Measurement of the ohmic electrode-tissue contact resistance and the voltage applied to myocardium

The electrical impedance of a pulse generator-electrode-heart system is a complex one. By analysis of an equivalent circuit developed for the above, a model was derived to describe the output voltage applied to an implanted electrode. On the basis of the dynamic behavior of the equivalent circuit when a pacing pulse was applied, a method for measuring true ohmic electrode-tissue contact resistance was developed, and a device was constructed to provide an instant digital readout of its value. The value of that risestance varied from 179 to 521 omega in 13 patients. When a variable resistance R, was connected in series with an implanted electrode, and a threshold voltage for every value of R was determined the actual voltage applied to the myocardium was computed for 16 patients.