Developed force of papillary muscle: what index correctly indicates contractile capacity?

We hypothesized that similar samples of the same normal heart should report similar contractile index values. We analyzed anterior (AP) and posterior (PP) papillary muscles (PM) of the same heart (n = 46), whose representation of force fulfills this premise calculating force (F: mN), tension (T: mN/mm2), and tension per milligram of myocardium (delta: mN/mm2/mg). In all analyses, F and +dF/dt as well as T and dT/dt values were higher in heavier PM. These differences disappeared for delta and ddelta/dt. There was a significant and positive correlation for F and T as well as its derivative with myocardial mass. Myocardial depression (verapamil) of PP, in comparison to AP, was not recognized by F or T, but was identified when reported as delta. We conclude that the normalization of tension for papillary muscle mass is the most appropriate form for reporting intrinsic contractile capacity in PM since F and T depend on the myocardial mass participating in contraction.