Strut fracture with Björk-Shiley 70 degrees convexo-concave valve. An international multi-institutional follow-up study

Approach to the analysis of cardiac valve prostheses as surgical pathology or autopsy specimens

Pathologists are likely to encounter substitute heart valves with increasing frequency. Informed evaluation of such valves provides valuable information that contributes to both patient care and our understanding of the pathobiology of host interactions with mechanical devices. This article summarizes the most important considerations underlying such analyses-including valve identification, common morphologic features and modes of failure, technical details of evaluation, and potential pitfalls.

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.

Redo surgery risk in patients with cardiac prosthetic valve dysfunction

INTRODUCTION

The aim of the study was to analyse the risk factors of early and late mortality in patients undergoing the first reoperation for prosthetic valve dysfunction.

MATERIAL AND METHODS

A retrospective observational study was performed in 194 consecutive patients (M = 75, F = 119; mean age 53.2 ±11 years) with a mechanical prosthetic valve (n = 103 cases; 53%) or bioprosthesis (91; 47%). Univariate and multivariate Cox statistical analysis was performed to determine risk factors of early and late mortality.

RESULTS

The overall early mortality was 18.6%: 31.4% in patients with symptoms of NYHA functional class III-IV and 3.4% in pts in NYHA class I-II. Multivariate analysis identified symptoms of NYHA class III-IV and endocarditis as independent predictors of early mortality. The overall late mortality (> 30 days) was 8.2% (0.62% year/patient). Multivariate analysis identified age at the time of reoperation as a strong independent predictor of late mortality.

CONCLUSIONS

Reoperation in patients with prosthetic valves, performed urgently, especially in patients with symptoms of NYHA class III-IV or in the case of endocarditis, bears a high mortality rate. Risk of planned reoperation, mostly in patients with symptoms of NYHA class I-II, does not differ from the risk of the first operation.

Intermittent acute aortic regurgitation of a mechanical bileaflet aortic valve prosthesis: diagnosis and clinical implications

Intermittent aortic regurgitation (AR) is an unusual complication after a mechanical prosthetic replacement. We describe a rare case of intermittent dysfunction of a bileaflet mechanical aortic prosthetic valve in a 41-year-old man with a 21 mm Tri-technologies prosthetic valve implanted 4 years before. Transthoracic echocardiography (TTE) before discharge was normal and prosthesis-patient mismatch was ruled out. He was admitted to our hospital because of mild dyspnoea at effort. TTE revealed acute and severe intermittent AR. The patient underwent surgery, during which abnormal proliferation of subvalvular pannus overgrowth on the inflow aspect of the prosthesis was found impeding the normal closure of one of the discs of the prosthesis. The pannus formation was resected, the Tri-technologies prosthetic valve was prophylactic explanted and a 23 mm St Jude Medical bileaflet mechanical prosthesis valve was implanted. We describe the role of TTE and the limitation of the cinefluoroscopy in the diagnosis of Tri-technologies prosthetic dysfunction.

How to deal with recipients of valves prone to structural failure in the 2000s: Padua experience with the TRI Technologies valve

BACKGROUND

TRI Technologies (TT) valves evidenced a propensity to structural failure, consisting in fracture of the pivoting system, leading to leaflet escape. At our institution, between 2000 and 2002, 36 TT valves were implanted in 34 patients. Here we report the final results of the Tritech survey program.

METHODS

In February 2002, the first valve-related death occurred. After the event, patients were enrolled in the TT valve survey program and strictly followed up. The option of a reintervention was advised to each patient and weighed against the redo operative risk. The prophylactic TT valve replacement program took place in two time frames, dependent on each patient's personal choice: between September 2002 and October 2003 (first phase), and between September 2004 and October 2004 (second phase). Overall, 22 (10 women, 12 men) patients underwent reoperation. Mean time interval between TT valve implantation and replacement was 23 +/- 11 months. Patients' mean age was 59 +/- 11 years (median age, 64 years).

RESULTS

All recipients adhering to the program successfully underwent reoperation. Operative mortality was 0%.

CONCLUSIONS

We believe that the timing of the second surgery was fundamental for the favorable outcome of each patient and the absence of operative mortality. We are convinced that the tailored programming of the reintervention, together with the strong motivation of each patient, contributed in minimizing the risks related to surgery. The circumscribed cohort of patients involved was compatible with a tailored therapeutic plan. We strongly advise prophylactic reoperation of recipients of TT valves.

Twenty-Five–Year Experience With the Björk-Shiley Convexoconcave Heart Valve

BACKGROUND

The first Björk-Shiley convexoconcave (BSCC) prosthetic heart valves were implanted in 1978. The 25th anniversary provided a stimulus to summarize the research data relevant to BSCC valve fracture, patient management, and current clinical options.

METHODS AND RESULTS

Published and unpublished data on the risks of BSCC valve fracture and replacement were compiled, and strategies for identifying candidates for prophylactic valve reoperation were summarized. By December 2003, outlet strut fractures (OSFs), often with fatal outcomes, had been reported in 633 BSCC valves (0.7% of 86,000 valves implanted). Fractures still continue to occur, but average rates of OSFs in 60 degrees valves are now <0.1% per year. OSF risk varies markedly by valve characteristics, especially valve angle and size, with weaker effects associated with other manufacturing variables. OSF risks are mildly lower among women than men but decline sharply with advancing age. The risks of valve replacement typically greatly exceed those of OSF. By comparing individualized estimated risks of OSF versus valve replacement, guidelines have been developed to identify the small percentage of BSCC patients (mostly younger men) who would be expected to have a gain in life expectancy should reoperative surgery be performed.

CONCLUSIONS

Twenty-five years after the initial BSCC valve implants, fractures continue to occur. Continued monitoring of BSCC patients is needed to track and quantify risks and enable periodic updating of guidelines for patients and their physicians.

Analysis of prosthetic cardiac devices: a guide for the practising pathologist

Pathologists all over the world increasingly encounter prosthetic cardiac devices. A good evaluation of these devices is a valuable source of information, which can contribute to patient care and the appreciation and understanding of the pathobiology involved in the changes occurring between the host and the implanted prosthetic device. This article summarises the considerations underlying the analysis of prosthetic devices (particularly prosthetic heart valves), including the identification of the devices, the major morphological features of the devices, their modes of failure, and some technical details about evaluation and pitfalls.

Decision Guidelines for Prophylactic Replacement of Björk-Shiley Convexo-Concave Heart Valves

Background— Because of risk of outlet strut fracture, prophylactic replacement should be considered for Björk-Shiley convexo-concave (BScc) valve recipients. We assessed the effects of epidemiological and decision-analytic guidelines on actual BScc valve replacement.

Methods and Results— We performed a retrospective cohort study including all 2263 Dutch BScc patients with a mean follow-up of 11.3 years (range, 0 to 23 years). Outcomes were outlet strut fracture, mortality, and BScc valve replacement. For the surviving patients in 1992 (n=1330), we calculated the expected differences in life expectancy (LE) with and without BScc valve replacement according to decision guidelines developed in 1992. Differences in LE were compared with actual replacements. During 8 years of follow-up, there were 494 deaths (40%), and 11 patients had suffered outlet strut fracture. Of 1330 patients, 96 (10%) had undergone BScc valve replacement, particularly in years after introduction of initial and updated guidelines. One hundred seventeen patients (9%) had an estimated gain in LE after BScc valve replacement. These patients were more likely to undergo replacement than patients with an estimated loss of LE (hazard ratio, 6.6; 95% CI, 4.4 to 10; P <0.0001). A loss in LE after reoperation was predicted for 8 of 11 patients who experienced outlet strut fracture after guidelines were available.

Conclusions— Valve replacement for BScc heart valve patients was largely in concordance with guidelines in the Netherlands. Individualized guidelines that are based on high-quality epidemiological data and are updated and implemented rigorously can influence clinical practice in complex decision problems.

Leaflet escape in a new bileaflet mechanical valve: TRI technologies

BACKGROUND

Leaflet escape is a mode of structural valve failure for mechanical prostheses. This complication previously has been reported for both monoleaflet and bileaflet valve models. We report 2 leaflet escape occurrences observed in 2 patients who underwent valve replacement with a TRI Technologies valve prosthesis.

METHODS AND RESULTS

At the University of Padua, between November 2000 and February 2002, 36 TRI Technologies valve prostheses (26 aortic and 10 mitral) were implanted in 34 patients (12 women and 22 men) with a mean age of 59.9+/-10.3 years (range, 30 to 75 years). There were 5 deaths: 3 in hospital, 1 early after discharge, and 1 late. Two patients experienced a catastrophic prosthetic leaflet escape; the first patient was a 52-year-old man who died 10 days after aortic valve and ascending aorta replacement, and the second was a 58-year-old man who underwent a successful emergency reoperation 20 months after mitral valve replacement. Examination of the explanted prostheses showed in both cases a leaflet escape caused by a leaflet's pivoting system fracture. Prophylactic replacement was then successfully accomplished so far in 12 patients, without evidence of structural valve failure in any of them. Among other significant postoperative complications, we observed 3 major thromboembolisms, 1 hemorrhage, and 1 paravalvular leak.

CONCLUSIONS

These catastrophes prompted us to interrupt the implantation program, and they cast a shadow on the durability of the TRI Technologies valve prosthesis because of its high risk of structural failure.

Importance of emergency identification schemes

BACKGROUND

Millions of people worldwide may have a hidden medical condition that could endanger their life in an emergency. These conditions may include cardiac conditions, severe allergies, or diabetes. Emergency identification schemes such as Medic Alert produce emblems that alert health care professionals to potential problems and can ensure appropriate and prompt treatment. This paper uses mechanical failure of the Björk-Shiley convexo-concave (BSCC) heart valve as an example of a hidden medical condition. These patients have been encouraged to carry information to alert staff in an emergency that they have a BSCC patient in their care and to be alert to the signs and symptoms of acute valve malfunction.

OBJECTIVE

To establish awareness and credibility of emergency identification schemes among emergency personnel and to assess if information on specific medical conditions would influence ambulance personnel regarding destination hospitals.

METHODS

Questionnaires were sent to senior staff (n=380) of accident and emergency (A&E) departments and operational directors of ambulance headquarters (n=39) throughout the United Kingdom. Hospitals were divided into regional divisions to assess differences in responses across regions.

RESULTS

The majority of respondents (99%) had heard of emergency identification schemes and felt that it was important for patients with special conditions to carry some form of identification. Nearly all ambulance respondents (97%) indicated it was routine to search for body worn emblems in contrast with only 71% of A & E staff. However, more than half of ambulance respondents (53.9%) stated information on emblems/cards would not influence their choice of destination hospital.

CONCLUSIONS

The importance of how information on pre-existing medical conditions can influence care, is highlighted by the BSCC valve issue, where immediate diagnosis is essential for patient survival. It is vital that all staff routinely search patients for this information and if necessary act upon the information provided.

Outlet strut fracture of Björk-Shiley convexo concave heart valves: the UK cohort study

OBJECTIVE

To investigate the risk of outlet strut fracture (OSF) in Björk-Shiley convexo concave (BSCC) valves in relation to patients' clinical and valve characteristics.

DESIGN

A cohort of 2977 patients with 3325 valves with a follow up of 18 years.

SETTING

38 cardiac implantation centres in the UK.

RESULTS

56 OSF events were reported with 43 occurring in mitral and 13 in aortic valves. The overall OSF rate was 0.17%/year. No dominant clinical factor of risk was found, but multiple regression analysis identified age, body surface area, valve size, shop order fracture rate, and manufacturing period as risk factors for OSF. A 4% (95% confidence interval (CI) 2% to 6%) decrease in the risk of OSF was observed for each advancing year of age and a fivefold (95% CI 2 to 13) increase in risk for a 0.5 m(2) increase in body surface area. The association between the risk of OSF and valve size was not constant over time. Excess risks among 31 mm and 33 mm sizes (mainly mitral valves) decreased over time while that for 23 mm (almost all aortic valves) increased. The risk of OSF increased by 40% (95% CI 20% to 50%) for a unit increase in the fracture rate of other valves in the same batch. For valves manufactured during 1981 to 1984 the risk of OSF was 4 (95% CI 2 to 12) times greater than for valves manufactured before 1981.

CONCLUSIONS

The OSF rates for 60 degrees BSCC valves observed in the UK are the highest among all monitored populations. The changing patterns of mitral and aortic valve OSF rates over time observed in this study have not been identified previously and highlight the need for continued monitoring of patients with the BSCC valve.

Outlet strut fracture of Björk-Shiley convexo concave heart valves: the UK cohort study

OBJECTIVE

To investigate the risk of outlet strut fracture (OSF) in Björk-Shiley convexo concave (BSCC) valves in relation to patients' clinical and valve characteristics.

DESIGN

A cohort of 2977 patients with 3325 valves with a follow up of 18 years.

SETTING

38 cardiac implantation centres in the UK.

RESULTS

56 OSF events were reported with 43 occurring in mitral and 13 in aortic valves. The overall OSF rate was 0.17%/year. No dominant clinical factor of risk was found, but multiple regression analysis identified age, body surface area, valve size, shop order fracture rate, and manufacturing period as risk factors for OSF. A 4% (95% confidence interval (CI) 2% to 6%) decrease in the risk of OSF was observed for each advancing year of age and a fivefold (95% CI 2 to 13) increase in risk for a 0.5 m2 increase in body surface area. The association between the risk of OSF and valve size was not constant over time. Excess risks among 31 mm and 33 mm sizes (mainly mitral valves) decreased over time while that for 23 mm (almost all aortic valves) increased. The risk of OSF increased by 40% (95% CI 20% to 50%) for a unit increase in the fracture rate of other valves in the same batch. For valves manufactured during 1981 to 1984 the risk of OSF was 4 (95% CI 2 to 12) times greater than for valves manufactured before 1981.

CONCLUSIONS

The OSF rates for 60° BSCC valves observed in the UK are the highest among all monitored populations. The changing patterns of mitral and aortic valve OSF rates over time observed in this study have not been identified previously and highlight the need for continued monitoring of patients with the BSCC valve.

Disk embolization of a Björk-Shiley convexo-concave mitral valve: a cause of sudden cardiovascular collapse and mesenteric ischemia

Strut fracture and disk embolization of a Björk-Shiley convexo-concave valve is uncommon, but it should always be considered as a cause of sudden cardiovascular collapse in patients with such valves. Recognition of this clinical scenario is essential, given the importance of early diagnosis and the prevalence of these valves worldwide. We present a fatal case of disk embolization of a mitral prosthesis presenting with cardiogenic shock and mesenteric ischemia.

Long-term survival after valve replacement with Björk-Shiley CC valves. Björk-Shiley Study Group

Information on the life expectancy of Bjork-Shiley convexo-concave (BScc) valve recipients is necessary when considering prophylactic replacement. However, little is known about the late results after valve replacement with BScc valves. We describe long-term survival and its determinants of the Dutch BScc cohort and compare mortality figures with those of the general population and those used in guidelines for prophylactic replacement. Follow-up was obtained on all Dutch BScc valve recipients (n = 2,264) (end of study 1996). Survival over a 15-year period and its determinants were described using the Kaplan-Meier product-limit method and Cox regression, respectively. Standardized mortality ratios (SMRs) were used to compare mortality rates of BScc valve recipients who survived at least 30 days after surgery with the Dutch population rates. Survival at 15 years for aortic, mitral, and double valve recipients was 55.0% (95% confidence interval [CI] 51.9 to 58.1), 40.8% (95% CI 37.1 to 44.4), and 38.6% (95% CI 33.2 to 43.9), respectively. The determinants of survival were patient, history, and procedure related. The SMR for all BScc valve recipients was 4.2 (95% CI 3.4 to 5.2) in the first year of follow-up, after which it decreased to 2.0 (95% CI 1.8 to 2.3) and remained constant until the 14th year. SMRs depended on time since implantation, age at the time of implantation, and position of the valve replaced. Most of life expectancy estimates in prophylactic replacement guidelines of BScc valves underrate the true survival estimates. Age, valve position, and time- specific risks of death after valvular surgery should be accounted for. Different excess mortality rates should be applied for patients from different age groups: the older the patient the lower the excess.

Decision analyses for prophylactic replacement of the Björk-Shiley convexo-concave heart valve: an evaluation of assumptions and estimates

Björk-Shiley convexo-concave (BScc) mechanical heart valves have a risk of outlet strut fracture. Decision-analytic models may support decision making regarding prophylactic replacement to avert the disastrous consequences of fracture. Assumptions and estimates from previous analyses were evaluated to develop an accurate new decision model, incorporating updated follow-up experience from 2,263 patients with BScc valves implanted between 1979 and 1985 in The Netherlands. The authors focus on estimation of fracture risks (50 events) and survival (883 deaths, excluding fractures). In previous analyses, fracture risk was estimated with widely varying combinations of patient, valve, and production characteristics. Two analyses assumed a constant fracture hazard during follow-up, while data from the present study suggest that risk decreases with increasing age during follow-up. An additive excess-risk model was applied in two analyses to estimate survival. The assumption of a constant additive excess risk was not supported by the Dutch data, which suggest that the life expectancies of patients currently alive with BScc valves may be shorter than previously believed. Based on the revised decision model, over 90% of the currently alive Dutch BScc valve patients do not benefit from replacement, since the fracture risk causes only a minor reduction of remaining life expectancy. The variation in essential assumptions of previous decision analyses directly affected the indication for prophylactic replacement. This study shows how detailed statistical analyses may guide modeling choices in a decision analysis.

Which manufacturing characteristics are predictors of outlet strut fracture in large sixty-degree Björk-Shiley convexo-concave mitral valves? The Björk-Shiley Study Group

BACKGROUND

Identification of predictors of outlet strut fracture is important for recipients of large (>/=29 mm) 60-degree Björk-Shiley convexo-concave mitral valves when it comes to decision making on prophylactic explantation. An association between the manufacturing process of Björk-Shiley convexo-concave valves and the risk of fracture has been suggested.

OBJECTIVE

The aim of this study was to determine which items from the manufacturing records, in addition to known risk factors, were predictive of fracture of large 60-degree Björk-Shiley convexo-concave mitral valves.

METHODS

All Dutch recipients (n = 2264) of Björk-Shiley convexo-concave valves were followed up until fracture, death, reoperation, or end of the study (July 1, 1996). Information was abstracted from the manufacturing records of large 60-degree Björk-Shiley convexo- concave mitral valves (n = 655) in Dutch recipients and included items that described the manufacturing process and items for which an association with strut fracture had been suggested. Manufacturing records were available for 637 valves (97%), including 25 fractured valves.

RESULTS

Multivariate analysis identified age at implantation (hazard ratio 0.95, 95% confidence interval 0.93-0.97), lot size (<175 valves versus >/=175 valves; hazard ratio 6.6, 95% confidence interval 2.2-20.1), number of hook deflection tests performed (0 or 1 versus >/=2; hazard ratio 4.7, 95% confidence interval 1.4-16.2), number of disks that were used (1 versus >/=2; hazard ratio 5.9, 95% confidence interval 1.9-18.5), and lot fracture percentage (hazard ratio 1.6, 95% confidence interval 1.4-1. 8) as independent predictors of fracture. Although the added predictive value of a model with these 5 variables was sizable compared with a model containing age only, it was only slightly better than a model with age, lot size, and lot fracture percentage.

CONCLUSION

If the serial number of a large 60-degree Björk-Shiley convexo-concave mitral valve is known, manufacturing information can add significantly to the prediction of fracture. Information on lot size and lot fracture percentage should be made available to clinicians for risk assessment of prophylactic explantation.

Likelihood of underreporting of outlet strut fracture from examination of the Dutch Björk-Shiley CC cohort

The Dutch Björk-Shiley convexo-concave (BScc) cohort serves as a reference population on the risk of outlet strut fracture and is being used to formulate guidelines for prophylactic replacement. Fractures, however, may be undetected at death. The aim of this study was to quantify the degree of underestimation of strut fracture in the Dutch BScc cohort. Multivariate Cox regression analysis was used to assess the relative and absolute risk of death from different causes within 14 years. The unexplained "excess" mortality among 70 degrees BScc valve recipients was attributed to unreported fatal strut fractures and used to estimate its extent in this group, which then was extrapolated to the 60 degrees BScc valve recipients. For 70 degrees BScc valve recipients, the adjusted hazard ratio for death from all causes except strut fracture was 1.2 (95% confidence interval [CI] 1.0 to 1.5). The 14-year absolute risks for 70 degrees and 60 degrees BScc valve recipients were 44% and 37%, respectively. Among 70 degrees and 60 degrees BScc valve recipients, underreporting of fracture was estimated to be 25% (95% CI 0 to 49) and 26% (95% CI 0 to 52), respectively. Estimates based on sudden death and fatal congestive heart failure yielded essentially the same results. Thus, underreporting of fatal strut fracture in the Dutch BScc cohort is estimated to be approximately 25%. Hence, the risk and lethality of fracture of BScc valves are underestimated and indications for prophylactic replacement should be adjusted accordingly. For example, the advantage of valve replacement in a 40-year-old patient with a 29-mm 60 micro BScc mitral valve would almost double to 0.82 years.

Prophylactic replacement of Björk-Shiley convexo-concave valves at risk of strut fracture. Björk-Shiley Study Group

OBJECTIVE

Prophylactic replacement of Björk-Shiley convexo-concave valves (Shiley, Inc., Irvine, Calif.) has been advised for selected groups of patients. If prophylactic replacement is considered, risks of postoperative morbidity and mortality have to be weighed against benefits of replacement. Here we report the results of prophylactic replacement of Björk-Shiley convexo-concave valves at risk of strut fracture in The Netherlands.

METHODS

We reviewed medical records of 36 patients undergoing prophylactic replacement of their Björk-Shiley convexo-concave valves before August 1995. Replacement was judged to be prophylactic if the risk of strut fracture outweighed that of death from reoperation, or the patient wished to have the valve replaced although it was not recommended. The procedure was also considered to be prophylactic if a concomitant pathologic condition, not likely to require cardiac surgery in the near future, was present or if preoperative examination revealed an unexpected cardiac pathologic condition.

RESULTS

Twenty-two 70-degree and 16 60-degree Björk-Shiley convexo-concave valves and one spherical valve were replaced (25 aortic and 14 mitral, including three double-valve replacements). Early mortality was 2.8% (1/36) (exact 95% confidence interval [CI] 0.1 to 14.5). Mean follow-up was 33 months. One- and 3-year survivals were 94% (95% CI 79% to 99%) and 91% (95% CI 74% to 97%), respectively. All three deaths were sudden.

CONCLUSIONS

If special care is taken in selecting patients, the risk of prophylactic replacement is comparable to that of primary valve replacement. More data are needed to assess whether the risk of sudden death is possibly increased.

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.

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

OBJECTIVE

To develop an easy-to-use tool for decision-making on prophylactic replacement of Björk-Shiley convexo-concave heart valves.

DESIGN

Decision analysis comparing elective replacement with observation.

SETTING

Referral centres for patients with artificial heart valves.

PATIENTS

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.

INTERVENTION

Elective valve replacement with a new artificial heart valve.

MAIN OUTCOME MEASURE

Loss of life-expectancy.

RESULTS

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.

CONCLUSIONS

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.

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

RATIONALE AND OBJECTIVES

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Reoperation on prosthetic heart values. Patient-specific estimates of in-hospital events

Reoperation on prosthetic heart valves is increasingly under consideration for both clinical and prophylactic indications. To determine the correlates of hospital events, including in-hospital mortality, new persisting neurologic deficit, and length of postoperative stay, a three-institution study of 2246 consecutive prosthetic valve reoperations performed on 1984 patients between 1963 and 1992 was undertaken. The combined experience ranged from high-risk patients coming moribund to the operating room to an important number of well individuals undergoing prophylactic reoperations on potentially failing valves. The risk-unadjusted hospital mortality was 10.8%, neurologic deficit at hospital discharge 1.1%, and length of stay 10 days (median). Multivariably determined correlates of outcome included age at reoperation, degree, severity, and acuity of impairment of cardiac function, extensiveness of valvular heart disease, coexisting morbid conditions, number of previous heart operations, and concomitant procedures. The risk-adjusted hospital mortality for the first elective reoperation in a good-risk patient was 1.3% (90% confidence limits 0.3% to 4.4%), neurologic deficit 0.3% (90% confidence limits 0.02% to 1.8%), and length of postoperative stay 7 days (90% confidence limits 4 to 13), emphasizing the wide variance in outcome events. Equations were developed to permit wide application of the results of the study for quantitatively estimating the risk of outcome events based on individual preoperative patient characteristics. These estimates should be useful for informed patient consent, considerations of prophylactic valve replacement, and cost and resource use.

Single-leg strut fractures in explanted Björk-Shiley valves

A retrospective follow-up study in the Netherlands on the risk of fracture of Björk-Shiley convexo-concave valves concluded that prophylactic replacement is advisable for certain groups of patients. We have examined valves explanted from twenty-two patients because they met epidemiological criteria for reoperation, with or without the presence of moderate cardiac impairment, or because there were other cardiac complaints not related to the valve. No information was available before explanation to suggest a valve defect. All patients survived their operations. Of the twenty-four valves, seven (29% [95% CI 13-52]) had fracture of one of the legs of the outlet strut (single-leg strut fracture [SLF]). Two other valves had features that suggested fatigue defects. As in the previous study, 70 degrees valves had the highest risk of SLF (five of sixteen, two aortic and three mitral). However, two of eight 60 degrees valves (both aortic) also had SLF. Current hazard calculations and explanation recommendations may need to be revised. Since several of the defective valves were welded by the same person, knowledge of manufacturing details may help in estimation of fracture risk for an individual patient.

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

BACKGROUND

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.

METHODS AND RESULTS

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.

CONCLUSIONS

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.

Should patients with Björk-Shiley valves undergo prophylactic replacement?

About 85,000 patients have undergone replacement of diseased heart valves with prosthetic Björk-Shiley convexo-concave (CC) valves. These valves are prone to fracture of the outlet strut, which leads to acute valve failure that is usually fatal. Should patients with these valves undergo prophylactic replacement to avoid fracture? The incidence of strut fracture varies between 0% and 1.5% per year, depending on valve opening angle (60 degrees or 70 degrees), diameter (less than 29 mm or greater than or equal to 29 mm), and location (aortic or mitral). Other factors include the patient's life expectancy and the expected morbidity and mortality associated with reoperation. We have used decision analysis to identify the patients most likely to benefit from prophylactic reoperation. The incidence of outlet strut fracture was estimated from the data of three large studies on CC valves, and stratified by opening angle, diameter, and location. A Markov decision analysis model was used to estimate life expectancy for patients undergoing prophylactic valve replacement and for those not undergoing reoperation. Prophylactic valve replacement does not benefit patients with CC valves that have low strut fracture risks (60 degrees aortic valves and less than 29 mm, 60 degrees mitral valves). For most patients with CC valves that have high strut fracture risks (greater than or equal to 29 mm, 70 degrees CC), prophylactic valve replacement increases life expectancy. However, elderly patients with such valves benefit from prophylactic reoperation only if the risk of operative mortality is low. Patient age and operative risk are most important in recommendations for patients with CC valves that have intermediate strut fracture risks (less than 29 mm, 70 degrees valves and greater than or equal to 29 mm, 60 degrees mitral valves). For all patients and their doctors facing the difficult decision on whether to replace CC valves, individual estimates of operative mortality risk that take account of both patient-specific and institution-specific factors are essential.