Introduction
Patients with symptomatic severe mitral valve disease due to severe mitral annular calcification (MAC) are often elderly with multiple comorbidities and have a high risk of cardiovascular death. Their surgical risk for standard mitral valve surgery is high due to comorbidities and technical challenges secondary to severe calcification. Many patients are not offered standard mitral valve replacement due to their high surgical risk. Transcatheter mitral valve replacement (TMVR) with the compassionate use of aortic transcatheter heart valves (THV) is emerging as an alternative to surgery. Most of the experience has been with the Edwards family of THVs (Edwards Lifesciences, Irvine, CA). The implantation technique has evolved. The first case reports used an open transatrial or transapical valve delivery access. Subsequent reports used a transseptal delivery approach. Although there have been a few case reports using other aortic THVs, including Lotus (Boston Scientific Corporation, Marlborough, MA) and Direct Flow (Direct Flow Medical, Inc., Santa Rosa, CA), or a dedicated transcatheter mitral valve such as the Tendyne Mitral Valve System (Tendyne Holdings, Roseville, MN, a subsidiary of Abbott, Chicago, IL), most of the procedures have been done using balloon-expandable aortic THV technology. This chapter will describe contemporary mitral valve-in-MAC (ViMAC) techniques using the SAPIEN 3 valve.
Indications
Transcatheter mitral ViMAC is a new technology that is currently performed off-label. Eligible patients have severe MAC resulting in either severe symptomatic mitral stenosis or regurgitation and are at prohibitive risk for conventional mitral valve surgery. Anatomic suitability is required and is described next.
Preprocedural planning, sizing, and other anatomic considerations
Adequate sizing of the mitral annulus is challenging due to its complex oval saddle shape and irregular patterns of calcification. The experience with this procedure remains in the early phase, and there is no consensus of the best sizing methodology defined at this time. Selecting a valve size based on diameter or perimeter may not be the best method due to the oval saddle shape. We recommend use of the mitral annular area ( Fig. 18.1 A) and size the THV as we do for transcatheter aortic valve replacement (TAVR). Oversizing is important to achieve proper anchoring. The SAPIEN 3 valve was designed to treat calcific aortic stenosis, not mitral valve disease. It does not have an anchoring mechanism, and therefore adequate oversizing becomes extremely important in ViMAC to achieve proper anchoring. The percentage of oversizing that is safe to achieve anchoring without increasing the risk of annular rupture has yet to be fully defined. In general, approximately 15% to 20% oversizing may be adequate, but this is a relative number, as we generally use additional contrast volume during initial valve deployment to flare the ventricular edge of the THV to decrease the risk of embolization into the left atrium. This additional contrast volume may result in more oversizing than initially estimated. In addition to facilitating anchoring, oversizing aids in decreasing the amount of paravalvular leak (PVL). Because the SAPIEN 3 valve is round, there is a risk of residual perivalvular gaps that may result in significant PVL when implanted in the mitral position, which has an oval shape. PVL risk may be lower with the use of dedicated transcatheter mitral valves that are designed with a D-shape to respect the geometry of the mitral annulus.
Another factor that plays an important role in anchoring is the pattern of calcification. The amount, distribution, and type of calcification (i.e., caseating calcification vs. noncaseating) play a role in providing support to anchor a SAPIEN 3 valve. A larger amount and distribution of calcium help provide more anchoring capacity. A nearly circumferential calcification would most likely result in adequate anchoring, provided that the THV size chosen is correct and the ventricular edge of the stent is flared in transseptal cases, or anchoring sutures are placed in transatrial cases. Less than 270 degrees of calcified circumference or calcium limited to the posterior aspect of the annulus, which is frequently the case, may not provide adequate anchoring (see Fig. 18.1 ). However, the exact percentage of circumferential involvement required for procedural success is not well understood. In addition, other factors may help facilitate anchoring in the absence of complete circumferential calcium, such as trigone calcification or the presence of a prosthetic valve in the aortic position, which may provide additional anterior support for anchoring. A CT-based MAC score has been created to help categorize MAC severity and predict valve embolization. A MAC score of 7 or greater is associated with lower embolization risk than MAC score of 6 or less.
Other anatomic features to consider in the preprocedural planning include the subvalvular apparatus and surrounding structures, in particular the left ventricular outflow tract (LVOT), which can be affected by interactions with the SAPIEN 3 valve in the mitral position. Permanent anterior displacement of the anterior mitral leaflet toward the LVOT space occurs after ViMAC. If the LVOT space is not large enough, this interaction may result in severe LVOT obstruction, which can be fatal. Patients with severe MAC often have concomitant calcific aortic stenosis or history of a prior aortic valve replacement. The importance of concomitant or prior aortic stenosis is that those patients often have left ventricular hypertrophy with associated small left ventricular cavity size, which is in turn associated with a small LVOT that puts them at higher risk of LVOT obstruction.
Role of cardiac computed tomography
Detailed analysis of the patient’s mitral valve anatomy using multi-imaging modality is key for technical success. Transthoracic and transesophageal echocardiography (TEE) are useful tools to evaluate the severity of mitral valve disease, the function of cardiac structures, and to rule out the presence of thrombus. Cardiac computed tomography (CT) has become an essential tool for mitral annular sizing, assessment of LVOT obstruction risk, access route, and overall procedural planning. Acquisition protocols are similar to TAVR protocols, with some variations. It is important to include all cardiac phases to allow measurement of the annular area in diastole, when is usually larger, and assess the risk of LVOT obstruction in systole, when it is usually worse. Cardiac CT is also helpful to determine the landing zone of the THV stent frame in the left ventricle. During transseptal cases, it is useful to identify a radiopaque structure in the ventricle at the desired location of the ventricular edge of the stent frame. During valve deployment, the stent frame will foreshorten from the left atrium, and the radio-opaque marker in the balloon moves. Because the ventricular edge of the stent frame does not move during deployment, it is helpful to identify the landing zone in the left ventricle before the procedure when possible ( Fig. 18.2 ). This is not needed during open transatrial access. Once the THV size and the landing zone are identified, the neo-LVOT area is determined through placing a virtual valve in that position ( Fig. 18.3 ). Detailed techniques to measure the neo-LVOT area on cardiac CT have been published. ,
Cardiac CT analysis also aids in planning the access route, particularly to determine the best transseptal or transapical access location ( Fig. 18.4 ) and to determine the valve deployment angle before the procedure (see Fig. 18.2 ).
Delivery access types
The transseptal route is the least invasive option and our preferred method when anatomy is favorable. However, not all patients are good candidates due to anatomy that puts them at high risk of embolization, LVOT obstruction, or both. In these situations, the open transatrial delivery can be used to overcome those challenges. The transapical route is more invasive than the transseptal, but may be an option in selected patients if the operators are not familiar with transseptal techniques or when transseptal access cannot be obtained due to unfavorable anatomy.
Transatrial ViMAC technique
The open transatrial TMVR technique is the most invasive. However, it may be the best option in patients with lack of circumferential calcium because it allows the operators to place anchoring sutures to decrease embolization risk. It may also be a better option for patients with high risk of LVOT obstruction who are not candidates for alcohol ablation or percutaneous laceration of the anterior mitral leaflet, as the open delivery approach allows surgical resection of the anterior mitral leaflet to decrease LVOT obstruction risk. However, not all patients are good candidates for this invasive approach. Although there were challenges in the early experience, outcomes have improved with better patient selection and modification of the technique. We recently reported the contemporary transatrial technique step by step. Therefore the focus of this chapter will be the fully percutaneous transseptal technique.
Transapical technique
The transapical access and closure technique is similar to the technique used for TAVR. Transapical access is obtained with an 18-gauge needle, a J wire, and a 7F sheath placed in the left ventricle. A Brite Tip sheath facilitates visualization of the sheath tip. Crossing the mitral valve in a retrograde fashion is more challenging, particularly when the pathology treated is mitral stenosis. Once the valve is crossed with a J wire, the trajectory can be flossed with a balloon catheter over the wire to ensure the wire is not through chordae. Then the wire is exchanged for a supportive wire such as Amplatz extra-stiff wire (Cook Medical, LLC, Bloomington, IN) placed in a pulmonary vein, with careful attention to avoid pulmonary vein perforation, or the use of a preshaped wire in the left atrium such as Safari2 guidewire (Boston Scientific, Marlborough, MA) or Confida Brecker guidewire (Medtronic, Inc., Minneapolis, MN). The sheath is then upsized to the Edwards sheath over the supportive wire. The valve deployment technique is similar to the one used in transseptal delivery described next.
Transseptal ViMAC technique
The procedure is performed under general anesthesia with TEE guidance in a hybrid cath lab/operating room suite. Absence of left atrial appendage thrombus should be confirmed with intraprocedural TEE at the start of the case. A 35-cm-long, 6F Brite Tip sheath is placed in the abdominal aorta via the left femoral artery. A long sheath is used to allow simultaneous left ventricular and aortic pressure monitoring during the procedure through a 5F pigtail catheter in the left ventricle and the side arm of the 6F long sheath in the descending aorta. A 35-cm-long, 7F Brite Tip sheath is placed in the inferior vena cava via the left femoral vein. A long venous sheath facilitates pacemaker placement and manipulation, as sometimes this may be challenging with a large-caliber THV delivery sheath in the inferior vena cava.
Right femoral venous access is obtained with a 6F or 7F sheath, and the site is preclosed with one Proglide closure device (Abbott Vascular, Abbott Park, IL) and a 7F or 8F sheath is placed. The baseline LVOT gradient is documented by measuring simultaneous left ventricular pressure and aortic pressure. If desired, baseline left ventriculography may be performed, but this is not always needed. Left ventriculography is particularly helpful to visualize the mitral valve annulus and landing zone of the SAPIEN 3 valve when it is not obvious under plain fluoroscopy, but is not always needed. A 5F transvenous pacemaker is placed in the right ventricle via the left femoral vein. The sheath in the right femoral vein is upsized to a 16F Edwards eSheath. Because the sheath is the venous system and the risk of bleeding may be the same with a 14F or 16F sheath in the vein, it is easier to use the same 16F sheath for all valve sizes to facilitate valve delivery manipulation. Transseptal puncture is performed with a 7F or 8F Mullins transseptal and BRK or BRK-1 extra-sharp needle (St. Jude Medical, St. Paul, MN) under TEE and fluoroscopic guidance at the predetermined location by cardiac CT (see Fig. 18.4 ). We favor a transseptal puncture in the inferoposterior portion of the fossa ovalis, similar to transseptal access for left atrial appendage closure procedures. In the initial experience, we have performed TMVR with a superior and posterior location of septostomy, similar to the transseptal puncture for MitraClip procedures. However, it is usually more difficult to navigate across the septum and deliver the SAPIEN 3 valve with superior punctures. If the operators have experience in transseptal access, low-dose heparin (3000 units) may be given after venous and arterial access before transseptal puncture to decrease the risk of thrombus formation in sheaths or on the transseptal needle. Full-dose heparin is given as soon as transseptal puncture is performed.
A 230-cm, 0.025″ Toray wire (Toray Industries, Inc., Tokyo, Japan) is then introduced in the left atrium, the Mullens sheath is removed, a 14F Toray dilator may be used to dilate the interatrial septum, and a deflectable sheath is introduced such as the 8.5F Agilis steerable introducer (St. Jude Medical, St. Paul, MN) or the 9.5F Dexterity deflectable sheath (Spirus Medical, LLC, Bridgewater, MA). Simultaneous left atrial and left ventricular pressures may be recorded through the Agilis sheath and the 5F pigtail catheter. The Agilis catheter is flexed to point toward the mitral valve under fluoroscopic and TEE guidance, and the mitral valve is crossed in the deployment fluoroscopy angle using a 6F pigtail catheter and a J guidewire ( Fig. 18.5 A). The J wire is left inside the pigtail to provide support, but it is not used to cross the valve with wire alone. The intention is to avoid wire entanglement through chordae—such risk is lower when crossing the valve with the pigtail catheter itself. Once the pigtail is in the left ventricle, a 0.035″ small or extra-small Safari wire or Confida wire is introduced and positioned in the left ventricular apex (see Fig. 18.5 B). Slow movements advancing and manipulating this wire may be needed, as it often tends to displace the pigtail catheter and Agilis sheath to the left atrium. The pigtail catheter is removed and a 10-mm or 12-mm balloon that is 4 cm long and has a 110- to 135-cm shaft is introduced to perform a septostomy ( Fig. 18.6 ). A 10-mm balloon is generally used for the 23- and 26-mm SAPIEN 3 valves and a 12-mm balloon for the 29-mm valve when the septum has not been instrumented during a prior surgery. In patients with prior cardiac surgery where the septum was opened and closed, or in patients with thick or calcified septum, a 12-mm balloon may be needed for the 23- and 26-mm valves and a 14-mm balloon for the 29-mm valve. The balloon is introduced to the tip of the Agilis sheath in the left atrium, and then the Agilis is retracted to expose the balloon and facilitate the positioning across the septum. Operators may encounter difficulty advancing the septostomy balloon across the septum if this is attempted after the Agilis sheath is pulled back. Operators should consider the length of the Agilis sheath when selecting the shaft length of the septostomy balloon. Longer balloon shafts will be required (usually 110, 120, or 135 cm). It is important to adequately prepare the septum to avoid challenges crossing with the valve delivery system—30-second inflations may be better than short inflations.
