Apparent malfunction of demand pacemakers due to spurious potentials generated by contact between two endocardial electrodes.

Malfunction of both temporary and permanent demand transvenous pacemakers was caused by contact between the two endocardial electrodes. Contact between these electrodes created spurious potentials which resulted in irregular inhibition of both demand units. The potentials were demonstrated by recording from the temporary wire. There was no interference with either pacemaker in the fixed rate mode and malfunction ceased when the temporary wire was removed.