Chronic mitral regurgitation (MR) is a common condition that, if left untreated, results in progressive heart failure, left ventricular (LV) cavity dilation and systolic dysfunction, left atrial enlargement, atrial fibrillation, and pulmonary hypertension. Although medical therapy may provide some symptomatic relief and is used to manage underlying ischemic heart disease and heart failure in patients with MR, it has not been shown to provide benefit in prevention of development of heart failure.1 The current mainstay of therapy, surgical correction with mitral valve repair or replacement, is unavailable in approximately 50% of patients with severe MR due to the invasive nature of open-heart surgery and frequent presence of comorbidities in this group.2 Consequently, percutaneous technologies, with the potential benefit of decreased morbidity, improved recovery time, and shorter hospital stay, provide an exciting treatment option for this patient population.
The 2 broad categories of mechanisms of MR include degenerative and functional MR.
DEGENERATIVE MITRAL REGURGITATION
Degenerative MR (dMR) implies presence of a primary anatomic abnormality involving the valve, which usually stems from 2 major groups of causes: (1) Barlow disease (myxomatous valve disease, mitral valve prolapse, or floppy valve) or (2) fibroelastic deficiency. Barlow disease typically presents earlier, with surgical referral at 40 to 50 years of age, and involves chordal elongation and thickening, thick leaflets with excessive tissue, and multiple segments of prolapse or flail. Fibroelastic deficiency tends to be seen in elderly patients (age ≥65 years), who have a brief history of MR and often present with a ruptured chord and leaflets that are thin, sparse, and frail except in prolapsing segment, which may be thickened. With single-leaflet prolapse or flail, often the P2 segment is affected.3 Other rare causes of dMR include Marfan syndrome, Ehlers-Danlos syndrome, and osteogenesis imperfecta.3
FUNCTIONAL MITRAL REGURGITATION
Functional MR (fMR) is caused by geometric derangement of the mitral valve apparatus secondary to LV remodeling in the setting of regional or global LV dysfunction and in the absence of a primary leaflet pathology, such that an imbalance between the closing (LV contractility, electrical synchrony, and annular contraction) and tethering (papillary muscle displacement, LV remodeling, and annular dilation) forces of the functional mitral unit are present.4 The most common etiologies of fMR are nonischemic (often global dilation) and ischemic (often regional dilation) dilated cardiomyopathy.5
Numerous technologies are aiming to address percutaneous treatment of chronic MR, and MitraClip (Abbot Laboratories, Abbott Park, IL) remains the best studied and most widely used system for percutaneous mitral valve repair. A V-shaped clip (MitraClip) that is attached to the mitral leaflets is delivered through a 24-Fr steerable delivery guide catheter via a transseptal approach. This effectively achieves a repair similar to the Alfieri stitch. Additional clips can be delivered adjacent to the original one in cases with significant residual regurgitation. This device is ...