Assessment of cardiac function during mechanical circulatory support: The quest for a suitable clinical index

A new index to assess left ventricular (LV) function in patients implanted with continuous flow left-ventricular assist devices (LVADs) is proposed. Derived from the pump flow signal, this index is defined as the coefficient (k) of the semiloga-rithmic relationship between “pseudo-ejection” fraction (pEF) and the volume discharged by the pump in diastole, (V d). pEF is defined as the ratio of the “pseudo-stroke volume” (pSV) to V d. The pseudo-stroke volume is the difference between V d and the volume discharged by the pump in systole (V s), both obtained by integrating pump flow with respect to time in a cardiac cycle. k was compared in-vivo with others two indices: the LV pressure-based index, MTP, and the pump flow-based index, IQ. MTP is the slope of the linear regression between the “triple-product” and end-diastolic pressure, EDP. The triple-product, TP = LV SP.dP/dtmax. HR, is the product of LV systolic pressure, maximum time-derivative of LV pressure, and heart rate. IQ is the slope of the linear regression between maximum time-derivative of pump flow, dQ/dtmax, and pump flow peak-to-peak amplitude variation, QP2P. To test the response of k to contractile state changes, contractility was altered through pharmacological interventions. The absolute value of k decreased from 1.354±0.25 (baseline) to 0.685±0.21 after esmolol infusion. The proposed index is sensitive to changes in inotropic state, and has the potential to be used clinically to assess contractile function of patients implanted with VAD.