Left ventricular mass is the most important cardiac parameter that predicts cardiovascular events, and MR imaging is the most accurate means of measuring cardiac parameters. The purpose of this study is to evaluate the effect of inclusion and exclusion of papillary muscle mass in relation to left ventricular (LV) function parameters and to correlate the papillary muscle mass with body composition variables and gender in an asymptomatic study population.

50 men and 50 women without known cardiovascular disease were included in the analysis. Using end-systolic short axis fast gradient cine magnetic resonance (MR) images, the contours of the papillary muscles were traced manually and the left ventricular wall contours were outlined semi-automatically. Blood pool, papillary muscle and left ventricular wall volumes were calculated using dedicated cardiac imaging software. Papillary muscle and left ventricular wall mass were calculated based on the density of normal myocardium using Simpson’s method.

Inclusion of the papillary muscles results in significantly higher total LV mass values (p<0.001) and lower end diastolic volume (EDV) values (p<0.001) compared to measurements excluding papillary muscles from the LV mass. The papillary muscle mass for men was significantly higher compared to that observed in women (p<0.001). Papillary muscle mass accounts for 8.9% of the total LV mass in both men and women and is correlated with LV wall mass (r=0.81, p<0.001). The proportion of the papillary muscle volume in relation to the EDV decreases with increasing EDV (r=-0.40, p<0.001) and increases with increasing total LV mass (r=0.34, p=0.004). Body surface area is proportional to papillary muscle mass (r=0.45, p<0.001).

Inclusion or exclusion of papillary muscle mass significantly affects LV function parameters with MR imaging and must be accounted for when predicting cardiovascular outcome based on MR parameters. In individuals with increased LV mass, the papillary muscle volume accounts for a relatively larger fraction of the EDV compared to individuals with lower LV mass.