Effects of acid-base imbalance on myocardial pacing thresholds.

The effects of acid-base imbalance on ventricular pacing thresholds were studied in anesthetized dogs with complete heart block with the use of an oscilloscope and current probe. Acidosis (base excess-15) and alkalosis (base excess + 15)both resulted in significant increases in threshold voltage and current requirements at all stimulus durations tested. Chronaxie, however, was not significantly affected by shifts in acid-base balance. Abnormalities of acid-base status may adversely affect the accuracy of threshold values obtained during evaluation of different electrode designs and during electrodes implantation for clinical cardiac pacing.