Cardiovascular implants

Surface-engineered endothelialization for artificial cardiovascular implants can be achieved either by allogenic EC seeding or inducing host EC reoccupation. These two strategies may work separately or in coordination. 

A wide number and great variety of clinically important cardiovascular implants and devises exist. Some (e.g., catheters) may only contact the blood once, and for a relatively short time others (e.g., kidney dialyzers and blood oxygenators) may be exposed to blood for hours, while tissue implants (e.g., heart valves and vascular grafts) will hopefully last for years, or the lifetime of the patient. All of these implants nd devices contain materials that are recognized by blood as foreign the result is a process of thrombosis often followed by formation of thromboemboli. This process generally involves a sequence of protein adsorption steps followed by blood cell interactions (especially involving platelets). 

Blood responses. Blood is the fluid which transports body nutrients and waste products to and from the extravscular tissue and organs, and as such is a vital and special body tissue. The major response of blood to any foreign surface (which includes most extravascular surfaces of the body s own tissues) is first to deposit a layer of proteins and then, within seconds to minutes, a thrombus composed of blood cells and fibrin (a fibrous protein). The character of the thrombus will depend on the rate and pattern of blood flow in the vicinity. Thus, the design of the biomaterial system is particularly important for cardiovascular implants and devices. The thrombus may break off and flow downstream as an embolus and this can be a very dangerous event. In some cases the biomaterial interface may eventually "heal" and become covered with a "passive" layer of protein and/or cells. Growth of a continuous monolayer of endothelial cells onto this interface is the one most desirable end-point for a biomaterial in contact with blood. Figure 10 summarizes possible blood responses to polymeric biomaterials. 

LTI carbon A silicon alloyed pyrolitic carbon deposited onto a substrate at low temperature with isotropic crystal morphology. It is highly compatible with blood and used for cardiovascular implant fabrication such as artificial heart valve. 

Hydrophobic coatings composed of silicon- and fluorine-containing polymeric materials as well as polyurethanes have been studied because of the relatively good clinical performances of Silastic , Teflon , and polyurethane polymers in cardiovascular implants and devices. Polymeric fluorocarbon coatings deposited from a tetrafluoroethylene gas discharge have been found to greatly enhance resistance to both acute thrombotic occlusion and embolization in small diameter Dacron grafts. 

Ajili, S. H., Ebrahimi, N. G., and Soleimani, M. 2009. Polyurethane/polycapro-lactane blend with shape memory effect as a projxjsed material for cardiovascular implants. Acta Biomaterialia 5 1519-1530. 

Blood-contacting materials have to fulfill particular requirements, as they are immediately exposed to all host defense mechanisms of the body. Thus, the contact of blood with foreign surfaces induces several cascade reactions and activation phenomena. These complex and highly interconnected reactions potentially create clinically significant side effects in the application of medical devices (e.g., cardiovascular implants, extracorporeal circulation, catheters) and interfere with the success of the medical treatments [64]. In certain cases, even the formation of thromboemboli or systemic inflammatory reactions were reported to occur as a consequence of the activation of coagulation enzymes and thrombocytes and/or the activation of the complement system and leukocytes (immune response) at the biointerfaces of the applied materials [65]. 

SVC, superior vena cava MRI, magnetic resonance imaging CIED, cardiovascular implantable electronic device... 

ECG, electrocardiogram TTE, transthoracic echocardiography TEE, transesophageal echocardiography CIED, cardiovascular implantable electronic device TLE, transvenous lead extraction... 

The echocardiographic examination in cardiovascular implantable electronic devices (CIED) is based on examination of the right heart, great venous vessels, and venous lead entry site. 

The indication for the extraction can explain different reimplantation settings. Generally, two different scenarios can be described patients with a cardiovascular implantable electronic device (CIED) infection and patients with a malfunctioning lead. Moreover, in the era of cardiac resynchronization therapy (CRT), a specific skill in biventricular device reimplantation is required in large-volume centers and will be described separately. 

Fig. 9 1 Timing of reimplantation in presence/absence of cardiovascular implantable electronic device (CIED) infection. Reimplantation must be always delayed in the presence of cellulites, fever, or active bacteremia...

Low flow in vivo venous modds have been suggested for hematocompatibiUty evaluation. However, these systems are not appropriately and adequatdy justified for use in assessing the long-term biocompatibility required for cardiac and cardiovascular implants. 

Hydrogels of CNCs have many desirable properties, including low cost, nontoxicity, hydrophilicity, biocompatibility, and biodegradability, all of which contribute to their potential applications in bioengineering and biomedicine. For example, CNC dispersed in a solution of cellulose, sodium hydroxide, and urea formed a gel that steadily released bovine semm albumin into a simulated body fluid [161]. Nanocomposites of CNC and poly(vinyl alcohol), a hydrophilic biocompatible polymer, exhibited a broad range of mechanical properties that could be tuned to mimic those of cardiovascular tissues and, therefore, have potential applications as cardiovascular implants [162]. 

To avoid missing out on unexpected opportunities, you may want to brand yourself broadly in the area of your interests and capabilities (for example, a specialist or generalist in medical devices ), yet with a marketable depth (for example, cardiovascular implantable technologies, but not too specific such as a specialist in patent foramen ovale catheters, unless it is absolutely necessary). 

Vascular grafts and patches, as well as heart valves, are among the oldest of cardiovascular implants. More recently, permanent internal devices include pacemakers, defibrillators, stents, left ventricular assist devices, and artificial hearts. 

The European Union Medical Device Directive (and various other national systems) has adopted a review scheme known as the Essential Requirements Checklist. The manufacturer must meet the essential requirements of the Directive, which is a standardized grouping of attributes for medical products. All devices, regardless of classification or conformity assessment route, must prove that the product meets the essential requirements. Where a harmonized standard exists for the product, and the product meets the standard, it is deemed to automatically meet the essential requirements, but for biotextUes, these are few and far between. One notable device-specific standard for a biotextile vascular graft is ISO 7198 First edition 1998-08-01 Cardiovascular implants - Tubular vascular prostheses, which is recognized by FDA. 

ANSI/AAMI/ISO 7198 1998/2001/(R)2010 - Cardiovascular implants -Tubular vascular prostheses , Association for the Advancement of Medical Instrumentation, 2010. 

Cardiovascular diseases and complications are the leading cause of death in the United States, which creates a large demand for biomaterials suitable for cardiovascular implantable devices. In general, in order for a biomaterial to be usable in a certain organ system in the human body, the material must be compatible with that system over the device s entire service life period. For a cardiovascular system, this includes compatibility with the patient s blood, especially with respect to immune responses and hemostatic/thrombotic responses and compatibility with blood vessels, if the device is in contact with them. 

ANSI/AAMEISO 7198 1998/2001/(R). Cardiovascular implants-tubular vascular pros-theses. 2010. 

Specific devices/ application ISO/TS 17137 2014 Cardiovascular implants and extracorporeal systems—cardiovascular absorbable implants ASTM F2502 Standard specification and test methods for absorbable plates and screws for internal fixation implants... 

The structural and functional characteristics of cardiovascular implants vary widely according to the site and structure they have to repair or substimte, such as valves or cardiac or vascular patches. These should ideally be as similar as possible to the native counterpart in order to preserve physiology and avoid the formation of stractural stress areas at the junction between tissues and biomaterials. 

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