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*Minimal transvalvular pressure gradient - Whenever a [[fluid]] flows through a restriction, such as a valve, a [[pressure]] [[gradient]] arises over the restriction. This pressure gradient is a result of the increased resistance to flow through the restriction. Natural heart valves have a low transvalvular pressure gradient as they present little obstruction to the flow through themselves (Fixme: Give indicative value). A desirable characteristic of heart valve prostheses is that their transvalvular pressure gradient is as small as possible.
*Non-[[thrombosis|thrombogenic]] - As natural heart valves are lined with an [[endothelium]] continuous with the endothelium lining the heart chambers they are are not normally thrombogenic. This is important as should [[thrombus]] form on the [[heart valve leaflets]] and become seeded with [[bacteria]], so called "[[bacterial vegetation|bacterial vegetations]]" will form. Such vegetations are difficult for the body to deal with as the normal [[physiology|physiological]] defense mechanisms are not present within the valve leaflets because they are [[avascular]] and largely composed of [[connective tissue]] (Fixme: Create article discussing the pathgonesis of leaflet bacterial vegetations.). Should bacterial vegetations form on the valve leafets they may continually seed [[bacteria]] into the [[arterial tree]] which may lead to [[bacteremia]] or [[septicaemia]]. Portions of the vegetation may also break off forming [[embolus|septic emboli]]. Septic emboli can lodge anywhere in the [[arterial tree]] (e.g. [[brain]], [[bowel]], [[lungs]]) causing local infectious [[foci]]. Even dislodged fragments from non-infectious vegetations (Fixme: Is this the correct terminology?) can be hazardous as they can lodge in, and block, downstream [[artery|arteries]] (e.g. [[coronary artery|coronary arteries]] leading to [[myocardial infarction]], [[cerebral]] arteries leading to [[stroke]]). A desirable characteristic of heart valve prostheses is that they are non or minimally thrombogenic.
*Self-repairing - Although of limited extent compared to well vascularised tissue (e.g. [[muscle]]), the valve leaflets do retain some capacity for repair due to the presense of regenerative [[cells]] (e.g. [[fibroblasts]]) in the [[connective tissue]] from which the leaflets are composed. As the human heart beats approximately 3.4x10<sup>12</sup> times during a typical human lifespan this limited but nevertheless present repair capacity is critically important. No heart valve prostheses can currently self-repair but replacement tissues grown using [[stem cell]] technology may eventually offer such capabilities.
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***Not framed
**[[Sternotomy]]/[[Thoracotomy]] implantation
***Tilting disk
***Bi-leaflet
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*Thrombogenesis
**Mechanisms:
***Forward and
***Static leakage shear
***Presense of foreign material (i.e. intrinsic coagulation cascade)
***Cellular masceration
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