By Ransdell Pierson and Bill Berkrot

WASHINGTON, March 30 (Reuters) - A non-surgically implanted heart valve meant to delay open heart surgery in children with congenital heart defects worked well for all but a few patients during a year of follow-up observation, in line with favorable results seen in original clinical trials of the Medtronic Inc product.

The Melody transcatheter pulmonary valve was approved in 2010 under a U.S. humanitarian device exemption, which allowed it on the market as long as a follow-up study was conducted to assess the product's reliability and safety. The valve is guided to the heart by a catheter, a minimally invasive procedure, and patients typically go home after only one night in the hospital.

In the study of patients who had been implanted with the valve there was no narrowing of the valve, or stenosis, after six months in some 96.7 percent of the 90 patients for whom data was available.

After a year, there was no narrowing, significant leakage or need for additional intervention in 94 percent of patients, researchers said on Sunday.

"The valves had excellent function during the first year, judged by no more than mild leakage and very few patients had narrowing of the valve," said Dr. Aimee Armstrong of the University of Michigan C.S. Mott Children's Hospital Cardiac Catheterization Laboratories, who was lead investigator for the follow-up study sponsored by Medtronic.

The mean age of patients in the trial was 20, with ages ranging from 5 to 45. The valve is made from a cow's jugular vein that is sewn into a metal stent, and then inserted into the patient's leg and advanced to the heart.

Within the first year of the study, eight adverse events were seen, including three cases of heart infections, two abnormal heart rhythms and one case each of bacterial infection, major stent fracture and blood clot in the lung.

Patients will continue to be followed for five years.

Results of the multi-center study were released at the annual scientific sessions of the American College of Cardiology in Washington.

Congenital heart defects are the most common type of birth defect in the United States, affecting an estimated one million adults and 800,000 children. Many patients are born with no pulmonary valve, which carries blood from the heart's right ventricle to the lungs, or only a very small pulmonary valve.

Some patients receive a connecting tube, or conduit, early in life, to provide blood flow. The conduits, typically made from cadaver pulmonary valves, from pig valves or bioprosthetic materials, are implanted during open heart surgery and essentially bypass the missing or inadequate pulmonary valve.