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EDITORIAL |
Humboldt Universtiy, Germany
The history of stentless aortic valves dates back as far as the history of valve replacement per se. The first stentless valves were homografts1 and as early as 1967 the Ross-operation has been performed with remarkable long term success.2 Binet3 was the first surgeon who described the use of porcine stentless xenografts, however, due to poor tissue fixation technology these valves were abandoned very soon. Since then the fate of stented as well as stentless bioprostheses has been closely related to tissue processing technology. Analogous to the experience with homografts, which had evidenced that stentless freehand sewn grafts lasted longer than stented ones, a renewed interest in stentless valves occurred.
The first generation of porcine stentless xenografts came along either as porcine root (Edwards Prima®, Medtronic Freestyle®) or fully scalloped for subcoronary implantation (SJM Toronto SPV®). Implants exhibited good hemodynamic performance, a low failure rate, a low rate of endocarditis and a low need for reoperation. Recently intermediate term performance of the early series of the Edwards Prima valve has been shown to be superior to any other stentless device.4 The versatility of the implants allows for minimally invasive implantation, allows for treatment of annulo-ectasia and ascending aortic aneurysms, and has been used successfully in the setting of acute endocarditis. So different and difficult aortic valve and root procedures could be safely treated with those implants.5 Implantation technique can be demanding in certain cases but most often has been shown to be very easy, provided accurate sizing has been performed.6,7 It seems to be very important to avoid any undersizing or oversizing with such devices.
Porcine aortic roots carry a muscle bar under the right coronary orifice, preventing the attached leaflet from complete opening. Modifications have been introduced as with the O’Brien composite stentless valve. Though O’Brien was able to show good results, the valve has not found widespread acceptance. One additional drawback from this first generation stentless valves is the fact that they are all treated with glutaraldehyde which has been shown to be toxic and also promotes tissue calcification on either immunological or chemical basis.
The second generation of stentless valves try to overcome technical difficulties related to the free-hand implantation of stentless valves. The Shelhigh Super Stentless® is one of those valves, requiring only one row of sutures as with any mechanical or stented valve. The tip of each commisssure is attached with an additional stitch to the aortic wall. In our hands this valve has been found very useful in patients with calcified aortic wall, when the subcoronary technique seems to be prohibitive. However, this valve is not a truly stentless valve as it has some external supporting device. Also it is a porcine aortic valve with the aforementioned drawbacks of this material and it is still prepared with glutaraldehyde, though the glutaraldehyde is claimed to have been neutralized by the so called No-React® procedure. This valve lacks the versatility of the root devices. As this device is easier to implant and has advantages in the calcified aortic wall in our daily practice the Shelhigh valve prosthesis is liberally used in the setting of calcium deposits within the aortic wall.
Stentless valves of the third generation are pericardial stentless valves. On the market is a bovine pericardial valve, the Sorin Pericarbon Freedom®. A cylinder will also be available shortly allowing for the same versatility as with the root devices. The pericardial valve is free from the compromises of the porcine aortic root, it is flexible, and easy to implant either with an interrupted or running suture technique. This pericardial valves show extremely good hemodynamic performance and became the valve of choice in our daily practice provided the aortic wall is free from calcifications. Subcoronary implantation of the Sorin pericardial stentless valve requires two sutures rows.
Towards easiness of implantation a new development which is still under clinical evaluation is the 3F® heart valve. This is a equine pericaridal valve. Horse pericardium is thinner, however, stronger than the bovine pericardium and also much more pliable. This valve is implanted only by one running proximal suture. The tips of the commissures are attached to the aortic wall by single stitches. This is a very simple implant technique and in a worldwide clinical trial to date approximately 100 implants have been performed. In our own series of 20 valves we had no failure and we could show that the valve yields low postoperative gradients. Implantation requires only short cross-clamp-times. So we are very pleased with the valve in the setting of subcoronary implantation. One drawback of this third generation stentless valves is that they still use glutaraldehyde for tissue fixation.
On the horizon is a fourth generation of stentless valves, the Matrix P for pulmonary and Matrix A for aortic pericardial valves. The valve is produced by a proprietary process without the use of any glutaraldehyde. The method delivers a very pliable valve with very low gradients. As no glutaraldehyde is used in the whole process lack of calcification and also lack of toxicity could be shown in animal experiments.8 The valve can be used out of the shelf in sizes of 15 – 29 mm. Also the tissue is able to serve as scaffold for tissue engineering9 as the absence of any toxicity and the unique conditioning technology paves the way for autologous repopularization of the valve in patients. Whether spontaneous repopularization in patients is sufficient or preimplantation seeding is needed to improve this process still has to be determined. Since 2000 in our institution and some cooperating hospitals in Europe and Asia more than 60 patients have received the Matrix P during Ross and Rastelli procedures with most favorable results. In the RVOT the valve shows unparalleled performance with extremely low gradients and no evidence for immunologic processes induced by the xenogeneic tissue.
During the recent 15 years stentless aortic xenografts have undergone remarkable changes. Design modifications range from the original porcine aortic root to full pericardial constructs. Tissue processing with the use of glutaraldehyde and the application of different anti-calcification treatments have been introduced and also xenografts treated without any glutaraldehyde are already in clinical use. In a landmark paper Jin and Pepper10 pointed out all the advantage of stentless valves over other implants. They tried to find an explanation for the paradox that in spite of the favorable results many surgeons are still reluctant with the use of stentless aortic valves. The authors encourage the wider use of those unique implants, an opinion which I share from 10 years personal experience with more than 1200 stentless aortic valve implants.
REFERENCES
This article has been cited by other articles:
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  S. Beholz, S. Dushe, and W. Konertz Continuous Suture Technique for Freedom Stentless Valve: Reduced Crossclamp Time Asian Cardiovasc Thorac Ann, April 1, 2006; 14(2): 128 - 133. [Abstract] [Full Text] [PDF]
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