Functional mitral regurgitation (FMR) in patients with chronic myocardial ischaemia/infarction or dilated cardiomyopathy results from significant left ventricular remodelling with papillary muscle displacement and restrictive leaflet motion.1,2 Almost invariably, the mitral annulus is dilated and deformed, whereas the valve leaflets are morphologically normal. Surgically, annular reduction can be achieved with an undersized ring3 and, in some cases, with a suture annuloplasty or pericardial bend.4,5 However, valve repair of a mitral valve with functional regurgitation remains a challenge for physicians around the world, mainly due to suboptimal results compared with the excellent surgical outcomes in patients with degenerative mitral regurgitation.6 Percutaneous interventions for FMR derived from surgical concepts may lower complication rates even if they are less efficacious than the surgical approaches, and are being developed.7,8
Mitralign Percutaneous Annuloplasty System
Mitralign, Inc. (Tewksbury, MA) has developed a proprietary mitral valve repair system called the Mitralign Percutaneous Annuloplasty System, which mimics surgical suture annuloplasty and aims to plicate the dilated posterior mitral valve annulus in patients with FMR. In essence, the Mitralign Percutaneous Annuloplasty System is a set of eight devices: a deflectable guide catheter, a steerable wiredelivery catheter, crossing wires, a two-arm (bident) translational catheter, pledget delivery catheters pre-loaded with pledget, a plication catheter pre-loaded with lock, a plication assistance device and a suture cutter. To simplify the set, some of the devices will be integrated in one single piece (see Figure 1).
The guide catheter is a deflectable 12.5Fr catheter with a haemostatic valve at the proximal end to minimise blood loss during the procedure. It provides retrograde femoral access to the left ventricle and is designed to direct all subsequent procedural catheters towards the posterior mitral annulus. The wire-delivery catheter is an 8Fr steerable catheter accessing points of interest on the ventricular side of the posterior mitral annulus and delivering crossing wires (see Figure 2). The radiofrequency (RF) crossing wire is a 0.019-inch (330cm)-long guidewire with polyester insulation and hydrophilic coating. It is connected to an RF generator and advanced across the mitral annulus and into the left atrium. The crossing wire serves as a rail over which the Bident translational catheter and the pledget delivery catheters are tracked. The Bident translational catheter is a double-leg catheter that is advanced over one crossing wire to provide positioning of a second wire.
Once the translation catheter is advanced to the mitral annulus, the two legs open up into a bident configuration spacing the wires 14 or 17mm apart (see Figure 2). The pledget delivery catheter is a 7Fr, 140cm catheter pre-loaded with a pledget implant. It is integrated with a handle that stores the suture and aids the delivery and cinching of the pledget across the annulus (see Figure 3). The catheter is pushed forward over the crossing wire through the annulus to deploy half of the pledget on the atrial side and the other half on the ventricular side of the annulus. The polyester pledget incorporates two platinum–iridium radiopaque markers to aid deployment and annulus plication. Basically, the pledget and the attached suture serve as a buttressed anchor for plication of the annulus. To plicate the annulus, a pair of pledgets has to be delivered and cinched together. The plication catheter is a 10Fr, 130cm catheter pre-loaded with a stainless steel locking implant (see Figure 4). It is tracked to the annulus over the two sutures. In conjunction with an external handle, the plication catheter provides a means for plication of the mitral annulus by pulling the two pledgets together. Once plication is achieved, the plication catheter deploys the lock onto the sutures, thereby securing the plication. The suture cutter performs the final suture cut following deployment of the lock. It is a 7Fr, 135cm catheter that is tracked over the two sutures to the lock and, by actuating a blade, cuts the sutures.
Mitralign Percutaneous Procedure
The Mitralign percutaneous annuloplasty is an echocardiography-guided cardiac intervention. General anaesthesia may be required in those patients who cannot tolerate a transoesophageal echocardiographic (TEE) probe for the length of the procedure. A long 14Fr introducer sheath is placed in the right femoral artery. Heparin is given to maintain an activated clotting time of more than 250 seconds throughout the procedure.
The deflectable guide catheter is advanced into the left ventricle over a long 0.035-inch guidewire, which is pulled back as soon as the aortic valve is crossed. A removable soft obturator, located at the tip of the guide catheter, aids the crossing of the aortic valve and ensures safe deflection of the guide catheter within the left ventricle. The catheter is deflected in order to be positioned over the posterior wall pointing up towards the mitral annulus.
The obturator is then removed and the catheter is ready to swing between the papillary muscles. As a next step, the wire delivery catheter is advanced through and extended beyond the tip of the guide catheter so that it can be steered to a target point at the P1 or P3 scallop location of the annulus (see Figure 2A and B). Once a target point is selected and touched by the tip of the steerable catheter, a crossing wire is placed in a position ready to penetrate the annulus. The crossing wire is connected to an RF generator (Valleylab Force FX-C® Generator; Boulder, CO) and, by applying RF energy for one to two seconds, is advanced 1cm through the annulus and into the left atrium. The wire is then pushed deeply into the left atrium and pulmonary vein to provide better support for the next catheter and decrease the risk of losing position during the subsequent exchange of the wire-delivery catheter with the double-leg bident catheter. Prior to using the Bident catheter, one of the legs needs to be selected as a leading leg and loaded on the crossing wire. The catheter is tracked over the wire until the leading leg exits the guide catheter and is positioned in close proximity to the annulus. The second leg, which is collapsed in adjunction to the leading leg, is then pushed forward so that the catheter opens up in a bident configuration with a span of either 14 or 17mm between the legs. A second wire is delivered through the non-leading leg and penetrates the annulus with radiofrequency as described above (see Figure 3).
While maintaining the positioning of two wires, the Bident catheter is withdrawn and a pledget delivery catheter is advanced over each of the wires, one at a time. The pledget delivery catheter is pushed through the annulus until a radiopaque marker, indicating the exit port for the pledget, arrives above the annulus. Using a slide mechanism on the handle of the catheter, the atrial half of the pledget is pushed out of the catheter, and, subsequently, using a cinching wheel on the handle, this straight pledget portion is folded to a small piece (see Figure 4B). The wire is removed, and the pledget delivery catheter is pulled back in the guide catheter until the folded portion of the pledget remains on the atrial side of the annulus and the proximal straight portion of the pledget exits the pledget delivery catheter and the guide catheter. Using the cinching wheel on the handle, the proximal portion of the pledget is folded on the ventricle side of the annulus, and tightened to the atrial half of the pledget (see Figure 4B).
When the pledget delivery catheter is withdrawn completely, the suture, which is attached to the pledgets, is freewheeled from the handle and exteriorised. A new pledget delivery catheter is tracked over the second wire to deliver a second pledget on the annulus. Once a pair of pledgets is implanted, the two sutures are exteriorised through the guide catheter and become a tracking rail for the plication catheter. This catheter is advanced up to the annulus so that the tip where the lock is located is positioned strictly underneath one of the pledgets. Using a plication assist device, tension is applied on both sutures and they are pulled together to achieve at least 50% plication. To secure the plication, the sutures are locked with the stainless steel lock. Finally, the plication catheter is exchanged with the suture cutter catheter, which cuts the sutures. Once the procedure is completed at one location (P1 or P3), a second pair of pledgets is delivered at the other scallop location (P3 or P1) and the plication is locked in place.
Echocardiographic Procedural Guidance
Traditionally, percutaneous cardiovascular interventions have used angiographic and fluoroscopic guidance, which is limited when interventions involve the mitral valve.9 As percutaneous therapy for mitral regurgitation continues to advance, it is inevitable that intraprocedural echocardiographic guidance will continue to evolve rapidly. TEE has been widely used as an alternative to transthoracic echocardiogram (TTE) in guiding complex procedures. TEE offers superior image resolution to TTE and excels at assessing anatomy and physiology, monitoring catheter position and performing dynamic evaluations to detect potential complications.10 A more recent application of cardiac ultrasound, intra-cardiac echocardiography (ICE), may have considerable potential for monitoring and guiding mitral valve annuloplasty. However, experimental and clinical studies have to demonstrate the feasibility of ICE in guiding mitral valve annuloplasty. Basically, TEE is an enabling imaging modality for the Mitralign annuloplasty procedure. The intervention is performed with close collaboration between interventional cardiologists and echocardiologists. Penetration of the mitral annulus with the RF crossing wire is a critically important step in determining the success of the procedure. The wire should go strictly through the mitral annulus and never through the myocardial wall or the posterior leaflet. Crossing through the myocardial wall involves a high risk of perforation, while crossing through the leaflet would not provide a stable position for the pledget and the plication. Ideally, the wire should cross the annulus 1 to 2mm outside the hinging point of the leaflet but at least 1mm inside the wall (see Figure 5).
Given the narrow crossing zone and the anatomical variability of the mitral annulus, selecting the crossing point with the tip of the steerable wire-delivery catheter or the non-leading bident leg presents significant challenges for the interventional cardiologist performing the procedure, and requires clear TEE guidance (see Figure 5). Even when the crossing point is selected correctly, the trajectory of the wire may be projected through the annulus but also further up through the wall so that an inadvertent puncture leading to complication may occur. Therefore, to increase the safety of the procedure, the trajectory of the wire-delivery catheter or the non-leading leg of the bident catheter has to be confirmed on echo before advancing the wire with RF. Once the wire has crossed the annulus, the crossing location and the crossing depth have to be assessed and confirmed with TEE. Finally, TEE needs to verify that the tip of the wire has passed into the left atrium and is free. The procedural risk can be decreased significantly if the wire crossing is assessed completely prior to advancing the larger pledget delivery catheter.
In addition, TEE provides adjunctive guidance for fluoro in terms of guide catheter positioning (see Figure 6), bident sizing and pledget implantation (see Figure 7). TEE is also used for monitoring mitral regurgitation and ruling out pericardial effusion or other procedural complications. The safety and feasibility of the Mitralign percutaneous annuloplasty is currently being studied in a first-in-man (FIM) study.