Computation of the Input Impedances of a Catheter for Cardiac Volumetry

Electrical impedances between the electrodes of a catheter in a spheroidal model of the left ventricle are calculated analytically. The fields in the configuration are computed using eigen function expansions of the Laplace equation. For certain realistic combinations of specific conductances of the blood and the myocardium, numerical results are given. These results show the dependence of the impedances on the volume of the ventricle while keeping the length of the major axis of the ventricle constant. Also, the accuracy of the model and the dependence of the total conductance of the ventricle on its shape, and on the conductivity of the tissues surrounding it, are discussed. The theoretical results are compared against the experimental values of conductances, measured post mortem in a canine heart, for different volumes.