In 2015 approximately 2.5 billion dollars were invested in mitral valve (MV) technology development and engineering, making this more promising for the treatment of aortic stenosis (AS) in patients considered at increased risk for conventional surgery. As a matter of fact, MR is the most common valve disease, considering that in developed countries the prevalence of rheumatic heart disease and consequent mitral stenosis encountered a dramatic reduction in the past decades.
Development of percutaneous treatment options for MV disease goes parallel with the much higher prevalence of this valvulopathy in the general population, combined with the increased group of high?risk elderly patients who could not benefit from the standard surgical treatment.
Insights into the Technical Challenges Between TMVR Versus transcatheter aortic Valve replacement
MV repair is traditionally used for Anatomical and pathophysiological reasons in comparison to replacement which laid to development of TMVR technology. Different devices are still ongoing or in their early stage developing better options in it. TMVR can provide some advantages over percutaneous repair, in virtue of an extended use in difficult or complex MV anatomical features and with a theoretical more predictable result in terms of MR reduction. Nevertheless, different challenges have been influencing the development and growth of TMVR, especially if compared with transcatheter aortic Valve replacement.
Demographic Variables shows differences for the age and can be encountered between patients with degenerative aortic and MV disease in surgical case series. The age of patients becomes even more important considering that the life expectancy of the treated patients can exceed the long?term durability of the valve itself. It has been estimated that a surgical bio prosthesis is prone to degenerate within 20 years. Percutaneous access site has visibility in transcatheter aortic valve. This replacement is generally easily performed within a transfemoral access, after an accurate computed tomographic scan or angiographic evaluation. In the event that iliofemoral access is not available, also transsubclavian, transcarotid, transaxillary, transaortic, or transapical access can be used.
Anatomical and pathophysiological reasons occurs as an isolated cardiac condition in patients with preserved left ventricle (LV) ejection fraction or in patients with impaired LV contractility, which may recover once the outflow obstruction is removed. transcatheter aortic Valve replacement allows the deployment of an aortic device in a tubular, rigid, calcified annular structure, providing a stability similar to the surgical intervention. On contrary, MV is a functional apparatus rather than a “valve,” and two completely different causes (primary or secondary) can be identified with various degrees of coexistence, particularly in elderly people. Both the surgical and percutaneous replacement of MV affects the overall performance of the LV, as a consequence of the impairment of the subvalvular structures. As discovered from transcatheter aortic Valve replacement, calcifications are important to ensure adequate valve anchoring and deployment of an aortic prosthesis, especially in the mitral position. As such, this technique is limited as severely calcified leaflets are uncommon in the MV.
TAVR Clinical Study
The treatment of AS in high? or intermediate?risk patients with transcatheter aortic Valve replacement is nowadays a consolidated therapy. Although initial experience of transcatheter aortic Valve replacement was conditioned by a limited number of early?generation prostheses, the widespread diffusion of this procedure has led over time to a growing interest to improve existing devices or develop newer ones, resulting in a wide selection being currently available. The results of these studies, which confirmed the noninferiority of transcatheter aortic Valve replacement against conventional surgical therapy, are valid for both balloon?expandable and self?expanding valves. Over time, these randomized clinical trials have also been accompanied by experiences coming from different multicenter or single?center registries that have enriched the wealth of information that we have today on this procedure.
TMVR Devices Under Clinical Study
Differently from transcatheter aortic Valve replacement, most of the TMVR technologies are still under clinical investigation or in their early experience in safety and feasibility trials so, information about their durability, structural deterioration, or comparison with surgery is still far. The CardiAQ alve is a nitinol self?expanding trileaflet valve, composed of bovine pericardial tissue, which was the first dedicated device for TMVR in 2012 in high?risk patients with severe MR. The second generation of the device was used for the first time in 2014. It is the only device that offers both a transapical and transfemoral?transseptal approach.
Another attractive system, the AltaValve was recently presented. This system presents a different concept in contrast with the other TMVR devices. Indeed, it is composed by a self?expanding supra?annular device, with a bovine tissue valve mounted into a spherical nitinol frame, inserted into the left atrium (with a transseptal or transapical delivery system), thus completely preserving the LV. Preclinical studies in animals were completed, and a first?in?human case was performed.
Various demographic, anatomical, and technical reasons contributed to the delayed development of TMVR in contrast with transcatheter aortic Valve replacement. This has been already confirmed safe and effective, whereas TMVR is still far from being part of the daily routine. However, although MV repair is often the preferred treatment, especially for MR, a replacement therapy will be the future when repair is not feasible or can lead to unsatisfactory results.