NONLINEARITY OF CARDIAC PACEMAKER ELECTRODES

Nonlinear properties of electrodes immersed in saline were studied in the time domain and frequency domain. Three electrode materials were tested: platinum-iridium, Elgiloy, and stainless steel. For time domain measurements, current pulses of 1.0 to 2.0 ms duration and varying amplitudes were applied to the electrodes. Frequency domain measurements of polarization impedance were made with an impedance bridge, utilizing sinusoidal currents of varying amplitudes at frequencies between 0.1 and 10 kHz. The limit voltage of linearity (threshold of nonlinearity) was approximately the same in both frequency and time domain measurements for all electrodes tested. In the frequency domain, the limit current of linearity decreased with decreasing frequencies; this substantiates results reported earlier. In the time domain, the limit current of linearity decreased with increasing pulse duration. Comparison of current levels utilized by present day pacemakers with those studied here shows that all pacemaker electrodes operate in the nonlinear range where accelerated electrochemical reactions may occur. Elgiloy and stainless steel exhibited hysteresis at these current levels, a finding suggesting the presence of irreversible changes at the electrode-saline interfaces. Copyright © 1969 by The Institute of Electrical and Electronics Engineers, Inc.