Content provided by the Faculty of the Harvard Medical School

ASK THE DOCTOR: Will there ever be an aspirin-only option for people with mechanical heart valves?

ASK THE DOCTOR

Will there ever be an aspirin-only option for people with mechanical heart valves?

Q. Sometime soon I will need to have my aortic valve replaced. I like the fact that mechanical valves last longer than biological valves, but I don’t like the fact that they require you to take the blood thinner Coumadin to prevent blood clots. I have heard that one of the new mechanical valves won’t require Coumadin, just aspirin. Is that so?

A. An artificial aortic valve that combines the durability of a mechanical valve with the anti-clotting surface of a bioprosthetic valve would be an important advance. The chance of it happening in the near future is slim.

As you point out, there are two models of artifical aortic valves. Biological valves come from pigs, cows, or donated human hearts. There’s usually no need for long-term warfarin (Coumadin) with these because blood clots generally don’t form on their surfaces. But they do tend to wear out and need replacement after 10–15 years. Mechanical valves are made of plastic, polyester fiber, or metal. They may last 30 years or more, but they also tend to generate small blood clots that can cause strokes. Warfarin helps prevent such clots.

Approximately a decade ago, almost 60% of aortic valve replacements were of the mechanical variety. In 2005, only about 25% are. What has driven this shift is a more sophisticated understanding of the lifetime costs of aortic valve replacement.

The biggest “cost” is the operation itself. At most hospitals, aortic valve replacement means opening the chest, stopping the heart and lungs, and circulating blood via a heart-lung bypass machine. Recovery from the surgery usually takes several weeks. A small percentage of people have heart attacks or strokes or die just from having the operation. You don’t want to undergo this operation more than once if you don’t have to.

However, a blood-thinning medication such as warfarin carries its own set of costs. It increases the chances of having a bleeding ulcer or bleeding into the brain (a hemorrhagic stroke). You need to have routine blood tests to make sure you aren’t taking too much or too little. You have to watch what you eat. And the worry factor — Is my warfarin okay? Should I be concerned about that bruise? What if I fall while skiing? — isn’t trivial.

Bioprosthetic valves may not last as long as mechanical valves, but they do all right. After 10 years, 93% are still working just fine. That’s 10 years during which you didn’t have to take warfarin, risk its side effects, or worry about it. The risks of a second valve replacement operation aren’t much higher than they are for a first one, and they are getting smaller.

At least one company is conducting studies to see if warfarin is necessary for its new mechanical valve. The On-X valve is coated with a different form of carbon than other mechanical valves, which its developer believes makes it less prone to generating blood clots. Clinical trials in Germany and South Africa are evaluating whether aspirin alone is as effective as warfarin at preventing the formation of blood clots and the complications that can ensue. Even if the results are positive, it is unlikely that the FDA would approve aspirin-only anticoagulation without further long-term testing.

I recommend that you talk with your doctor again about replacing your ailing aortic valve with a bioprosthetic valve. Not having to take warfarin is a definite benefit. And if you are worried about the risk of a reoperation, keep in mind that the field is constantly advancing. Some surgeons replace aortic valves using a “keyhole” approach much like that now used to remove gallbladders and repair hernias.

And researchers are hotly pursuing a no-surgery option that would enable doctors to replace the aortic valve without opening the chest at all. Like artery-opening angioplasty, one such approach involves threading a catheter into the heart from a blood vessel in the leg, stretching the diseased aortic valve with a balloon, and wedging a new one into place.

— Thomas H. Lee, M.D. Editor in Chief, Harvard Heart Letter

E-mail This | Print This

Last updated:	August 21, 2006