Evidence-Based Referral Results in Significantly Reduced Mortality After Congenital Heart Surgery
* Pediatric Cardiology, Wichita Clinic, Wichita, Kansas
Department of Cardiology, Children’s Hospital, Boston, Massachusetts
Pediatrix Medical Group, Wichita, Kansas
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ABSTRACT |
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Objective. Significant interinstitutional variation in mortality after congenital heart surgery has been demonstrated. Noting an association between reduced mortality and higher volume, a center with a small annual case volume began in August 1998 to selectively refer to high-volume surgical centers based on published or "apparent" low mortality rates for specific cardiac lesions. This study was undertaken to evaluate the effect of evidence-based referral in this practice.
Design, Setting, and Participants. A retrospective cohort comparison over a 10-year period for a small Midwestern pediatric cardiology practice. The institutional database was retrospectively reviewed for children (<18 years) undergoing surgery from August 1992 to July 2002. Data were divided into 3 time periods (August 1992 to July 1995, period 1; August 1995 to July 1998, period 2; and August 1998 to July 2002, period 3). Hospital discharge abstract data from 5 states (California, Illinois, Massachusetts, Pennsylvania, and Washington) in 1992, 1996, and 1998 provided contemporaneous benchmarks. Risk adjustment was performed using the Risk Adjustment in Congenital Heart Surgery-1 method. Risk category, age at surgery, prematurity, and major noncardiac structural anomaly were entered into a multivariate logistic regression model to compare in-hospital mortality adjusting for case-mix differences.
Results. A total of 514 congenital heart surgical cases were identified from August 1992 to July 2002; 507 cases (98.6%) were assigned to a risk category and analyzed further. Unadjusted in-hospital mortality rates were 9.3% in period 1, 5.9% in period 2, and 1.3% in period 3. Unadjusted mortality rates for cases from benchmark data were 6.4% in 1992, 4.8% in 1996, and 3.7% in 1998. Risk adjusted mortality was comparable to the benchmark data in periods 1 and 2, but superior outcomes (odds ratio = 0.24) were demonstrated in period 3.
Conclusions. Evidence-based referrals from a small-volume pediatric cardiac center to large-volume institutions resulted in a reduction in mortality after congenital heart surgery.
Key Words: evidence-based referral • congenital heart disease • outcomes research • volume-outcome
Abbreviations: CHD, congenital heart disease • OR, odds ratio
Surgical results for congenital heart disease (CHD) have dramatically improved over the last 25 years.1–3 Many low-complexity operations are approaching survival rates of 100%,4,5 and in some institutions even the most complex lesions have low mortality.6 Improvements in diagnostic techniques, anesthesia, perfusion, postoperative care, and surgery have altered the natural history of these conditions. However, there remains marked institutional variability in the surgical outcome of patients with CHD.5,6
In response to the recently demonstrated relationship between institutional volume and outcome for CHD surgery,1,4–6 a small Midwestern practice with 
50 cases per year instituted a practice change in August 1998. Cases were selectively referred to high-volume (>300 cases/year) surgical centers based on published or "apparent" low mortality rates for specific cardiac lesions (evidence-based referral). After 4 years of experience, we undertook this study to assess the effects of this new policy.
Risk adjustment is essential in assessing results in CHD surgery, with many different procedures of variable complexity. Recently, a consensus-based method of risk adjustment for surgery for CHD was published that allows more meaningful comparisons of in-hospital mortality.7 We took advantage of this tool to determine the impact of our practice change on the in-hospital mortality of children cared for at our center by comparing them to average outcomes achieved in population-based data from a similar time period.
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METHODS |
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Data Source
Information for the institutional database was collected prospectively and retrospectively analyzed to identify eligible patients. Wesley Medical Research Institute granted a waiver of signed informed consent.
Case Selection
All cases of congenital heart surgery in children <18 years of age from a single pediatric cardiology center between August 1992 and July 2002 were identified. Patients referred for cardiac transplantation and interventional catheterization procedures were excluded, as were newborns 
30 days of age undergoing ligation of a patent ductus arteriosus only.
In the 2 earlier time periods (1992–1998), cases needing surgery were operated on locally or were referred to 1 of 9 primary pediatric cardiology/cardiovascular institutions, based on the local established practice. Patient referral decisions were based on the experience in the particular operation at the referral institution, or parental wishes, without formal regard for volume or outcome. "Apparent" differences in outcome for patients referred to different centers were noted anecdotally, which prompted consideration of a practice change.
After August 1998, cases needing surgery were exclusively referred to centers with annual case volume >300 cases per year that had either "apparent" clinical excellence in the particular operation, based on previous experience of the referring cardiologist or "demonstrated" published data with a particular operation. Case volume and outcome data for various institutions were obtained by direct contact with cardiologists and surgeons at those centers. One cardiologist (S.W.A.) made the determination of which referral centers to discuss with the family. In most instances >1 referral center was discussed, and the family made the final decision. Referrals were made to a total of 4 of the previous 9 Midwestern institutions located between 165 and 914 miles from the referring center. Cases were divided into 3 time periods (August 1992 to July 1995, period 1; August 1995 to July 1998, period 2; August 1998 to July 2002, period 3) to adjust for time sensitive variation in surgical outcomes. Period 3 reflects the change in referral practice.
Benchmark Data
Hospital discharge abstract data from 5 states (California, Illinois, Massachusetts, Pennsylvania, and Washington) for the calendar years 1992, 1996, and 1998 were used to provide a benchmark for the evaluation of trends in mortality over time. Table 1 lists the source of these data. These administrative data sets contain information from all acute care hospital discharges occurring within the given year. In addition to demographic and billing information, up to 25 diagnosis codes and 21 procedure codes based on the International Classification of Diseases Ninth Revision, Clinical Modification are included. All cases <18 years of age with International Classification of Diseases Ninth Revision, Clinical Modification codes indicating surgical repair of a congenital heart defect were selected; cases with codes for cardiac transplantation, interventional catheterization, or ligation of a patent ductus arteriosus only in newborns 30 days of age were excluded.
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Case-Mix Adjustment
The Risk Adjustment in Congenital Heart Surgery-1 method7 was used to adjust for case-mix differences when comparing in-hospital mortality. Cases were initially assigned to 1 of 6 predefined risk categories, based on the presence or absence of specific diagnosis and procedure codes. Category 1 has the lowest risk for death and category 6 the highest. Combinations of cardiac surgical procedures (eg, coarctation of the aorta and ventricular septal defect closure) were placed in the category corresponding to the single highest-risk procedure. Cases that could not be assigned to a risk category were excluded from further analysis. Clinical variables included as part of the Risk Adjustment in Congenital Heart Surgery-1 case-mix adjustment were: age group (
30 days, 31 days to 1 year, 
1 year), prematurity (gestational age at birth <36 weeks), presence of a major noncardiac structural anomaly (eg, cleft lip or palate), and the presence of combinations of cardiac procedures.
Data Analysis
Unadjusted in-hospital mortality rates for the study site were compared across the 3 time periods using the Fisher exact test. The Fisher exact test was also used to compare the site’s mortality rates in each consecutive time period to those for the hospital discharge benchmark data in calendar years 1992, 1996, and 1998, respectively. Logistic regression models with the single binary covariate study site were used to calculate the unadjusted odds of in-hospital death relative to the benchmark data, which served as the reference group; separate analyses were performed for each time period. To generate odds ratios (OR) adjusted for case-mix differences, binary covariates representing risk categories 2, 3, 4, and 6 (the 2 cases in risk category 5 were excluded), age groups 30 days and 31 days to 1 year, prematurity, presence of a major noncardiac structural anomaly, and presence of combinations of cardiac surgical procedures were included in the logistic regression models.
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RESULTS |
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A total of 514 surgical cases <18 years of age were referred for congenital heart surgery between August 1992 and July 2002. Of these, 507 (98.6%) could be placed in a risk category for further analysis. There were no deaths in the 7 cases not classified to a risk category. Figure 1 displays the total number of patients in each risk category in the 3 time periods. After August 1998, patients were referred to 1 of 4 hospitals performing >300 surgeries per year, except for 1 instance where parents chose to return to a site that had performed prior surgery. There was no decrease in local practice volume during the 4 years after the implementation of the evidence-based referral strategy. In-hospital mortality was 4.5% (n = 23 deaths) for the entire cohort.
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The in-hospital mortality rates for each risk category are shown in Table 2. Grouping by age showed 24.7% of cases were
30 days of age, 43.0% 31 days to 1 year, and 32.3% 1 year old. Twenty-one (4.1%) of the cases were preterm; 19 (3.7%) had a major noncardiac structural anomaly. There were 18 (3.6%) cardiac surgeries, 14 planned or staged therapy, and 4 reoperations during the same admission with a reoperation rate of 0.8%. There was no in-hospital mortality in the planned or staged cases or in the reoperation cases.
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The unadjusted in-hospital mortality rates for our surgical cases were 9.3%, 5.9%, and 1.3% in the 3 time periods (P = .001). There were no differences between the unadjusted mortality rates in our sample and the population-based benchmark data from 5 states for periods 1 and 2 (6.4% and 4.8%, respectively P = .23 and .46), although the difference in period 3 approached statistical significance (1.3% vs 3.7%, P = .07, Fig 2). Unadjusted odds of death relative to the benchmark data were 1.49, 1.26, and 0.35 (Fig 3). After risk adjustment, results in our surgical cases remained similar to the benchmark data before August 1998. However, there was a significant reduction in mortality in period 3, resulting in a 4-fold decrease in the odds of death (OR = 0.24; P = .02) when compared with other institutions during the same time period.
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We are not aware of any adverse medical event associated with transportation to or from the referral institutions. One patient required an emergency atrial septal defect balloon dilatation procedure for excessive cyanosis on arrival at the referral institution. No denial of care from an insurance provider, private or Medicaid, was encountered. All children referred for surgery were operated on at the center to which they were referred.
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DISCUSSION |
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Although the presence of a volume-outcome relationship has been demonstrated for a number of diseases, including CHD,4,5,7–9 stakeholders have struggled to respond appropriately to this information, especially since larger case volumes cannot be equated with quality of care. We report the impact of a practice change implemented by a Midwestern pediatric cardiac center, prompted by several literature reports of a volume-outcome relationship for congenital heart surgery, as well as by large variations in institutional mortality.4–6 This center chose to exclusively refer cases to centers within 1000 miles performing large numbers of cases annually, and further, to individualize referrals to specific centers based on "apparent" or "demonstrated" expertise with different types of surgery. Our study documents a 4-fold reduction in odds of death for infants and children cared for by this center, in comparison to population-based contemporaneous benchmarks, in the period following the change in practice. Reductions in mortality of this magnitude, as a result of evidence-based referral, have not been reported previously.
The presence of a volume-outcome relationship seems indisputable for an increasing number of conditions. The Institute of Medicine held a comprehensive workshop on the topic entitled "Interpreting the Volume-Outcome Relationship in the Context of Health Care Quality" on May 11, 2000.10 An extensive literature review was performed by Drs. Halm, Lee, and Chassin to provide background for the workshop. Of 88 papers evaluating the relationship for 8 conditions, ie, coronary artery bypass graft surgery, pediatric cardiac surgery, carotid endarterectomy, abdominal aortic aneurysm, cancer surgery, coronary angioplasty, acute myocardial infarction, and acquired immunodeficiency syndrome, 79% of studies demonstrated a positive effect of higher volume on outcome. No study found a negative effect on outcome.10 The breadth of conditions for which a relationship has been demonstrated was confirmed recently by Birkmeyer et al.9 Mortality was significantly reduced for 14 types of cardiovascular and cancer procedures at institutions performing a higher number of each procedure.
Jenkins et al5 reported significantly lower in-hospital mortality for congenital heart surgery at higher volume institutions, with the greatest reduction when institutional annual volume was >300 cases. Hannan et al4 found a similar relationship, with empirically determined thresholds at 100 cases per year for institutions and 75 cases per year for individual surgeons. Sollano et al11 also found a continuous relationship between case volume and mortality for congenital heart surgery. Centralization of pediatric cardiac surgical care in Sweden from 4 cities to 2 reduced mortality from 9.5% to 1.9%.12 Similar findings from England and Wales6 demonstrated a reduction in mortality with centralization of care, introducing the notion of supraregional centers. Recently, Chang and Klitzner13 developed a model that predicted a theoretical reduction in mortality with regionalization of care. They defined 170 cases per year as high volume, based on the case volume distribution in California.
Despite these literature reports, there is no consensus regarding appropriate responses from the congenital heart community. In the 2002 guidelines for Pediatric Cardiovascular Centers,14 the writing group suggested that centers should 1) strive to participate in a regional health care network; 2) use modern information technology; and 3) maintain adequate case volumes to achieve and demonstrate high-quality therapeutic outcomes.
Nonetheless, one of the authors (S.W.A.) evaluated the experience at a small volume Midwestern center in 1998, and concluded that large improvements in outcome were potentially achievable if referrals were directed from Wichita to large volume centers.
However, since hospital case volume is only 1 determinant of outcome for congenital heart surgery,15–17 and since lower mortality at larger institutions is not universal, the center further analyzed specific high volume institutions based on additional information. In some cases, referral institutions had published outcome data for specific types of surgery. In other cases, more unpublished data were sought, including prior experience and direct communication with the referral institution. Thus, the center attempted to refer patients selectively to high-volume centers that had "apparent" or "demonstrated" superior results in the particular operation for each child, "cherry-picking" the "best" institution. After completing this process and after considering the available patients and community resources, the institution agreed collectively to implement an evidence-based referral strategy.
Mavroudis and Jacobs17 supported this approach with their suggestion that all surgeons and centers should be evaluated on the basis of their individual results. A threshold of >300 cases per year was chosen at the onset, based on evaluation of the literature.5
Concerns about increases in travel distance and displacement of families were important. In a theoretical regionalization scenario, the average travel distance increased 12.7 miles to 58.1 miles for all patients and to 98.2 miles for transferred patients when all patients were referred to a high volume center.13 Our patients traveled considerably longer distances because of geographic circumstances without any identified adverse medical events. This is similar to the data from the Swedish experience.12 Further impacts on families, such as parental coping, effects from lack of support structures, or financial obligations, although extremely important, were not evaluated.
Data in adults demonstrate a preference for local care in 45% of patients, even with as much as a 2-fold increase in mortality locally compared with a regional center 4 hours away.18 No similar published data are available in children. We did not perceive reluctance on the part of parents to travel a distance for care at the specified center. When families were made aware of the documented relationship between volume and outcome on in-hospital mortality for pediatric cardiac surgery, parents seemed to universally prefer transfer to a center based on the expected medical outcomes for their child. We did not, however, examine the emotional and economic impact in our population.
Evidence-based referral is increasingly being implemented by payors. The Leapfrog Group has used the volume-outcome link to identify high-volume hospitals and encourage its members to reward providers that meet evidence-based criteria.19 DeMone et al20 demonstrated that Medicaid programs have higher mortality with CHD surgery compared with private or managed care in some states over 2 different time periods. The notable exception of improvement was in Florida, where patients with Medicaid insurance were restricted to a few institutions based on demonstrated outcomes.21 All insurance providers in our area have allowed patients to be referred to the center selected based on evidence-based referral strategy. Typically, this required a discussion with the plan’s medical director and a small amount of education to the insurance provider by the referring cardiologist.
Unlike changes in care for children with CHD reported previously, this change in referral pattern was not legislated, mandated, or a result of an inquiry of questionable outcomes.12,22 Key decision-makers including the cardiologist, the directors of both the Neonatal and Pediatric Intensive Care Units, and others agreed to promote patient transfers to optimum centers. Before the implementation of the new policy, there was concern about a potential reduction in primary newborn and infant referrals, as cardiac surgery would no longer be provided; however, no reduction was observed throughout the study period.
Potential limitations in our findings include use of hospital discharge data as our reference. Although data were population-based and approximately contemporaneous, the quality of the datasets may not be identical to that achieved in the prospectively collected series.23 In addition, although our results achieved significance in the third time period, because our annual number of referred cases was not large, estimates of mortality for each time period have fairly wide confidence limits, based on our small sample size. Additionally, a single pediatric cardiologist guided referrals; thus, the reproducibility of results achievable by evidence-based referral over a wide range of practice styles was not tested. Furthermore, the threshold chosen (>300 cases per year) is only 1 of several suggested by the literature, and may be overly conservative. In fact, the contribution to reduction in mortality attributable to referral based on volume, as opposed to demonstrated outcomes, was not analyzable. It is possible that the volume criterion was not necessary and that similar results could have been achieved with an exclusive use of an outcome standard as the basis for referral. Finally, additional important outcomes, such as long-term morbidity or impact on families, were not evaluated.
Despite these limitations, the magnitude of reduction in odds of death achieved at a small volume Midwestern institution for the infants and children undergoing congenital heart surgery is substantial. As many institutions work toward an appropriate response to variable institutional outcomes, the specific practice change outlined in this paper appears to have considerable promise for improving the care for children with congenital heart defects.
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WHAT SPECIALISTS SPEND ON MEETINGS/SEMINARS/PER YEAR |
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Pediatricians, $1500 Family Practice, $1970 Internists, $1484 Ob-Gyn, $3318 Cardiologists, $5818 Surgeons, $3026
Medical Economist. December 9, 2002:38–41
Noted by JFL, MD
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FOOTNOTES |
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Received for publication Oct 18, 2002; Accepted Jan 22, 2003.
Address correspondence to Steven W. Allen, MD, Wichita Clinic, 3311 E Murdock, Wichita, KS 67208. E-mail: allensamk{at}aol.com
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