SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Artificial heart valve

28

Restricting our scope to the dynamical motion of the leaflets, we present a computational model for a symmetric, tri-leaflet, bioprosthetic heart valve (BHV) at the end of five complete cardiac pressure cycles, reaching the steady state of deformation during both closing and opening phases. To this end, we utilized a highly anisotropic material model for the large deformation behavior of the tissue material, for which an experimental validation was provided. The important findings are: (1) material anisotropy has significant effect on the valve opening/closing; (2) the asymmetric deformations, especially in the fully closed configuration, justify the use of cyclic symmetry; (3) adopting the fully-open position as an initial/reference configuration has the advantage of completely bypassing any complications arising from the need to assume the size and shape of the contact area in the coaptation regions of the leaflets that is necessary when the alternative, commonly-used, approach of selecting the fully-closed position is used as a reference; and (4) with proper treatments for both material anisotropy and tissue-to-tissue contact, the overall BHV model provide realistic results in conformity with the ex vivo/in vitro experiments.

Concepts: Thermodynamics, Symmetry, Geometry, Young's modulus, Attractor, Artificial heart valve, Asymmetry, Point groups in three dimensions

28

The concept/phenomenon of valve prosthesis/patient mismatch (VP-PM), described in 1978, has stood the test of time. From that time to 2011, VP-PM has received a great deal of attention but studies have come to varying conclusions. This is largely because of the determination of prosthetic heart valve area [called effective orifice area index (EOAi)] by projection rather than by actual measurement, variable criteria to assess severity of EOAi and the timing of determination of EOAi. All prosthetic heart valves have some degree of VP-PM which must be placed in a proper clinical perspective. This can be done by determining its effects on function and outcomes. For mortality one needs to focus especially on severe/critical degree of VP-PM and determine the cause of death was due to VP-PM. For the period “beyond 2011” a road map is suggested that will have uniformity of assessment of VP-PM and a focusing on the important goals of VP-PM.

Concepts: Focusing, Artificial heart valve, Valves, Heart valve

27

Rothia mucilaginosa is increasingly recognized as an emerging opportunistic pathogen associated with prosthetic device infections. Infective endocarditis is one of the most common clinical presentations. We report a case of R. mucilaginosa prosthetic valve endocarditis and review the literature of prosthetic device infections caused by this organism.

Concepts: Immune system, Bacteria, Opportunistic infection, Infective endocarditis, Prosthesis, Valvular heart disease, Artificial heart valve, Endocarditis

25

A rare, yet serious, complication of mechanical heart valves is symptomatic obstructive prosthetic valve thrombosis. The risk of valve thrombosis is magnified in patients who are nonadherent to prescribed anticoagulation. In this case report, we describe a 48-year-old male patient with a history of mechanical aortic valve replacement surgery, who stopped taking prescribed warfarin therapy 2 years before presentation and subsequently developed acute decompensated heart failure secondary to valvular dysfunction. Low-dose alteplase therapy was administered successfully with no bleeding complications and a complete return of valvular function.

Concepts: Cardiology, Heart failure, Stroke, Warfarin, Aortic valve, Valvular heart disease, Artificial heart valve, Acute decompensated heart failure

20

Warfarin is the mainstay of anticoagulation for patients with mechanical heart valves. However, warfarin has well-known limitations, including interactions with food and drugs and the requirement for lifelong monitoring of the international normalized ratio (INR).(1) Variability of the INR is the strongest independent predictor of reduced survival after mechanical valve replacement.(2) Thus, there is a pressing need for alternatives to warfarin, and the advent of the target-specific oral anticoagulants has been highly anticipated. Eikelboom et al.(3) now report in the Journal the results of a study whose primary aim was to validate a new dosing regimen for dabigatran, as compared . . .

Concepts: Stroke, Atrial fibrillation, Warfarin, Anticoagulant, Heparin, Dabigatran, Anticoagulants, Artificial heart valve

13

Although surgery was the mainstay of treatment for valvular heart disease, transcatheter valve therapies have grown exponentially over the past decade. Two types of artificial heart valve exist: mechanical heart valves (MHV), which are implanted surgically, and bioprosthetic heart valves (BHV), which can be implanted via a surgical or transcatheter approach. Whereas long-term anticoagulation is required to prevent thromboembolism after MHV replacement, its value in patients receiving BHVs is uncertain. Patients undergoing transcatheter BHV replacement are at risk for thromboembolism in the first few months, and recent data suggest that the risk continues thereafter. BHV thrombosis provides a substrate for subsequent thromboembolism and may identify a reversible cause of prosthesis dysfunction. Hereafter, the authors: 1) review the data on prosthetic valve thrombosis; 2) discuss the pathophysiological mechanisms that may lead to valve thrombus formation; and 3) provide perspective on the implications of these findings in the era of transcatheter valve replacement.

Concepts: Cardiology, Stroke, Warfarin, Implants, Prosthesis, Valvular heart disease, Artificial heart valve, Heart valve

8

The present study investigated the neural correlates associated with gait improvements triggered by an active prosthesis in patients with drop-foot following stroke during the chronic stage. Eleven patients took part in the study. MEG recordings in conjunction with somatosensory stimulation of the left and right hand as well as gait analyses were performed shortly before or after prosthesis implantation surgery and 3-4 months later. Plastic changes of the sensorimotor cortex of the ipsi- and contralesional hemisphere were revealed. Gait analysis indicated that all patients improved their gait with the active prosthesis. Patients with larger plastic changes within the lesioned hemisphere maintained their improved gait performance even when the prosthesis was turned off. Patients with larger contralesional changes also improved their gait with the active prosthesis. However, their gait measures decreased when the prosthesis was turned off. The current data provide the neural basis of gait improvement triggered by an active prosthesis and has important implications with respect to the choice of the type of active prosthesis (implantable vs removable) and to the selection procedure of the patients (length of testing period).

Concepts: Present, Better, Improve, Left-wing politics, Neuroscience, Cerebral cortex, Amputation, Artificial heart valve

6

Background In patients undergoing aortic-valve or mitral-valve replacement, either a mechanical or biologic prosthesis is used. Biologic prostheses have been increasingly favored despite limited evidence supporting this practice. Methods We compared long-term mortality and rates of reoperation, stroke, and bleeding between inverse-probability-weighted cohorts of patients who underwent primary aortic-valve replacement or mitral-valve replacement with a mechanical or biologic prosthesis in California in the period from 1996 through 2013. Patients were stratified into different age groups on the basis of valve position (aortic vs. mitral valve). Results From 1996 through 2013, the use of biologic prostheses increased substantially for aortic-valve and mitral-valve replacement, from 11.5% to 51.6% for aortic-valve replacement and from 16.8% to 53.7% for mitral-valve replacement. Among patients who underwent aortic-valve replacement, receipt of a biologic prosthesis was associated with significantly higher 15-year mortality than receipt of a mechanical prosthesis among patients 45 to 54 years of age (30.6% vs. 26.4% at 15 years; hazard ratio, 1.23; 95% confidence interval [CI], 1.02 to 1.48; P=0.03) but not among patients 55 to 64 years of age. Among patients who underwent mitral-valve replacement, receipt of a biologic prosthesis was associated with significantly higher mortality than receipt of a mechanical prosthesis among patients 40 to 49 years of age (44.1% vs. 27.1%; hazard ratio, 1.88; 95% CI, 1.35 to 2.63; P<0.001) and among those 50 to 69 years of age (50.0% vs. 45.3%; hazard ratio, 1.16; 95% CI, 1.04 to 1.30; P=0.01). The incidence of reoperation was significantly higher among recipients of a biologic prosthesis than among recipients of a mechanical prosthesis. Patients who received mechanical valves had a higher cumulative incidence of bleeding and, in some age groups, stroke than did recipients of a biologic prosthesis. Conclusions The long-term mortality benefit that was associated with a mechanical prosthesis, as compared with a biologic prosthesis, persisted until 70 years of age among patients undergoing mitral-valve replacement and until 55 years of age among those undergoing aortic-valve replacement. (Funded by the National Institutes of Health and the Agency for Healthcare Research and Quality.).

Concepts: Epidemiology, Medical statistics, Prosthetics, Mitral valve, Mitral valve prolapse, Prosthesis, Artificial heart valve, Age groups in Scouting and Guiding

4

Cardiovascular Magnetic Resonance is often used to evaluate patients after heart valve replacement. This study systematically analyses the influence of heart valve prostheses on phase contrast measurements in a phantom trial.

Concepts: Heart, Nuclear magnetic resonance, Circulatory system, Valvular heart disease, Artificial heart valve, Aortic valve replacement

4

Aims: Transcatheter aortic valve implantation (TAVI) has become a viable option for selected high-risk patients with severe and symptomatic aortic stenosis. First- and second-generation TAVI devices are either self- or balloon-expandable, and are often not repositionable or not fully retrievable, leading to suboptimal positioning in some cases. This may result in paravalvular regurgitation, AV conduction delay, or compromise of coronary perfusion. A broader application of TAVI requires advances in both valve and delivery systems. Therefore, in order to facilitate accurate positioning, to minimise paravalvular leakage, possibly to reduce the risk of AV conduction delay, and possibly to be able to abort the procedure, a “next-generation” TAVI system has been developed which is repositionable and retrievable, the TRINITY heart valve system. Methods and results: The TRINITY heart valve system was implanted in a first-in-human study using the transapical approach to demonstrate feasibility and procedural success. All endpoints were adjudicated according to VARC definitions at seven and 30 days. The TRINITY heart valve system was implanted in a 74-year-old patient with severe symptomatic aortic valve stenosis. In this case, repositioning of the TRINITY resulted in optimal position without paravalvular leakage and with perfect function. Conclusions: The TRINITY heart valve is a repositionable and retrievable TAVI system. Both the implantation result and short-term clinical and haemodynamic outcome were excellent.

Concepts: Cardiology, Heart, Tricuspid valve, Left ventricle, Valvular heart disease, Artificial heart valve, Aortic valve stenosis, Aortic insufficiency