1.
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Is there an immunologic
window of opportunity in neonates who require heart or lung transplantation?
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| Although the immune system is not mature at birth and will not mature for
as long as six months, the assessment of this potential advantage in a transplanted
newborn is difficult. Acute rejection and transplant coronary artery disease (assuming it
is immune-mediated) are two indices of this in cardiac transplantation. Our experience has
shown a similar incidence of acute rejection in neonates, older children, and adults. All
rejection episodes have been confirmed histologically. However, a study from the Pediatric
Heart Transplant Study Group demonstrated less rejection in patients transplanted at less
than six months as compared to those older than ten years. Six months after the
transplant, 45% of the infants were free from rejection; whereas, only 30% of the older
children were free from rejection. This study was flawed in a number of ways including
method of rejection detection and lack of uniform immunosuppression regimen. The series of
neonates transplanted for hypoplastic left heart syndrome at Loma Linda has shown a 70%
freedom from severe graft coronary artery disease (detected angiographically) in their
late follow-up out to seven years. The generally accepted figure in adult transplantation
is 50% incidence of this complication five years post-transplant. Thus, there may be some
immunologic advantage for neonates as expressed in this relatively modest difference in an
entity which may or may not be primarily modulated by the immune-responsiveness of the
recipient. Interestingly, in our limited experience of lung transplantation in infants
less than 3 years of age, the incidence of rejection is much less (n = 13, 23%) than that
seen in older children (n = 57, 67%) for the first six months post-transplant. Likewise,
the incidence of bronchiolitis obliterans has also been much less. As greater numbers of
patients are accumulated and the follow-up progresses, these immunologic indices may
equilibrate, but, for now, there appears to be an age-related advantage for infants
requiring lung transplantation. |
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2.
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How does transplantation in
a neonate affect growth?
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| A major concern about infant transplantation has been on the impact on
the growth of the individual. For cardiac transplant recipients, growth has been around
the 25th percentile for normal individuals, for both weight and height. This is holding
true out to greater than four years post-transplant. Steroids have been blamed for the
poor growth seen previously in other solid organ transplant recipients. Most centers make
every effort to wean their cardiac transplant recipients from steroids during the first
year post-transplant. Some have advocated cyclosporine monotherapy as well. This has no
doubt contributed to the favorable results seen in growth for these children thus far. Results
with lung transplant recipients are not as clear. There have not been as many infants
undergoing lung transplantation over a prolonged period to allow for evaluation. Older
children frequently suffer from systemic illnesses (such as cystic fibrosis), which may
have an independent impact on growth. Virtually all lung transplant recipients must stay
on steroids because of the higher incidence of rejection compared with heart transplant
recipients. Although we are still gathering data, it seems likely that the growth of lung
transplant recipients will not be as favorable as those who have received a heart
transplant. |
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3.
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What are the indications
for heart-lung transplantation as opposed to isolated lung transplantation?
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| Virtually every diagnosis for which isolated lung transplantation is
performed now has been treated in the past with heart-lung transplantation. Heart-lung
transplantation has several advantages over isolated lung transplantation. Technically, it
is simpler and you do not encounter the same problems with airway healing. However, the
disadvantages of using a donor heart when not clearly necessary and taking it out of the
general pool of donors available to those needing isolated cardiac transplantation and
adding the risk of cardiac rejection and the development of coronary vasculopathy, clearly
should push one toward looking for ways to do isolated lung transplantation whenever
possible. We reserve heart-lung transplantation for individuals with pulmonary parenchymal
or vascular disease who also have poor left ventricular function, single ventricle
anatomy, or for whom the repair of the cardiac lesion is so complex that a prolonged
ischemic time will be necessary. Several patients have undergone lung transplantation with
concomitant repair of a cardiac lesion. Those entities repaired include patent ductus
arteriosus, ventricular and atrial septal defects, AV canal, partially anomalous pulmonary
venous return, tetralogy of Fallot with pulmonary atresia, pulmonary vein stenosis, and
aortopulmonary window. The distribution scheme for heart-lung blocks through the United
Network of Organ Sharing dictates that donor hearts first be offered to those recipients
awaiting heart transplantation who are status I before going out as a heart-lung block to
potential heart-lung recipients. As waiting times have progressed over the past six years,
more and more recipients become status I prior to their heart transplant. Thus, the
likelihood of getting an offer is diminishing, particularly for infants. The age group for
which the fewest number of recipients are listed is six to ten years; it is in that age
group that one would have the greatest chance of getting an offer. |
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4.
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What is the long-term
survival for heart, lung, and heart-lung transplant recipients?
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| Generally speaking, when a left superior vena cava is present, the
innominate vein is absent so that the major source of venous drainage for the left side of
the head and left arm is via this left SVC into the right atrium via the coronary sinus.
This occurs in 5% of all our patients with hypoplastic left heart syndrome. For patients
who do not have a Glenn shunt using this vein, the recipient cardiectomy can be altered so
that the incision for the free in fero-lateral left atrial wall is in the
atrio-ventricular groove, leaving the coronary sinus in place. The coronary veins cut when
doing this are easily closed with the left atrial suture line. The right atrial
anastomosis is altered minimally and the left SVC now drains into the right atrium via the
recipient coronary sinus. For patients who have had a Glenn shunt, a segment of innominate
vein should be taken when performing the donor cardiectomy and direct anastomosis to this
can be performed in conjunction with direct SVC anastomosis between the recipient and
donor. |
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5.
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What is the long-term
survival for heart, lung, and heart-lung transplant recipients?
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| As in the approach to congenital cardiac lesions, the focus for
survival in children undergoing transplantation must be for twenty years and beyond.
Statistics regarding three- and five-year survival are informative, but we must be able to
provide hope to parents that they might have a reasonable opportunity to see their child
grow into an adult. Having said that, we only have data for the relatively short periods
of three and five years of follow-up. For heart transplantation, the actuarial survival
curve is relatively flat beyond 12 - 18 months post-transplant at around 75%. Six to seven
years post-transplant there appears to be a downward trend again in survival that is
likely related to graft coronary vasculopathy. For lung transplantation in children the
survival at one year is around 75 - 80%, dropping off to 60% at three years. Bronchiolitis
obliterans, for which there is no cure, is the major cause of death beyond this point and
the number of patients developing this increases with time post-transplant. Much work
needs to be done in this area if we have hope to flatten the survival curve for lung
transplantation. The data available for heart-lung transplantation in children are quite
limited. What is available from UNOS registry shows a one-year survival of around 70% and
a three-year survival of 60%--numbers fairly similar to isolated lung transplantation. The
major barrier to long-term survival here is again bronchiolitis obliterans. |
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References
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| 1. |
Razzouk AJ, Chinnock RE, Gundry SR, et al. Transplantation as a primary treatment for
hypoplastic left heart syndrome. Ann Thorac Surg 1996; 62, 1-8. |
| 2. |
Hosenpud JD, Novick RJ, Breen TJ, et al. The registry of the international society for
heart and lung transplantation: twelfth official report--1995. J. Heart Lung Transplant
1996; 14, 805-15. |
| 3. |
Hirsch R, Huddleston CB, Mendeloff EN, et al. Infant and donor organ growth after
heart transplantation in neonates with hypoplastic left heart syndrome. J Heart Lung
Transplant 1996; 15, 1093-1. |
| 4. |
Bridges ND, Spray TL. Lung transplantation in children. Advances in Cardiac Surgery
1996; 131-46. |
| 5. |
Sweet SC, Spray TL, Huddleston CB, et al. Pediatric lung transplantation at St. Louis
Childrens Hospital. Am J Resp Crit Care Med. |
| 6. |
UNOS Update. 1996; Sept, 42-63. |
| 7. |
UNOS Update. 1996; May, 58. |
| 8. |
Bailey L, Kahan B, Nehlsen-Cannarella S, et al. The neonatal immune system: window of
opportunity?. J Heart Lung Transplant; 828-38. |
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