Outlet strut fracture of Björk-Shiley convexo-concave valves: can valve-manufacturing characteristics explain the risk?

Long-Term Stability and Biocompatibility of Pericardial Bioprosthetic Heart Valves

The use of bioprostheses for heart valve therapy has gradually evolved over several decades and both surgical and transcatheter devices are now highly successful. The rapid expansion of the transcatheter concept has clearly placed a significant onus on the need for improved production methods, particularly the pre-treatment of bovine pericardium. Two of the difficulties associated with the biocompatibility of bioprosthetic valves are the possibilities of immune responses and calcification, which have led to either catastrophic failure or slow dystrophic changes. These have been addressed by evolutionary trends in cross-linking and decellularization techniques and, over the last two decades, the improvements have resulted in somewhat greater durability. However, as the need to consider the use of bioprosthetic valves in younger patients has become an important clinical and sociological issue, the requirement for even greater longevity and safety is now paramount. This is especially true with respect to potential therapies for young people who are afflicted by rheumatic heart disease, mostly in low- to middle-income countries, for whom no clinically acceptable and cost-effective treatments currently exist. To extend longevity to this new level, it has been necessary to evaluate the mechanisms of pericardium biocompatibility, with special emphasis on the interplay between cross-linking, decellularization and anti-immunogenicity processes. These mechanisms are reviewed in this paper. On the basis of a better understanding of these mechanisms, a few alternative treatment protocols have been developed in the last few years. The most promising protocol here is based on a carefully designed combination of phases of tissue-protective decellularization with a finely-titrated cross-linking sequence. Such refined protocols offer considerable potential in the progress toward superior longevity of pericardial heart valves and introduce a scientific dimension beyond the largely disappointing 'anti-calcification' treatments of past decades.

Acute aortic regurgitation secondary to disk embolization of a Björk-Shiley prosthetic aortic valve

Having passed the 30th anniversary of the first implantation of a Björk-Shiley convexo-concave tilting mechanical valve, recognition of the life-threatening complication of strut fracture is not widespread. The authors report the case of a 48-year-old man with acute-onset chest pain and dyspnea found to have strut fracture and disk embolization of a 26-year-old Björk-Shiley prosthetic aortic valve. The value of echocardiography in the diagnosis of this condition is discussed.

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.

Detecting broken struts of a Björk-Shiley heart valve using ultrasound: a feasibility study

The Björk-Shiley (BScc) mechanical heart valve has extensively been used in surgery from 1979 to 1986. There is, compared with equivalent valve types, increased occurrence of unexpected mechanical failure of the outlet strut of the valve, with a high incidence of mortality, when it occurs. Many approaches have been attempted to noninvasively determine BScc valve integrity. None of the approaches resulted in adequate assessment, mostly due to a lack of either sensitivity or specificity demonstrated in in vitro and/or in vivo studies. In our study we analyze leg movement of the BScc valves outlet strut during the cardiac cycle with ultrasound. For a broken strut, the movement of both legs will be significantly different, whereas the difference will be negligible for an intact strut. BScc valves were mounted in the mitral position in an in vitro pulse duplicator system. A focused single-element transducer was used to direct ultrasound on a leg of the outlet strut. Correlation-based time delay estimation was used to estimate differences in time of flight of the outlet strut echoes to determine outlet strut leg movement. The movement of an intact valve and a valve with a single-leg fracture with both ends grating against each other (SLF), the most difficult fracture to diagnose, has been studied. The results showed no significant difference in movement between both legs of the outlet strut of the intact BScc valve (amplitude of movement 9.2 microm +/- 0.1 microm). Whereas for the defective valve, the amplitude of movement of the broken leg of the SLF valve was 12 microm +/- 1.6 microm vs. 8.6 microm +/- 0.1 microm for the intact leg. In conclusion, the proposed method has shown to be feasible in vitro and has potentials for in vivo detection of BScc valve outlet strut fracture.

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.

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

OBJECTIVES

Outlet 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 degrees 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.

METHODS

A matched case-control study design was used including 416 outlet strut fracture cases and 803 controls.

RESULTS

Analyses 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.

CONCLUSIONS

Multiple 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.

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.