The salty dog: serum sodium and potassium effects on modern pacing electrodes

This study was conducted to characterize the behavior of chronic modern endocardial electrodes with capacitively coupled constant voltage pulse generators in canines.

Five animals were studied with chronic paired unipolar microporous platinum, and porous steroid-eluting electrodes in the ventricle. Screw-in and passive fixation electrodes were also implanted in the atrium. IV infusions of 500-800 mL of 50 meq KCl in 500 mL Ringer's solution, and 3% NaCl were given over periods of 120 and 80 minutes, respectively, during separate anesthetized monitors.

Mean maximum Na+ and K+ achieved was 158 and 8.3 meq/L, respectively. During KCl infusion, ventricular threshold, current, and energy decreased. In the atrium, half the leads went to exit block at approximately 7.0 meq/L K+. Others continued to perform acceptably. The atrial electrogram decreased 70% with no change in the ventricular signal. No change in impedance occurred. During NaCl infusion, no changes in atrial or ventricular threshold occurred while current increased 21%-32%. This resulted in a 40%-55% increase in energy due to a 20% decrease in impedance. The atrial electrogram decreased 32%-36% while the ventricular amplitude decreased 25%. Slew rate decreased 19%-27%. Control studies for effects of heart rate, fluid volume, and anesthesia duration did not cause any changes.

These data support the conclusion that threshold is a voltage mediated response. Thus, voltage thresholds, not energy, current or pulse duration is the most relevant parameter for safety margin determination. Atrial parameters should be followed during electrolyte imbalances. Correlation in humans is needed.