Tissue Valve Types
Tissue Valve Types
There are several types of tissue valves.
The first major classification is based on whether they have a stent. A stent is a ring that is used to hold the shape of the valve. It goes around the inside of the outside edge of the valve, where the valve rests against the aortic wall. Picture this as the aorta, with the logical nots (|) as the aortic wall, the apostrophes as the stent, and the dashes as the valve: |'-----'|
Although they make them very slim now, a stent does slightly narrow the valve opening, so it somewhat impedes the blood flow. In no case does it do so to an extent that it interferes with the heart's remodelling (shrinking back to normal size) during recovery. The two major contenders with stents are the Carpentier-Edwards Perimount Magna and the Medtronics Mosaic.
The CEPM is a manufactured valve, stitched together from bovine pericardial tissue (the tough tissue that surrounds a cow's heart). Its stent is positioned supraannularly (above a "shelf" in the aortic wall) when sewn in, which reduces its profile and allows a larger valve opening. Released in 2001, the CEPM's design is taken from the CE Perimount series, which has been in use since 1980, having a track record of 90% freedom from explant (replacement) at the 20-year mark for patients over 60 years old. The CEPM is based on this history, with the addition a few years ago of anticalcification treatments and a fixation process that is nondamaging to the replacement valve's tissues. The Magna has a lower gradient than the Mosaic, but there is no measured difference in heart recovery or remodelling from this.
The Mosaic is an actual porcine valve fitted with a slim, half-width stent and a sewing cuff. It has its own anticalcification treatment and a zero-G fixation process that doesn't damage the tissues in the replacement valve. The Mosaic is also receiving good reviews. It has been used since 2000, and with anticalcification for only a few years. Its basis was many years of use of unprotected Medtronic and other porcine valves, which averaged about 15 years of use in patients over 60.
St. Jude does have a treated mixed porcine/bovine valve, but its anticalcification treatements are not approved yet in the US, so it's available mainly in Europe and Asia. Indications are that it is performing well.
Stentless valves generally allow greater bloodflow than stented valves, which is their main draw. They also lack the alterations required for adding a stent. The main stentless contenders are the Toronto porcine stentless, marketed by St. Jude, and the Freestyle porcine stentless from Medtronics. They are treated porcine products that are very similar in style. With these products, the aortic wall associated with the valve is also implanted, providing the structure that stent provide in the other valves.
The Toronto SPV has a history of 15-18 average years in the over 60 crowd, and it undergoes no anticalcification process. It was the first valve of its type, and has been in use in the US since 1991.
A stentless valve does not always require the root to be replaced, but the Freestyle allows it to be done either way. The root is included in the piece, but is removed by the surgeon and just the valve-related part implanted. The Freestyle is extremely similar to the Toronto (by its nature - they're basically both the same porcine parts). As such, some longevity inference could be drawn by the Toronto's history. The Freestyle does have the Medtronic anticalcification treatment and zero-G fixation process that avoids damaging the tissue in the replacement valve. Freestyle has a lower gradient than the Toronto, but there is no measured difference in heart recovery or remodelling from this. Freestyle was released in 1993, and it was based on the success of the Hancock series (1978) and the Hancock II series.
These are all xenografts, as they come from animals. The other tissue valve is a homograft, a treated aortic valve from a human donor. These can average 15-18 years in the over-60 crowd. They are more expensive, and except in certain cases, are usually bypassed for the xenografts that have similar lifespans and capabilities. Some surgeons believe they have greated longevity in younger patients, but results from very young patients tend to be all over the map.
A note about strategy: I would personally consider a valve that doesn't last quite as long to be a better strategy for the early fifties. If your valve (and your basic health) lasts 15-18 years, you're still young enough to rebound reasonably well from the next replacement. A 25-year valve would get you to the average lifespan, but leaves you in need of a replacement valve at 75+, which is a riskier age for surgery. However, percutaneous valves may be another way to go at that point, should they improve over the next quarter-century.
Best wishes,
Marguerite
