to make data collection, input, and validation practical, and to develop a strategy to maintain confidentiality in an environment of information sharing.

Data Collection The scope of data collection will define the database. Four possible scenarios for data collection are listed in Table 1. Scenario 1 (some data for all patients) in its simplest form would be a record of how many patients were treated during a specified period of time, such as 1 month. The database would generate the number of patients treated each month. Therefore, it is a registry of activity: a registry database. A secretary could track the number of patients per month, and a computer would not be necessary. However, one would soon expect more of the registry, such as the names of the patients, their age, diagnosis, treatment, and at least their early outcome after treatment. The resources (people) dedicated to data collection and entry are the practical limit to the extent of information in the database. In practice, 20 to 30 fields of information would require a dedicated part-time data manager for data entry, validation, and routine reporting. In this scenario, the surgeon is responsible for data collection, but the data manager who cross-references the monthly patient lists with the operating room staff and a clinical coordinator confirms the surgeon’s compliance. Scenario 2 is to be avoided. Collecting some data on only some patients does not provide any useful information and is likely to generate misleading information. Both the numerator (data

Registry database Integrated database Academic database

points) and the denominator (number of patients) are incomplete, and therefore cannot be representative of the total population. Scenario 3 (all of the data for all of the patients) is the ideal objective for a database. Finite resources dictate a practical limit to data collection and preclude collection of all data for all patients at the present time. In the future, however, it should be possible to integrate computerized databases from every area that patients encounter, including the clinic, laboratories, catheterization laboratory, echocardiography suite, operating room, and critical care unit. We should be working toward this ideal of an integrated database, and establishing standardized protocols for collecting information. Scenario 4 (all of the data for a defined subset of patients) is a practical solution for a database designed to investigate a specific population of patients to generate new knowledge. It will contain sufficient data to allow sophisticated statistical analysis to clarify the determinants of good and poor outcome, including early, mid- and longterm follow-up information. This type of database we refer to as an academic database.

Comparison of a Registry and an Academic Database To illustrate the differences in these two database types, we compare the Hospital for Sick Children (Toronto, Ontario Canada) Division of Cardiac Surgery Database (CVSDB) as an example of a registry database ([email protected]) with the Congenital Heart Surgeon’s Society (CHSS) database, an academic database (Table 2). The CVSDB began in 1982 and has registered every cardiac operation in the division. Each operative record consists of 29 fields of information. To date there are 15,885 operative records for 11,647 patients. The total file size is 9.5 megabytes. One data manager maintains the CVSDB.

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Table 2. Comparison of a Registry and Academic Database

Inception date Entry criteria No. of patients No. of variables File size Personnel

CVSDB-Registry

CHSS-Academic

1982 All surgical patients 11,647 29 9.5 MB 1

1983 Specific diagnostic groups 4,000 400 to 700 100 MB 3.5

Abbreviations: CHSS, Congenital Heart Surgeon’s Society database; CVSDB, Hospital for Sick Children Division of Cardiac Surgery database.

The CHSS database began in 1985 and includes only eight specific diagnostic groups of neonates who were admitted to one of the participating CHSS institutions. Each patient record contains between 400 and 700 fields of information (the number of fields varies with the diagnostic group). To date, 4,000 patients have been entered. The total file size is 100 megabytes. The CHSS data center employs 3.5 full-time people. In essence, the academic database contains 10 times more information on one third as many patients and requires 3.5 times as many staff compared with the registry database. It is important to keep these differences in mind when planning a database.

Registry Database The international nomenclature agreements7-8 will allow the creation of a multicenter registry database for congenital heart surgery and establish a range of early outcomes. Inferences about surgical centers that fall outside the range, or indeed even those within the normal range, may not be statistically valid because of the variation of risk factors among centers. For example, variation in the complexity of case mix or patient risk factors may account for the apparent paradox of a center that is performing below the normal range, actually providing better care than one within the normal range. This paradox has been considered in the extensive experience of the reports from the Congenital Cardiac Care Consortium of University Hospitals9-11, and is apparent in the New York State results of congenital heart surgery.12

Data Fields for a Registry Database The international nomenclature committee’s concept of a basic mandatory dataset is an excel-

lent beginning. Their agreement on nomenclature for diagnoses and procedures resolves the uncertainty of trying to apply different names to the same entity. However, we also must agree on basic definitions and data concepts to construct a registry.

Registry Definitions and Concepts The purpose of a registry database is to record the essential information needed to maintain a quality assurance program. One must first agree on entry criteria. Then the dataset must include basic demographics of the patients, patient and institutional variables, diagnostic and operative codes, and outcome.

Diagnosis/Procedure The list of diagnoses and procedures in the nomenclature report are very comprehensive for a surgical registry.7 The hierarchical concept is valid for an academic database, but impractical for most surgical units, and unnecessary for registry purposes. There have been some changes in the lists of diagnoses and procedures, and there will be future changes, but this is a strength of the nomenclature system, as it must evolve to accept refinements. Individual patients often have more than one diagnosis or procedure. Data entry must differentiate the importance of these multiple entries. A simple list, perhaps alphabetically ordered, would be very difficult to discriminate during data analysis. When there are more than one diagnosis or procedure, the database must indicate a primary and a secondary list of entries in order of clinical importance. Primary and secondary entries are entered in separate fields. The database also must match the primary diagnosis and the primary operation. For example, a neonate with

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transposition and coarctation would have a primary diagnosis of coarctation, secondary of transposition if the operation is coarctation repair. If the operation were a one-stage total repair, the primary diagnosis would be transposition, secondary coarctation, and the primary operation transposition repair, secondary, coarctation repair. A sample data entry from our registry database for one patient is illustrated in Fig 1. These rules of data entry have evolved from pragmatic experience with data analysis.

Risk Factors There is no question that a number of patient, institutional, and time-related variables have important effects on patient outcome, including operative mortality.

Figure 1. This print out of an operation record illustrates the data entry information and format for the registry database. Note that both diagnosis and operation have primary and secondary entries and that primary diagnosis and primary operation are concordant. Outcome of the operation is indicated in the Result field. Long-term follow-up of the patient is maintained in a related and separate master file.

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In an academic database it is important to include all possible variables to discern their positive or negative effects. Often this data cannot be retrieved from reports of tests, but only by an individual review of the raw data, such as viewing an echocardiogram or angiogram. For a registry database, practicality limits the data collection and entry. The temptation of including too much information must be avoided, because with incomplete data, inferences may be incorrect. One may be reporting compliance of the data collection process rather than information about the patients. For example, the presence or absence of noncardiac anomalies may influence outcome. However, a noncardiac syndrome may be present or absent, but more often

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is not recorded either because it was not looked for, not recognized, or not remembered. With all of these possibilities, it would be unhelpful to record that some patients had a syndrome without being certain of the status of all of the other patients.

Operations Versus Patients What defines an operation? Most are obvious, and the nomenclature list is comprehensive. However, one must differentiate between interventions that are “procedures,” such as chest tube placement and “operations,” such as delayed sternal closure. Nor does the site of intervention define an operation, as operations may be performed in the critical care unit or catheterization laboratory. These decisions need to be agreed upon, especially when more than one institution is involved in a registry. An individual patient with congenital heart disease may have more than one operation. For example, a neonate with pulmonary atresia and ventricular septal defect may have a palliative shunt before a planned repair; ie, two planned operations for one patient, probably occurring during two separate hospital admissions. If the same child had a one-stage repair but required delayed sternal closure, the child would have two operations on the same admission, one planned, the other (probably) unplanned. How do these scenarios affect analysis? We find it useful to separate patient mortality from operative mortality. Death after repair in either of the above examples would be a “patient mortality” of 100%. In the first scenario, two admissions for two operations, the first admission would be 100% survival, the second admission a 100% mortality. Patient and operative mortality for each admission are the same. In a registry database, the fact that the two operations occurred in the same individual would not be considered. In an academic database, they would be linked. In the second scenario, with both operations during one admission, there is a 50% operative mortality and a 100% patient mortality, ie, patient and operative mortality are not the same. Patient mortality ⫽ Number of deathsⲐNumber of patients Operative mortality ⫽ Number of deathsⲐNumber of operations

But which operation is to be “charged” with the death when more than one operation occurs during the same admission? We indicate that the outcome of the first operation was that another operation during the same admission was required and that the patient died during that admission. At data analysis, this type of entry discriminates both the death and the “reoperation during the same admission.” The other alternative is to assign the death to one of the operations, but how this is done (whether by the surgeon or the data manager) may cause discrepancies. Assigning death to a specific operation may lead to discrepancies in reporting mortality rates. In the example of an infant with transposition plus coarctation, how would the child’s death be reported in a review of transposition surgery, and how would the death be reported for a series of coarctation repairs? Would the death be included in both? We believe it should, with the caveat that the child had an additional lesion complicating either repair.

Outcome The outcome for each patient and of each operation in the registry must be indicated. A basic minimum entry is whether the child survived. Pragmatically, a registry survival definition is limited to the date of hospital discharge. The time of hospital discharge seldom meets the required 30-day postoperative mortality definition. Therefore, registry mortality will inherently be somewhat underestimated and appear to be better than that reported in published reports. While the addition of data fields to indicate postoperative complications is desirable, reliable collection of the information may not be practical. Indirectly, the length of stay and prevalence of reoperation during the same hospital admission will reflect morbidity. As a practical point, it is useful to include in the outcome field “patient still in hospital.” This entry permits regular search for patients whose outcome has not been entered.

Interval Reports With a registry, reports can be generated for activity and results during any specified period of time. Because data entry in a registry is a continuous process, there are inherent errors in isolating a specific time period. For example, a re-

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port of surgical activity and results for the month of January will include patients who were operated on the previous month if they required reoperation during January. In addition, the outcome of a child whose operation was in January may be dependent on a reoperation in February. Consequently, there may be variations in reported results for January depending on whether these patients are included or excluded as either numerators or denominators. Therefore, we report the number of new patients during the interval, and the number of patients who had a previous operation and required reoperation during the interval (Fig 2).

The Impact of Databases The reports of two recent, separate, and very expensive judicial inquiries into a “cluster” of deaths after pediatric cardiac surgery emphasize the importance of registry databases.13,14 The Winnipeg report13 recommends that the institution “. . .develop an appropriate database for all surgical procedures, but particularly for pediatric cardiac surgical operations.”13 Further recommendations include “. . .that Pediatric cardiac surgical data be collected in a way that makes it possible to compare Winnipeg procedures with those performed in other centres for the proper monitoring of surgical trends within a given program or for a particular surgeon.” The Bristol inquiry14 recommendations include “. . .the creation of the National Patient Safety Agency [and] that there be a national system for reporting adverse healthcare events and certain specified near misses.”14 They recommend that the national system be “. . .rooted in sound, standardized local reporting system” and that the “. . .national and local systems are interdependent and mutually supportive.” These inquiries, and the widely recognized interest of patients, the public, government, and third-party payers, demand that information about the results of congenital heart surgery be readily available. Computerized database technology and the internet are tools that can provide this information. There is little question that access to the information will be developed, with or without our input. Surgeons who are willing to facilitate the data collection, collation, and analysis must assure that these processes are done

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well and are accurate. Those of us in the specialty of congenital heart disease are obligated to provide our expertise so that meaningful, honest reporting is assured.

Registry Database Reports A registry should be able to generate a report for any given time period from one’s office computer. A sample report from our division’s database is shown in Fig 2. These reports can be specified for the individual surgeon or for the division. This type of information could easily be shared among a group of participating institutions. In addition, customized reports to show trends in outcome, such as the cumulative sums graph (Fig 3), can be generated for any time period and for each of the138 procedures in the primary operation field. The registry also can generate spreadsheets of data for any permutation and combination of fields using a query program. These searches are invaluable in initiating a clinical review of a specific topic, using the basic database fields as a starting point for collecting other information retrospectively.

Academic Database Reports The impact of an academic database is more difficult to measure. The publications of the Congenital Heart Surgeon’s Society15-30 have tried to add new knowledge about the management of specific subsets of neonates with congenital heart disease (Table 3). The criterion for patient entry is somewhat unique in that only the neonate’s admission to a CHSS institution, rather than an operation per se, qualifies for inclusion in the various studies. The entry criteria did not influence patient management and the analysis includes infants who may not have had surgery. Important risk factors, including institutional variables that affect early and intermediate outcomes, have been identified by multivariate analysis. A short summary of published CHSS results follows.

Transposition Data Data collection of the transposition group by the CHSS coincided with an important change in surgical management from an atrial to an arterial repair. Although mortality was high in that era (80% for 1-year survival), it was equivalent

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Figure 2. The sample printout illustrates the basic data report that can be generated for any specified period of time. The report includes subset results for specific age categories at surgery. It can be surgeon-specific or for the entire divisional experience. Another report (not shown) summarizes the same information for any consecutive 7-year interval. Either report can be generated from the registry database program within 1 minute. Alternately, the registry may be queried using Microsoft Access to produce spreadsheet output for single or multiple selection criteria. for either the atrial or arterial operation.15 Improvement in survival occurred with increasing experience with the arterial repair, but not the atrial repair. Further, for infants with associated

ventricular septal defect (VSD) or low birth weight, the arterial operation, unlike the atrial repair, provided survival comparable to that for neonates with isolated transposition.15

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Figure 3. The cumulative sum graph portrays the consecutive number of operations for any given time period along the horizontal axis, and the cumulative number of deaths along the vertical axis. The graph can be generated for any of the 138 primary operation codes. A change in the slope of the graph indicates a changing trend in operative survival.

Death before intended repair was more likely with an atrial switch protocol.16 Risk factors for repair with either type of operation were low birth weight, earlier date of repair, and institution.16 An analysis of the arterial switch operation showed that age greater than 2 weeks increased operative mortality for both simple and transposition⫹VSD patients, inferring that early repair in the first 2 weeks of life was preferable for simple and transposition⫹VSD.17

Coronary artery pattern influenced arterial operative mortality, as did multiple but not a single VSD.18 Risk factors for mortality were a long myocardial ischemic time (greater than 120 minutes), long circulatory arrest time, and institutional experience. As experience increased beyond 30 to 35 cases, high-risk institutions achieved the same results as the six low-risk institutions, although the rate of improvement was not consistent for all institutions.18

Table 3. Congenital Heart Surgeon’s Society Data Collection Series Diagnostic Group

Era

N

Transposition PA/IVS Critical PS Interrupted aortic arch Coarctation Aortic valve atresia Aortic valve stenosis Tricuspid atresia Total of 8 series

1985-1989 1987-1993, 1995-1997 1987-1993 1987-1993, 1995-1997 1990-1993 1994-2000 1994-2000 1999-2001

895 457 223 476 965 610 488 85 4,199 children

Abbreviations: PA/IVS, pulmonary atresia with intact ventricular septum; PS, pulmonary stenosis.

Reference 15-19, 23, 29 20 21 22, 24 25 26 27, 30 16 publications

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Outlet obstruction after arterial repair occurred in 17% of children by 10 years after operation. Obstruction occurred at either valvar or subvalvar level (proximal) or in the pulmonary branches (distal), or at both levels.19 Right-sided obstruction was 10 times more prevalent than left-sided obstruction. Proximal right-sided obstruction had a single early hazard phase and was more likely with side-by-side great arteries, earlier experience, and use of nonautologous patches. In contrast, distal obstruction had both an early and a late immutable phase of risk and its risk factors included a left coronary arising from sinus 2, or an intramural coronary artery course.19 The report by Turley and Verrier23 compared the excellent results from a single member institution of the CHSS with the results for the rest of the Society during the 1985 to 1989 era. During that era, their management protocol changed from a late Senning repair to a neonatal Senning and to neonatal arterial operation. Unlike the other institutions, improvement over time was observed in the Senning operation, probably because of a learning curve for the neonatal Senning. A cross-over from a neonatal Senning to arterial operation was not associated with increase mortality. Otherwise, the experience of the institution was reflective of the multicenter data, confirming that intermediate survival with either operative strategy was similar, and that the arterial switch led to fewer arrhythmias than an early or late Senning. A 10-year follow-up of neonates who had an atrial repair, either Mustard (n ⫽ 108) or Senning (n ⫽ 173), showed better early and late survival with the Mustard operation (95% v 78%).29 There is a late constant hazard phase for both operations (0.78%/year for Senning v 0.23%/ year for Mustard). Risk factors for death are an associated VSD, lower weight and age at surgery, anomalies of cardiac position, concomitant surgery on the left ventricular outlet, and the Senning operation. Late reoperation was not common, 5% at 10 years, but was associated with a high mortality of 36%. The need for permanent pacing (9% at 10 years) was more likely among children with a VSD, a Senning operation, or with previous atrial septectomy.29

Pulmonary Atresia/Intact Ventricular Septum The initial analysis of 171 neonates entered between 1987 and 1991 showed the importance of the tricuspid valve size (Z value) as a correlate of right ventricle size, or right ventricle-dependent coronary blood flow (present in 45%), of the initial intervention, and as a risk factor for eventual two-ventricle repair.20 The analysis led to recommendations for surgical management based on the Z value of the tricuspid valve. Importantly, this initial report predated catheter-based perforation and dilation of the right ventricular outflow tract.

Pulmonary Stenosis/Intact Ventricular Septum Unlike pulmonary atresia/intact ventricular septum, critical pulmonary stenosis in the neonate seldom has marked morphologic variation, and the tricuspid valve diameter correlates poorly with right ventricular size.21 Survival is better with pulmonary stenosis than with pulmonary artery/intact ventricular septum (4-year survival; 81% v 64%). Initial valvotomy results for balloon or by surgery with cardiopulmonary bypass were equivalent. Systemic-to-pulmonary artery shunt is only required in the unusual circumstance of a small right ventricle (15% of neonates).

Coarctation Overall survival among the 326 neonates analyzed was 84% at 2 years. No repair technique was associated with improved survival, but a patch aortoplasty had the highest risk of reintervention (21%). For neonates with an associated moderate or large VSD, the highest 2-year survival (97%) occurred with a two-stage preliminary pulmonary artery banding and coarctation repair, followed by early (1 to 2 weeks) VSD repair/debanding, rather than a one-stage primary repair.25

Interrupted Aortic Arch Survival of neonates with interrupted aortic arch (63% at 3 years) is less favorable than for those with coarctation. Risk factors for death include low birth weight, younger age at repair, type B interruption, presence of an outlet or trabecular VSD, smaller size of VSD, and subaortic narrowing. The study concluded that a single-stage repair with aortic arch augmentation provided optimal care.22

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Chin and Jacobs24 observed that the morphology of the VSD in type B interruption usually was associated with maldevelopment of the outflow tract, whereas type A were less prone to outflow tract anomalies. Their observations support the view that the mechanism of development of type B is likely different than for type A.

Aortic Atresia Neonates with aortic atresia (n ⫽ 323) were managed by choice of the admitting CHSS institution by three protocols: Norwood/Fontan track (n ⫽ 253), heart transplant (n ⫽ 49), or palliative care (n ⫽ 21). Overall survival at 36 months was 50%. There was no statistically important difference in survival between Norwood and transplant, either in all institutions or among the four institutions that achieved significantly better survival. Risk factors for death were low birth weight, associated noncardiac anomalies, and a protocol of palliative care.26

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The practical difficulty of data collection should be obviated by limiting information to a basic minimum dataset. Multi-institutional pooling of more detailed information will be of increasing importance in generating new knowledge to foster improved therapy for patients with congenital heart disease.

Acknowledgment Development and maintenance of these databases would not be feasible without talented and dedicated people. We have been fortunate to have the marvelous support of the CHSS data center staff, especially our coordinator Geraldine Cullen-Dean and data manager Jay Joseph. The divisional database would not have been a success without the consistent effort and thought provided by data manager M. Gail Williams and our programmer Jan Koreska.

Critical Aortic Stenosis Survival among 320 neonates admitted with critical aortic stenosis was only 60% at 5 years. An important conclusion of the analysis was that as many as 50% of neonates managed with a biventricular repair would have better predicted survival if they had received a Norwood operation instead. Conversely, 20% who had a Norwood would have had a better survival estimate with a biventricular repair. Morphologic and functional factors can be used to predict a survival advantage for one- versus two-ventricle repair.27 The multivariate equation to calculate predicted survival for neonates with critical aortic stenosis was posted on the website for general use.28 Valvotomy in neonates, either balloon or surgical, yields comparable survival and freedom from reintervention rates.30 Risk factors for mortality were the need for ventilation before intervention and smaller aortic annulus, sino-tubular junction, or subvalvar area.30

Summary and Conclusion The agreement on nomenclature for surgical diagnosis and procedure codes of congenital heart disease has paved the way for the development of a multi-institutional registry database. The registry could provide a standard of care reference for early results after congenital heart surgery.

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consortium of university hospitals. Am J Cardiol 74:959960, 1994 Gutgesell HP, Massaro TA: Management of hypoplastic left heart syndrome in a consortium of university hospitals. Am J Cardiol 76:809-811, 1995 Hannan EL, Racz M, Kaven R-E, et al: Pediatric cardiac surgery: The effect of hospital and surgeon volume on in-hospital mortality. Pediatrics 101:963-969, 1998 Sinclair CM: The Report of the Manitoba Pediatric Cardiac Surgery Inquest. An inquiry into twelve deaths at the Winnipeg Health Sciences Centre in 1994. http://www. pediatriccardiacinquest.mb.ca (accessed July 2001) Kennedy I, Jarman B, Howard R, et al: Final Report, chapter 26, The Safety of Care. Learning from Bristol: The report of the public inquiry into children’s heart surgery at the Bristol Royal Infirmary 1984-95. The Bristol Royal Infirmary Inquiry, July 2001. http://www.bristolinquiry.org.uk/index.html (accessed July 2001) Trusler GA, Castan ˜eda AR, Rosenthal A, et al: Current results of management in transposition of the great arteries, with special emphasis on patients with associated ventricular septal defect. J Am Coll Cardiol 10:1061-1071, 1987 Castan ˜eda AR, Trusler GA, Paul MH, et al: The early results of treatment of simple transposition in the current era. J Thorac Cardiovasc Surg 95:14-28, 1988 Norwood WI, Dobell AR, Freed MD, et al: Intermediate results of the arterial switch repair. A 20-institution study. J Thorac Cardiovasc Surg 96:854-863, 1988 Kirklin JW, Blackstone EH, Tchervenkov CI, et al: Clinical outcomes after the arterial switch operation for transposition. Patient, support, procedural, and institutional risk factors. Congenital Heart Surgeons Society. Circulation 86:1501-1515, 1992 Williams WG, Quaegebeur JM, Kirklin JW, et al: Outflow obstruction after the arterial switch operation: A multiinstitutional study. Congenital Heart Surgeons Society. J Thorac Cardiovasc Surg 114:975-987, 1997 Hanley FL, Sade RM, Blackstone EH, et al: Outcomes in neonatal pulmonary atresia with intact ventricular septum. A multiinstitutional study. J Thorac Cardiovac Surg 105:406-427, 1993

21. Hanley FL, Sade RM, Freedom RM, et al: Outcomes in critically ill neonates with pulmonary stenosis and intact ventricular septum: A multiinstitutional study. Congenital Heart Surgeons Society. J Am Coll Cardiol 22:183-192, 1993 22. Jonas RA, Quaegebeur JM, Kirklin JW, et al: Outcomes in patients with interrupted aortic arch and ventricular septal defect. A multiinstitutional study. Congenital Heart Surgeon’s Society. J Thorac Cardiovasc Surg 107:10991109, 1994 23. Turley K, Verrier ED: Intermediate results from the period of the Congenital Heart Surgeons Transposition Study: 1985 to 1989. Congenital Heart Surgeons Society Database. Ann Thorac Surg 60:505-510, 1995 24. Chin AJ, Jacobs ML: Morphology of the ventricular septal defect in two types of interrupted aortic arch. J Am Soc Echocardiogr 9:199-201, 1996 25. Quaegebeur JM, Jonas RA, Weinberg AD, et al: Outcomes in seriously ill neonates with coarctation of the aorta. A multiinstitutional study. J Thorac Cardiovasc Surg 108:841-851, 1994 26. Jacobs ML, Blackstone EH, Bailey LL: Intermediate survival in neonates with aortic atresia: A multiinstitutional study. The Congenital Heart Surgeons Society. J Thorac Cardiovasc Surg 116:417-431, 1998 27. Lofland GK, McCrindle BW, Williams WG, et al: Critical aortic stenosis in the neonate: A multi-institutional study of management, outcomes, and risk factors. Congenital Heart Surgeons Society. J Thorac Cardiovasc Surg 121:10-27, 2001 28. Joseph JJ, McCrindle BW, Williams WG: A website calculator for estimating risk with one vs. two ventricle repair for neonates with critical aortic stenosis. http:// www.ctsnet.org/aortic_stenosis-_calc/ (accessed July 2001) 29. Wells WJ, Blackstone EH: Intermediate outcome after the Mustard and Senning procedures. A study by the Congenital Heart Surgeons Society. Semin Thorac Cardiovasc Surg Pediatr Card Surg Ann 3:186-197, 2000 30. McCrindle BW, Blackstone EH, Williams WG, et al: Are outcomes of surgical versus transcatheter balloon valvotomy equivalent? Circulation 104:I-152–I-158, 2001