Biological Versus Mechanical Valve Replacement of the Pulmonary Valve After Multiple Reconstructions of the Right Ventricular Outflow Tract

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On May 3, 2006, I had the privilege of moderating a debate between Dr. John W. Brown and Dr. Joseph A. Dearani. The debaters were selected on the basis of their extensive experience and expertise in the area of right ventricular outflow tract (RVOT) reconstruction. Twenty years ago, reports on the use of mechanical valves (MV) in the RVOT concluded that the short- and long-term outcomes were inferior to those reported for bioprostheses (BP) and homografts (HG). In this debate, each participant carefully reviewed the 40+ year history of RVOT reconstruction at their institution and then they addressed the potential role of an MV in the RVOT.

Dr. Brown reported that only three patients have received a mechanical valve in the RVOT at Indiana University. All three of these patients had another mechanical valve in place. Dr. Brown quoted the Mayo Clinic data to indicate that late reoperation for re-replacement of an adult-sized porcine bioprosthesis in the RVOT was rarely necessary. He stated that, in his extensive personal experience, 75% of adult-sized bioprosthesis in the RVOT were still in place at 25 years. This statement was supported by an actuarial curve which is not reproduced in his manuscript. Dr. Brown also discussed monocusp RVOT valves and bovine jugular valved conduits in the RVOT. Dr. Brown summarized seven publications describing the use of a mechanical valve in the RVOT. Although recent reports suggest that a mechanical valve might be appropriate in the RVOT, Dr. Brown concluded that implanting an isolated mechanical valve in the RVOT would be very rarely indicated. In his opinion, there is relatively low risk in re-replacing a bioprosthesis. He suggested the routine use of a Gore-Tex pericardial substitute to facilitate reentry sternotomy and stressed the need to oversize a bioprosthesis in the RVOT whenever possible.

In his presentation, Dr. Dearani referred to a patient population consisting of 2265 patients undergoing RVOT reconstruction at the Mayo Clinic since 1965: 1540 patients received a bioprosthesis; 697 patients received an HG; and 28 patients received a mechanical valve (1.2%). Dr. Dearani conceded that the early reports regarding a mechanical valve in the RVOT were not favorable. However, he was inclined to give some credibility to recent reports suggesting that there may be a role for a mechanical valve in the RVOT. Dr. Dearani presented his technique for implantation of a mechanical valve in the RVOT. Dr. Dearani also discussed the issue of proper anticoagulation for a person with a mechanical valve in the RVOT. Little hard data exist regarding the optimal anticoagulation regimen for patients with a mechanical valve in the RVOT. It has been suggested that a mechanical valve in the RVOT is probably slightly more thrombogenic than the same valve in the aortic position. Accordingly, Dr. Dearani recommends a target INR of 3.0 (range 2.5 to 3.5). In addition to warfarin, the Mayo Clinic group prescribes one 81-mg aspirin tablet per day. Dr. Dearani emphasized that there is an increased risk, documented in the literature, for patients undergoing their fourth sternotomy, ie, multiple reoperations may not be as benign as Dr. Brown suggested. His presentation was more encouraging on the subject of the mechanical valve in the RVOT since he thinks that safer anticoagulation medications may become available in the future. If a lower risk anticoagulation regimen became a reality, the durability of a mechanical valve could become an important consideration when deciding on the appropriate RVOT prosthesis for an individual patient.

In the rebuttal section of the debate, Dr. Brown reiterated his concerns about committing patients to a lifetime of anticoagulation. Dr. Brown also mentioned the possible effect on adjacent structures when the rigid mechanical valve is inserted. He stressed that a mechanical valve would be inappropriate for a young female contemplating pregnancy. He concluded that the role for a mechanical valve in the RVOT was probably limited to those patients that already had a mechanical valve in another position.

In rebuttal, Dr. Dearani reviewed his presentation and emphasized that many patients require associated procedures at the time of RVOT surgery. While both debaters concluded that the role of a mechanical valve in the RVOT was limited utilizing present prostheses and anticoagulation regimens, Dr. Dearani seemed more willing to consider the use of an isolated mechanical valve in the RVOT.

I found the debate quite enjoyable and informative. Interestingly, neither debater suggested any role for HG valves in adult patients undergoing late re-reconstruction of the RVOT. I suspect that this shift away from HG valves in older patients reflects the need for a valve that will be competent for many years before failing. I am personally a bit skeptical regarding the long-term (15 to 20+ years) function of the current generation of bioprosthesis (porcine stented/nonstented, and bovine pericardial) in younger patients. I anticipate that most young adults with satisfactory cardiac function following repair of complex congenital heart defects will outlive their adult-sized prostheses. Dr. Brown’s actuarial curve predicted that some patients will have a porcine bioprosthesis that “lasts” 25 years. The statistical veracity of this statement was hard to assess since there were no numbers or confidence limits on his graph. The duration of time that a bioprosthesis is deemed functional is not only a reflection of its durability, it is also a reflection of the indications for re-replacement. The current indications for re-replacement of a bioprosthesis in the RVOT remain a bit subjective. In asymptomatic patients that are free of objective signs of right ventricular dysfunction or arrhythmias, a moderate degree of bioprosthetic stenosis/insufficiency can be well tolerated for years.

In summary, I believe that there will be an increasing role for mechanical valves in the RVOT and I look forward to advances in the field of therapeutic anticoagulation, which will permit relatively risk-free long-term anticoagulation. At the conclusion of the debate, I posed a question to the debaters: Should an adult patient requiring reoperation on the RVOT be offered the option of a mechanical valve as part of informed consent? The debate concluded without a real answer to that question. At my institution, the answer to this question is yes.