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Deaths Following Cardiac Surgery and Invasive Interventions
Published in Mary N. Sheppard, Practical Cardiovascular Pathology, 2022
The first tilting disc valve was developed by the Swedish surgeon, Björk, and the American engineer, Shiley, in 1969. The slightly biconvex disc was plastic while the struts within which the disc tilted were of metal, as was the annulus. The sewing ring, as in all replacement heart valves, was covered in cloth. Like the Starr–Edwards, the Björk–Shiley valve has undergone modifications, both to improve its haemodynamic characteristics and to reduce the incidence of thromboembolism. The current model is made entirely of pyrolytic carbon (see Fig. 9.37). There have been several other tilting-disc valves but none has been as universally used as the Björk–Shiley.
Aortic Valve Mechanics
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
J. Dallard, M. Boodhwani, M. R. Labrosse
Available prosthetic valves can be classified into mechanical and bioprosthetic valves (Zhao et al., 2016). The majority of the aortic valve replacements (AVRs) involve a mechanical valve: out of 120,000 valves implanted each year in the United States, 60% are mechanical valves (Alemu and Bluestein, 2007). Contemporary mechanical valves commonly feature two leaflets and are mostly made from pyrolytic carbon (Rajashekar, 2015). However, because the rigid structure of mechanical heart valves damages red blood cells and induces blood clotting, the patients who receive mechanical heart valves need to be treated with life-long anticoagulation therapy.
Microbial Biofilms
Published in Chaminda Jayampath Seneviratne, Microbial Biofilms, 2017
Chaminda Jayampath Seneviratne, Neha Srivastava, Intekhab Islam, Kelvin Foong and Finbarr Allen
The formation of biofilms on indwelling medical devices is influenced by factors related to the microorganisms, device properties and host microenvironment. These include irreversible attachment of microorganisms to the exposed surfaces of the device, the number and types of cells in the liquid to which the device is exposed, the flow rate of liquid through the device and the physicochemical characteristics of the surface [63,65]. For instance, it has been shown that adhesion of S. epidermidis and P. aeruginosa are dependent on pyrolytic carbon surface, free energy and roughness. On the contrary, adhesion of S. aureus is independent of the foregoing factors [66]. When the indwelling medical devices are inserted, a conditioning film from the organic matter present in the surrounding fluid is deposited on it. The source of this film could be host-derived proteins such as fibrinogen, fibronectin and collagen which influence the subsequent adherence of microorganisms. Thus, an in vitro model cannot mimic the composition and structure of biofilms formed in vivo. For this reason, the results derived from in vitro biofilm models should be interpreted with caution and in vitro studies should be complemented with ex vivo or in vivo models for more clinically relevant results. Some common medical device–associated biofilm infections are discussed in the following subsections.
Development of a New Model of Humeral Hemiarthroplasty in Rats
Published in Journal of Investigative Surgery, 2023
Efi Kazum, Eran Maman, Zachary T. Sharfman, Reut Wengier, Osnat Sher, Amal Khoury, Ofir Chechik, Oleg Dolkart
Apart for incongruent joint mating surfaces, the main cause of cartilage wear is generally considered to be the tribology of the joint material surfaces [5]. Pyrolytic carbon prothesis demonstrate a modulus of elasticity that resembles that of hyaline cartilage, and are therefore considered to offer favorable joint wear properties [6]. Testing new materials used for arthroplasty bearing surfaces requires valid in vivo models that are generally expensive and somewhat impractical. Some models using a free interpositional arthroplasty concept for the shoulder, in which the humeral head is exchanged by a ball shaped prosthesis, have already proved successful and been termed “The snooker ball arthroplasty” [7,8]. Kramer et al. [9] described a rat model for the development of shoulder rotator cuff arthropathy related to massive rotator cuff tears. However, rat models for the development of hemiarthroplasty-related shoulder osteoarthritis have yet to be described.
Progress in surgical interventions for aortic root aneurysms and dissections
Published in Expert Review of Cardiovascular Therapy, 2022
Shamini Parameswaran, Bulat A. Ziganshin, Mohammad Zafar, John A. Elefteriades
The anticoagulation landscape may undergo a sea of change within the next two years. The On-X valve (FDA approved) (CryoLife, Kennesaw, Georgia) is a bileaflet mechanical valve that was specifically designed to be thromboresistant. The surface of the pyrolytic carbon is smoother, the leaflets move a full 90% in the open position, and the hinges lift gently above their pivots, permitting ubiquitous washing of the entire mechanism. Patients with an On-X aortic valve can safely run at INRs of 1.5 to 2.0, instead of the traditional 2.0 to 3.0 for mechanical aortic valves. Patients who had On-X aortic valves placed manifested a lower incidence of major and minor bleeding complications and had similar incidences of thrombotic complications compared with patients who continued standard anticoagulation. Furthermore, the incidence of TIA, stroke, total neurologic events, and all-cause mortality was found to be similar among both groups [7]. Now, the PROACT Xa trial has begun, in which On-X aortic valve or composite graft patients are treated without coumadin, with apixaban (Eliquis) 5 mg po bid and ASA 81 mg daily. There is no need for INR evaluations or dose adjustments. As this article goes to press, the earliest patients have been treated in this fashion for 1 year, without apparent detriment. When the last patient reaches 2-year follow-up, the trial will be halted and detailed outcomes assessed. The potential for a coumadin-free future coupled with the durability of a bileaflet mechanical valve looms bright on the horizon.
Increased utilization of bioprosthetic aortic valve technology:Trends, drivers, controversies and future directions
Published in Expert Review of Cardiovascular Therapy, 2021
Steven S. Qi, Rosemary F. Kelly, Richard Bianco, Frederick J. Schoen
Following Albert Starr’s use of a caged ball mitral valve [5] and Dwight Harken’s implantation of a caged ball aortic valve [6] in the early 1960s, MVs of many designs and materials using mobile occludes supported by a guiding frame were introduced; nearly all types were fabricated from rigid synthetic materials. Bileaflet tilting disk mechanical valves with two semi-circular pyrolytic carbon disks mounted in a carbon housing became popular in the late 1970s, and remain today the leading MVs used. However, thrombosis and thromboembolism and the consequent need for chronic anticoagulation constitute a persistent problem with all MVs. Thus, valves composed of tissue, which can be constructed from relatively thromboresistant biomaterials and have more natural flow patterns than MV, were and continue to be the attractive alternative.