New Transcatheter Mitral Valve Treatment
unstable). There were no major events during the implant procedure. Four devices were removed uneventfully at follow-up and three patients underwent surgery due to device migration and/or loss of efficacy. PTOLEMY II is currently active in Canada and Europe.
Monarc Percutaneous Transvenous Mitral Annuloplasty Device The development of the Monarc PTMA device (Edwards Lifesciences, Inc., evolution of the Viking device) has been discontinued. An angiographic substudy of 50 patients treated confirmed the possibility of coronary flow compromise with these devices: coronary compression was demonstrated in 15 patients, three of whom experienced clinical events at follow-up.
Despite initially high expectations, the CS approach is developing more slowly than expected, with only over 200 patients treated to date. Several factors may explain this issue:
• The devices have had to undergo redesign due to problems with the nitinol (fractures).
•
There is a risk of potentially compressing the coronary arteries. Coronary sinus and great cardiac vein may cross over adjacent arteries, compromising flow and originating ischaemia. Different studies have shown that the CS crosses over the left circumflex artery (LCX) in up to 63–85% of patients.14–16
•
Cardiac venous anatomy is highly variable and this may preclude device implantation in some patients. Coronary sinus, great cardiac vein and middle cardiac vein are relatively constant structures, but there is evident anatomical variability in the distribution and number of the posterior and marginal veins of the LV,14,17,18
particularly in
patients with a prior history of acute myocardial infarction (AMI). Therefore, knowledge of the individual venous anatomy seems essential for planning a percutaneous approach.
•
The reduction in MR has been variable and somehow less than expected. This may be in part due to the complex anatomical relation between the CS and the MA, which are three-dimensional structures that do not lie in the same plane.14
In fact, in most cases
the CS does not lie directly over the MA but is located in a higher position on the LA wall and therefore, in most cases, these devices will not directly cinch the MA but rather, they will shrink the inferior portion of the LA close to it.14,15,19
Consequently, evaluation of CS and cardiac vein anatomy, as well as their relation to MA and other adjacent structures (basically coronary arteries) is of great relevance prior to planning a percutaneous approach. Multidetector computed tomography (MDCT) seems a very useful tool in patient evaluation prior to the procedure. It has shown excellent correlation with invasive angiography for the identification of cardiac venous structures in small series17
and it not only allows for
evaluation of the cardiac venous system, but also for the anatomical relation between the CS and the coronary arteries and the CS and the MA.14
Direct Annuloplasty
These techniques reduce the dimensions of the MA acting directly on it. Therefore, they should theoretically overcome the limitations inherent to annuloplasty through the CS. There are two different venues ongoing.
The first one implants several anchors in the posterior MA and connects them with a wire/suture that applies tension in order to
INTERVENTIONAL CARDIOLOGY
bring them closer and reduce posterior MA dimensions. This includes two different technologies, with about half a dozen patients treated to date:
Mitralign Device
In the case of the Mitralign device (Mitralign, Tewksbury, Massachusetts, US) the LV is accessed through a retrograde approach and a fork-like device is placed on the ventricular portion of the posterior MA. A catheter is also placed in the CS through a venous access. There are magnets in the extremes of the fork-like structure and on the CS catheter, which once coupled, stabilise the whole system. Next, three anchors are delivered and sutured to the ventricular side of the MA with stitches applied from the ventricular to the atrial side of the MA. These anchors are connected with a suture and when tension is applied to this suture, the MA is cinched. There are ongoing feasibility studies in humans in Paraguay and Germany.
Accucinch Annuloplasty System
In the Accucinch Annuloplasty system (Guided Delivery Systems [GDS, Santa Clara, California, US]), anchors, connected by a wire, are similarly placed in the subannular region of the LV through a retrograde approach. Technical feasibility studies in animals have demonstrated a reduction in the MA perimeter when tension is applied to this wire and a feasibility study in humans was started in Europe.
The second approach is in pre-clinical development and is based on the application of radiofrequency energy to the atrial region of the posterior MA (QuantumCor device, San Clemente, California, US) in order to originate scarring and constriction of the tissue treated. Transeptal access to the LA is necessary to introduce a catheter with a loop tip on which the radiofrequency electrodes are placed. No device is left in place in the atrium.
In addition, ReCor Medical (Ronkonkoma, New York, US) is working on a new technology that utilises therapeutic ultrasound to heat and shrink the collagen-rich MA. Through a transeptal access, a non-occlusive ‘floating’ balloon with the capability to beam ultrasound is positioned in the mitral orifice. The heat generated by the ultrasound acts on the collagen present on the MA, inducing its shrinkage and reducing MA dimensions.
Assymetric Annuloplasty
The PS3 was based on the concept of atrial remodelling in an attempt to reduce septal-to-lateral distance of the MA. Nevertheless, this research programme has been discontinued due to economical issues.
Left Ventricular Remodelling
The goal is to compress the LV to geometrically remodel the chamber, treating the target problem in functional MR that is ventricular distortion. Subsequently, the MA is also distortioned and compressed.
The percutaneous iCoapsys technology is based on the off-pump Coapsys surgical system (Myocor, Maple Grove, Minnesota, US), which places pads on both sides of the LV connected by a cord that traverses the LV cavity in a submitral position, approximately 2cm below the MA, therefore applying tension to the MA and basal LV wall. Initial surgical data indicated that the device can be implanted safely with acute reduction in MR and positive LV remodelling.21 Results of the Randomized Evaluation of a Surgical Treatment for Off-Pump Repair of the Mitral Valve (RESTOR-MV) study, comparing
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