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Purpose: Hydrodynamic performance testing is one of the core in vitro assessments required by the ISO 5840 series of standards for all prosthetic heart valves. A round-robin study carried out in 2005 in accordance with ISO 5840:2005 revealed significant variabilities in prosthetic heart valve hydrodynamic performance measurements among the participating laboratories. In order to re-examine the inter-laboratory variability based on the "state-of-the-art" under ISO 5840-1 and 5840-2:2015, the ISO Cardiac Valve Working Groups decided in 2016 to repeat the round-robin study. Methods: A total of 13 international laboratories participated in the study. The test valves were chosen to be the St. Jude Medical Masters Series mechanical valves (19 mm aortic, 25 mm aortic, 25 mm mitral, and 31 mm mitral), which were circulated among the laboratories. The testing was conducted according to a common test run sequence, with prespecified flow conditions. Results: The study revealed improved, yet still significant variability among different laboratories as compared to the 2005 study. The coefficient of variation ranged from 7.7 to 21.6% for the effective orifice area, from 10.1 to 32.8% for the total regurgitant fraction, and from 14.7 to 45.5% for the mean transvalvular pressure gradient. Conclusions: The study revealed the ambiguities in the current versions of the ISO 5840 series of standards and the shortcomings of some participating laboratories. This information has allowed the ISO Working Group to incorporate additional clarifying language into the ISO 5840-1, -2, and -3 standards that are currently under revision to improve in vitro assessments. The results presented here can also be used by the testing laboratories to benchmark pulse duplicator systems and to train and certify testing personnel. [ABSTRACT FROM AUTHOR]

After implantation of a transcatheter bioprosthetic heart valve its original circular circumference may become distorted, which can lead to changes in leaflet coaptation and leaflets that are stretched or sagging. This may lead to early structural deterioration of the valve as seen in some explanted transcatheter heart valves. Our in vitro study evaluates the effect of leaflet deformations seen in elliptical configurations on the damage patterns of the leaflets, with circular valve deformation as the control. Bovine pericardial tissue heart valves were subjected to accelerated wear testing under both circular (N = 2) and elliptical (N = 4) configurations. The elliptical configurations were created by placing the valve inside custom-made elliptical holders, which caused the leaflets to sag or stretch. The hydrodynamic performance of the valves was monitored and high resolution images were acquired to evaluate leaflet damage patterns over time. In the elliptically deformed valves, sagging leaflets experienced more damage from wear compared to stretched leaflets; the undistorted leaflets of the circular valves experienced the least leaflet damage. Free-edge thinning and tearing were the primary modes of damage in the sagging leaflets. Belly region thinning was seen in the undistorted and stretched leaflets. Leaflet and fabric tears at the commissures were seen in all valve configurations. Free-edge tearing and commissure tears were the leading cause of valve hydrodynamic incompetence. Our study shows that mechanical wear affects heart valve pericardial leaflets differently based on whether they are undistorted, stretched, or sagging in a valve configuration. Sagging leaflets are more likely to be subjected to free-edge tear than stretched or undistorted leaflets. Reducing leaflet stress at the free edge of non-circular valve configurations should be an important factor to consider in the design and/or deployment of transcatheter bioprosthetic heart valves to improve their long-term performance. [ABSTRACT FROM AUTHOR]

Purpose: To develop and validate the efficacy and accuracy of a three-dimensional (3D) computed tomography (CT) reconstructive rapid prototyping drill template for cervical pedicle screw placement.Methods: CT thin-layer scans were obtained from 12 adult cadaveric cervical specimens and reconstructed. The ideal screw channels were chosen by analyzing the cross sections of the reconstructed 3D images. The navigation templates were designed and printed based on the optimal screw channels. The pedicle screws were placed on the cadaver specimens under template guidance, and the cadaver specimens were scanned and reconstructed. The pre- and post-operative models were compared. Entry point and exit point data of these two models were collected and compared using the Chi-square test.Results: A total of 164 cervical pedicle screws were placed; among them, six punctured the cortical bone of the vertebral pedicle reaching an accuracy of 96.3%. Among the outside screws, all of the deviation distances were <2 mm. The Chi-square test results showed that when a deviation of 1.2 mm was used as a standard for the entry point, there was no difference between the two groups (χ 2 = 1.346, p = 0.248); when a deviation of 2.2 mm was used as a standard for the exit point, there was no difference between the two groups (χ 2 = 3.250, p = 0.061).Conclusion: The 3D CT reconstructive rapid prototyping drill template combined with the screw tunnel design based on 3D cutting technique can help facilitate accurate cervical pedicle screw insertion. [ABSTRACT FROM AUTHOR]

Although generally manufactured as circular devices with symmetric leaflets, transcatheter heart valves can become non-circular post-implantation, the impact of which on the long-term durability of the device is unclear. We investigated the effects of five non-circular (EllipMajor, EllipMinor, D-Shape, TriVertex, TriSides) annular configurations on valve leaflet stresses and valve leaflet deformations through finite element analysis. The highest in-plane principal stresses and strains were observed under an elliptical configuration with an aspect ratio of 1.25 where one of the commissures was on the minor axis of the ellipse. In this elliptical configuration (EllipMinor), the maximum principal stress increased 218% and the maximum principal strain increased 80% as compared with those in the circular configuration, and occurred along the free edge of the leaflet whose commissures were not on the minor axis (i.e., the 'stretched' leaflet). The D-Shape configuration was similar to this elliptical configuration, with the degree to which the leaflets were stretched or sagging being less than the EllipMinor configuration. The TriVertex and TriSides configurations had similar leaflet deformation patterns in all three leaflets and similar to the Circular configuration. In the D-Shape, TriVertex, and TriSides configurations, the maximum principal stress was located near the commissures similar to the Circular configuration. In the EllipMinor and EllipMajor configurations, the maximum principal stress occurred near the center of the free edge of the 'stretched' leaflets. These results further affirm recommendations by the International Standards Organization (ISO) that pre-clinical testing should consider non-circular configurations for transcatheter valve durability testing. [ABSTRACT FROM AUTHOR]

To assess the short-term outcome of unilateral pedicle screw fixed intervertebral fusion surgery for degenerative disc disease via MAST QUADRANT minimally invasive system. Thirty patients with degenerative lumbar disease from September 2009 to September 2011 were enrolled and divided into two groups: (1) unilateral pedicle screw fixed intervertebral fusion via MAST QUADRANT system; and (2) conventional bilateral pedicle fixed intervertebral fusion via open surgery. The perioperative parameters (operation time, intraoperative blood loss, and length of stay) and the follow-up clinical curative effect parameters (VAS and ODI) were compared between two groups. All patients successfully completed surgery and were followed up for more than 1 year. The perioperative parameters of MAST QUADRANT system group were significantly better than the control group ( P < 0.05). And the clinical curative effects were similar to conventional surgery ( P > 0.05). Unilateral pedicle screw fixed intervertebral fusion via MAST QUADRANT system is a less invasive and safer surgical techniques. It offers a quick recovery and effective surgical option in the treatment of lumbar degenerative diseases. [ABSTRACT FROM AUTHOR]

A mechanical heart valve (MHV) prosthesis made of pyrolytic carbon (PyC) coated graphite is a long-term implant that operates continuously for lifetime in patient's body. The ceramic-like PyC coating is brittle and is prone to contact damages. The high-level local contact stress may lead to the initiation of microcracks, as well as accelerated propagation of preexisting cracks. In this paper, the effect of changing coating parameters on Hertzian contact stresses is investigated for a trilayer PyC/graphite laminate undergoing a spherical indentation test, by means of a finite element analysis. It is shown that by suitably changing Young's modulus, Poisson's ratio, and the thickness of the coating material, the stress levels at critical locations can be greatly modified. This can be accomplished effectively within a small range of variations of the coating parameters. Low Young's modulus, large Poisson's ratio, and relatively thick coating are found to be beneficial in general. The results obtained may be useful in the design of MHV components for improving resistance against contact-induced damages by elaborately controlling the deposition process of PyC coating. [ABSTRACT FROM AUTHOR]

In the 1994 Replacement Heart Valve Guidance of the Food and Drug Administration (FDA), both cavitation and damage tolerance analyses are required for mechanical heart valves (MHV). Cavitation results from a sequence of events. First, vaporous bubbles are generated in the blood flow. They then collapse to form high-speed micro liquid jets, striking against the solid valve boundary, and subsequently causing pits on the surface. Micro cracks may initiate around the pitted areas under repeated jet impacts superimposed with cyclic loading. These events are, of course, closely related to the shape and size of an MHV. The factors specified in the current FDA guidance and considered by many authors for calculating working stresses, including static stresses, dynamic stresses, residual stresses, and stress concentrations, appear to be inadequate. The local high pressure caused by cavitation jets is another important factor which may aggravate crack propagation. The present paper is aimed at quantitatively assessing the influence of cavitation jets on the safe service life of an MHV using a damage tolerance approach. A new fracture mechanics model for estimating service lives of MHV prostheses is proposed, in which bubble dynamics and cavitation phenomenon are incorported. Numerical results show that the local high pressure is dominant, and is large enough to cause a crack to propagate at a greater rate, and resulting in much shorter fatigue life for an MHV. [ABSTRACT FROM AUTHOR]