Measurement of Pacing Threshold

Thresholds in constant current and constant voltage are reported for 405 CPI 4118 (Cardiac Pacemakers, Inc.) tined leads. In 98% of the cases, the constant current threshold was equal to or lower than 0.6 mA. A constant voltage threshold was equal to or lower than 0.5 V in 96% of the cases. Three external pacemakers and two pacing system analyzers were evaluated as threshold testing devices. For analyzing the waveforms of current and voltage stimuli, a calibrated isolation amplifier was used. We could not find a definite difference between the value, at which pacing is lost with reduction of the pulse generator output, and the value at which increase reestablishes pacing.