Page 23 - Journal of Structural Heart Disease Volume 1, Issue 3

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Original Scientific Article
tricular systole, occurring as a result of failure of the mitral leaflets to undergo complete coaptation (fail- ure of leaflet tips to meet) or apposition (failure of the leaflets to overlap sufficiently). A simple classification system divides the etiology of mitral valve disease into either primary or functional (secondary) (Figure 2). Classification of MR has relevant implications for therapeutic intervention. In primary MR, the standard treatment is repair or replacement of the affected valve. In functional MR, therapy involves manage- ment of the underlying left ventricular dysfunction. For select patients in whom medical therapy is opti- mized, there may be a role for surgical correction.
The most common cause of primary MR is degen- erative disease involving morphological changes to the valve due to thickening and stretching of leaflet tissue. The severity of these changes can range from involvement of a single scallop to both leaflets in their entirety. Fibroelastic deficiency describes a prolapsing segment, which is often normal in appearance. The pro- lapse is due to focal chordal elongation with or with- out rupture. Barlow’s disease refers to myxomatous changes to both leaflets, more commonly affecting the posterior leaflet, associated with chordal thinning and elongation. Accordingly, segments of both leaflets prolapse into the left atrium. A more severe manifesta- tion is a flail leaflet, characterized by complete eversion of the leaflet edge into the left atrium. A flail may be present in the event of primary chordal rupture and is often associated with severe mitral regurgitation. Oth- er less common causes of primary mitral valve disease include infective endocarditis, congenital mitral cleft, and rheumatic mitral disease. The latter results in mi- tral stenosis with characteristic commissural fusion, with thickening and rigidity of the leaflets, eventually leading to regurgitation.
Functional MR occurs in the context of morpholog- ically normal leaflets on a background of an under- lying idiopathic cardiomyopathy or coronary artery disease. The regurgitation is due to geometric alter- ations of the left ventricle, which may or may not be associated with dilatation. Regional or generalized wall motion abnormalities of the left ventricle can al- ter the position of the papillary muscles during systo- le, resulting in chordal tension and leaflet restriction. Ventricular dilatation causes subsequent annular
dilatation, resulting in failure of leaflet coaptation or inadequate apposition.
Clinical Outcomes and Procedural Indications
The clinical course of MR is usually slow and pro- gressive, except for the rare circumstance of acute MR due to papillary muscle rupture in the setting of an acute myocardial infarction. The insidious nature of the disease is a result of the ability of the heart to compensate for increasing regurgitant volume, initially through enlargement of the left atrium. As the regur- gitation becomes severe, the left ventricle is subject to overload, dilatation, dysfunction, and eventual failure. The presence of left ventricular dilatation and systol- ic dysfunction, particularly in the context of symp- tomatic functional impairment, heralds a very poor prognosis if left untreated. Annual mortality rates with medical treatment in patients aged 50 years or older are approximately 3% for moderate regurgitation and approximately 6% for severe regurgitation [3, 4]. Until recently, surgical valve repair or replacement was the only treatment proven to improve symptoms and pre- vent heart failure. Valve repair improves outcome com- pared with valve replacement and reduces mortality of patient with severe organic mitral regurgitation by about 70%. As expected, the best results are obtained in asymptomatic patients operated on in advanced repair centers with low operative mortality (<1%) and high repair rates (>80%) [5]. These results highlight the importance of early detection, assessment and man- agement of mitral regurgitation.
Current AHA/ACC and ESC guidelines recommend surgical intervention, preferably repair, in symptom- atic patients with chronic severe primary MR and in asymptomatic patients with chronic severe primary MR with evidence of systolic dysfunction or left ven- tricular dilatation [6, 7].
For patients with secondary MR, surgical interven- tion carries a higher rate of operative mortality com- pared to that for primary MR, largely due to the severe comorbidities of these patients. As such, the AHA and ESC guidelines suggest surgery for patients with se- vere secondary MR and preserved systolic function only when undergoing CABG or AVR [6, 7].
While surgery remains the gold standard of treat- ment, there are patients who are either at prohibi-
Sharma, R.A. et al.
An Overview of the MitraClip Procedure