Interventional Cardiology
Figure 4: New Generation of Transcatheter Aortic Bioprostheses
A C D
B
system is fully retrievable and can be redeveloped before final detachment from the catheter delivery system. Preliminary results of initial clinical experience are encouraging. Temporary implantation of the AorTx valve in eight patients (23–76 years of age) with severe AS was successful without any valve migration and resulted in excellent haemodynamics and minimal or no paravalvular leak.36
A: Sadra lotus valve prosthesis; B: Direct flow valve; C: AorTx percutaneous aortic valve in the middle; D: JenaValve.
Sadra Lotus Valve Prosthesis
The Lotus percutaneous aortic valve (Lotus Valve, Sadra Medical, CA) (see Figure 4A) represents the first example of a retrieval and repositioning percutaneous aortic bioprosthesis.33
It uses a nitinol
frame with a bovine pericardial trileaflet valve that shortens as it is positioned, generating radial force for anchoring. Currently, the frame-valve assembly is attached to the catheter delivery system by 15 fingers, which makes the release procedure extremely complex and challenging; thus, a new three-finger device has been developed that will make deployment of the prosthesis more simple. The main advantage of this device is that it can be re- elongated, retrieved and repositioned at any time before final release from the catheter. The first-in-man (FIM) study has been concluded: 10 patients were enrolled and successful prosthesis implantation was achieved in six of them.
Direct Flow Heart Valve
The Direct Flow Valve (Direct Flow Medical Inc., Santa Rosa, CA, US) (see Figure 4A) represents a new-generation stentless, inflatable, fabric-cuff, bovine pericardial tissue valve.34
It is the first device that is
not based on stent technology. The stentless tissue valve with bovine pericardial leaflets is connected to two inflatable rings with high flexibility and deliverability. It is immediately competent upon initial inflation. Implantation does not require rapid pacing or cardiac support and it is performed under general anaesthesia using TOE guidance. The valve is repositionable, retrievable and available in two sizes. The lower ring is inflated and the valve is positioned in the left ventricle (LV) outflow tract and then pulled against the aortic annulus. After inflation of the upper ring, valve performance is controlled and eventual repositioning performed. Once the optimal position is achieved, contrast and saline solution are replaced with a permanent polymer and the device is disengaged from the catheter.
In the FIM experience,35 implantation was acutely successful in 12
(80%) of the 15 patients enrolled. The main benefit of the highly flexible prosthesis is that it gives the operator unprecedented freedom to handle the device during implantation; it can be easily settled even through a calcified aortic arch, allowing repeated advancement and retraction across the native annulus for correct positioning, and functions immediately upon expansion.
AorTx
The AorTx percutaneous aortic valve (Hansen Medical, Mountain View, CA, US) (see Figure 4C) has a triple-hinged supporting ring with rotational crimping to 18Fr and is available in 19–27mm sizes. The
68
JenaValve
The Jena Clip (see Figure 4D) is a new low-profile and retrievable device, composed of a porcine valve mounted on a self-expanding nitinol frame that applies high radial force and with small hooks that fix it to the aorta. This structure permits a very short stent. Currently, the implantation is realised through a transfemoral approach, although a transapical system is being developed that has been tested on animal models.37
Complications
The most important benefit of TAVI with respect to SAVR is the lower incidence of complications, although ongoing randomised studies (Placement of AoRTic traNscathetER [PARTNER] Investigational Device Exemption [IDE] trial) comparing the two techniques have not come to any conclusions yet. Nevertheless, global first-year experience has shown that TAVI may present potential procedural and peri-procedural complications. The most frequent situation is the presence of paravalvular leak, which is frequently mild and well tolerated. It is diagnosed and quantified with angiography and echocardiogram after valve placement, but in particular with left catheterisation, which provides decisive information about the importance of paravalvular leak. In cases of severe paraprosthestic regurgitation provoking haemodynamic consequences, there are two alternatives. When under-expansion is observed, post-balloon dilatation could be a feasible option. In cases of sub-optimal deployment (‘too high’ or ‘too low’), a second prosthesis can be implanted inside the first one (‘valve-in-valve’ technique)38,39
or, only
with the CRS, the valve can be partially repositioned using a snare. When the sizing and positioning are accurate, prosthesis migration is an unusual event. Coronary ostia impairment by prosthetic frame or mobilisation of calcium is a rare complication if the aortic valve and the aortic root fulfil the anatomical criteria requested by the manufacturers. Anterior mitral valve leaflet impairment occurs when the prosthesis (the self-expandable CRS) is placed too low inside the LV outflow tract. Development of high-degree atrioventricular disorders that require permanent PM implantation is the most common complication of this procedure. It might occur because of trauma to ventricular conduction tissues adjacent to the aortic valve, which is damaged by prosthesis expansion; it is more frequent with the CRS, but it can also occur with the ES.40–42
Access-site
complications (pseudo-aneurism, femoral occlusion, dissection) are not rare complications, occuring in particular when bigger catheters are used. Cerebrovascular events (stroke and transient ischaemic attack) due to mobilisation of atheroemboli when advancing catheters through calcific aorta or during valvuloplasty or prosthesis expansion sometimes occur. Finally, more rarely ventricle perforation by stiff wires may occur; this is a dramatic event that requires urgent surgical management.
Percutaneous Mitral Valve Therapy
Whereas percutaneous balloon mitral valvuloplasty for rheumatic mitral stenosis now has a 20-year track record with excellent success in patients with suitable valvular and subvalvular morphology,43
until
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