Transcatheter valve therapy is one of the fastest growing and most exciting areas of interventional cardiology.  In those with congenital heart disease, pulmonary valves have been replaced in this way for some time now¹, and in the elderly population experience with transcatheter aortic valve implantation for calcific aortic stenosis is growing rapidly, with some very promising results².

With regards to the mitral valve, though, techniques for valve replacement have lagged behind. A number of devices exist for percutaneous mitral valve repair, of which the most well known is probably the Mitraclip device³, however, a transcatheter replacement valve is not currently available. The reasons for this include the intricate nature of the mitral valve complex; its contribution to left ventricular structure and function, and consequent highly mobile nature. In addition there is a lack of a suitable landing zone in which to site a prosthesis.

However, if a landing zone is present, such as in patients with a previously inserted bioprosthesis or annuloplasty ring, this can facilitate deployment.  Earlier this year Webbs department in Canada published a case series of valve-in-valve deployments for deteriorating mitral bioprostheses⁴, although all of these procedures were performed from a transapical, rather than a fully percutaneous, approach.

The focus of this editorial is the recently published preclinical study into percutaneous transvenous mitral valve replacement (PTMVR) by Shuto et al⁵ in the Journal of the American College of Cardiology.

The aim of the study was to demonstrate the feasibility of PTMVR within a surgically implanted annuloplasty ring in an ovine model, using the Melody transcatheter pulmonary valve replacement⁶. 

One week after having a surgically implanted annuloplasty ring five sheep underwent the transcatheter procedure via the iliac vein.  Intracardiac echocardiography was used to guide transeptal puncture, with subsequent placement of a wire into the LV. The valves (all 22mm) were crimped onto angioplasty balloons, passed over the wire and deployed once correctly located. The residual atrial septal defect was sealed on the way out with a closure device and post deployment left heart catheterisation and echocardiography were performed to assess valve position and function.

Animals were euthanized after 6 hours and necropsy was performed for visual inspection of the valve.

The procedure was successful in all animals. The only difference between pre and post deployment haemodynamics was an increase in pulmonary artery pressure (33.8 3.7 mmHg vs. 38 4.8 mmHg; p=0.008). There was a trend towards an increase in cardiac output; however, this did not reach statistical significance (4.10.7 l/min vs. 5.2 0.9 l/min; p=0.06). There was no significant change in left ventricular, left atrial or aortic pressures.

Three animals had centrally located mitral regurgitation post deployment. This was graded as trivial to mild in two and moderate to severe in one. In the animal with moderate to severe regurgitation the annuloplasty ring was large (28mm) and therefore the valve was over expanded, resulting in poor coaptation of the leaflets.

There was no paravalvular regurgitation, aortic regurgitation or left ventricular outflow tract obstruction noted in any of the animals.  Post mortem visual inspection of the valves showed that they were all securely anchored, although there was no objective measure of post mortem valve stability documented.  Procedure time ranged from 45-60 minutes.

This study successfully proves the feasibility of transcatheter PTMVR within surgical annuloplasty rings. Despite the equipment used not being specifically designed for this indication, as well as the valves being previously handled and cosmetically flawed, they appeared to be deliverable, with good immediate functionality. Procedure times were relatively short, and the group did not seem to experience any major procedural complications.  Importantly, there was no early negative effect on left ventricular or aortic valve function.  It is unclear what the cause for the increase in pulmonary pressures was but clearly the numbers are small and results limited.

It would have been useful to have some testing of the post mortem valve in order to gain more objective evidence of the stability of the implant.

Further study on longevity (short to mid-term) of devices deployed in this fashion is crucial and also perhaps the development and testing of dedicated equipment for this indication.

This is clearly a small proof of concept study but the results suggest that this technique, or something similar, may well develop into a clinical procedure in the years to come.

1. Khambadkone S, Coats L, Taylor A, et al. Percutaneous pulmonary valve  implantation in humans: results in 59 consecutive patients. Circulation 2005;112:1189-97.

2. Leon MB, Smith CR, Mack M, et al. Transcatheter aortic-valve implantation for aortic stenosis in patients who cannot undergo surgery. N Engl J Med 2010;363:1597-607.

3. Rogers JH, Franzen O. Percutaneous edge-to-edge MitraClip therapy in the management of mitral regurgitation. Eur Heart J 2011;32:2350-7.

4. Cheung AW, Gurvitch R, Ye J, et al. Transcatheter transapical mitral valve-in-valve implantations for a failed bioprosthesis: a case series. J Thorac Cardiovasc Surg 2011;141:711-5.

5. Shuto T, Kondo N, Dori Y, et al. Percutaneous Transvenous Melody Valve-in-Ring Procedure for Mitral Valve Replacement. J Am Coll Cardiol 2011;58:2475-80.

6. McElhinney DB, Hellenbrand WE, Zahn EM, et al. Short- and medium-term outcomes after transcatheter pulmonary valve placement in the expanded multicenter US melody valve trial. Circulation 2010;122:507-16.