Non-invasive assessment of left ventricular longitudinal impedance using color M-mode Doppler echocardiography

The authors hypothesised that a measured mitral valve diameter and a color Doppler M-mode image of left ventricular inflow provide sufficient information for the non-invasive estimation of the left ventricular longitudinal impedance of left ventricular filling. The aim of this study was therefore (1) to develop the algorithms for calculation of left ventricular longitudinal impedance from a color Doppler M-mode image and (2) to study the feasibility of this calculation in an in vitro experiment. In a cardiovascular simulator consisting of a left ventricular pulse duplicator system connected to a hydraulic model of the arterial tree, color M-mode images of left ventricular inflow were captured. Pressure differences are calculated by implementing the Euler equation. Velocity at the level of the mitral valve is used for the calculation of flow. Pressure gradients and flow are used for calculation of the longitudinal impedance in the frequency domain. No influence on the amplitude of the calculated longitudinal impedance was observed (p>0.05) for a change in heart rate and systolic pressure. However, the calculated longitudinal impedance was significantly altered for a smaller valve and a different test fluid (p<0.05). In conclusion: longitudinal impedance of left ventricular inflow can be derived non-invasively from color Doppler M-mode images and provides a quantitative interpretation of the numerical velocity information in a color Doppler M-mode image with potential clinical useful information