Insight

Fall 2004

Cardiology Program at VTH Helps Improve Treatment of Children with Congenital Heart Defect

The Cardiology and Cardiac Surgery program at the James L. Voss Veterinary Teaching Hospital has a number of firsts in veterinary medicine – creating the first open-heart surgery program for animals, pioneering surgical heart-valve repair and replacement in dogs, innovating pacemaker implantation in animals, and more. But what many don’t realize is that the program also is at the cutting edge of helping to improve human heart health through a cooperative research program with Children’s Hospital in Denver.

Specifically, the team of researchers at the Cardiology and Cardiac Surgery program have worked with Dr. Mark Boucek, head of the Heart Transplant Program at Children’s, to develop a new nonsurgical technique to improve outcomes in children born with a congenital heart defect known as Hypoplastic Left Heart Syndrome (HLHS).

“Using studies in lambs, we helped Dr. Boucek develop a nonsurgical way of palliating children born with a serious congenital heart defect,” said Dr. Jan Bright, a Professor in the Department of Clinical Sciences and member of the cardiology team. “The technique developed creates a connection between the pulmonary artery and aorta so the child can continue to get blood to the tissues of the body. At the same time, small, self-expanding, flow-limiting devices are placed into the left and right pulmonary arteries to protect the lungs from damage by high blood flow and high pressure. Done through a catheter, this nonsurgical approach is far less risky to the infant than surgery and gives them a better shot at successful ongoing care to correct their heart defect.”

Congenital heart defects occur in approximately eight out of every 1,000 children born today, an estimated 35,000 to 40,000 cases each year. There are 35 recognized heart defects, including HLHS, which is diagnosed in about 1,000 neonates annually. In HLHS, the left side of the heart does not develop properly while the baby is in the mother’s womb. The parts of the heart usually affected are the mitral valve, ventricle, aortic valve, and aorta. In a normal heart, red blood returning from the lungs flows from the heart’s left upper chamber through the mitral valve to the left ventricle, where it is pumped through the aortic valve and out to the body. In babies with HLHS, the left side of the heart is underdeveloped and cannot pump enough blood to meet the body’s needs.

Without treatment, 95 percent of babies with HLHS die within the first month of life. Treatment means either a three-stage heart surgery or a heart transplant. Dr. Boucek and Dr. Bright were interested in developing a nonsurgical, palliative (first-stage) procedure that would provide adequate blood flow to body tissues yet not compromise the long-term health of lung tissue. Their procedure has the additional advantage of facilitating and improving outcomes of the necessary additional surgeries used for long-term management of HLHS (second- and third-stage correction or heart transplant).

The new procedure takes advantage of a newborn’s basic physiology. There is a fetal blood vessel joining the pulmonary artery and the aorta called the ductus arteriosus (DA). This vessel is present in all babies but normally closes within the first few days of life. The ductus arteriosus allows the blood to flow from the right ventricle out to the body, bypassing the nonfunctioning fetal lungs and left side of the heart. After birth, this fetal vessel closes to separate the left and right sides of the circulation. Unfortunately, children with HLHS develop severe, fatal effects of inadequate perfusion to body tissues when the DA closes. Lamb studies showed that pediatric cardiologists could use a catheter to place a stent in the fetal vessel so that it cannot close. This, however, is not sufficient to prevent damage to the lungs from overcirculation.

“Dr. Boucek had us test a novel idea,” said Dr. Bright. “We protected the lungs from overcirculation by placing flow-limiting devices Dr. Boucek had designed in both main pulmonary arteries. Because of the success of the lamb studies and follow-up work to further refine the novel flow-limiting devices, Dr. Boucek was able to begin to use this nonsurgical palliative approach on his patients at Children’s Hospital, and since then, five other medical centers have adopted the procedure.”

While the catheter approach does not repair the heart defect over the long term, it does buy time for infants who are on a wait list for heart transplantation and for those who will get a surgical repair for their heart defect, rather than transplantation.

“The surgery used in the first week of life prior to the development of this procedure was very high risk in neonates,” said Dr. Bright. “I think we can say that it is also a very difficult and brutal surgery. The catheter approach minimizes the trauma to the child, while achieving the goal of sustaining blood flow and maintaining healthy lung tissue. I know transplant surgeons love this approach because they have more success with these patients in heart transplants.”

For Dr. Boucek, the clinical dividends provided by the cardiology research team at CSU have been incalculable.

“The faculty and staff at the James L. Voss Veterinary Teaching Hospital made a revolutionary treatment for infants with lethal heart disease possible,” said Dr. Boucek. “I can say with certainty that, without the cardiac program at the CSU-VTH, we would not be successfully treating these kids today.”