Transcatheter aortic valve implantation (TAVI) has become an established therapy for inoperable and high-risk patients with aortic stenosis, which has led to the feasibility of using transcatheter mitral valves to treat mitral regurgitation to be investigated. Anson Cheung (University of British Columbia, St. Paul’s Hospital, Vancouver, Canada) is co-principal investigator of the ongoing TIARA-1 feasibility study, which is investigating the use of the Tiara transcatheter mitral valve (Neovasc) in inoperable and high-risk patients with severe mitral regurgitation. He speaks to Cardiovascular News about the potential benefits of transcatheter mitral valve implantation.
What are the limitations of mitral valve surgery for mitral regurgitation?
At the moment, a lot of patients with mitral regurgitation are not being referred for treatment because they are seen as being too old, too fragile, or as having too many comorbidities to undergo surgery. Therefore, some patients with the condition are being under treated.
Another issue is that for patients with functional mitral regurgitation, surgery may not be beneficial even if they are eligible for surgery. Surgery may provide symptomatic relief for some patients if they are referred at an early stage, but we are probably not providing benefit if we treat them at the end stage.
What are the limitations of MitraClip (the most established transcatheter option for the mitral valve)?
There are many reasons why a patient may be ineligible for undergoing treatment with the MitraClip (Abbott Vascular). For example, the anatomy of the mitral leaflet, the amount of calcification, the amount of coaptation height and, in degenerative disease, how severe the prolapses are. Many patients require multiple clips and the effectiveness of the treatment may also be a barrier to treatment with the MitraClip. Additionally, the procedure itself is very long and quite complicated.
How could transcatheter mitral valve implantation potentially overcome these limitations of the MitraClip?
The MitraClip does not completely eliminate mitral regurgitation. You might reduce the grade of it, but you never completely get rid of it. Studies indicate that residual mitral regurgitation is associated with worse outcomes. With transcatheter mitral valves, such as the Tiara valve, you aim to completely eliminate the regurgitation.
Also, the Tiara valve does not rely on the leaflet geometry; therefore, some patients who are excluded from undergoing treatment with the MitraClip may be able to undergo transcatheter mitral valve implantation with the device.
What are the aims and goals of the TIARA-1 study?
We are aiming to recruit 30 patients in a multinational and multicentre trial—we have centres in Canada, Belgium, Germany and the USA. The aim is to determine if transcatheter mitral valve implantation with the Tiara valve is a safe and effective treatment for patients with mitral regurgitation who cannot undergo surgery. The primary follow-up is one year but we will try to follow patients for five years. We have just recruited and successfully treated the first patient, so hopefully completion of recruitment will be done by the end of 2015. After this feasibility study is completed, presuming its results are positive, the next step will be a pivotal trial in the USA and a CE-mark trial in Europe.
You performed the first-in-man procedures with the valve. What have been the outcomes of these procedures?
I performed the first four first-in-man procedures and all of the procedures went very smoothly. There were been no procedure-related mortality despite that the fact the patients were very sick, with ejection fraction ranging from 15% to higher than 35%. The first patient who underwent the procedure did die after 69 days, but they had multiple comorbidities, including end-stage renal failure as well as heart failure. All of the others [at the time of writing] are still doing well with well-functioning Tiara valves.
Given that there are now many different TAVI devices available on the market (in Europe at least), why do you think so comparatively few devices for the transcatheter management of mitral valve disease have been developed?
First of all, the money has been spent on developing the first- and second-generation TAVI valves rather than on devices for the mitral valve. Secondly, the mitral valve is much more difficult to treat than the aortic valve because of its anatomy. It is not circular (ie. it is saddle-shaped), has complex anatomy including the atrium, annulus, leaflets, subvalvular apparatus, ventricle, and left ventricular outflow tract, etc. There is no calcification on the valve structure for you to anchor the valve to.