Determination of left ventricular volume changes by intracardiac conductance using a biventricular electrode configuration

The feasibility of determining left ventricular (LV) volume changes by LV conductance measurements with an implantable device was investigated in an animal model. The haemodynamic state of six mongrel dogs was altered by overpacing with rates up to 140 bpm and by isoprenaline infusion with dosages up to 0.2 microg/kg/min. The LV conductance, aortic blood flow, and LV and aortic pressure were recorded. Conductance measurements were carried out using the two electrodes of a bipolar right ventricular pacing lead for current injection and two epicardial leads screwed into the mid-lateral LV wall for measuring the resulting voltage. Stroke conductance (SY) was correlated with the LV stroke volume (LVSV), which was computed from the aortic flow. The LVSV rose to 188+/-14% with increasing isoprenaline dosage. A strong correlation between the LV conductance SY and the LVSV was found (mean r=0.97). The LVSV decreased to 68+/-8% with an increasing pacing rate. Again, a strong correlation between SY and LVSV was found (mean r=0.89). This animal study confirms the feasibility of assessing changes in LVSV by determining the LV intracardiac conductance. This creates the possibility of continuous haemodynamic monitoring with implantable devices.