Percutaneous Approaches for Treating Mitral Regurgitation

10.1

Mitral Regurgitation: Etiology, Prevalence, and Clinical Background

MR is a heterogeneous disease reflecting multiple underlying etiologies that converge on systolic regurgitation of the MV. Carpentier, Barlow, and others have described three general categories of MR with associated subclassifications ( Figure 10–2 ). Degenerative MR (DMR; Carpentier Type II dysfunction) results from structurally abnormal leaflets or chordae and occurs in fibroelastic deficiency with leaflet prolapse, myxomatous leaflet degeneration, or Barlow disease with diffuse excess tissue and chordal elongation. Over the course of 10 years, 90% of patients with severe MR caused by a flail posterior leaflet will either die or require MV surgery. Surgical MV repair is the preferred treatment for degenerative MR because it is associated with improved postoperative outcomes and survival when compared to MV replacement. Multiple surgical repair techniques exist, including leaflet repair with resection, chordal transfer, use of polytetrafluoroethylene neochordae, and prosthetic ring or band annuloplasty. Novel therapies addressed later in this chapter include percutaneous approaches to these leaflet and chordal repair strategies.

Functional MR (FMR; Carpentier Type I or IIIb) results from underlying LV dysfunction and annular dilation, leading to impaired coaptation of otherwise structurally normal leaflets. Surgical correction of FMR improves functional class and LV remodeling, but it is uncertain whether this is associated with reduced mortality. Even with modern surgical annuloplasty techniques, up to one third of patients with FMR develop recurrent moderate or greater MR within 1 year of surgery. A number of predictors for recurrent MR after restrictive annuloplasty have been identified, including LV end-diastolic diameter greater than 65 mm, posterior leaflet angle of 45 degrees or greater, and MV coaptation depth of 11 mm or more. As many as 500,000 people in North America have clinically significant congestive heart failure–associated MR, but the majority of those patients are not offered any MV intervention. Given that even asymptomatic patients with severe MR have higher 5-year rates of death, heart failure, and atrial fibrillation, a significant need exists for improved FMR therapies. Many of the devices discussed in this chapter attempt to address percutaneous approaches for treatment of FMR, primarily through percutaneous annuloplasty.

From an anatomic and interventional perspective, technologies for addressing MR can be categorized into treatments focused on leaflet repair, annuloplasty, chordal implants, LV remodeling techniques, and percutaneous MV replacement ( Table 10–1 ). The following discussion examines interventional techniques in development for each of these approaches.

10.2

Leaflet Repair

Other Leaflet Repair Technologies

The Cardiosolutions Percu-Pro system (Cardiosolutions Inc., Stoughton, Mass.) is a percutaneously delivered polyurethane-silicone polymer “Mitra-Spacer.” The spacer is balloon-shaped, occupies the regurgitant mitral orifice, and is anchored to the LV apex ( Figure 10–3 ). The spacer has the ability to “self-center” within the regurgitant orifice. Animal studies have shown that the device is not associated with any significant inflammatory response, and early clinical trials are underway.

Middle Peak Medical (Palo Alto, Calif.) is developing a unique solution that involves minimally invasive or transcatheter implantation of a posterior “neoleaflet.” The potential advantage of this approach is that the neoleaflet can restore coaptation with the anterior leaflet despite a variety of underlying degenerative or functional etiologies. Because the device consists only of this thin neoleaflet, the delivery profile is much smaller than a complete transcatheter mitral replacement. Since native posterior leaflet function is rendered inactive by the neoleaflet, no complex repair strategies are required. The implant does not interfere with the mitral support apparatus, so that ventricular–annular mechanical coupling is preserved. At publication, the device is undergoing preclinical development; a schematic of the technology is shown in Figure 10–4 .

The MOBIUS device (Edwards Lifesciences, Irvine, Calif.) utilized an innovative transseptal catheter that possessed suction capability in order to grasp the leaflets. Once the leaflets were grasped, a suture was delivered to the leaflets to create a double-orifice valve. In the initial in-human experience, the procedure was performed successfully on 15 patients. Nine of the patients had acute reduction of MR by 1 grade or more, and 6 patients had sustained improvement at 30 days. This device is no longer in further development because of the lack of apparent durability in the initial studies.

10.3

Chordal Implantation