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J Thorac Cardiovasc Surg 2008;135:421-427
© 2008 The American Association for Thoracic Surgery
Cardiothoracic Transplantation |
a Division of Cardiothoracic Surgery, Children's Hospital of New York–Presbyterian and Columbia University College of Physicians and Surgeons, New York, New York
b International Center for Health Outcomes and Innovation Research, Department of Surgery, Children's Hospital of New York–Presbyterian and Columbia University College of Physicians and Surgeons, New York, New York
c Department of Pediatrics (Cardiology), Children's Hospital of New York–Presbyterian and Columbia University College of Physicians and Surgeons, New York, New York
Received for publication June 29, 2007; revisions received August 30, 2007; accepted for publication September 19, 2007. * Address for reprints: Jonathan M. Chen, MD, Pediatric Cardiac Surgery, Children's Hospital of New York, 3959 Broadway, Suite 2-273, New York, NY 10032. (Email: jmc23{at}columbia.edu).
| Abstract |
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Methods: The United Network for Organ Sharing provided deidentifed patient-level data. The study population included 2532 transplantations performed on patients less than 19 years old in status 1/1A/1B between 1995 and 2005. Mechanical circulatory support was used in 431 patients: 241 (9.5%) received ventricular assist devices, 171 (6.8%) underwent extracorporeal membrane oxygenation, and 19 (0.8%) received intra-aortic balloon pumps.
Results: Patients supported on ventricular assist devices had similar levels of hospitalization and intensive care use and less need for inotropic support (P < .0002) than had those not needing support. Five- and 10-year posttransplantation survival was better in patients receiving ventricular assist devices and patients not receiving mechanical circulatory support than in patients receiving extracorporeal membrane oxygenation or intra-aortic balloon pumping (P < .0001). Among mechanically supported patients, patients with a body surface area of less than 0.30 (odds ratio, 1.70; 95% confidence interval, 1.18–2.43) and those requiring extracorporeal membrane oxygenation (odds ratio, 1.65; 95% confidence interval, 1.15–2.35) or intra-aortic balloon pumping (odds ratio, 1.91; 95% confidence interval, 1.02–3.56) had higher long-term mortality. The use of a ventricular assist device at transplantation did not predict higher long-term, posttransplantation mortality.
Conclusions: Pediatric patients requiring a pretransplantation ventricular assist device have long-term survival similar to that of patients not receiving mechanical circulatory support. Early survival among patients undergoing extracorporeal membrane oxygenation and infants is poor, reinforcing the need for improvements in device design and physiologic management of infants and neonates.
| Introduction |
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Historically, extracorporeal membrane oxygenation (ECMO) has been used to support pediatric patients with end-stage heart failure. Children with heart failure have been supported for significantly longer on ECMO than have adults.5-7
More recently, the development of ventricular assist devices (VADs) suitable for implantation into children has increased VAD use in these patients.8
Heretofore, most reports of VAD use in the pediatric population have been anecdotal, and few reports have directly compared the variety of options for MCS in this population.
This report uses data from the United Network for Organ Sharing (UNOS) database to assess posttransplantation outcomes in patients requiring MCS at transplantation. Our goals were to (1) compare the clinical status at transplantation of patients with the various methods of MCS and (2) to identify risk factors for short- and long-term mortality in these groups.
| Materials and Methods |
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Study Population
The study population consists of 2532 transplantations performed on patients less than 19 years of age in status 1/1A/1B between January 1, 1995, and December 31, 2005. Patients were stratified by the presence and type of MCS at the time of transplantation: none, VAD, ECMO, or intra-aortic balloon pump (IABP).
Data Analysis
Data were analyzed by using SAS 9.13 software for Windows (SAS Institute, Cary, NC). The primary outcome was survival; other outcomes were 30-day mortality and in-hospital complications. Continuous variables are reported as means ± standard deviation and were compared by using the Student t test (with the Bonferroni correction). Ordinal variables were compared by using the
2 test. All P values are 2-sided. Multivariate regression (stepwise, P < .05) was also performed. Kaplan–Meier analysis and Cox proportional hazards regression (stepwise, P < .05) were used for time-to-event analysis; patients without accurate follow-up times were excluded from these analyses. Risk, odds, and hazard ratios are reported, with 95% confidence intervals (CIs) in parentheses. Survival function estimates for strata of the explanatory variables were calculated by using the BASELINE statement of PROC PHREG.
| Results |
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Patients requiring MCS
Among patients requiring MCS, Cox hazards for poor long-term survival included a BSA of less than 0.30 m2 (hazard ratio [HR], 1.70; 95% CI, 1.18–2.43) and the need for ECMO (HR, 1.65; 95% CI, 1.15–2.35) or IABP (HR, 1.91; 95% CI, 1.02–3.56) at transplantation. Predicted survival curves based on patient size and need for mechanical support demonstrate the significant effect of these factors in determining long-term outcomes (
Figure 3) Cox regression of patients without congenital heart disease revealed similar predictors of poor posttransplantation survival (see Table E1).
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| Discussion |
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The late drop off in survival apparent in the VAD group (Figure 1) appears to be attributable largely to the overrepresentation of older patients (>13 years) in that group. These older patients were at higher risk for transplant atherosclerosis and consequent graft failure over the long term. We speculate that this is largely due to poor compliance with the immunosuppressive regimen in the adolescent population, a phenomenon previously described both in heart transplantation and abdominal organ transplantation.9,10
Although VADs were associated with excellent posttransplantation outcomes, similar outcomes were not seen in patients bridged with ECMO. Previous series have demonstrated the marginal survival associated with the use of ECMO, whether for temporary postcardiotomy support7,11
or longer-term bridge to transplantation. In the series published by Fiser and associates,12
only 34% of patients could be successfully bridged to transplantation with ECMO. Although slightly better results were reported by the group from Michigan, still only 57% of listed patients survived to transplantation.13
Our results demonstrate that the high risk of death associated with the use of ECMO does not end when the device is explanted and a new heart is implanted. Especially in the first 30 days after transplantation, patients undergoing ECMO before the operation had higher rates of end-organ failure (especially renal failure) and incurred a resultant higher mortality rate. Notably, the effect of ECMO on early posttransplantation survival was independent of the cause of heart failure.
After this early period, the survival curves among all 3 groups (those without MCS, ECMO, and VAD) are parallel, and ECMO ceases to be a predictor of poor outcome among patients surviving the initial 30 days. Thus, those patients who reach transplantation with adequate end-organ function and survive the perioperative period appear to have equivalent long-term outcomes, regardless of the need for or type of mechanical support.
The poor clinical and functional status of patients bridged with ECMO can be clearly seen in the high rate of ventilator and inotropic support and in the nearly universal need for intensive care. The high requirement for inotropic support in patients using ECMO illustrates the poor ventricular off loading and marginal hemodynamics provided by venoarterial ECMO. In contrast, patients with VADs had a significantly lower need for inotropes and had hospitalization and intensive care rates nearly identical to those of patients not requiring mechanical support.
Unfortunately, although VAD implantation had better outcomes than those with ECMO independent of patient size, the smallest patients continued to do poorly with mechanical support, whether VAD or ECMO. It is likely that most of the patients with BSAs of less than 0.30 m2 included in the study population were supported by centrifugal pumps rather than pulsatile VADs. Such pumps do not convey the same advantages as the pulsatile VADs, including patient mobility and improved rates of extubation and hospital discharge, and therefore might contribute to the poorer outcomes in this population. These results can improve with the ongoing development of VADs specifically designed for implantation into the pediatric population.
| Limitations |
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As such, we could not analyze the length of time supported by a particular device, which might have been a particularly strong predictor of end-organ dysfunction and poor outcome. More importantly, without information about clinical status at device implantation, we are unable to answer the most important questions: "Which patients are likely to benefit from mechanical support, and when should it be initiated?" The nature of the UNOS dataset further limits our ability to answer these questions because it does not capture those patients who have a VAD but are not bridged to transplantation (either because they recover or die before listing).
Finally, although data submission at these time points is mandated, the completeness of submitted data is not; therefore several variables that might have been of interest were insufficiently populated and were eliminated from analysis.
Fortunately, several of these limitations, most importantly the question of clinical status at initiation of mechanical support, might soon be addressed by the Interagency Registry for Mechanically Assisted Circulatory Support database.14
| Conclusions |
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| Acknowledgments |
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| Footnotes |
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| References |
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