Jason H. Rogers, Ehrin J. Armstrong and Steven F. Bolling

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).^6–8 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.⁹ 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.¹⁰ Multiple surgical repair techniques exist, including leaflet repair with resection, chordal transfer, use of polytetrafluoroethylene neochordae, and prosthetic ring or band annuloplasty.¹¹ 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,¹² but it is uncertain whether this is associated with reduced mortality.¹³ 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.^14–16 A number of predictors for recurrent MR after restrictive annuloplasty have been identified, including LV end-diastolic diameter greater than 65 mm,¹⁷ posterior leaflet angle of 45 degrees or greater,¹⁸ and MV coaptation depth of 11 mm or more.¹⁹ 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).²⁰ The following discussion examines interventional techniques in development for each of these approaches.

10.2 Leaflet Repair

10.3 Chordal Implantation

Annular Shape-Change Approaches

Surgical annuloplasty is often a stand-alone treatment for FMR and is an important adjunct to leaflet repair procedures for DMR. The importance of annuloplasty to durable long-term results has led to the concept that multiple transcatheter interventions (e.g., both MitraClip and annuloplasty) may be necessary to treat MR in a given patient.

Most percutaneous approaches for annuloplasty have attempted to reshape the annulus “indirectly” by reshaping the coronary sinus (CS). The CS travels in close proximity to the mitral annulus (Figure 10–6). Importantly, however, the CS does not directly lie in the annulus, but rather travels 5 to 10 mm superior and diagonally to the plane of the mitral annulus.²⁴ Any conformational change in the CS must be transmitted through sinoannular tissue, which attenuates any applied force. Additionally, the sinoannular tissue may remodel and redilate over time, thereby compromising durability of MR reduction. Several devices have been developed for placement within the CS. Each of these systems creates focal tension to reduce the circumference of the mitral annulus and the septal–lateral (SL) dimensions, with resulting reduction in MR. Although these devices are relatively easy to deploy, reproducible efficacy is a limitation because of the variable relationship of the CS to the annulus, and these devices all harbor the risk of circumflex coronary artery compression.²⁵

Figure 10–6 Indirect mitral annuloplasty using the coronary sinus.
A, The CS encircles the posterior mitral annulus. B, Computed tomography scan of subject with FMR showing relationship of CS (arrow) to the MV. Note that they are not coplanar. C, Movement of the CS with device results in narrowing of the left atrial lumen above the MV (double-headed arrow), with secondary indirect decrease in the mitral annulus diameter. Ao, Aorta; CS, coronary sinus; LA, left atrium; LV, left ventricle; MV, mitral valve.

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