A bovine model for detecting high intensity transient signals originating from mechanical heart valves.

In patients with mechanical heart valves (MHVs), transcranial Doppler methods commonly detect high intensity transient signals (HITS) representing microemboli. These microemboli, which are presumably gaseous, may cause stroke and cognitive deterioration. A bovine model was therefore developed for studying the relationship between mitral MHV induced HITS and potential etiogenic factors.

Strut fracture mechanisms of the Björk-Shiley convexo-concave heart valve.

Investigations of convexo-concave (C/C) valve outlet strut fractures (OSFs) were initially confounded by knowledge that the strut was subject to bending forces in arresting the opening disc. Pulse duplicator studies subsequently showed that closing loads were all born by the inlet strut, along with an understandable focus on the nature of the welds, where most fractures occurred. As observations of explanted valves accumulated, certain features pointed to unusual closing loads that might be contributory factors, but these hypothetical forces could not be verified.

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.

Time-frequency analysis of the first heart sound: Part 3: Application to dogs with varying cardiac contractility and to patients with mitral mechanical prosthetic heart valves.

The cone-kernel distribution (CKD) is first applied to the analysis of the intracardiac and the thoracic first heart sound (S1) of dogs in various cardiac contractile states, and secondly to the S1 of patients with mitral mechanical prosthetic heart valves. The CKD of native S1 in dogs shows that the dominant components of S1 are generally concentrated in a band at around 50 Hz with a horizontal flat or a semi-lunar shape, independently of the myocardial contractile state. There is no significant systematic rising frequency component.

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

Background: 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.

Methods And Results: 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.

Evaluation of disc retention of Björk-Shiley Delrin heart valves.

Background And Aims Of The Study: Impact wear grooves have been observed in the occluder discs of clinically explanted Björk-Shiley Delrin (BSD) heart valves due to repetitive closing impacts against the inlet strut. We examined whether this impact wear could increase the disc-to-strut gap, which could in turn affect the retention of occluder disc.

Materials And Methods: Three BSD heart valves with deep wear grooves were tested in a left ventricular assist device set-up simulating dynamic conditions that would facilitate the dislodgement.

A comparison of wear patterns in vivo and in vitro for Björk-Shiley Delrin heart valve discs.

Materials And Methods: Wear patterns for 33 explanted Björk-Shiley Delrin heart valve discs with known implant durations were compared and contrasted with the wear patterns for 17 discs from accelerated wear tested (AWT) valves. Previous test reports and the current study provided data for the maximum depth of wear grooves for a total of 56 explanted BSD valve discs with implant durations up to 22.4 years.

Surface and edge wear of Björk-Shiley Delrin heart valve discs.

Background And Aims Of The Study: Wear of Björk-Shiley Delrin (BSD) heart valve discs is known to have occurred in some patients, possibly contributing to increased regurgitation. This paper specifically addresses surface and edge wear that have been observed on some discs of explanted BSD valves after implant durations up to 22.4 years.

The Björk-Shiley Delrin tilting disc heart valve: historical perspective, design and need for scientific analyses after 25 years.

The Björk-Shiley Delrin (BSD) tilting disc heart valve was first used clinically in 1969. It is estimated that up to 24,000 BSD heart valves were implanted between 1969 and 1981, of which 7,000 may still be implanted in patients. The BSD valve provided a low-profile, quiet prosthesis with excellent hemodynamics.

Pressure distribution near the occluders and impact forces on the outlet struts of Björk-Shiley convexo-concave valves during closing.

Background And Aims Of The Study: An in vitro study of the mechanics of closure of Björk-Shiley convexo-concave (BSCC) valves is presented in order to investigate the mechanics of outlet strut fracture reported in a small fraction of the implanted valves.

Materials And Methods: Four BSCC 29 mm valves instrumented with strain gages on the outlet strut legs were mounted in the mitral position of an axisymmetric flow chamber of a mock pulsatile flow loop. Measurements of the pressure field in the vicinity of the occluder, closing velocity of the occluder tip in the major orifice, and the impact force between the occluder and outlet strut at the instant of valve closure were obtained at a range of physiologic flow rates.

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.

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.

Low frequency analysis of opening sound for detection of single leg separation of Björk-Shiley Convexo-Concave heart valves.

The aim of the study was to evaluate the potential of low frequency analysis of valve opening sounds in order to detect the presence of single leg separation of the outlet strut of Björk-Shiley convexo-concave (BSCC) valves. Single leg separation is believed to precede outlet strut fracture. Phonocardiograms (PCG) of 28 patients with BSCC mitral valves were recorded and filtered to limit the frequency bandwidth between 90 and 1400 Hz (-20 dB).

Velocity of closure of Björk-Shiley Convexo-Concave mitral valves: effect of mitral annulus orientation and rate of left ventricular pressure rise.

The purpose of this study was to determine analytically the hemodynamic factors that affect the closing velocity of the disc of Björk-Shiley convexo-concave (BSCC) prosthetic mitral valves. The motion of the BSCC disk was modelled by Newton's second law written in the form of a second order differential equation which expressed the instantaneous angle of the disc with respect to the valve ring as a function of the instantaneous pressure drop across the mitral valve, delta P(t), and the angle of the pressure gradient vector acting upon the disc during closure. The disc closes in response to the negative pressure drop created by the crossover of left atrial and left ventricular (LV) pressures.

Dynamics of Björk-Shiley Convexo-Concave mitral valves in sheep.

The outlet strut of Björk-Shiley (BSCC) Convexo-Concave heart valves has fractured in some implanted valves resulting in disc escape and emergency reoperation or death. The closing dynamics of BSCC heart valves was studied in situ to determine the forces acting on the outlet strut during valve closure. BSCC valves with strain gages attached to the outlet strut were implanted in the mitral position in sheep.

The effect of left ventricular dP/dt on the in vitro dynamics of the Björk-Shiley Convexo-Concave mitral valve.

Left ventricular (LV) dP/dt is considered an important hemodynamic factor influencing the dynamics of mechanical heart valve prostheses. LV dP/dt is dependent on patient factors including age, cardiac activity, health, and medication. The objective of this study was to determine the effect of LV dP/dt on the closing dynamics of mechanical heart valve prostheses in the mitral position.

Regurgitation of prosthetic heart valves: dependence on heart rate and cardiac output.

Prosthetic heart valves exhibit closure and leakage backflow; however, no well-controlled study to evaluate the influence of factors such as cardiac output and heart rate on backflow has been reported to date. Four clinically used prosthetic aortic valves (size 27 mm)--St. Jude Medical, Björk-Shiley Spherical Disc, Björk-Shiley Convexo Concave, and Starr-Edwards model 1260--were studied in the aortic chamber of a pulse duplication system at heart rates of 50, 80, 110, and 140 beats/min, cardiac output of 2, 4, 6, and 8 liters/min, and mean aortic pressure of 100 mm Hg.