Current Percutaneous Coronary Sinus Mitral Annuloplasty Devices in Patients with Dilated Cardiomyopathy (pp. 461-472)
Authors: (Tohru Takaseya, and Kiyotaki Fukamachi)
Abstract: Mitral regurgitation (MR) is an important clinical entity in which blood leaks from the left ventricle (LV) back into the left atrium during systole. Patients with significant MR may suffer from shortness of breath, symptoms of congestive heart failure, and atrial arrhythmias. MR is caused by a variety of different mechanisms and pathologies affecting various components of the mitral valve. The father of surgical mitral valve repair, Alain Carpentier, MD, PhD, described a three-tier classification system (types I, II, and III), which incorporates annular size, leaflet mobility, and coaptation, as well as LV and papillary muscle function in determining the structural changes causing MR. This classification remains relevant to the modern-day surgeon and in the new era of percutaneous mitral valve repair  (Figure 1).
The terms functional and ischemic MR are often used interchangeably in clinical medicine, but some relevant differences exist. Functional MR usually occurs when mitral leaflets fail to coapt despite normal leaflet motion (Carpentier type I dysfunction) and can be seen with increased LV sphericity [2,3], papillary muscle tethering from nonischemic LV enlargement , or mitral annular dilatation . Myocardial infarction, often with regional involvement of the posterolateral LV wall and the posterior papillary muscle, can also result in LV/mitral annular enlargement and so-called ischemic MR. Ischemic MR arises from apical papillary muscle displacement with primarily posterior leaflet tethering and restricted motion during systole (Carpentier type IIIb dysfunction). Apical displacement of both leaflets with restricted motion in systole and diastole, often with associated rheumatic valve disease, results in type IIIa dysfunction. Almost half the patients with LV dysfunction have at least moderate MR [6, 7]. Due to its vicious downward cycle, the prognosis is poor in patients with functional MR [6, 8]. Chronic ischemic MR, also called ―Functional‖ MR or ―Secondary‖
MR, is an independent predictor of higher mortality and higher risk of developing heart failure in the post myocardial infarction population [8, 9].
Ischemic MR occurs in 10-20% of the patients with coronary artery disease (CAD) , translating to an incidence of approximately 50,000 to 100,000 patients. Despite the increased mortality and risk of heart failure, there is currently no therapy that demonstrates a survival benefit for the ischemic MR population [10-13]. Prosthetic ring annuloplasty is a key in most cases of surgical valve repair because there is always some degree of annular dilation in severe chronic MR. Surgical mitral annuloplasty is widely used to treat chronic MR, either in isolation or, most often, in combination with other techniques. However, the operative procedure requires access to and manipulation of the valve annulus via a left atriotomy and stitching of the ring is a time-consuming process. Furthermore, the procedure currently requires the patient to be placed on cardiopulmonary bypass (CPB) to facilitate the treatment. Research indicates that CPB constitutes a greater risk to patient outcomes than does the access means associated with the procedure (sternotomy, thoracotomy). Longer CPB times have been suggested as a cause of minor neurological deficits following open-heart procedures, and the use of heparin during CPB results in an increased risk of stroke complications. Finally, the outcome of the annuloplasty ring placement cannot be adequately assessed until the patient is weaned from CPB. These complications result in added procedural and anesthetic times and are typical reasons for increased morbidity/mortality rates in treated patients. Surgery may be high risk or even contraindicated in a substantial group of patients due to the presence of severe comorbidities and/or very severe LV dysfunction.