Patients kitted out with a certain kind of artificial heart valves are being urged to replace them, since the risks of their breaking are greater than supposed.
According to a study of more than 2000 patients in Holland, the risks of fracture of the 70 degree valve were 17.4 per cent after eight years in place. The risk of breakage with the 60 degree valve is 4.2 per cent after the same period of time.
In the study, performed at Utrecht University, nearly 700 of the more than 2000 patients died.
Some 5,000 people in Britain have been fitted with these kinds of heart valves, produced by Shiley Inc, a subsidiary of the American drug company Pfizer.
The Dutch study recommended that all heart valve patients have the 70 degree valve replaced and young patients have the 60 degree valve replaced.
The replacement procedure itself is not without risk; only three quarters of those with a failing heart valve survive.
The Dutch authors recommend that patients needing replacement select hospitals with a good track record in this sort of operation.