Ann Thorac Surg 2001;71:S293-S296
© 2001 The Society of Thoracic Surgeons
Bioprosthetic valves and conduits: new developments
Comparison of three different types of stentless valves: full root or subcoronary
Hans H. Greve, MDa,
Ibrahim Farah, MDa,
Manfred Everlien, MDa
a Department of Cardiothoracic Surgery, Klinikum Krefeld, Krefeld, Germany
Address reprint requests to Dr Greve, Department of Cardiovascular Surgery, Klinikum Krefeld, Lutherplatz 40, D-47805 Krefeld, Germany
e-mail: HC{at}Klinikum-Krefeld.de
Presented at the VIII International Symposium on Cardiac Bioprostheses, Cancun, Mexico, Nov 3–5, 2000.
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Abstract
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Background. It is believed that, compared with stented valves, stentless bioprostheses at the aortic position offer a larger orifice area.
Methods. During the past 45 months, we have implanted 211 various types of aortic prostheses in our clinic. In the subcoronary position, we have used the Medtronic Freestyle, Toronto SPV, and Cryolife O’Brien prostheses, and as an aortic root replacement, the Medtronic Freestyle. There were no special indications for selection of each prosthesis except in 8 patients suffering from a disease of the ascending aorta in addition or in a redo procedure because of endocarditis or valve degeneration in which we implanted the full root Freestyle prosthesis. All patients had echocardiographic examinations postoperatively and after 1 year.
Results. Although the implantations took significantly longer time initially, recently the complication rate has shown itself to be no greater than in comparable patients with stented prostheses. The hemodynamic results are very good with the exception of the Freestyle prosthesis implanted in the subcoronary position. The gradients of the remaining three prosthesis after 1 year are between 5 mm Hg and 10 mm Hg, and the effective valve orifice is between 2 and 3 cm2 depending on valve size.
Conclusions. The use of stentless tissue valves offers better hemodynamic results than that of stented valves with essentially no increased operative risk.
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Introduction
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The surgical treatment of diseased heart valves with mechanical or biologic prostheses or the transplantation of homografts is a well-established procedure. However, an ideal procedure is still not yet available. Bioprostheses in the form of chemically treated stented prostheses made from pig valves or bovine pericardium are currently used all over the world in approximately 40% of patients [1]. Equipped with suture rings, they are much easier and faster to implant, and thus they were produced by many companies in addition to mechanical prostheses. During the recent decade, it turned out that stentless tissue valves have much better short-term and long-term results with regard to hemodynamics because of the greater effective valve orifice. This can easy be explained by leaving out the stents and the suture ring because the latter requires at least 6 mm of the diameter. Therefore, these prostheses have the advantage of a less constricted orifice cross-section [2]. In particular, this constriction appears to be completely avoidable by replacing the entire aortic root. Known for a long time, the use of human valve replacement in the form of a homograft is associated with the disadvantage of limited availability [3], especially in the needed size, but also with a limited service life [4]. The second improvement is in reference to durability. Because no sutures are necessary to fasten the biologic material at the stents, weak points are avoided. A further improvement is now obtained by using new fixation and antimineralization procedures in addition to the advantages of the valve design. Investigations in randomized studies have shown that new bioprostheses versus a homograft not only exhibit a reduced tendency toward calcification, but also improved hemodynamic behavior shortly after implantation [5].
Tissue valves possess significant advantages by not exhibiting a thrombogenic effect. This means anticoagulant therapy, which could cause bleeding complications, is not required. Furthermore, the risk of acute valve failure as a result of thrombosis or an embolism into the peripheral arteries is minimal.
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Material and methods
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Primarily because of the good hemodynamic properties of the stentless tissue valves and their improved fixation techniques, but also because valve failure is not expected to occur until much later, we started to implant this type of biologic aortic valve prosthesis in 1997. Initially we used the Medtronic Freestyle prosthesis in a subcoronary implantation according to the surgical technique of Westaby and associates [6]. Later we also implanted the Toronto SPV prosthesis–St. Jude Medical [7] and the O’Brien prosthesis model 300–Cryolife [8]. The Medtronic Freestyle prosthesis, which was initially used exclusively in a subcoronary implantation, was later used in aortic root replacement only (full root) because of unsatisfactory short-term hemodynamic results of our valves implanted in the subcoronary position. But if a valve exchange might become possible, which is more likely in patients younger than 60 years of age, this procedure is questionable, and we introduced the other implantable prostheses in a subcoronary position.
These considerations led us to prefer the implantation of the O’Brien and the Toronto SPV prostheses during the last 18 months in a subcoronary position for hemodynamic investigation of two different stentless valves and to use the Freestyle valve in cases with an aortic root aneurysm or calcification not including the coronary ostia.
A total of 211 stentless aortic tissue valves were implanted by 2 surgeons: 108 with the O’Brien prosthesis, 75 with the Freestyle valve in a full root replacement, 15 with the Toronto SPV, and 13 with the Freestyle valve in a subcoronary position. During the last 4 years, 613 aortic prostheses were implanted, except double-valve replacements. In 279 patients a mechanical valve was used, and in 334, a tissue valve. Accordingly, the amount of stentless valves is approximately 63% of all tissue valves. Primarily we used this device rarely because of the difficult implantation technique. Having more experience, we implanted stentless tissue valves even in older patients and in combined procedures. Now we offer healthy patients younger than 55 years of age a Ross procedure; after this age, a subcoronary implanted stentless valve, or after approximately 68 years of age, a full root procedure. This device is implanted if a special indication is given: very small aortic annulus, aneurysm of aortic root, or dissection. After 75 years of age, in the stage of heart failure, in combined procedures, or if the patient has other relevant diseases, a stented valve is implanted to finish the operation as quick as possible.
One hundred thirteen male and 98 female patients were operated on; 99 of them had the diagnosis of aortic stenosis, 33, regurgitation, and 99, a combined disease. The mean age was 69 years, and the mean New York Heart Association classification was 2.9.
Significant differences among the four groups could not be calculated. All patients were operated on in a state of cardioplegic cardiac arrest (Custodiol [cardioplegic solution], Dr Franz Köhler Chemie GmbH, Alsbach-Hähnlein, Germany); in most of the cases with stenosis, 69 were perfused in an antegrade manner, and 132 cases were perfused in a retrograde manner into the coronary sinus. In this type of application, additional cardioplegic solution was also infused directly into the right coronary orifice in 10 cases. Moderate general hypothermia to 31°C was used in the first 145 cases; later the operation was performed in normothermia.
Simple valve replacement was performed in 137 patients; in 74 cases the operation was accomplished by combined procedures. Fifty-nine patients additionally received up to four coronary bypasses, and reconstruction or replacement of the mitral valve occurred in 8 patients. Several noteworthy events, including reoperation, also occurred. The aortic root was replaced in 6 patients because of conduit formation associated with an aneurysm of the ascending aorta; it was replaced once because of acute dissection. Additionally, the Freestyle prosthesis was used twice in cases of endocarditis of the valve prosthesis, and once in a second reoperation.
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Results
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The cross-clamp times vary according to the duration of the operation and the type of prosthesis used. The duration of ischemia was shortened with increasing practice. The replacement of the aortic root with the Freestyle prosthesis required more time. In addition to the two anastomoses, the coronary orifices had to be mobilized and then connected to the prosthesis. In later procedures, the mean time was 90 minutes (106 minutes in combined procedures), in the Freestyle implanted in the subcoronary position it was 92 minutes (n = 143), in the Toronto SPV 78 minutes (n = 92), and in the O’Brien 60 minutes (n = 73). The cross-clamp time of the O’Brien prosthesis replacement is significantly shorter in comparison with all the others (p < 0.001).
Although the complications—mortality, bleeding, and low output syndrome—after the initial procedures were at a higher rate, the later procedures had the same complication rate as other aortic valve replacements. Of the last 80 of 108 patients who received an O’Brien valve, the mortality rate dropped to 3.75%, of the 13 patients with a Freestyle prosthesis implanted in the subcoronary position, nobody died, and of the 15 with a Toronto SPV, one patient died after a reoperation combined with coronary artery bypass graft procedure. Of the 7 patients who died after Freestyle full root replacement, 6 had ether a reoperation because of endocarditis, aneurysm of the ascending aorta with dissection, or mitral valve reconstruction, or were an emergency case for other reasons. Most cases of reopening had to be performed in the group who received the full root replacement using the Freestyle prosthesis: 14% altogether because of the difficulty in sealing the anastomoses. This is significantly higher (p > 0.001) than the reopening rate of 2% of all the others.
The smallest prosthesis had a diameter of 23 mm; this is an indication for a larger orifice area of the stentless prostheses. Whereas size 27 was mainly used in root replacement, subcoronary implantations mostly used size 25. This again speaks for the better hemodynamic values of the root replacement.
At discharge and 1 year later, the pressure gradients and the effective valve areas were measured by Doppler echocardiography. Figures 1–4 show the early results. The lowest pressure gradients were observed in the full root Freestyle prosthesis, particularly in the larger sizes. The effective valve orifices were approximately the same in all stentless prostheses with the exception of the Freestyle prosthesis implanted in the subcoronary position. At the investigation 1 year after implantation, the pressure gradients are further diminished, including the subcoronary Freestyle. However, this prosthetic aortic valve keeps a relatively high gradient compared with the other prostheses. Particularly in the larger sizes the pressure gradient of the stentless prostheses except the subcoronary Freestyle tends toward zero. As mentioned the cross-sections even of this substitute increase during the first year. Nonetheless, it does not achieve the same value as the other valve prostheses.
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Fig 1. Mean and standard deviation of transvalvular pressure gradients for each valve size before discharge from hospital. (Freestyle f.r. = Freestyle stentless prosthesis in a full root position; Freestyle s.c. = Freestyle stentless prosthesis in a subcoronary position.)
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Fig 2. Mean and standard deviation of effective valve area for each valve size before discharge from hospital. (Freestyle f.r. = Freestyle stentless prosthesis in a full root position; Freestyle s.c. = Freestyle stentless prosthesis in a subcoronary position.)
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Fig 3. Mean and standard deviation of transvalvular pressure gradient for each valve size after 1 year. (Freestyle f.r. = Freestyle stentless prosthesis in a full root position; Freestyle s.c. = Freestyle stentless prosthesis in a subcoronary position.)
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Fig 4. Mean and standard deviation of effective valve area for each valve size after 1 year. (Freestyle f.r. = Freestyle stentless prosthesis in a full root position; Freestyle s.c. = Freestyle stentless prosthesis in a subcoronary position.)
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The differences between the hemodynamic results are not significant, probably because of the small numbers. Only the extremely different transvalvular gradients in the Freestyle prosthesis implanted in the subcoronary position are strongly significant at hospital discharge and after 1 year (p < 0.001). The difference among most of the implanted prostheses, the Freestyle and the O’Brien valve, is of more interest: only the pressure gradient of the 25-mm size prosthesis is of significant difference (p < 0.005).
Altogether we reviewed 435 patient-years of follow-up of all implanted stentless prostheses. During this time, two O’Brien prostheses from the initial implantation series with less experience had to be replaced because of regurgitation, and 1 patient who had a full root Freestyle prosthesis experienced an early valve degeneration after an endocarditis that was successfully treated with antibiotics, necessitating reoperation 3 years after the first valve replacement. All other patients are in good condition. During this period no deaths occurred, and no other valve-related complications were reported.
Altogether 10 patients with subcoronary stentless prostheses, but none of the patients with a full root substitute, exhibited a minimal transvalvular regurgitation.
Until now, only a small number of patients were investigated after 2 and 3 years, therefore only the 1-year results are included in this article.
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Comment
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The implantation of stentless bioprostheses is technically more difficult than the use of stented valves. However, the hemodynamic values measured are very good and attain nearly normal values while at rest. The higher gradient immediately after the operation can be explained by the subvalvular left ventricular hypertrophy; it decreases during the further course of recovery.
It is interesting to note the different gradients and effective orifice cross-sections of the various prostheses. With respect to the valve size, these yield better results than the stented prostheses. However, the subcoronary Freestyle prosthesis clearly deviates from this. The pressure gradient of the prosthesis implanted in the subcoronary position at discharge from hospital is much higher than that of the others, although it is very low in all the other valves, particularly in the larger sizes.
The reason for the poor hemodynamic results of the Freestyle prosthesis implanted in the subcoronary position may be that our first implantations of stentless valves were performed using this prosthesis and we tended to oversize the prosthesis. Another reason may be that the prothesis has to be cut manually by the surgeon, and an injury of the nearly fastened leaflets has to be avoided. As a result, the corresponding distances of the aortic sinuses and the remaining part of the prosthesis wall may differ, so that the wall of the prosthesis bulges into the aortic lumen and diminishes the diameter of the aortic annulus cross-section.
The good results of the Freestyle prothesis implanted in the full root position can be easy explained: no tissue material is implanted inside the aorta and the aortic annulus, and it is possible to use a larger prosthesis after incising the aortic annulus. The other subcoronary prostheses also show low gradients and large valve orifices. Only a few patients exhibited valvular insufficiency.
Stentless tissue prostheses imitate almost the normal aortic valve. But it is not a total correction. We must keep in mind that our patients have an artificial prosthesis implanted, with the risk of degeneration, albeit after a long time, and the risk of endocarditis.
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References
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Abstract
Introduction
