Impedance to transesophageal atrial pacing: significance regarding power sources

Transesophageal stimulation is an expeditious method of atrial pacing. Using pulse widths of 10 msec results in reduction of current requirement to values that are usually less than 15 mA. An unknown variable in transesophageal atrial pacing has been impedance. In this study, we investigated the impedance to transesophageal atrial pacing in ten patients using a stimulator with a 63 V power source capable of delivering constant current to 20 mA against an impedance of 2,000 ohms. A bipolar electrode was used to deliver stimuli with a current of 15 mA. Voltage across a known resistance and current were measured on an oscilloscope and the impedance was calculated. Pacing thresholds were also performed and ranged from 6.2 to 16.5 mA (mean 9.4 +/- 2.9 mA, SD). Impedance varied between 720 and 2,670 ohms (mean 1,750 +/- 540 ohms). The stimulator used to measure impedance in man and two other commercially available stimulators were bench tested against known resistances of 500 to 2,000 ohms. The other stimulators with power sources of 12.5 and 15 V had attenuation of the delivered current at resistances of between 1,000 and 2,000 ohms. Thus, this study has demonstrated that transesophageal atrial pacing incurs impedances two to five times greater than incurred with intracardiac pacing leads. Therefore stimulators with high power sources are required to deliver the programmed current against these impedances.