Tissue Valves vs. Mechanical Valves

TISSUE VALVES VS. MECHANICAL VALVES Allen Graeve: Replacement valves generally come in two broad categories, Tissue or Mechanical. The tissue kind are usually made out of either bovine or porcine parts. The Bovine pericardium, the cow pericardium is fashioned into leaflets, or in case of the porcine it's the usually the actual pig leaflet that becomes part of the leaflet that is replacement part. John Puskas: Biological valves are removed from animal hearts typically pig or cow valves, and they are prepared on a scaffolding that allows us to sew them into the heart. Allen Graeve: In terms of the tissue valves we don't have a perfect tissue valve, one that last as long. Somewhere between 10 and 15 years we begin to see deterioration of these tissue valves to the point where these valves start to deteriorate, and either the patient is recommended for surgery, or has surgery, or maybe because the patient is now too old, surgery is simply denied. In terms of mechanical valves the first ever mechanical valve really stands from this area was the Star-Edwards valve in Portland and it was really a ball in a cage. It was life-saving for many people, and still is probably in use in a few select places. But it's been supplanted by more successful mechanical replacements. John Puskas: Mechanical valves are man-made valves. They are designed by engineers and manufactured in factories here in America. Allen Graeve: The bileaflet valves have for the most part supplanted valves that just had one leaflet and that leaflet might move up and down, or might move like a door, opening and closing, or move up a strut and then move down. Right now bileaflet valves basically are the mechanical valves. John Puskas: The mechanical valve is a permanent device that never wears out, and the biological valve of course, since it comes from an animal and animals don't live or last forever, they do eventually wear out. There are relative benefits of one over the other though. Mechanical valves, the number one benefit is that they last forever. They do not ever wear out. Allen Graeve: Durability of the mechanical valve is probably life-long for most patients. There are things that could make you replace, or remove a mechanical valve. It can leak around the edge. It can become infected, it can actually become obstructed either by clot or by pannus. John Puskas: Then cause a stroke or a heart attack or other problem, unless the blood is thinned, to prevent it from clotting on the mechanical valve. Allen Graeve: But these things are not inherent to the mechanical nature of the valve. If nothing obstructs it like pannus or clot, if it doesn't become infected, if it doesn't leak around the edge, then it should last lifetime, in fact, last many years longer than the patient has. John Puskas: They do however require a blood thinner. Allen Graeve: There has been no mechanical valve that has been able to be successfully run without Coumadin, deliberately run without Coumadin. There have been some attempts and sometimes people have neglected Coumadin, the blood thinner of choice has it right now for all mechanical valves. I believe there are other blood thinners in the pipeline that might be used to - in place Coumadin some day, but right now Coumadin is the standard. Coumadin or Di-cumarol worldwide is a standard for use with the mechanical valves. John Puskas: Coumadin is the most common blood thinner used for mechanical valves. It's a very effective medicine, it prevents blood from clotting easily or normally, and giving in the right dose range, it will prevent blood from clotting on chemical valves quite reliably, but not perfectly. And of course if one takes too much of it we have bleeding problems. So we are always balancing the risk of too much Coumadin, which causes bleeding complications, nose bleeds, hemorrhoidal bleeding, bleeding around the gums, ulcers, for instance. On the one hand taking too much, but if you take too little, you have risk for clots forming on your mechanical valve. So we try to be in the sweet spot that happy medium between, too much and too little, and that's where we try to keep patients. But Coumadin is not an easy drug to take, because there are some things that change or affect its effectiveness. For instance, if you stop eating if you are suddenly on a crashed diet, your Coumadin is much more effective. The antidote to Coumadin in a sense is food, specifically the food that has Vitamin K in it. So if you have balanced your diet accurately with your Coumadin dose you can stay in a nice range of blood thinner, but on the other hand if you change your diet suddenly or change the amount leafy green vegetables that contain Vitamin K in your diet than your Coumadin dose then can go out of whack quite dramatically and quite quickly. And that can be dangerous, it can push one towards the bleeding problem or the clotting problem. Allen Graeve: Coumadin is also metabolized by the liver. So anything that affects the overall liver health might affect Coumadin's metabolism. Alcohol is in for example makes monitoring and be taking Coumadin difficult. John Puskas: So the big plus of the mechanical valve again is durability, it lasts forever. The minus is that it requires a blood thinner. The opposite is true with the biological valves. The valves derive from pig or cow hearts never require blood thinner, but they do not last forever. So you sort of pick your poison, and as you might guess, patients who are very young looking to avoid a second heart operation will typically choose a mechanical valve, because they don't -- they expect to live a long time. They don't want to have another operation and they are willing to take the blood thinner. On the other hand older patients who are not outlive a pig valve or cow valve typically better off with a biological valve, and avoiding the potential side-effects and complications of the blood thinner. Allen Graeve: The advantage of the tissue valve is it usually doesn't thrombus, a pannus could form around it, but it's not a common problem. And the one advantage of a tissue valve, which is slight over mechanical valves is there is a slightly lower risk of hemorrhage and that hemorrhage could be into your brain, or into your gut, or anywhere. And that hemorrhage comes from taking the Coumadin. So when you are looking these valves side-by-side, basically what you are looking at with mechanical valve is you are looking at durability, but up till now the inconvenience of taking Coumadin and monitoring it for life. When you looked at the tissue valve you were looking at the convenience of not taking Coumadin, but you were looking at lesser longevity on the valve, and you were also getting a slightly lowered risk of hemorrhage for a lifetime. That risk might have been 0.5 to 1% per year. John Puskas: We believe that controlling blood pressure will reduce the wear-and-tear on biological valves. We certainly know that the flip side is that some disease processes they go on and patients make the valves last less long. So for instance renal failure, kidney failure, dialysis is associated with much shorter duration of the biological valves. The mechanical valves in the other hand basically last indefinitely and there is not much that you can do to make them last longer or shorter. As long as you take your blood thinner those valves are pretty much are life long fixed. Allen Graeve: Well, the mechanical valve clearly last longer. Unless you pick and choose the patients so well that you know their life expectancy is not statistically longer in the valve you are going to implant. So for a while the cut off seem to be around 60 years of age, people under 60 were getting mechanical valves, people older than 60 were getting tissue valves. I personally have removed quite a few valves from patients whose valve was placed in their late 50's or early 60's and it was a tissue valve, and ten years later I am taking it out because the valve has failed, the valves are obstructing. And of course the re-operation and the risk for that is considerable. It's much higher than standard valve replacement. John Puskas: It's age, but more specifically little more frankly it is life expectancy. There are some 50-year-olds who may not live to be 60, because of other medical problems and they don't need to have a mechanical valve. On the other hand there are some 60-year-olds who may live to be 90 and they may benefit from a mechanical rather than a biological valve. So it's really life expectancy at the time of surgery rather than age of the time of surgery. Allen Graeve: We do have valves out there that have detested time for 30 years with mechanical leaflets. There are in people that I have been placed 30 years ago. But the structural deterioration for tissue valves is something that occurs as a natural process. Some people think it even goes back to how the tissue valve is treated in the first place. You couldn't put a bovine or a porcine part into someone else into a human being without anti-rejection drugs if it weren't first treated some way. These valves have to be treated in such a way as the antigenicity disappears. A low grade antigenicity may remain on the valves. So they are not rejected like a kidney would be if it would put into someone without rejection of the medicine. But over a period of time it may contribute to their deterioration and what happens over time is the valve leaflets can tear or stiffen, thicken and calcify. That seems to happen somewhere between 10 and 15 years in the aortic position. It seems to happen about twice - it takes about half as long for it to happen in the mitral position. John Puskas: Lately biological valves have improved in their design and in their durability. So that the biological valves presently available to us are better than those that were available 15 years ago, and they do last longer, but they do not indefinitely. Once a valve degenerates the patient develops the same symptoms they had before. If they had a leaky valve and now they've got a new leaky valve they know it, because they are short of breath again, fatigued, maybe developing congestive heart failure again. Allen Graeve: There is some association between osteoporosis or calcium metabolism in valves. For example we know that patients who have renal failure tend to have high rates of failure of tissue valves. And it in some way have to do with calcium metabolism. Osteoporosis, I am not sure.