**2. Evaluation of severity**

#### **2.1. Echocardiography**

Echocardiography is essential in the diagnosis and quantification of the severity of MS. Transthoracic echocardiography (TTE) provides sufficient data in most patients and should be performed in patients at initial presentation, in those with changing symptoms, and in asymptomatic patients periodically (**Figure 1**). It shows the restriction of the mitral valve opening caused by commissural fusion and the so-called doming of the mitral valve, thickness and calcification of the leaflets, and chordal thickening. A mitral valve area (MVA) ≤ 1.5 cm<sup>2</sup> and a pressure half-time (PHT) ≥ 150 ms correspond to severe MS. PHT is affected by left ventricular (LV) diastolic dysfunction and the severity of mitral and aortic regurgitation, while planimetry-derived MVA is more accurate and should be used for decision-making in most patients [6]. Mitral valve resistance might be a better predictor of hemodynamic burden of MS and can be used to determine the need for BMV in borderline cases [7]. The other parameters that are evaluated include transmitral valve gradient, MR severity, concomitant valvular involvement, atrial size, left and right ventricular functions, and pulmonary arterial pressure. Transesophageal echocardiography (TEE) is valuable when the images derived from TTE are not satisfactory or when the patient is candidate for BMV to rule out clots in the left atrium (LA) and the left atrial appendage (LAA) as well as for a detailed evaluation of MR severity.

#### **2.2. Hemodynamic study**

Cardiac catheterization, aside from guiding the procedure, is indicated when echocardiography is nondiagnostic. It is not routinely indicated; however, it is necessary when the results from echocardiography are ambiguous, when the severity of other valvular lesions is evaluated, and when there is a suspicion of coronary artery disease. Before BMV, measurement of the mitral valve gradient, pulmonary arterial pressure, and MVA using the Gorlin equation can be helpful in borderline cases and for confirming the severity of MS.

**Figure 1.** 3D echocardiography revealing bicommissural fusion, fish-mouth appearance of the mitral valve, and planimetryderived mitral valve area of 0.89 cm<sup>2</sup> .
