Mitral regurgitation (MR) is one of the most frequent valve lesions, both in North America and in Europe, and its prevalence is increasing owing to the aging of the population. There are 2 main categories of MR: Organic Mitral Regurgitation (OMR) and Ischemic Mitral Regurgitation. Organic or primary MR is caused by an anatomic alteration of the valvular or subvalvular mitral apparatus and refers to rheumatic MR and degenerative MR that includes mitral leaflet prolapse and flail leaflet. In the past 20 years, degenerative MR has become, by far, the most frequent cause of severe MR leading to surgery in the western world. However, the best current treatment for OMR remains uncertain and controversial. This is, in large part, due to the lack of prospective data on the determinants of OMR progression and outcome. Furthermore, we have obtained preliminary data showing that OMR is a dynamic lesion. Hence, the echocardiographic evaluation of MR at rest, as generally performed during routine clinical exam, does not necessarily reflect the status of MR during patient's daily activities and thereby does not adequately assess the risk of rapid progression and poor outcome in these patients.

The general objective of this study is thus: to identify the independent predictors of disease progression and outcome in patients with asymptomatic chronic OMR and to develop and validate novel imaging and circulating biomarkers to improve risk stratification and therapeutic decision-making process in patients with chronic asymptomatic primary OMR.

The specific aims of the study are: (1) To obtain and analyze: a) the dynamic changes in MR severity, pulmonary arterial pressure, and LV function during exercise; b) the maximum exercise capacity; c) the metabolic profile; d) the plasma natriuretic peptides, e) the degree and localization of myocardial fibrosis measured by cardiac magnetic resonance Imaging (MRI); f) the blood markers of myocardial extracellular matrix (ECM) turnover; g) the progression of MR severity and LV dysfunction during follow-up; and h) the occurrence of adverse clinical outcomes (i.e. symptoms, LV dysfunction, atrial fibrillation (Holter ECG), pulmonary hypertension, heart failure, cardiovascular death) during follow-up in a series of 440 patients with at least moderate OMR and no symptoms at baseline. (2) To analyze the valve tissue samples explanted from the patients who will undergo mitral valve repair with quadrangular resection during follow-up in order to document the presence of lipids, inflammation, and expression of metalloproteinases (MMPs). (3) To obtain and analyze the postoperative changes in LV geometry and function, pulmonary arterial pressure, symptoms, and exercise capacity in the subset of patients who will undergo mitral valve surgery during follow-up. (4) To evaluate the usefulness of the exercise induced changes in MR severity, pulmonary arterial pressure, and LV function (i.e. contractile reserve), and of the blood levels of natriuretic peptides and ECM biomarkers for the prediction of rapid progression to LV dysfunction and adverse events. (5) To examine the relationship between the metabolic abnormalities linked to visceral obesity and the progression and outcome of OMR. (6) To determine, among the baseline clinical, echocardiographic, MRI, metabolic, and biomarkers variables, those which are independently associated with the progression of MR severity and LV dysfunction, and the occurrence of adverse clinical outcomes in patients with OMR.