Pig heart valves, a promising alternative to defective aortic valves in human patients, fail much earlier and more often than expected, says a report from cardiac surgeons.
Between 2001 and 2005, four out of 106 patients with the pig valves implanted in the aortic position developed severe impairment after less than four years, and the patients required surgery to replace the valves.
Jennifer S. Lawton, Washington University (WU) cardio-thoracic surgeon at Barnes-Jewish Hospital, notes that the valves are expected to last 10 to 15 years in patients over 70. All four patients who needed a "redo" operation were over 70.
"We noticed an increased incidence of this complication," says Lawton, also associate professor of surgery at the WU School of Medicine.
"We were very concerned, and we believe it is important for others to know about it. A four percent failure rate may not sound like a lot, but we would not expect that many of the valves would fail in such a short period of time."
In the four patients affected, the pig valves failed after 3, 14, 19 and 44 months. Each patient underwent a second operation to replace the defective valve with one made from cow heart tissue. No patient died as a direct consequence of the pig heart valve impairment.
WU pathologists and at the valve manufacturer examined the failed pig heart valves. The valves' leaflets had thickened and stiffened making them much less mobile than normal, which would interfere with blood leaving the heart through the aorta.
Estimates are that one in eight people age 75 or older in the US have at least moderate heart valve disease, and more than 100,000 heart valve procedures are performed each year, said a WU release.
These include procedures to either repair defective heart valves or replace them with mechanical valves or with tissue replacement valves - usually pig heart valves or valves formed from the pericardial sac of cow hearts.
In general, mechanical valves tend to last longer than tissue valves, but patients who receive them have an increased risk of blood clots and must take anti-coagulants.
These findings were published in the June issue of the Journal of Thoracic and Cardiovascular Surgery.