Non-invasive evaluation of left ventricular function by means of impedance cardiography

Simple, accurate, continuous non-invasive cardiac monitoring during the peri- and postoperative periods for patients at risk of cardiac failure would be very useful. Electrical impedance cardiography (EIC) has been proposed as an accurate method for non-invasive measurement of cardiac function. However, in recent years the accuracy of EIC in stroke volume (SV) measurement has been questioned and this prevented global acceptance of the method. Beside SV, EIC is capable of measuring several other left ventricular contractility indices, which are measured directly from the impedance signal. The aim of this study was to compare these variables with the echocardiographically derived left ventricular wall motion score (WMS) as the reference method.

In a group of eight coronary artery disease patients we performed a pharmacologically (dobutamine) induced stress test. Echocardiographic and impedance cardiographic recordings were performed simultaneously during four levels of dobutamine infusion. WMS was derived from the simultaneously displayed four-stage echocardiographic image.

Analysis of variance showed that the majority of indices changed significantly during the test. Direct correlation with the wall motion score gave very satisfactory results over all stages with the RZ time (r = 0.75, P < 0.001) and Heather index (r = -0.78, P < 0.001). Other correlations were substantially lower.

The Heather index has to be preferred as indicator of the left ventricular performance. Since EIC is capable of giving continuous information of the left ventricular performance, it might be a valuable method for peri- and postoperative monitoring.