Replacement Heart Valves Built to Last, and Even Grow
Aug. 4, 2000 -- New artificial heart valves made from pig tissues -- including one in which the heart patient's own cells actually grow into and become part of the valve -- could make life much easier for the 80,000 Americans who get replacement heart valves every year, experts say.
These valves don't require the daily doses of sometimes-risky blood-thinning drugs that mechanical valves do. But they are expected to last far longer than the 15 years seen with current "biologic" replacements from pigs, cows, or human donors -- thus sparing the usually 50- or 60-something valve-disease patients from a second replacement operation.
Biologic replacement heart valves like the Mosaic Heart Valve by Medtronic or the experimental SynerGraft, by CryoLife Inc., may soon come with a 25-year warranty, announcements this week suggest. (Medtronic has a partnership with Healtheon/WebMD.)
"That's the goal -- 25 years," says Eric Jamison, MD, a professor of surgery at the University of British Columbia. Jamison is one of the Canadian surgeons who helped develop the Mosaic valve, which was approved by the FDA last month.
The Mosaic valve is a pig heart valve that has been treated with alpha amino oleic acid, a compound found in olive oil. The AOA may help prevent calcium buildup, which is what usually causes heart valve transplants to malfunction, Jamison says. The Mosaic valves were also designed to stop structural failure due to "fatigue" caused by stress.
"We implanted the first valve in Canada in 1994," Jamison tells WebMD. Later this month, at an International Society of Cardiothoracic Surgery meeting in Vancouver, Jamison will present data about a series of Mosaic valve implants. "We implanted 801 valves between 1994 and 1999," he says. So far, he says, all of these valves are still working well, and none has been removed for structural failure, a problem that plagued some earlier biologic valves.
Another option is the experimental valve from CryoLife, which Roy Vogeltanz, the company's vice president for corporate communications, says is "dramatically different than the Mosaic."
The big breakthrough for this valve is that it uses engineered tissue: a pig heart valve with the pig's genetic material removed. What's left is a sort of cellular framework called a collagen matrix. A valve made from this matrix functions the same way as a human heart valve, says Vogeltanz.
But -- and this is what is stirring most of the excitement about SynerGraft -- after the new valve is implanted, human cells start taking over where the pig cells once were. The goal is that, "when implanted, the valve will be slowly remodeled with the patient's own cells," Vogeltanz says. "We implanted the valve in juvenile sheep. ... When [the sheep were] sacrificed at one year, we found all sheep cells on the pig valve matrix." This holds great hope for pediatric valve replacement, he says, because "the new valve could grow with the child."