TAVR is the new state of the art Aortic valve replacement procedure done by cardiologists .Nearly 200 thousand implants have been done , and it is
backed up by major trials What keeps the Aortic prosthesis in situ in the aortic root/Annulus ?
The valve is not actively fixed but passively positioned in aortic root by either self expanding or balloon expanded valve system .It retains the position by two different forces acting on the valve in two difffernt directions , but work coherently to keep the valve static .The radial force of the hardware is centrifugal and the elastic force exerted by annulus is centripetal .It may appear mysterious how these oppose each other in a balanced way and arrest the valve in the desired site. Fortunately, there is little supero- inferior force operating and hence the chances of dislodgement is low .It should also be mentioned we are not yet clear about the best site for TAVR. Annular , supra annular ,or is it at lower virtual annulus , all has some advantages and disadvantages.
Is progressive aortic annular dilatation possible in these degenerative aortic valve ?
Aortic stenosis is chronic degenerative disease. Generally we expect the annulus is narrow and fixed. However for some reason if the aortic annulus loses it constricting force or the root dilates or fresh calcium deposits, there is definite risk (Not theoretical :See Reference ) of valve destabilisation , dislodgement and embolisation . *It is vital to understand the para-valvular leak could be a remote precursor of such potential dislodgement as it represents micro gaps in the prosthetic / tissue interface.
How many such embolisation of valves are reported following TAVR ?
While the incidence of para valvular leak is common ,(up to 20%) fortunately valve embolisation is reported between .3 to 7.5% (Ref 2). Stastically , subclinical destabilisation, malpostion and dislodgement should be more common. The timing of displacement is not clearly reported in literature .It can occur at any time between few hours after implantation to a much delayed (months after ) complication .
TAVR is a major break through in Interventional cardiology .It gives us hope for possible TAMR (mitral) and other valve repair modalities .Though dislodgement of prosthesis appear a rare event it is tempting to ask , whether we should work towards a actively fixing valve in aortic root ? That remains a open question !
2.Thirty-day results of the SAPIEN aortic Bioprosthesis European Outcome (SOURCE) Registry: A European registry of transcatheter aortic valve implantation using the Edwards SAPIEN valve.Thomas M, Schymik G, Walther T, et al. Circulation 2010;122:62-9.
3.Migration of the transcatheter valve into the left ventricle Christopher Cao , Su C. Ang , Michael P. Vallely Mart Annals of Cardiothoracic Surgery Vol 1, No 2 (July 2012 4.Delayed Transcatheter Heart Valve Migration and Failure Vuyisile T. Nkomo, Rakesh M. Suri, ,J Am Coll Cardiol Img. 2014;7(9):960-962.