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To the Editor.—
We read with interest the paper by Chang et al1 on the management of hypoplastic left heart syndrome (HLHS) in newborn infants. They used data from the Nationwide Inpatient Sample (NIS) covering the years 1988–1997 to examine trends in the use of the Norwood procedure, heart transplantation, and mortality over time. They also examined patient and hospital characteristics to assess whether they had any influence on management decisions. Chang et al claimed the in-hospital mortality rate fell from 54.4% in 1988 to 38.1% in 1997 and use of the Norwood procedure increased from 8% to 34% over the same time period. They also found that hospitals in the South were more likely to use the Norwood procedure relative to other regions of the country—a finding that "cannot be easily explained." In this letter, we address these findings.
Central to the Chang et al analysis is the development of the sample from the NIS. They claim to have identified patients in the NIS with multiple hospitalizations. This is not possible, because the NIS does not contain unique individual identifiers (A. Elixhauser, PhD, written communication, 2003). This error led Chang et al to include patients in their sample that were transferred to an acute care hospital "not included in the NIS data." The result of this sample-selection procedure was to artificially increase the sample size by the inclusion of >500 patients who were coded as "transfers." Their inclusion lowered both the estimated mortality rate and the rate of patients receiving a Norwood procedure.
A second concern with the Chang et al analysis involves the identification of patients undergoing the Norwood procedure. Because there is no specific procedure code for the Norwood procedure, Chang et al identified patients based on an algorithm where cardiopulmonary bypass was present (International Classification of Diseases, Ninth Revision–Clinical Modification code 39.61) and 
1 of the following codes: surgical creation of a septal defect (which was listed incorrectly as 34.42 rather than 35.42), repair of heart or pericardium (37.4), incision excision, or occlusion of aorta (38.14), and systemic to pulmonary shunt (39.0). Reliance on such an algorithm may be too strict for administrative databases. It may be more accurate to rely on the inclusion of any evidence that a procedure occurred. A patient may have a code for cardiopulmonary bypass but not have any of the other 4 codes in the Chang et al algorithm. Use of an algorithm based on "or" criteria without evidence of transplantation seems more appropriate.
Chang et al also incorrectly listed the actual procedure codes they used in identifying Norwood patients. Our replication of the Chang et al analysis found 284 Norwood patients using the codes provided, compared to 346 reported by Chang et al. The code 37.4 was found in <1% of HLHS patients, as was the code 38.14.
In our analysis of NIS data, we found a much higher rate of Norwood patients and overall mortality rate compared to Chang et al. For example, we found that >50% of patients received a Norwood procedure in 1997 (33% over all of the study years), and the mortality rate approached 50%. We also found no significant difference in Norwood procedure rates by region of the country.
The different sample-selection methods and algorithms to identify Norwood patients lead to different results. Our findings are consistent with findings from a consortium of university hospitals.2 Chang et al assert an overrepresentation of aggressive surgical strategies in the consortium study. We believe the difference in findings results from their sample-selection methods and algorithm to identify Norwood patients.
REFERENCES
In Reply.—
Tilford et al provide thoughtful comments regarding our study on the clinical management of hypoplastic left heart syndrome (HLHS).1 We appreciate their efforts to offer an alternative approach to the analysis of the Nationwide Inpatient Sample (NIS) data using different assumptions.
Tilford et al correctly point out that the NIS database identifies each hospitalization, not each patient. Using the unique sequence numbers in the NIS database helped us to eliminate duplicate records but not patients with multiple hospitalizations. It is important to note that the unit of analysis in our study was each hospitalization, not each patient. Additionally, a typographical error was made in the International Classification of Diseases, Ninth Revision–Clinical Modification code for surgical creation of septal defect, which should be 35.42. We apologize for the misrepresentation of this code reported in our article; however, the correct code was used in our analysis.
The determination of a Norwood procedure in an administrative database can be controversial. Whether one should use the strict algorithm that was used in our study or a more-inclusive algorithm remains a topic for additional debate. We chose to use the case-selection algorithm reported by Gutgesell and Massaro.2 We are concerned that using cardiopulmonary bypass as the only selection criteria for Norwood procedure may 1) increase the chance of selecting miscoded cases and 2) select some milder forms of HLHS that undergo procedures such as surgical aortic valvotomy.
As we acknowledge in the article,1 a major limitation of our study is the use of data from an administrative database rather than a clinical database. Because of many known deficiencies in administrative data, various assumptions such as criteria for identification of cases and the determination of Norwood procedure were required to conduct our analysis. Furthermore, our study focused on the clinical management of HLHS in cardiac center-based hospitalizations as the units of analysis, not patients. Therefore, we listed "transfer" as a separate group in our analysis and did not exclude patients transferred from one hospital to another, as suggested by Tilford et al. We agree with Tilford et al that it is more appropriate to exclude pretransfer hospitalizations in studies using each patient as the unit of analysis.3
REFERENCES
This article has been cited by other articles:
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  J. G. Berry, C. G. Cowley, C. J. Hoff, and R. Srivastava In-Hospital Mortality for Children With Hypoplastic Left Heart Syndrome After Stage I Surgical Palliation: Teaching Versus Nonteaching Hospitals Pediatrics, April 1, 2006; 117(4): 1307 - 1313. [Abstract] [Full Text] [PDF]
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