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J Thorac Cardiovasc Surg 1998;116:242-246
© 1998 Mosby, Inc.
Cardiothoracic Transplantation |
From The Department of Surgery, Division of Cardiothoracic Surgery,a The Department of Pediatrics, Division of Cardiology,b The Department of Medicine,c and The Department of Preventive Medicine and Biometrics,d University of Colorado Health Sciences Center and the Children's Hospital, Denver, Colo.
Read at the Twenty-third Annual Meeting of The Western Thoracic Surgical Association, Napa, Calif., June 25-28, 1997.
Received for publication July 8, 1997. Revisions requested Oct. 10, 1997; revisions received Feb. 25, 1998. Accepted for publication April 13, 1998. Address for reprints: Max B. Mitchell, MD, Division of Cardiothoracic Surgery, University of Colorado Health Sciences Center, 4200 E. Ninth Ave., Box C-310, Denver, CO 80262.
| Abstract |
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0.10. Actuarial survivals were estimated (Kaplan-Meier) and compared by the log-rank test.| Introduction |
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Infants currently comprise the largest segment of pediatric patients undergoing heart transplantation in our center. ISHLT data indicate a similar worldwide trend, with the total number of infant heart transplantations performed numbering fewer than 100 per year.
1 Unfortunately, the scarcity of donor organs in this age group has limited the experience of most pediatric heart transplant programs to fewer than 35 infants.
3-5 The only larger reported series is from Loma Linda, California.
6,7 Consequently, few single-center data are available regarding intermediate outcomes and perioperative risk factors for infant heart transplantation.
Our cumulative experience with heart transplantation in patients 18 years and younger now totals 112 transplants in 110 patients. We
8 have previously reported intermediate results in our patients older than 6 months at the time of transplantation. The purposes of this study are (1) to review our experience with heart transplantation performed in infants listed at age less than 6 months, (2) to identify risk factors for 30-day mortality in this age group, and (3) to compare early and intermediate outcomes between our early and more recent experience.
| Methods |
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Preoperative management
The primary diagnostic tool in all cases was transthoracic two-dimensional echocardiography. Cardiac catheterization was used selectively to clarify anatomy not clearly delineated by echocardiography and for preoperative palliative procedures. Pulmonary vascular resistance was not specifically determined because of the young age of this population. Pulmonary artery banding was undertaken to protect the pulmonary bed in patients with high-flow left-to-right shunts (e.g., unbalanced atrioventricular septal defects) when deemed appropriate. The preoperative management of hypoplastic left heart syndrome (HLHS) evolved considerably during the course of this study. Patients with HLHS and ductus-dependent systemic circulations were maintained on intravenous alprostadil (prostaglandin E1). Initially, strategies to reduce preoperative pulmonary vascular resistance were used in the hope of avoiding donor right heart failure after transplantation. More recently, we followed strategies to increase pulmonary vascular resistance to maintain hemodynamic stability while awaiting transplantation.
9 Inhaled nitrogen was administered to limit pulmonary blood flow during the initial management of patients with HLHS. Most patients were weaned from nitrogen within 6 weeks. Atrial septal defects were left restrictive unless excessive hypoxemia mandated balloon atrial septostomy. Diuretics and inotropic support were minimized. Mechanical ventilation was avoided whenever possible. Patients with HLHS variants (i.e., Shone's syndrome) anticipated to have adequate antegrade aortic arch flow to support systemic circulatory requirements long enough to allow transplantation underwent ductal division and coarctation repair.
Perioperative management
Perioperative pulmonary artery pressures and mixed venous oxygen saturations were continuously measured in all patients with oximetric pulmonary artery catheters (Abbott Laboratories, Inc., Chicago, Ill.). Donor hearts were procured in standard fashion including extra great vessel lengths as dictated by recipient anatomy. Roe's solution was used for donor cardioplegia. Whenever possible, total ischemia time was limited to less than 4 hours. The majority of cases were performed by a cardiothoracic surgery resident assisted by an attending cardiothoracic surgeon. Circulatory arrest was used during the entire implantation procedure for all ductus-dependent patients with HLHS and when required by patient anatomy or small size. Circulatory arrest followed by low-flow bypass was not used. Isoproterenol and dopamine were routinely used for inotropic support. Dobutamine and epinephrine were used when additional inotropic support was required. Beginning in October 1993, inhaled nitric oxide and intravenous milrinone infusions were routinely used when elevated pulmonary vascular resistance was anticipated or encountered. Perioperative immunosuppression consisted of cyclosporine (INN: ciclosporin), azathioprine, and methylprednisolone. Induction therapy with antithymocyte serum (American Medical Resources, Nashville, Tenn.) was used with rapid discontinuation of methylprednisolone. Serial echocardiograms were used extensively to detect early rejection according to established criteria.
10
Long-term management
After hospital discharge, infants were serially examined and echocardiograms performed frequently. Corticosteroids were not used for long-term immunosuppression. Cyclosporine and azathioprine were given for the first 18 months. More recently, mycophenolate mofetil was used in lieu of azathioprine. Endomyocardial biopsy was used only rarely in the assessment of acute rejection. Routine catheterizations with endomyocardial biopsies and coronary angiograms (recently including intravascular ultrasound) were performed 18 and 36 months after transplantation to detect chronic rejection and cardiac allograft vasculopathy. In the absence of chronic rejection and cardiac allograft vasculopathy, azathioprine was discontinued after 18 months, and cyclosporine monotherapy was used thereafter. Functional development was subjectively assessed by nurse coordinators and transplant cardiologists at each follow-up visit. For purposes of outcome analysis, functional development was determined by review of most current follow-up documentation and categorized as good or developmentally delayed.
Definitions
Waiting list time for patients listed in utero was calculated from the date of birth. Pretransplantation procedures were defined as any operative or catheter-based intervention attempted to correct or palliate a congenital cardiac defect. Total ischemia time was defined as the time between donor aortic clamping and reperfusion of the donor heart. Warm ischemia time was considered to equal the circulatory arrest time or recipient total aortic clamp time when standard bypass techniques were used. The heterogeneous group of congenital heart diseases in this series cannot allow meaningful risk analysis by individual lesion; therefore diagnoses were categorized as HLHS or non-HLHS. July 15, 1993, was the chronologic midpoint of this series and was chosen as the dividing point between our early and recent experience. Respiratory failure was defined as postoperative mechanical ventilation exceeding 10 days. Delayed posttransplantation interventions were defined as any operative or catheter-based intervention (excluding routine biopsies and angiography) required as a direct consequence of transplantation and occurring more than 30 days after transplantation.
Data analysis and statistical methods
Patient height and weight at the time of transplantation and at most recent follow-up were compared with National Center for Health Statistics growth curves.
11 Potential predictors of 30-day mortality included diagnosis, recipient weight, donor/recipient weight ratio, age at transplantation, time awaiting transplantation, preoperative dependence on mechanical ventilation, preoperative dependence on inotropic agents, total ischemia time, warm ischemia time, prior sternotomy, recipient blood type, and nonidentical ABO match. These predictors were evaluated by univariate analysis by means of Fisher's exact test for categorical variables and nonparametric Wilcoxon rank-sum test for continuous variables. Multivariable analysis was performed with logistic regression including all variables with p values
0.10 by univariate analysis. Age at listing, age at transplantation, recipient weight, donor/recipient weight ratio, diagnosis, waiting time to transplantation, total ischemia time, warm ischemia time, hospital stay, intensive care stay, time of mechanical ventilation, time of inotropic support, and 30-day mortality were compared between early and recent groups by means of Fisher's exact test for categorical variables and the nonparametric Wilcoxon rank-sum test for continuous variables. Survival curves were estimated with the use of the Kaplan-Meier method and survival curves were compared between the early and recent series by means of the log-rank test. The Cox proportional hazards model was used to model survival for the early and recent series with transplantation as a time-dependent covariate. Patients listed but not undergoing transplantation were included in the latter analysis. Patients electively removed from the waiting list were excluded. All statistical analyses were performed with the SAS System version 6.12 (SAS, Inc., Cary, N.C.).
12
| Results |
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Table VI details perioperative comparisons between the early and recent series. The percentages of patients with and without HLHS were nearly identical between series (early group, 45% HLHS; recent group, 52% HLHS). The only variable different between groups was a smaller donor/recipient weight ratio in the early group (1.4 ± 0.5 vs 2.0 ± 0.6, p = 0.003). Given the larger number of 30-day deaths in the early group and smaller number of patients in this group, differences in hospital and intensive care stays are masked by the relatively shorter outcomes of these patients; however, this effect is countered by 2 outliers in the early group with hospital stays of 439 and 235 days. Excluding all 30-day deaths from both the early and recent series and the 2 outliers in the early group as mentioned above, hospital stay for the recent series was shorter than in the early experience (mean 20.8 vs 12.8 days, p = 0.03). Similarly, intensive care stay also declined (mean 17.8 vs 9.6 days, p = 0.04). Although not statistically significant, the 30-day mortality difference of 30% versus 10% (p = 0.07) suggests improved early outcome in the recent series.
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| Discussion |
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Previous reported single-center experiences with infant heart transplantation have not demonstrated perioperative risk factors for mortality, most likely because of relatively small sample sizes.
3-5 The Loma Linda series, despite 153 patients, also did not delineate any preoperative risk factors predictive of mortality.
6 One report by Turrentine and colleagues
13 suggested that a donor/recipient weight ratio greater than 2.5 adversely affected survival. However, a much larger study specifically examining donor/recipient weight ratio found that size mismatching did not influence perioperative mortality.
14 Within the range of our data, we did not observe an influence of donor/recipient weight ratio on 30-day mortality. By multivariable analysis the Loma Linda series suggested an association between graft total ischemia time greater than 240 minutes and operative mortality (p = 0.07). We did not observe this association; however, the median ischemia time of our series was 240 minutes compared with 270 minutes in the Loma Linda series. In addition, the power of their series was much greater, with a threefold larger sample size.
Our results indicate that prior sternotomy increases the risk of 30-day mortality after heart transplantation in infancy. However, the wide 95% confidence intervals for this variable (Table V
) and the small size of our study introduces inherent uncertainty, and this result must be interpreted with this provision in mind. Interestingly, prior sternotomy was predictive of operative mortality in a recent multiinstitutional analysis of 141 infants (age < 1 year) who underwent heart transplants.
15 This report from the PHTS identified three other independent predictors of operative mortality in this age group: nonidentical blood type donor, recipient non-blood group A, and donor cause of death other than head trauma. Unfortunately, our data were too incomplete to allow analysis of donor cause of death as a risk factor, and we did not observe an association between nonidentical donor-recipient blood type or any blood group with 30-day mortality. The small sample size of our data, however, clearly limits the power of our series to delineate these factors.
The PHTS report found no association between total graft ischemia and early mortality; however, warm ischemia time was not assessed.
15 In addition, no other single-center reports have examined this variable. Although the p value is only at the 90% confidence level, we observed a possible association between warm ischemia and 30-day mortality that we believe is clinically relevant. The reported warm ischemia times in our data (range 37 to 99 minutes) were considered to equal the crossclamp and circulatory arrest times recorded by the perfusionists during each case. Consequently, these times overestimate the true warm ischemia times because our practice is to keep the donor heart on ice until the native heart is excised. From our logistic model the odds ratio for early death at any duration of warm ischemia x (within the range 37 to 99 minutes) is given by the formula EXP(ß[x 37]), where ß = 0.675 (i.e., the parameter estimate for this variable). Thus the duration of warm ischemia had an exponential effect on the risk of 30-day mortality. The uncertainty in our data owing to small sample size and the p value of only 0.10 implies that this function should not be directly applied by other investigators, although it is logical to expect a marked increase in the risk of early mortality at extended warm ischemia times. Clinically, efforts to minimize warm ischemia should improve outcomes.
Overall 1-month survival in the current series was 82% (95% confidence limits: 72% to 93%), which is comparable with most other series.
3-7,13,15 Causes of early death were similar to those reported previously in this age group. As noted by Chinnock and colleagues,
6 heart transplantation in infants carries a significant learning curve. The clinical characteristics of our early and more recent series were nearly indistinguishable (Table VI
). Although not statistically significant, 1-month survival appears to have improved to 90% (95% confidence limits: 74% to 96%) over the last 3 years of this study compared with 70% (95% confidence limits: 49% to 86%) in the first 3 years. Hospital and intensive care unit stays decreased significantly. Renal failure was less common in the latter half of our series, as only one patient in the recent half required peritoneal dialysis compared with five in the early half. In addition to increased experience, we believe that other advances have improved our results. The perioperative management of pulmonary vascular resistance has improved with the use of milrinone and the recent addition of nitric oxide, and the aggressive use of ECMO has also allowed salvage of three patients who would otherwise have died of excessive pulmonary vascular resistance. Second, in addition to improving pretransplantation survival in patients with HLHS, our strategy to maintain systemic perfusion has improved the hemodynamic stability of these patients, allowing us to avoid the use of mechanical ventilation and inotropic support before transplantation.
9 Recently, we have discharged several infants with HLHS to home while awaiting transplantation. Other authors have noted that the perioperative management of infants with HLHS is particularly challenging.
3,4,13 The HLHS early mortality in our experience (12%) is similar to that of other series.
Long-term survival in this series is comparable with that of other reports and supports the efficacy of transplantation in this age group, with 2-year survivals of 78% overall and 86% more recently. ISHLT data indicate an overall 2-year survival of 62% for children younger than 1 year of age at transplantation.
1 Similarly, the PHTS reported a 2-year survival of 69%.
14 The improvement in long-term outcome we found with increased experience was most heavily influenced by the lower early mortality (Fig. 2
). Posttransplantation malignant disease and cardiac graft vasculopathy were rare in our experience. With longer follow-up the incidence of these complications may increase.
6,16 We believe that these results support our immunosuppression regimen. In particular, avoidance of corticosteroids for long-term immunosuppression appears advantageous in infants and young children. In our experience, growth is satisfactory with progression to higher growth curves during follow-up. In contrast, one center that used long-term triple drug immunosuppression reported that infants undergoing transplantation tended to remain at the same percentile on the growth curve.
3 Development of these infants, although only subjectively assessed, appears quite good and compares favorably with that of other children who have undergone major corrective procedures for congenital heart disease during infancy.
In conclusion, our results further support the role of heart transplantation in infants with end-stage heart disease. The large number of pretransplantation and delayed posttransplantation interventions and the substantial incidence of perioperative complications indicate that infant transplantation is an extremely labor-intense endeavor. Furthermore, substantial resources must be invested in the long-term follow-up of these patients, and the learning curve associated with developing a program for infant heart transplantation is significant. Unfortunately, the scarcity of infant donor hearts is likely to contribute to continued mortality while awaiting transplantation. Advances that improve pretransplantation survival are gratifying but may serve to further increase demand on a limited donor supply. Alternative solutions including xenograft transplantation and mechanical heart systems deserve further research.
| Appendix: Discussion |
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The authors have demonstrated, as have several others in the past, that there is a significant learning curve in infant heart transplantation and it is only when a center commits a large resource in terms of time and people to acquiring this learning curve that the results so dramatically increase. Perhaps most important is the fact that the authors have adopted a hands-off approach to the management of infants in the preoperative period. Perhaps you would like to comment on that. What have you found that has allowed these infants to survive for 3 or 4 months while awaiting transplantation?
Dr. Mitchell. Our hats have to go off to our cardiologists for really flying in the face of conventional management of these children, particularly those with HLHS. Obviously, all of these children have to be managed with prostaglandins to keep their ducts open to provide systemic perfusion. We have tried to minimize pulmonary flow and preserve systemic perfusion. To accomplish this, we have administered inhaled nitrogen to the children during the early days of life, and usually within 6 weeks they can be weaned from nitrogen. The objective is to try to preserve distal organ function and systemic flow by reducing flow into the lungs, thereby reducing the need for mechanical ventilation and reducing the need for preoperative inotropic support. This strategy has actually worked far better than we anticipated. In fact, in the past 6 months three children with HLHS have actually been sent home with long-term infusions of prostaglandins while awaiting transplantation. We try not to use a lot of diuretics. In fact, we have found that the children can maintain their own fluid balance if they are allowed to eat what they want and if we try not to manipulate their system other than to keep their ducts open and to limit pulmonary blood flow.
Dr. Gundry. We had the same experience. Our neonatologists pioneered this, that is, the less they did, the less mechanical ventilation, the less intravenous solutions in these children, the better the children fared. Second, you noted that your warm ischemia time correlated with a decreased survival. Recently, we have changed our technique, particularly in the children with HLHS, to continue to perfuse the body through the cannula, through the snared ductus, while excising the heart and using sucker bypass to reimplant the right atrial and left atrial anastomoses. Only at that time do we institute circulatory arrest to reconstruct the arch. This has allowed us to cut our circulatory arrest time to approximately 15 minutes in the last 50 children whom we have treated. Do you think that the warm ischemia time with lessened survival implies that more complex reconstructions were needed in these groups, or does it imply that perhaps you had trouble in these patients? You said that two of your deaths were the result of technical errors in complex reconstructions.
Dr. Mitchell. I think the answer to that is yes and no; for example, if you look only at the group of children with HLHS, the total ischemia times averaged 66 minutes, which was above the mean average for the entire group. However, their mortality was the lowest of the three groups. On the other hand, in the children with more complicated defects, there is certainly a longer requirement for ischemia to insert those grafts in. You referred to the two technical problems: One was a child with anomalous pulmonary venous return in whom we could not adequately identify all of the pulmonary venous return, and we never weaned that child off the pump. The second was a child who had very small pulmonary arteries, which we did not realize in the preoperative workup, again setting us up for acute right heart failure. More complicated cases are going to be associated with longer ischemia times. Certainly there are some confounding influences between time and the particular diagnosis.
Dr. Gundry. Last is your fairly new use of nitric oxide and milrinone in the postoperative management of these children. This is intriguing to me because we have not seen any evidence of pulmonary hypertension, particularly in the children with HLHS, even undergoing transplantation at age 5 or 6 months. Do you think that pulmonary hypertension in your patient population is related to the high altitude at which these children are kept and your operations are performed?
Dr. Mitchell. We think that may be a factor. The problem becomes more severe the longer the children have to wait. However, since we do not have enough numbers to show that statistically, I did not even try. Just anecdotally, several children have waited 5 months and one 6 months. Two of three at that duration have survived, but it has been much more difficult, and some of those children have required ECMO to get through the operation.
| Appendix: Commentary |
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Thomas L. Spray, MD
Philadelphia, Pa.
12/6/92475
| References |
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