Assessment of cardiac function using the modified ejection fraction as an indicator of myocardial circumferential strain

Although cardiac strain has been used as a practical mechanical indicator to estimate cardiac functions, measurement of strain is still difficult due to the need for operator proficiency and special equipment to perform echocardiography and magnetic resonance imaging (MRI). Hence, a modified indicator that can be calculated more easily at the bedside is needed to assess cardiac function based on cardiac morphology. The circumferential strain of the left ventricular (LV) wall and the contraction potential energy were numerically investigated in this study using a thick-walled cylindrical model under different myocardial thicknesses, stiffnesses, and diastolic pressures for given specific ejection fractions (EFs) or end-diastolic volumes. The LV wall was modeled as a visco-hyperelastic, continuous material. We proposed the modified ejection fraction (mEF), which is the product of EF and the contractility percentage of the internal volume within the epicardium, as an indicator of circumferential strain. Calculated peak circumferential strain was better estimated by mEF than EF. Furthermore, the contraction potential energy correlated well with circumferential strain and mEF. Our results regarding mEF are consistent with those obtained in 7 previous clinical studies. mEF may be a useful and practical indicator of the reduced contraction potential energy of the local myocardium and of heart failure, regardless of imaging modalities and vendors.