The objective of this study was to characterize current practice patterns for clinical exercise stress testing (EST) in children in the United States. We conducted a survey of 109 pediatric cardiology programs and 91 pediatric pulmonology programs at children’s hospitals or university hospitals in the United States. A total of 115 programs from 88 hospitals responded (response rate, 58%). A higher percentage of cardiology programs (98.7%) have exercise laboratories compared with pulmonology programs (77.5%). Sixty-three percent of respondents have both a treadmill and a cycle ergometer. A larger proportion of respondents (76%) rely primarily or exclusively on treadmill, whereas a smaller number use cycle ergometer (24%). Sixty-seven percent of respondents reported that they include metabolic measurements in EST protocols. Respondents have varying minimum age criteria for EST, with 9% reporting ≤ 4 years, 25% reporting 5 years, 31% reporting 6 years, 16% reporting 7 years, and 20% reporting ≥8 years. Programs using cycle ergometers tend to test children at a younger age and to measure metabolic parameters. Seventy-nine percent of respondents use Bruce and modified Bruce protocols. Institutional protocols are used by 14%. Ninety percent of respondents use technicians to perform EST and 8% use nurses, but 76% require physician presence during testing. The majority of respondents (57%) perform <100 pediatric tests per year.

In the present study, we combined optical Ca(2+) imaging with immunocytochemistry studies to characterize autonomic regulation of Ca(2+) cycling during early development in isolated embryonic mouse hearts. At embryonic days 9.5-11.5 (E9.5-E11.5), the Ca(2+) transient originated in the superior portion of the right atrium, propagated rapidly through both atria, slowly through the atrio-ventricular (AV) ring, and rapidly through both ventricles. Isoproterenol (ISO) significantly increased heart rate, increased Ca(2+) transient amplitude, rate of rise (RR) and a rate of decay, and shortened AV conduction time, indicating the presence of functional beta-adrenergic receptors. The muscarinic agonist carbachol (CCh) had no effects until 1 day later at E10.5. Both beta1-adrenergic and M2 muscarinic receptors were detected in ventricular muscle sections by immunochemistry at E10.5. Growing nerves, labeled using growth-associated protein 43 antibodies, were detected at the E14.5 stage, but not at E10.5, whereas mature sympathetic nerves, detected by tyrosine hydroxylase (TH) labeling, were not yet present at E14.5. These results demonstrate that functional regulation of Ca(2+) cycling by beta-adrenergic receptors occurs earliest in developing embryonic mouse hearts, followed a day later by muscarinic receptor responsiveness, with autonomic innervation developing later. These results define the functional and structural sequence of autonomic regulation of Ca(2+) transient in the embryonic mouse heart.

OBJECTIVES:The purpose of this study was to evaluate adult congenital heart disease (CHD) training among U.S. cardiology fellowship programs. BACKGROUND:Although training recommendations for caring for adults with CHD exist, the educational patterns and numbers of specialists remain unknown. METHODS:We surveyed U.S. directors of 170 adult cardiology and 45 pediatric cardiology (PC) fellowship programs. Adult program surveys contained 1 single-response and 10 multiple-choice questions; pediatric program surveys contained 1 single-response and 13 multiple-choice questions. RESULTS:Ninety-four adult cardiology fellowship directors (55%) and 34 PC directors (76%) responded. Of adult programs, 70% were in university hospitals and 40% were associated with PC groups. Those with PC-affiliation had more adult CHD clinics (p < 0.02) and more adult CHD inpatient (p < 0.02) and outpatient (p < 0.002) visits than those without PC affiliation. Most PC programs were in children's hospitals (38%) or children's hospitals within adult hospitals (50%). Eighty-two percent had associated adult cardiology programs. Pediatric programs followed adult CHD patients in various care settings. Over one-third of adult and pediatric programs had < or = 3 lectures annually regarding adult CHD. Nine adult and 2 pediatric programs offered adult CHD fellowships, and only 31 adult and 11 pediatric fellows pursued advanced CHD training in the last 10 years. CONCLUSIONS:Adult CHD didactic and clinical experiences for cardiology fellows vary widely. Few programs offer advanced CHD training, and the number of specially trained physicians is unlikely to meet projected workforce requirements. Adult cardiology programs with PC affiliation have increased CHD experience and might provide good educational models.

OBJECTIVE:To explore parental preference in the choice between a local and a referral hospital for children undergoing heart surgery.METHODS:One hundred three parents or adult primary caregivers of children referred to a pediatric cardiology clinic were interviewed. Participants were presented with hypothetical scenarios in which they or their children had a heart condition requiring elective surgery. The surgery could be performed at either a local hospital or a regional referral hospital. The travel time to the referral hospital was initially presented as 2 h, and the mortality rate was set at 3% for both the local and the referral hospitals. The parents were then presented with scenarios that sequentially increased the mortality of the local hospital and the distance to the referral hospital, and were asked to choose between the local and regional referral hospitals.RESULTS:When the regional referral hospital was 2 h away and the mortality rates for the referral hospital and the local hospital were equal at 3%, 82.5% of participants chose the local hospital for their children. The percentage of participants choosing the local hospital decreased progressively as the mortality rate of the local hospital increased (to 9.7% at 18% mortality). Between 5% and 10% more participants chose the local hospital when the distance to the referral hospital was increased from 2 h to 4 h. There was no difference in age, sex, ethnicity, language, type of insurance, level of education and availability of personal transportation between participants who chose the regional referral hospital and those who chose the local hospital. Participants who lived closer to the hospital at which the survey was conducted were more likely to choose the local hospital.CONCLUSION:The present study defines a relation between potential outcome improvement and increasing travel distance from a patient or parent's perspective. This trade-off is an important consideration when planning for regionalization.

Care for children with congenital heart disease requires specialized services and various healthcare resources. The purpose of this article is to provide an updated overview of healthcare resources for infants and children with heart disease. In 2001, there were 1609 certified pediatric cardiologists in the United States. The ratio was approximately 45,000 children younger than 18 years per pediatric cardiologist. It is estimated that more than 19,000 cardiac surgeries are performed in children younger than 18 years in the United States each year. This article also reviews the effect of patient characteristics on access to healthcare and use of pediatric cardiac services, and discusses issues related to optimal use of these resources and the development of an organized approach toward service management by regionalization. The authors believe that improved access to high-quality facilities and providers coupled with thoughtful changes in the healthcare delivery system represent an excellent opportunity for optimizing outcomes for children with heart disease.

Background— The purpose of this study was to investigate whether sex disparity in cardiovascular outcomes exists in children who undergo cardiac surgery. Methods and Results— Statewide hospital discharge data from California from 1995 to 1997 were used. Children <21 years old who had a procedure code (by ICD9-CM) that indicated cardiac surgery were selected. The outcome variable was binary, in-hospital death versus alive at discharge. Twenty-three surgical procedures were selected and adjusted for risk by procedure type. We used logistic regression analysis to evaluate the effect of sex on in-hospital mortality, controlling for age, race and ethnicity, type of insurance, home income, type of admission, date and month of surgery, hospital case volume, and type of procedure. There were 6593 cases of cardiac surgery, with 345 in-hospital deaths (mortality rate 5.23%). Crude mortality rates for males (4.98%) and females (5.54%) were not significantly different. However, fewer females were neonates, and females had more low-risk procedures than males. Multivariate logistic regression showed that females had a higher odds ratio (OR) for mortality than males (OR 1.51, P <0.01). The OR for mortality was 3.86 for neonates and 2.98 for infants compared with children aged ≥1 year. Low-volume hospitals had higher mortality rates than high-volume hospitals (OR 1.67, P <0.01). The risk-adjusted length of hospital stay and charges were similar between females and males. Conclusions— For children undergoing cardiac surgery, female sex was associated with 51% higher odds of death than male sex. The mechanism by which female sex acts as a risk factor requires further investigation.

To the Editor.—We read with interest the article by Chang et al1 on the management of hypoplastic left heart syndrome (HLHS) in newborn infants. Chang et al 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. Chang et al claim to have identified patients in the NIS with multiple hospitalizations. This is not possible because the NIS does not contain unique individual identifiers (personal communication with intramural staff at the Agency for Healthcare Research and Quality). This error led Chang et al to include patients in their sample who 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 over 500 patients who were coded as “transfers.” Their inclusion lowered both the estimated mortality rate and the rate of patients receiving a Norwood.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 or more of the following codes: surgical creation of a septal defect (which was incorrectly listed 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 appears 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 with 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 with Chang et al. For example, we found that >50% of patients received a Norwood 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.In Reply.—Tilford and colleagues provide thoughtful comments regarding our study on the clinical management of hypoplastic left heart syndrome (HLHS).1 We applaud their efforts to offer an alternative approach to the analysis of the Nationwide Inpatient Sample (NIS) data using different assumptions.Tilford et al correctly pointed 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. Additionally, a typographical error was made in the International Classification of Diseases, Ninth Revision code for surgical creation of septal defect, which should be 35.42. We apologize for this misrepresentation of the International Classification of Diseases, Ninth Revision code reported in our paper; however, the correct code was used in our analysis.We do not agree with Tilford et al that including patients who were transferred to another hospital in our analysis artificially increased the sample size and decreased the measured prevalence of the Norwood procedure. Patients who were transferred from other hospitals to a NIS hospital would also affect the sample size and Norwood procedure prevalence. Following the argument of Tilford et al, an analysis that excludes all patients who were transferred out should also exclude patients who were transferred in. In the “admission source” of the 1986 patients in our study, 740 patients (37.3%) were transferred from other hospitals. This number is comparable to the number of patients who were transferred out (N = 520). The patients whose admission source was “transferred from other hospitals” had a Norwood procedure rate of 26.6%, which was significantly higher than patients who were not transferred from other hospitals (12.0%). As we have stated in the “Discussion” section of our article, the effects of patients who were transferred out are likely to be offset by patients who were transferred in to NIS hospitals. However, we agree that it may be difficult to determine the magnitude of the “offset effect” of patients transferred in and patients transferred out.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 as suggested by Tilford et al remains a topic for further debate. We are concerned that using cardiopulmonary bypass as the only selection criterion 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 aortic valvotomy. Moreover, when we assigned patients in the Norwood procedure group, we examined all of the first 4 procedure code fields, which may explain the higher number of cases which we found, as compared with the analysis performed by Tilford et al.It is not surprising that by excluding the patients in the NIS dataset who were transferred out Tilford et al would obtain results similar to the study by Gutgesell and Massaro,2 which used data from a consortium of university hospitals. Our data indicate that patients who were transferred between hospitals were more likely to undergo aggressive management. Given the nature of tertiary referrals to university hospitals, it is likely that these hospitals receive more transfers in and a lower proportion of transfers out, thus raising the overall prevalence of the Norwood procedure in these hospitals.As we acknowledge in our 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. We recognize that our study can be repeated using different assumptions, and that this process may lead to somewhat different findings.

BACKGROUND:Studies in animal cell preparations suggest that azimilide may produce a more desirable rate-dependent profile of class III action as a result of its effects on both the slowly (I(Ks)) and rapidly (I(Kr)) activating components of potassium current (I(K)). However, relatively little is known about the effects of azimilide on K(+) currents in human atrial cells. The present study investigated the effect of azimilide on the inward rectifier potassium current (I(K1)), delayed rectifier potassium current (I(K)), ultrarapid delayed rectifier current (I(Kur)), and transient outward potassium current (I(to)) in isolated single human atrial myocytes.METHODS:The tight-seal, whole-cell voltage clamp technique was used to investigate the acute effects of azimilide on K(+) currents in single human atrial myocytes. The cells were isolated enzymatically from atrial tissues that were obtained from patients undergoing open-heart surgeries, with the approval of the local Institutional Review Board.RESULTS:The average cell capacitance of the human atrial myocytes was 77.5 +/- 2.8 pF (Mean +/- standard error of mean, total 28 cells from 17 patients). We found that 100 microM of azimilide in the extracellular solution significantly inhibited the inward rectifier potassium current (12.3 +/- 3.1 vs 6.7 +/- 2.0 pA/pF, n = 12, P < 0.05) at the testing potential of -100 mV. Superfusion with 100 microM of azimilide for 10 minutes inhibited I(K) by 51.7 +/- 5.1% (from 3.4 +/- 0.5 to 1.6 +/- 0.2 pA/pF, n = 9, P < 0.01) at the clamping membrane potential of +40 mV. Human atrial cell I(Kur) was inhibited with 100 microM of azimilide by 38.6 +/- 4.4% (from 3.9 +/- 0.5 to 2.3 +/- 0.2 pA/pF, n = 9, P < 0.01, test potential = 40 mV). We also found that the average peak current amplitude of I(to) in these cells was significantly inhibited with 100 microM of azimilide by 60.3 +/- 5.9% (from 10.3 +/- 1.5 to 3.6 +/- 0.3 pA/pF, n = 6, P < 0.01, test potential = 50 mV).CONCLUSION:The present study provides direct evidence that azimilide inhibits multiple cellular transmembrane K(+) currents in freshly isolated human atrial myocytes. Inhibition of these K(+) currents by azimilide, especially of I(Ks) and I(Kur) is likely to be the electrophysiologic basis for the prolongation of the action potential duration in the human atria which mediates its known antifibrillatory effects in atrial fibrillation and flutter.

OBJECTIVESTo evaluate changes in the clinical management of infants with hypoplastic left heart syndrome (HLHS) over a 10-year period.BACKGROUNDOrthotopic heart transplantation (OHT) and the Norwood procedure have emerged as the treatment options for HLHS over the last 2 decades.METHODSWe used 1988-1997 hospital discharge data from the National Inpatient Sample dataset. Patients < or =30 days of age with a principal diagnosis of HLHS were identified. Clinical management included the Norwood procedure, OHT, in-hospital death without surgery, discharge home without surgery, and transfer to another hospital. Multivariate logistic regression was used to evaluate variables associated with the choice of management.RESULTSThere were 1986 cases of HLHS with 812 in-hospital deaths, yielding a mortality rate 40.9%. The in-hospital mortality rate decreased from 54.4% in 1988 to 38.1% in 1997. The proportion of patients treated with the Norwood procedure increased from 8% in 1988 to 34% in 1997. The proportion of patients who died in the hospital without surgery decreased over time while the percentage discharged from the hospital without surgery or transferred to another hospital remained relatively unchanged. The in-hospital mortality rate was significantly lower in the OHT group compared with the Norwood group (26.2% vs 46.0%). We found no differences in gender, race, type of insurance, or home income between patients treated with the Norwood procedure compared with those who received comfort care. Patients from a later era, in the South, and in teaching hospitals were more likely to undergo the Norwood procedure.CONCLUSIONSBetween 1988 and 1997, the proportion of infants with HLHS treated with the Norwood procedure increased while the use of comfort care decreased. Gender, race/ethnicity, type of medical insurance, and home income did not correlate with treatment choices.

OBJECTIVE:The association between high case volumes and better patient outcomes has been demonstrated for many surgical procedures and medical treatments, including surgery for children with congenital heart disease. To simulate the effects of regionalization of pediatric cardiac surgery, we assessed the impact of reducing the number of pediatric cardiac centers on surgical mortality and patient's travel distance.METHODS:This study used abstracted statewide hospital discharge data from California from 1995 to 1997. Case volume and in-hospital mortality for pediatric cardiac surgeries at each hospital were calculated. All hospitals that performed > or =10 pediatric cardiac surgeries in 1995 to 1997 were included in the analysis. To simulate regionalization, we "closed" the hospital with the lowest case volume and redistributed patients from this hospital to the nearest remaining hospitals. The number of in-hospital deaths was then recalculated using the original mortality rate of each remaining hospital multiplied by its new case volume. A multivariate logistic regression was conducted to determine the odds ratios of mortality of various types of surgery compared with closure of ventricular septal defect. This result was used for adjusting for the case-mix of the hospitals. Regionalization simulation analysis was repeated, and the number of deaths was recalculated using this adjustment of hospital case-mix. We also examined the increase in travel distance of patients to the hospitals as a result of the regionalization simulation.RESULTS:In California, 6592 children underwent cardiac surgeries in 1995 to 1997 with 352 in-hospital deaths (overall mortality rate: 5.34%). A quadratic regression model demonstrated that a high surgical volume was associated with a low mortality rate. We found demarcations between low- and medium-volume hospitals at 70 cases per year and medium- and high-volume hospitals at 170 cases per year. With adjustment for hospital case-mix, we found that 41 deaths could be avoided when all patients from low-volume hospitals were referred, and 83 deaths could be avoided when all patients from low- and medium-volume hospitals were referred to high-volume hospitals (overall mortality rate decreased to 4.08%). The average travel distance for pediatric cardiac surgery was 45.4 miles, which increased by 12.7 miles when all surgeries were referred to high-volume hospitals. When only the 733 high-risk patients were referred from low- and medium-volume hospitals to high-volume hospitals, 49 deaths could be avoided, yielding an overall mortality rate of 4.60%.CONCLUSIONS:Theoretical regionalization of pediatric cardiac surgery is associated with a reduction in surgical mortality from 5.34% to 4.08% when all cases were referred to high-volume hospitals, or decrease to 4.60% when high-risk cases were referred. Although regionalization is associated with an important decrease in the number of deaths, it also increases the travel distance for patients. Additional studies on the costs and benefits of regionalization are needed to determine the best strategies to improve outcomes for children who undergo cardiac surgery.

This study was carried out to compare echocardiographic findings of children taking tacrolimus and cyclosporin A (CsA) after orthotopic liver transplantation (OLT). Echocardiograms of 19 children were reviewed during hospitalizations after OLT, and echocardiograms were performed on 23 children who returned to the clinic for a routine follow-up visit after OLT. Measurements were made of the left ventricle (LV) end-diastolic dimension, and of the thickness of the LV free wall (LVFW) and the inter-ventricular septum (IVS). From these measurements, the LV mass was calculated. LV outflow; gradient was measured by using Doppler interrogation. Comparisons were made between patients on CsA and patients on tacrolimus, Children with hypertrophic cardiomyopathy (HCM) were identified. Two patients from the in-patient tacrolimus group were found to have HCM. These two patients had asymmetric septal hypertrophy with dynamic LV outflow obstruction and were successfully treated with propranolol, with or without discontinuing tacrolimus. In the out-patient studies, there was no difference in LVFW and IVS thickness, or LV mass index, between children on CsA and children on tacrolimus. Hence, tacrolimus is associated with the development of HCM in children. The effect of tacrolimus on HCM development may be acute and temporary. More data are needed to determine the incidence of HCM in children on tacrolimus therapy and to establish guidelines for clinicians who followup these children.

Background Although amiodarone has been referred to as a class III antiarrhythmic agent, it also possesses electrophysiologic characteristics of the three other classes (classes I and IV and minor class II effects). Previous studies have demonstrated that amiodarone inhibits Ca2+ channel current in intact cardiac myocytes. However, it is not clear whether this response reflects a pure class IV effect (direct Ca2+ channel inhibition) or a class II effect (β-adrenergic receptor blockade) of amiodarone. Methods In the current study, the effects of amiodarone on Ca2+ current were studied in the absence of sympathetic regulation using a Xenopus oocyte expression system. The L-type Ca2+ channel α1C subunit was coexpressed with the α2Δ and β2a subunits in enzymatically digested Xenopus oocytes. Ca2+ currents were recorded using the cut-open oocyte preparation. Results We found that perfusion of 10 μM isoproterenol produced no significant change in peak Ca2+ current (from 223±33 to 210±29 nA, mean±SEM, n=5, P=not significant), indicating the absence of a functional stimulatory sympathetic signal pathway in these oocytes. After 10 minutes of exposure to 10 μM amiodarone, Ca2+ current amplitude was significantly decreased from 174±33 to 100±26 nA (n=8, P<0.01; control group: 220±33 to 212±29 nA, n=5, P=not significant). These effects were similar to those of 10 μM nifedipine (201±48 to 108±48 nA, n=6, P<0.05), a typical Ca2+ channel blocker. On the other hand, neither amiodarone nor nifedipine significantly altered the Ca2+ current activation or inactivation kinetics. Conclusions These results demonstrate that amiodarone inhibits Ca2+ current in the absence of a functional intrinsic β-adrenergic stimulatory system and, therefore, represents a true class IV effect.

OBJECTIVE:Previous studies have shown that children with congenital heart disease (CHD) who live in nonurban areas or who do not have private insurance are at risk for delayed referral to a pediatric cardiologist. However, the effect of these factors on the age at which cardiac surgery is performed has not been evaluated. This study is designed to evaluate the factors that influence the age at which definitive surgical repair is performed.METHODS:Data on hospital discharges for 1995 and 1996 in California were obtained from the Office of Statewide Health Planning and Development database. Children <18 years who underwent surgical repair for atrial septal defect (ASD), ventricular septal defect (VSD), tetralogy of Fallot (TOF), or atrioventricular canal (AVC) were included in the study. Age at surgery was evaluated using type of CHD, gender, race, type of insurance, surgical centers, urban or rural home location, and distance between home and surgical center as independent variables.RESULTS:In 1995-1996, 666 children underwent ASD closure (mean age: 5.1 years; median: 4.0 years), 582 VSD closure (mean age: 2.8; median: 1.1 years), 394 TOF repair (mean age: 1.7; median:.9 years), and 177 AVC repair (mean age: 1.1; median:.6 years). Comparing median and mean age at surgery, we found: AVC<TOF<VSD<ASD (< indicates younger than). A consistent trend for all 4 types of CHD was seen indicating that for median age at operation: private insurance<managed care<Medicaid. Gender or race had no effect on age at operation, although Asians tended to be older at surgery for all 4 types of CHD. There is a significant negative correlation between the case volume of surgical centers and median age at operation for ASD (r = -.37), VSD (r = -.49), TOF (r = -.63), and AVC (r = -.17). In addition, significant positive correlation was found between degree of urbanization of home locations (measured by population density) and median age at operation for ASD (r =.50), VSD (r =.77), and TOF (r =.18). No significant correlation was found between distance to surgical center and age at operation.CONCLUSIONS:Many medical and nonmedical variables play important roles in determining age for definitive repair of CHD in children. Type of insurance, a recognized surrogate for access to care, may play an important role. In addition, centers with higher surgical case volume were more likely to operate at a younger age. Finally, children in urban areas tend to be older at the time of surgery for ASD, VSD, and TOF.