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Ann Thorac Surg 1995;60:1663-1664
© 1995 The Society of Thoracic Surgeons
DR BRACK G. HATTLER (Pittsburgh, PA): I congratulate Dr Fukushima and colleagues for this nice piece of work. I recognize them as pioneers in the area of neonatal heart transplantation.
After receiving a copy of their report I looked at our last 12 neonatal heart transplants to determine the relation between donor heart size, recipient size, and growth of the graft. In this much smaller cohort of patients my colleagues and I have been able to confirm what Dr Fukushima and his colleagues have so thoroughly presented today.
Certainly the severe shortage of neonatal organ donors has led to the frequent transplantation of oversized cardiac allografts. The mechanism that produces autoregulation of the donor heart, slowing down its growth and letting the recipient essentially catch up to the donor heart, is a mechanism that we do not understand. It is, however, a very important biological process. I want to concentrate my comments, therefore, by asking the Loma Linda group several questions about things that have puzzled us.
We know that the myocyte terminally differentiates at about 3 months of gestation and that growth of the heart from this point on is largely due to intrinsic factors, among which myocardial growth factors have been implicated. Have you found any evidence that there are intrinsic factors that are still at work in the neonatal period, or are we simply witnessing all extrinsic factors at work that simply allow the transplanted heart to accommodate to body weight and size of its new recipient?
Second, do you have any data on stroke volume in these oversized hearts? One might hypothesize that the oversized heart pumping into a smaller vascular space would encounter significantly increased afterload, which could act as an ongoing stimulus for continuing hypertrophy of the heart. Because this does not occur in the early intervals, what are some of the physiologic parameters that you may have measured that would give us a better insight into what is actually happening?
And last of all, in 3 of our 12 patients in whom the donor-recipient size ratio was much greater than 2, we had to do a delayed closure of the chest because the patient became severely hemodynamically unstable every time the chest was closed. All 3 of these patients did well, with return to the operating room in 5 to 7 days for closure of the chest. Have you encountered a similar problem with some of these larger oversized hearts?
Again, I congratulate Dr Fukushima and his colleagues on a very excellent report, and I thank The Society for the opportunity of discussing it.
DR FUKUSHIMA: Thank you for the comments. For the first question, we did not check any intrinsic factors after heart transplantation, so we do not know whether graft growth after transplantation depends on any intrinsic factors or not. As we have shown that the graft grew concomitantly with recipient weight, an extrinsic factor such as weight is a more important factor to determine how the heart graft grows.
For the second question about stroke volume, we have already shown that left ventricular volume immediately after transplantation in the oversized graft group was larger than that in the normal size graft group, but heart rates were not different. Therefore, stroke volume immediately after heart transplantation in the oversized graft group was larger than that in the normal-sized graft group. We sometimes use verapamil or other drugs to reduce heart rates and contractility to prevent hypertrophy, and this works well.
We also have had 2 cases of delayed sternal closure. We were able to close the chest, and there was no trouble after then.
Related Article
Ann. Thorac. Surg. 1995 60: 1659-1663.
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