Bjork-Shiley Convexo-Concave Research Articles

Nondestructive Evaluation of BSCC Artificial Heart Valves

The subject of investigation is a set of four artificial heart valves made of electrically conductive material, namely the alloy Ti-6Al-4V. Notches of defined geometry with gradually increasing depth were formed on these BSCC (Bjork-Shiley Convexo-Concave) valves. These defects are created on the so-called output strut, which serves as a support mechanism for the controlled movement of the so-called occluder disc and they have been investigated. The method which was used is ultrasonic infrared thermography, where the object was excited by the UTVIS EDEVIS ultrasonic system and the response was detected by the FLIR SC 7200 infrared camera. The postulate for the use of this method is that the excitation signal may be periodically pulsate or in any other way modulated by certain amplitude frequencies, called "lock-in frequency". Lock-in thermography is a type of active lock-in method. The results of damage detection on these relatively complicated objects are compared and discussed.

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.

Artificial Heart Valve Inspection Using Eddy Current Techniques

This paper discusses about minimally invasive techniques to detect the single leg fracture in special type of artificial heart valve called Bjork Shiley Convexo - Concave (BSCC). The fracture affects the outlet strut of these artificial heart valve and it is needed to detect it. For this purpose the electromagnetic methods based on eddy current testing were used. The coils are excited in the selected range of the frequencies for identification of the fractures in the outlet strut. The fractures occurring in BSCC heart valve and their numerical simulations are described. The results obtained with a prototype setup are presented and they demonstrate the usefulness of described techniques for detection of the outlet strut fractures in BSCC artificial heart valve.

Noninvasive evaluation of Bjork-Shiley convexo-concave prosthetic heart valves

Prosthetic heart valves of the Bjork-Shiley convexo-concave (BSCC) type have been used extensively in implants; however, there have been reports of cases where one component of the valves failed, leading to the demise of the patient. This paper presents a new method for noninvasive electromagnetic evaluation for this type of valve, using an eddy current transducer with orthogonal coils. In vitro experiments on BSCC prosthetic heart valve replicas have shown that discontinuities of outlet strut with depths equal or larger than 0.4 mm can be detected with a probability of detection (POD) of 86.4%, and in the case of discontinuities with depth equal or larger than 0.6 mm with POD of 97%. Blind tests effectuated on 32 BSCC prosthetic heart valves have shown that, using the proposed method, the tested valves have been correctly classified.

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.

An innovative technique to detect the single leg separation (SLS) in the bjork-shiley convexo-concave (BSCC) mechanical heart valves Edmond Rambod, Mostafa Fatemi, James F. Greenleaf. California Institute of Technology, Pasadena, CA, MAYO Clinic, Rochester, MN

An innovative technique to detect the single leg separation (SLS) in the bjork-shiley convexo-concave (BSCC) mechanical heart valves Edmond Rambod, Mostafa Fatemi, James F. Greenleaf. California Institute of Technology, Pasadena, CA, MAYO Clinic, Rochester, MN

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.

Getting the Bad News about Your Artificial Heart Valve

When the manufacturer of a medical device alone bears the responsibility for alerting recipients that the device may be defective, there is a certain temptation to gloss over the risk. The story of the Bjork-Shiley Convexo-Concave heart valve is a case in point. If the steering mechanism on your car is found to have a manufacturing or design defect, the National Highway Transportation Safety Administration directs the manufactuer to send a letter to all owners of the model (a registry is kept for this purpose) with instructions concerning replacement or repair. Owners are thus warned about the problem and given information about what to do about it, and manufacturers are prepared to make the necessary adjustments. This arrangement assumes that owners have a right to know about relevant defects, manufacturers have an obligation to inform and repair, and the government has the responsibility to oversee this process. While this arrangement is not perfect, it acknowledges the vulnerability of consumers and the corresponding obligations of the manufacturer and the government to protect them. What happens if a similar situation arises with your implanted artificial heart valve? Is there a similar system to warn recipients and provide information about what to do? The recent failure of hundreds of Bjork-Shiley Convexo-Concave (C/C) mechanical heart valves provides a case study on how information about the risk of failure was communicated to patients and the medical community. Unlike automobile recalls, the arrangements for dealing with defective heart valves were--until recently--indirect, ineffective, and marked by serious conflicts of interest. None of the three groups responsible for protecting patients with artificial heart valves--the Food and Drug Administration, the physicians and surgeons whose patients received the device, or the manufacturer (Shiley, Inc., of Irvine, California)--adequately responded to the discovery that the C/C valves were susceptible to strut fracture. The system placed commercial and professional interests over the rights of patients. Mechanical Heart Valves The development of mechanical heart valves is one of the success stories of contemporary medicine. Many persons with diseased heart valves become seriously disabled and soon die unless a prosthetic valve can be installed. The first mechanical heart valves were implanted in 1960, and since then their use has grown rapidly. Today about 40,000 American receive artificial heart valves each year.[1] Shiley, Inc., has been a pioneer in the development of mechanical heart valves. In 1974 they developed their radial spherical (R/S) valve, consisting of a disk attached to two wire struts that allow it to swing open and shut in response to blood flow. The struts are welded to a metal ring that is covered with a teflon sewing ring for attachment to the heart. In 1979 Shiley introduced a similar valve, the 60[degrees] Convexo-Concave (C/C), which they believed would improve blood flow through the valve. A C/C valve that opened to 70[degrees] was also manufactured, but it was not approved for sale in the United States. Blood clots (thromboses) caused by the presence of artificial implants are a serious problem and are responsible for the greatest percentage of complications that occur. Because the movement of blood is obstructed by the valve, there are areas of relatively stagnant flow where clots can form. They may form on the valve, preventing it from fully opening or closing, or they may break free and cause strokes, heart attacks, and other serious complications. Drugs to thin the patient's blood and reduce clotting are an essential part of the treatment after implantation, but there is a limit to their ability to reduce the incidence of thromboembolism--blood clots that break free and lodge in an artery, cutting off blood flow to tissues or organs. Shiley's 60[degrees] C/C valve, which appeared to allow better blood flow and promised a lower incidence of thromboembolism, was regarded as a significant improvement in heart valve technology. …

Canine model for long-term evaluation of prosthetic mitral valves

The evaluation of mechanical prosthetic heart valves would be aided by a more satisfactory animal model. For acute assessment, a variety of animals have been used, but for chronic studies, only larger animals (pigs, calves, baboons) have been employed, creating an expensive model with laboratory management difficulties. Previously, the use of dogs for chronic evaluation has been unsatisfactory because of the frequent occurrence of early sepsis and valve-related thrombotic deaths. We have modified our existing acute dog protocol to produce a successful chronic model. Our model employs perioperative systemic antibiotics, short cardiopulmonary bypass period (range 35–60 min), a minimum of perioperative intravenous lines, postoperative anticoagulation therapy, and strict postoperative antiseptic technique for blood sampling. To evaluate this model, 11 consecutive mongrel dogs underwent mitral valve replacement with either a standard Dacron sewing skirt or a newly devised carbon-coated Teflon sewing skirt No. 23 mm Bjork-Shiley Convexo Concave (CC) prosthetic valve. Nine animals (82%) survived and were evaluated after a predetermined observation interval of either 3 or 6 months for valve function, pannus formation, and possible carbon particle migration. At sacrifice, all animals had good hemodynamics and valve function, minimal pannus formation and no carbon washout. Consequently, this model provides a relatively inexpensive, reproducible method of chronic in vivo evaluation of prosthetic valve modifications.