Convexo-concave Heart Valves Research Articles

The Björk-Shiley Convexo-Concave Heart Valve Experience from the Perspective of the Supervisory Panel

The 20-year activities of a medical supervisory panel appointed under the terms of a settlement agreement of the Bowling v. Pfizer class action suit involving the Björk-Shiley convexo-concave (BSCC) heart valve are detailed. Of approximately 86,000 valves implanted, catastrophic failure of the valve was reported in 663 patients from 1978 to 2012. In 1994, a 7-member medical panel consisting of cardiologists, cardiovascular surgeons, epidemiologists, and a nontechnical chairman was appointed by the federal court. The panel collected clinical and manufacturing data, supported epidemiologic studies assessing risk factors for valve fracture, and developed guidelines for payment for explanting potentially defective valves in patients. Three sets of guidelines, based on comparisons of estimated risks of valve fracture versus risks of valve replacement surgery, were issued by the panel to help guide patients and their physicians in decisions about explanting valves. In addition, the panel supported research directed at identifying valves at risk for outlet strut fracture. The primary techniques evaluated included analyzing acoustic signals from the valves, imaging valves for potential cracks in the struts, and structural analyses of Björk-Shiley convexo-concave valves, but none proved applicable for large-scale surveillance of the patient population. The panel also became a patient advocate and acted as an intermediary between the manufacturer and the attorneys initiating the legal settlement. The panel's experiences may help inform future strategies for guideline development for other medical devices or procedures involving risk-benefit comparisons.

Noninvasive detection of artificial heart valve outlet strut fracture using sweep frequency eddy current testing

Thepaper proposes utilizationof eddy current inspection fordetection ofdefects intheartificialheart valve. Artificial heart valves are prosthetic replacements which are used if the function of the natural heart valve is limited. A special type of prosthetic heart valve replacements is the Bj¨ ork Shiley convexo-concave (BSCC) heart valve. The fractures of the BSCC artificial heart valve usually affect the outlet strut. If the fracture of the strut is not detected in time the patient can die of heart attack. Detection of the fracture in the outlet strut is the concern here. Experimental measurements are performed in order to evaluate the detection capability of the technique and the sensitivity of response signal to dimensional parameters of a fracture. A BSCC heart valve prototype having the electromagnetic characteristics of the Co-Cr (Hayness 25) alloy is inspected with a probe. A non-conductive defect is positioned in the outlet strut and its dimensions are varied. The probe is positioned above the centre of the crack and the frequency of exciting signal is changed in a wide range. The presented results demonstrate that the sweep frequency technique can enhance eddy current inspection of a defect in BSCC heart valve.

Prediction of Failure in Existing Heart Valve Designs

Abstract Artificial heart valves must be designed to survive greater than 109 cycles over 40 years of operation. Thus, fatigue represents one of the primary driving forces for safe operation of these devices. The inability to maintain the long term performance of critical devices in the future may lead to catastrophic failure and patient loss of life. The Bjork-Shiley convexo-concave (BSCC) heart valve provides an excellent case study in heart valve design. Approximately 86 000 valves were implanted from 1979 to 1987 and approximately 1 % of the valves experienced failure due to fatigue. Failures of this type are likely to yield a 70 % mortality rate in patients. To understand the conditions that produced failure, a detailed engineering assessment was conducted to determine valve designs, manufacturing processes, and physiologically related loading conditions that gave rise to an increased risk of failure. The material used in constructing the valve, Haynes 25, possesses good long crack threshold fatigue properties (ΔKth=4.5MPam). However, continued operation of the valves produced cracking under certain physiological circumstances. These assessments indicate that a small subset of valves may operate under conditions that are close to the boundary between continued safe operation and catastrophic failure. These findings should be considered when using materials with inherently lower threshold fatigue properties. Crack growth data show that Nitinol has a threshold stress intensity factor MPa ≈2MPam, or less than half that of Haynes 25. Thus, current heart valve designs that use Nitinol should incorporate lessons learned from analyses of the BSCC heart valve to assess the likelihood of premature valve failure due to repeated loading.

Could It Happen Again?

Most readers of “Twenty-Five–Year Experience With the Bjork-Shiley Convexoconcave Heart Valve: A Continuing Clinical Concern” in this issue of Circulation have not heard of the valve.1 Many elements of its story parallel those of cerivastatin2,3⇓ and rofecoxib,4 but with a twist: Recalling a heart valve may entail greater risks than leaving a possible “time bomb” in place. The Bjork-Shiley story raises many questions about balancing the benefits of drugs and devices with their risks to public safety. For example: See p 2850 My personal involvement began when a lawyer for Shiley, Inc, with a biostatistical degree read our account of the Braunwald-Cutter heart valve and wanted to understand why the University of Alabama at Birmingham and the Mayo Clinic decided to prophylactically remove every one.5 Subsequently, I served on scientific panels, spearheaded a multi-institutional effort to quantify the risks of prosthesis explant,6 and suggested ways to use this information for the tough decision making ahead.7 The Bjork-Shiley heart valve, developed by Shiley, Inc, in collaboration with Dr Viking Bjork of Sweden, was …

Use of flexibility tests in the manufacturing process of 60° björk-shiley convexo-concave valves and the risk of outlet strut fracture

ObjectivesOutlet strut fracture remains a concern for 30,000 patients living with a Björk-Shiley convexo-concave heart valve (Shiley, Inc, Irvine, Calif, a subsidiary of Pfizer, Inc). Previous studies (Netherlands and United Kingdom) investigating valve manufacturing aspects identified multiple performance of the hook deflection test as a risk factor for 60° valves. The present study validated this finding using new data with a greater number of valves implanted worldwide. Risks of outlet strut fracture associated with other manufacturing aspects were also investigated. MethodsA matched case-control study design was used including 416 outlet strut fracture cases and 803 controls. ResultsAnalyses similar to that of the Dutch and United Kingdom studies produced odds ratios of 3.4 (95% confidence interval [CI]: 1.1-10.3) and 2.8 (95% CI: 1.1-7.3), respectively, for multiple hook deflection tests. Load deflection test, which replaced the hook deflection test, showed a statistically significant association with outlet strut fracture: odds ratio of 5.0 (95% CI: 2.1-11.8) and 6.2 (95% CI: 2.2-18.0) for single and multiple load deflection tests, respectively. An analysis where hook deflection tests were separated from load deflection tests showed significantly elevated odds ratios with performance of any type of flexibility test, and the highest odds ratio was observed with a combined performance of load and hook deflection tests. ConclusionsMultiple hook deflection tests can now be considered for inclusion in the risk model used for guidelines on explant surgery to improve prediction of outlet strut fracture and provide patient reassurance. Load deflection tests and combined performance of hook and load deflection tests were found to be significant risk factors. No outlet strut fractures were reported for valves manufactured after March 1984 when the load deflection test was still in place. Examining manufacturing documents for these valves may identify new risk factors that could be responsible for the outlet strut fractures risk that remains unexplained to date.

The Complexity of External Acoustic Detection of Defects in Björk‐Shiley Convexoconcave Heart Valves

Abstract: Fractures in Björk‐Shiley convexoconcave (BScc) heart valves have raised questions about the feasibility of early diagnosis of technical defects by means of acoustic assessment. Three laboratory tests were conducted. To establish acoustic fingerprints, 66 valves with a defect, such as single‐leg fracture (SLF) or single‐leg separation (SLS), or without a defect were connected with a contact sensor and excited by dropping a small metal ball onto the outlet strut. In the second test, we simulated the valve sound propagation within the thorax. In the third test, intact, SLF, and SLS valves were placed in a mock heart immersed in a large water tank. We observed a resonance frequency corresponding with valve size and presence of defects. The second test showed that both the chest wall and the lungs created numerous reflections. This led to a substantial overlap of the original pulse frequencies and the frequencies measured. The third test confirmed that submersion of the chest in water can significantly reduce chest wall reflections. Reliable noninvasive assessment of BScc valve clicks for the presence of defects of the outlet strut is hampered by complex sound propagation within the thorax and variability of valve excitation. Acoustic fingerprints to diagnose mechanical defects should be integrated in valve design.

The complexity of external acoustic detection of defects in Björk-Shiley convexoconcave heart valves.

Fractures in Björk-Shiley convexoconcave (BScc) heart valves have raised questions about the feasibility of early diagnosis of technical defects by means of acoustic assessment. Three laboratory tests were conducted. To establish acoustic fingerprints, 66 valves with a defect, such as single-leg fracture (SLF) or single-leg separation (SLS), or without a defect were connected with a contact sensor and excited by dropping a small metal ball onto the outlet strut. In the second test, we simulated the valve sound propagation within the thorax. In the third test, intact, SLF, and SLS valves were placed in a mock heart immersed in a large water tank. We observed a resonance frequency corresponding with valve size and presence of defects. The second test showed that both the chest wall and the lungs created numerous reflections. This led to a substantial overlap of the original pulse frequencies and the frequencies measured. The third test confirmed that submersion of the chest in water can significantly reduce chest wall reflections. Reliable noninvasive assessment of BScc valve clicks for the presence of defects of the outlet strut is hampered by complex sound propagation within the thorax and variability of valve excitation. Acoustic fingerprints to diagnose mechanical defects should be integrated in valve design.

Detection of Björk-Shiley Convexo-Concave Heart Valve Outlet Strut Single Leg Separations: Consensus Image Acquisition and Interpretation Using Two Different Cineradiographic Imaging Technologies

Background: Conventional cineradiology has been used clinically to detect partially broken outlet struts (single leg separations, SLSs) in normally functioning Björk-Shiley convexo-concave (C/C) heart valves. The value of radiographic screening has, however, been debated in the medical literature. This study uses the same radiographic technique in sheep implanted with known-status C/C valves in combination with a newly developed geometric image magnification radiography system. This study was designed to test whether sensitivity and specificity of radiographic screening of C/C valves in detecting SLSs could be improved through the combination of readers and imaging modalities. Methods: Twenty-one sheep with mitral C/C valves were studied on both systems. Five were used for extensive scanning training. When operators were expert on both systems, 16 blinded study valves (4 intact and 12 with outlet strut SLSs) were scanned twice on both systems, first on a modified conventional and then a prototype geometric image magnification (Feinfocus^TM) cineradiographic system by two expert physicians working together. Results: Among the 32 scanned valves, the two combined expert physicians were required to evaluate 40 intact legs and 24 with an SLS. For all SLS valves, the conventional and Feinfocus systems separately detected 50 (12/24) and 54% (13/24), respectively. When the two systems were combined, the final consensus score was correct in 67% (16/24) of all SLS valves. Conclusions: Combined modality, paired expert physicians detected 67% of all SLSs. The Feinfocus system might be best reserved for those patients in whom the Siemens screening study demonstrates in minimally suspicious (grade 2) or suspicious (grade 3) appearance of a C/C valve outlet strut leg.

In Vivo Accuracy Of Two Radiographic Systems In The Detection Of Björk-Shiley Convexo-Concave Heart Valve Outlet Strut Single Leg Separations

Objective: Modified cineradiographic systems have been used clinically to detect partially broken outlet struts in normally functioning Björk-Shiley convexo-concave heart valves. Almost all such valves were explanted, presuming that full failure would likely follow. Inasmuch as the clinical setting only rarely permits examination of normally rated valves, the accuracy of radiographic detection cannot be clinically defined. This study uses the clinical radiographic technique in sheep implanted with known-status convexo-concave valves, comparing its accuracy and that of a newly developed, geometric image magnification radiography system. Methods: Twenty-one sheep with mitral convexo-concave valves were studied on both systems. Five were used for extensive training. When operators were expert with both systems, images of four intact valves and 12 valves with outlet strut single leg separations, along with a seventeenth single leg separation valve used for calibration, were integrated into 112 image sets organized into a balanced incomplete block design for evaluation by eight trained, blinded reviewers. Results: Cineradiography sensitivity was 24% versus 31% for direct image magnification. The odds ratio for detection of single leg separation by direct image magnification versus cineradiography was 2.0 (95% confidence interval, 0.76 to 5.9; p = 0.13). Cineradiography specificity was 93% versus 90% for direct image magnification. Sensitivity and specificity varied markedly by reviewer, with sensitivity ranging from 8% to 55% and specificity from 51% to 100% for the combined technologies. Conclusions: The data support the need for more intensive training for convexo-concave valve imaging and further investigation of unconventional radiographic technologies. Clinical cineradiography of convexo-concave valves may detect as little as 25% of valves having a single leg separation, underestimating the prevalence of single leg separations and thereby implying more rapid progression to full fracture than is actually the case. (J Thorac Cardiovasc Surg 1998;115:582-90)

Non-destructive assessment of 62 Dutch Björk-Shiley convexo-concave heart valves.

Non-destructive assessment of 62 Björk-Shiley convexo-concave heart valves in view of the risk of fracture and possible detection of defects by means of X-ray or acoustics. Scanning electron microscopy and stereomicroscopy of an unselected sample of valves, representing approximately 70% of the valves explanted between 1991 and 1996. Mean duration of implantation was 10.7 +/- 1.9 years. Six of the 62 valves had a fracture with disk escape. Of the remaining 56 valves, 11 (19.6%) had a single-leg fracture and seven (12.5%) showed a crack. Valves, 24 (42.8%), revealed no significant defect. After 4600 days of implantation, large valves (i.e. > or = 29 mm) showed a 6.7 time increase in the risk of crack or single-leg fracture compared with smaller valves (OR 6.7, 95% CI 1.8-24.6, P = 0.04). In a small in-vitro experiment with single-leg fracture, rapid smearing occurred, resulting in strut leg separation upon some movement. After approximately 400 x 10(6) cycles, 42.5% of the retrieved intact valves was without significant defect, while 32% had a serious prefracture defect. Time evolution from defect to fracture remains unpredictable. Also, detection of prefracture defects, including single-leg fracture, remains difficult, because a "well-detectable' fracture with dislocation is just a brief condition. However, technical knowledge can enhance the epidemiological and manufacturing information used for clinical decision making.

Acoustic assessment of the physical integrity of Björk-Shiley convexo-concave heart valves.

Several lines of evidence indicate a two-stage failure mode for the Björk-Shiley convexo-concave (C/C) heart valve, in which one of the two outlet strut legs separates from the flange before the other, potentially providing an opportunity to identify and prophylactically replace failure-prone valves. Radiographic single leg separation (SLS) detection, although successful, is subjective and skill intensive, implying a need for both an objective preliminary screen and subsequent corroboration of the radiographic findings. We developed a time-windowed, power density analysis of C/C valve closing sounds to detect the vibrational resonance that characterizes the presence of an intact outlet strut in clinically functioning, 29-mm-flange size C/C valves. Recordings from more than 800 patients enrolled in radiographic SLS detection studies were analyzed, and the assessment algorithm was evaluated through a blinded test of 32 study valves for which the true status became known consequent to an autopsy or surgical explantation. Valves were objectively scored on a 0-to- 1 scale, with 1 being assuredly intact and scores of < 0.50 indicating a probable SLS. All except five valves (incorrectly designated probable SLS) were classified correctly, for a sensitivity of 1.00 (95% confidence interval, 0.79 to 1.00) and a specificity of 0.69 (0.41 to 0.89). This level of accuracy is sufficient to serve as an effective preliminary screen, potentially allowing a threefold concentration of SLS prevalence among the C/C valves of patients undergoing radiographic assessment. The value of acoustic classification in avoiding unnecessary operations prompted by false-positive radiographs is less certain.

Systemic accident analysis of deaths due to failed Björk-Shiley heart valves

The Björk-Shiley convexo-concave artificial heart valve has a significant risk of failure which is often fatal.Elective explantation has a mortality of approximately 5%. Follow-up studies provide the basis for clinical decision making whether or not to explant the valve. So far, the contribution of technical, organizational, ethical, and professional considerations to success or failure of any risk control strategy have hardly been considered. A string of six consecutive deaths due to valve failure initiated a systemic rather than an epidemiological analysis of the problem. Systemic failure analysis not only yields sound explanations, but also warrants acceptable solutions on the basis of assembling multidisciplinary knowledge and experience.

Quantitative detection of outlet strut separations in Björk-Shiley convexo-concave mitral valves.

As of January 31, 1995, 564 outlet strut fractures (OSFs) of Björk-Shiley convexo-concave (BSCC) heart valves had been reported to the Shiley Heart Valve Research Center, of which approximately two thirds resulted in the death of the patient. Previous studies indicate that one leg of the outlet strut separates (single-leg separation, SLS) from the valve before the second leg breaks, which results in complete OSF. To identify those valves at risk of complete OSF, an in vivo radiographic imaging technique is being developed to evaluate the strut leg integrity. The goal of the present study was to develop an objective postprocessing technique to evaluate outlet strut leg integrity quantitatively in these cineradiographic images. Twenty-two sets (12 intact valves, 10 SLS valves) of cineangiographic images were obtained from individuals whose valve status was subsequently verified ex vivo. Several quantitative measures of SLS were evaluated to identify possible loss of metal or gaps in the SLS legs. Two of these measures, decrease in pixel intensity (DIPI) ratio and gap half-width, are diagnostic metrics of SLS: i.e., the maximum likelihood estimate of the area under the receiver operating characteristic curve was 0.892 (SD, 0.066) for a model based on DIPI ratio and 0.802 (SD, 0.093) for gap half-width. We have developed a postprocessing technique that can be used to objectively evaluate outlet strut integrity in cineradiographic images of BSCC heart valves. At an estimated specificity of 1.0, the estimated sensitivity of the objective review was comparable to that of a subjective expert review panel.

Prophylactic replacement of Björk-Shiley convexo-concave heart valves: an easy-to-use tool to aid decision-making in individual patients.

To develop an easy-to-use tool for decision-making on prophylactic replacement of Björk-Shiley convexo-concave heart valves. Decision analysis comparing elective replacement with observation. Referral centres for patients with artificial heart valves. Quantitative estimates were obtained from a follow up study conducted in The Netherlands, including 2303 patients with a mean follow up of 6.6 years and from recently published studies. Elective valve replacement with a new artificial heart valve. Loss of life-expectancy. A simple graph was constructed to present the loss of life-expectancy caused by strut fracture for combinations of basal life-expectancy (life-expectancy without strut fracture) and lethal fracture risk (strut fracture risk multiplied by lethality of fracture). This loss can be compared directly with the loss of life-expectancy caused by surgical mortality. This quantitative approach takes into account individual patient characteristics, such as age, gender, cardiac comorbidity, and position of the valve, but the final estimation of surgical mortality also requires clinical judgement. The calculations can be made easily by hand or with a simple computer application. This decision support tool enables the direct estimation of the gain or loss of life-expectancy that is likely with replacement of a Björk-Shiley convexo-concave heart valve. It can be used to evaluate individual patients as well as groups of patients, and allows for easy incorporation of revisions of fracture risk estimates.

Stress Corrosion Cracking in Björk-Shiley Convexo-Concave Prosthetic Heart Valves Due to Random in vivo Electrochemical Pulsing

Welded downstream struts of Björk-Shiley Convexo-Concave heart valves show failure in vivo, but not in in vitro testing. A pyrolytic carbon pivoting disk occluder closes against a Haynes 25 alloy ring, which is electrochemically machined from solid with the upstream retaining struts. The weld area is de-alloyed, with residual porosity and carbide inclusions. The valve becomes a short-circuited electrochemical cell when fully open or closed. It is an aggressive chloride electrolyte, whose high pulsed flow (2 m/s) ensures that supply of oxygen-rich cathode reactant is not mass-transport-limited. During the flight of the occluder, the cell is randomly at open circuit. A random current pulse is applied to the metal parts on circuit closure. Failure is not from simple mechanical fatigue, but from stress-corrosion-cracking and erosion of the less noble weld area caused by these pulses. All welded valves of this type may be susceptible to ultimate in vivo failure.

A risk assessment and control model for the failing Björk-Shiley convexo-concave heart valve.

For risk assessment and control of the failing Björk-Shiley convexo-concave heart valve, we present a life cycle-based complex system model and a risk intensity assessment model, allowing consistent analysis of this complex medical problem and identification of all pertinent aspects of product-related risks to patients.

A working cardiac valve phantom for radiographic assessment of prosthetic heart valves

A working valve phantom (WVP) that both exercises the valve occluder and simulates movements of the mitral annulus is described. It was designed to develop a method for radiographic detection of a single broken leg of the two-legged Björk-Shiley convexo-concave (C/C) heart valve outlet strut. The WVP consists of a pneumatically driven left ventricular assist device immersed in 22 cm of water. Left ventricular assist device annulus movements are generated by systolic turgor and diastolic relaxation of the aortic outflow graft within limits set by the holding fixture design. WVP images were comparable in attenuation, valve motion, and diagnostic sensitivity to clinical C/C valve images and were effective in assessing leaflet excursions in another valve model. Techniques developed in the WVP have proved successful in the clinical detection of C/C valves that have a single broken leg but that show normal function in all other tests. The WVP can be a useful tool for developing refined radiographic assessments of prosthetic heart valves.

Radiographic detection of strut separations in Björk-Shiley convexo-concave mitral valves.

The outlet struts of Björk-Shiley convexo-concave heart valves can occasionally fracture. By December 31, 1994, 564 complete strut fractures had been reported to the manufacturer, approximately two thirds of which were fatal. There are no reliable diagnostic methods to detect valves that may be at risk for strut fracture. The outlet strut has two legs, and one leg often appears to break before the other, potentially permitting detection of the single-leg separation while the valve is still functionally intact. We used high-resolution cineradiography and defined valve profiles to evaluate 315 patients selected on the basis of their having mitral convexo-concave valves with an estimated fracture rate of 0.46 percent or higher per year. Two examinations were scheduled six months apart, with early reimaging performed when initial ratings were indeterminate. Three patients had unsatisfactory studies, the most recent examinations in 277 patients were rated as apparently normal, 23 had findings considered minimally suspicious, and 1 had findings termed suspicious. The number of false negative results in this study group is unknown. Eleven cineradiograms were rated as showing probable or definite single-leg separations. All five "definite" ratings and five of the six "probable" ratings were confirmed by removal of the valves. One valve with a "probable" rating was intact. Two complete outlet-strut fractures occurred three and seven months after apparently normal radiographic examinations. Unsuspected new positive findings were not found at six months among 288 patients who completed the examination cycle. Cineradiographic imaging can detect some single-leg separations in mitral convexo-concave valves and may help the estimated 41,000 patients with these valves worldwide and their physicians decide about elective valve removal.

What can be done to improve the safety of heart valves?

In the Netherlands, the incidence of fractured Björk-Shiley convexo-concave heart valves led to investigations regarding the extent, impact, and management possibilities of this public health problem. Apart from an epidemiological study, we performed a safety management study. This study led us to conclude that: (1) the Björk-Shiley convexo-concave heart valve is perceived as a safety risk by patients, doctors, and health care administrators alike; (2) doctors and health care administrators rely heavily on the technical information regarding artificial heart valves that is provided by the manufacturer; (3) the professionals best qualified to assess and control the risks of heart valve replacement are cardiac surgeons. Based on these conclusions, this report provides recommendations regarding safety risk assessment and the participation of doctors in preimplantation and clinical research programmes in order to improve the safety of newly designed heart valves.

Age thresholds for prophylactic replacement of Björk-Shiley convexo-concave heart valves. A clinical and economic evaluation.

Björk-Shiley convexo-concave heart valves have an increased risk of mechanical failure. One might consider prophylactic rereplacement as a preventive measure to avert the disastrous consequences of these failures. We investigated the effect that prophylactic rereplacement has on survival of individual patients and on the medical costs. Quantitative estimates for the surgical risks of prophylactic replacement of Björk-Shiley valves, long-term survival, and the risk of outlet strut fracture were derived insofar as possible from a detailed analysis of a follow-up study conducted in The Netherlands, including 2303 patients with a mean follow-up of 6.6 years. On the basis of these estimates, we calculated life expectancy with and without prophylactic replacement. For the various valve types, age thresholds were determined below which rereplacement prolongs (discounted quality-adjusted) life expectancy. We also calculated the cost per year of life gained as a function of age. The age thresholds below which prophylactic rereplacement increases life expectancy (expressed in simple future years of life) for male patients without comorbidity, if the surgical mortality after rereplacement is equivalent to that of primary replacement, are 27, 48, 51, and 65 years for small and large 60 degrees and for small and large 70 degrees mitral valves, respectively. For aortic valves, these age thresholds lie somewhat higher: 39, 52, 56, and 76 years, respectively. Repeat analyses indicated that for women, all age thresholds lie about 1 or 2 years higher. These age thresholds decrease considerably if the surgical mortality after rereplacement is considered to be higher after prophylactic rereplacement than after primary replacement or if comorbidity is present. The costs per discounted and quality-adjusted year of life gained depend on type and position of the Björk-Shiley convexo-concave heart valve and rise steeply as the patient's age approaches the threshold for rereplacement. The results of the Dutch follow-up study allow guidance for prophylactic replacement of the Björk-Shiley convexo-concave valve on an individual basis. Rereplacement compares favorably with expectant management in some patient subgroups with both 60 degrees and 70 degrees valves. Age thresholds may serve as a first step in identifying patients in whom rereplacement might be beneficial.