Transthoracic echocardiography (TTE) is the most useful imaging tool for obtaining comprehensive information about the MV. The severity and extent of fusion, thickening, shortening, calcification, thrombus, and mitral regurgitation are all meticulously studied. A semiquantitative score of the MV pathology has been used to predict the efficacy of PTMC and select the appropriate patient (Table 20.2). A score of less than 9 with not more than mild MR is considered most suitable for PTMC [2]. With a higher MV morphology score and/or moderate degree of MR, one should balance the risk of PTMC and surgical open mitral commissurotomy (OMC). PTMC is an option if the patient is a high-risk candidate for OMC. The MV morphology score however does not quantify commissural fusion or calcification. As splitting of the fused commissure is essential for relief of MS, commissural fusion and calcification must be studied in detail.

Transesophageal echocardiography (TEE) is necessary to exclude thrombus in the LA, especially in the appendage. It is desirable in all patients before PTMC and mandatory in patients with atrial fibrillation or previous embolism and in patients with suboptimal TTE images.

Inoue’s method using an inflatable nylon-latex balloon catheter (NLBC) is the most widely used technique and is described in detail below. Two types of NLBC are currently available: Inoue balloon catheter (Toray, Tokyo, Japan) and Accura balloon catheter (Vascular Concepts Limited, Hallstead, United Kingdom). The NLBC is designed to expand initially in its distal portion and then sequentially in its waist and proximal part. The low compliance in its waist allows the balloon to take a dumbbell shape centered in the narrowest part of the mitral valve and expand to the desired diameter (Fig. 20.1). The differences between Inoue and Accura balloon catheters are shown in Table 20.3.