MEDICAL

Manufacturers of mechanical heart valves have not had an easy time of it. A third major mechanical heart valve maker with manufacturing facilities in Orange County, Medtronic, is having to worry about the possibility of fatal malfunctions.

Medtronic acknowledged this week that in June it advised surgeons to watch out for possible malfunctions in 349 heart valves it sold overseas. Medtronic spokeswoman Celia Barnes said the company became concerned after three valves fractured, leading in one instance to death.

Barnes said the problem valves are of the Medtronic Hall D-16 variety sold only outside the United States. She said the variety was designed to provide features preferred by overseas physicians and has not been approved by the Food and Drug Administration to be marketed in the United States.

Although 33,000 Medtronic Hall D-16 heart valves have been sold in the foreign market and 27,000 of those have been implanted, Barnes said, only 349 valves have been identified as susceptible to fracturing. She said the problem valves have an unusually thick coating of pyrolitic carbon on the disc that strikes a ring protector when the valve shuts. She said the company “assumes” that all the problem valves have been implanted, although any still on the shelf are being recalled.

Barnes said Medtronic has added quality controls that it believes will prevent the manufacture of more faulty valves and has continued production of the Hall D-16 valve model. She added that all of the Hall D-16 valves are manufactured at Medtronic’s Minneapolis headquarters. She said other varieties of heart valves are manufactured at Medtronic’s plants in Irvine and Anaheim.

Medtronic claims to have captured 18% of the worldwide mechanical valve market. The Hall D-16 model, Barnes said, produces half of the company’s mechanical valve revenue, which she would not disclose.

Two of Medtronic’s competitors have experienced valve problems of their own.

Irvine-based Edwards Cardiovascular Systems Division of Baxter International in Deerfield, Ill., earlier this year halted production and sales of its Edwards-Duromedics Aerotic Bileaflet Valve Model 3160 and Mitral Bileaflet Valve Model 9120 following reports of six deaths linked to malfunctions.

Shiley Inc., an Irvine subsidiary of New York-based Pfizer, recalled several production batches of its Bjork-Shiley 60-degree Convexo-Concave heart valves because of fatal malfunctions before it stopped making the valves altogether in 1986.