Mitral valve-in-MAC

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.