early homograft failure

[rimom1964]

My 6 year old with Noonan Syndrome was born with partial AV canal and pulmonary stenosis.  He has had 2 repairs and in the most recent one when he was 4 yrs. 10 mos. his mitral and pulmonary valves were replaced.  His St. Jude's in the mitral position is doing great but the homograft failed within 9 months.  It is currently stented but needs replacement soon.  I have 2 questions:
1.  How frequently do homografts fail this early?
2.  When they do fail, what is the typical replacement protocol (if there is a "typical")?

Thank you!

[Jeffrey R Boris, M.D.]

Dear Rimom,

You are finding a problem that is something we have been dealing with for a while—there is no such thing as a perfect replacement valve in pediatric patients.  For our other readers, a homograft is a cadaveric tissue valve that is either frozen (cryopreserved) or preserved in glutaraldehyde.  The valve comes with the attached artery as well as some of the support structure.  At the time that it is needed for surgical placement, it is trimmed and sewn into place.  It was thought that this could be a good medium term solution for kids, with the hope that it might grow.  Usually, in older kids and adults, homografts can reasonably last five to ten years.  Unfortunately, it doesn’t do that very well.  In fact, it seems to create somewhat of a rejection-like response that causes it to calcify.  The valve can become obstructive (stenotic), leaky (regurgitant), or both.  And, for the younger children, especially those under age 3 years, that process can be quite fast; your child, though nearly five when his homograft was place, still had fairly rapid failure.  From what you’ve told me, I am not sure how his homograft is failing, but since it was stented, my guess is that it became stenotic.  For our other readers, a stent is an expandable metal cage that is inserted into a blood vessel on the end of a balloon-tipped catheter.  The stent is placed in the area that it is needed, and the balloon is inflated; this expands the stent to enlarge the blood vessel.  There is recent literature to support the stenting of homografts.  It may even tolerate a second balloon angioplasty, although these typically don’t last particularly long, either.  I don’t know that there is a specific replacement protocol, as each patient is individually evaluated for how bad the homograft stenosis or regurgitation is, how high the right ventricular pressure is, how long it is felt that the patient can tolerate these conditions, and what the risks are of reoperation.

The other alternative is a mechanical prosthesis, like the St. Jude valve that your son has in the mitral position.  The problems with this valve are that they do not grow with the child, and they require anticoagulation to prevent them from clotting.  Because of the low velocity flow on the right side of the heart and concern for clotting, mechanical valves have not routinely been used in the pulmonary position, though there are some places that are re-examining this concept.

Finally, something that has been on the horizon for a while is the concept of a tissue-engineered valve.  This is a valve that is grown with the patient’s own cells on a biodegradable mesh scaffold.  We hope that this will be the future of all valve replacement, but this is still rather far away at this time.

[rimom1964]

Thank you very much for the information.