Left ventricular contractance: A new measure of contractile function

Myocardial contractility is poorly defined and difficult to compare between studies. Contractance or myocardial active strain energy density (MASED) measures the mechanical work done per unit volume (with units of kJ/m³) by any cardiac tissue during contraction. Contractance is an ideal candidate for measuring contractile function as it combines information from both stress and strain.

Data obtained from three previously published experimental studies using trabecular tissue was used to provide contemporaneous nominal stress and strain data in 18 different scenarios with different loading conditions. Contractance varied in the differing loading conditions with values of 1.16 (low preload), 2.02 (high afterload) and 3.76 kJ/m³ (normal). Contractance varied between 0 with isometric loading and 2.14 kJ/m³ with an isotonic and moderate afterload. Increasing inotropy increased contractance to 4.7 kJ/m³.

We showed that calculating MASED was feasible and provided a measure of energy production (work done) per unit volume of myocardium during contraction. The new term for contractile function, contractance, can be defined and quantified by MASED. Contractance measures contractile function in differing preload, afterload and inotropic settings. The method of measuring contractance is transferable to the assessment of global and regional systolic function.