Reference values describing the normal mitral valve and the position of the papillary muscles

In patients with functional mitral regurgitation (MR), the principal mechanisms are insufficient coaptation due to dilatation of the mitral annulus (MA), global ventricular dysfunction with tethering of leaflets, or restricted leaflet motion with incorrect apposition due to regional ventricular dysfunction and displacement of the papillary muscles (PMs). These different entities often coexist and for this reason, knowledge of the normal reference values describing the shape and size of the MA and the position of the PMs is essential. In the present study, we describe the MA dimensions and the position of the PMs in a group of normal individuals (n = 38, 60% women, age [mean +/- SD] 51 +/- 9 years and BSA 1.83 +/- 0.16 m(2)) investigated with transthoracic echocardiography. The anteroposterior dimension (AP) of the ellipse-shaped MA was measured in a parasternal long axis, while the distance from the posteromedial (PoM) to the anterolateral (AL) commissure was measured in a parasternal short axis (CC). The annular area was calculated assuming elliptic geometry. The MA shape was described by the ratios AP/CC and AP/length of the anterior leaflet. The PMs' position was described by the following distances: (a) from the MA to the tip of the PoM and AL, PMs measured in a modified two-chamber view where both PMs could be identified, (b) the interpapillary distance, and (c) the tethering distance from the tip of the PM to the contralateral MA. These data on the normal mitral valve morphology should provide useful information when assessing the underlying mechanism of functional MR.