Determination of the mitral papillary muscle positions by the septal-to-free wall arc ratio method.

Determination of mitral papillary muscle positions is of increasing interest in wide spectrum of clinical cardiology fields. Particularly, relative positioning of the papillary muscles between the inter-ventricular septum and the left ventricular free wall is of interest. A reproducible method for determination of papillary muscle positions has not been established. In this study a new 'septal-to-free wall arc ratio' (SFAR) method for measuring papillary muscle positions is presented. The reproducibility of the SFAR method between echocardiographic (ECHO) and magnetic resonance (MRI) modalities and between observers is tested. Twenty subjects with structurally normal hearts in whom both MRI and ECHO were performed in 2007 were included in the study. Papillary muscle positions were determined using the SFAR method. Inter-modality (ECHO and MRI) and inter-observer reproducibility of the methods was assessed by calculating correlation coefficients and the mean difference from agreement. The inter-modality correlation of the SFAR method was 0.80 (P < 0.0001) for both papillary muscles. The mean difference of measurements from agreement was 4% for the superior and 2% for the inferior papillary muscle. The inter-observer correlation was 0.93 (P < 0.0001) for superior and 0.90 (P = 0.0002) for inferior papillary muscle. The mean inter-observer difference from agreement was 2% for superior and 3% for inferior papillary muscle. The SFAR method may be applied in wide range of both scientific and clinical medical fields as a reproducible method for determination of papillary muscle positions with the benefit of estimation of relative papillary muscle positions both from the septum and the free wall.