A mechanism for "false" inhibition of demand pacemakers

Certain variations in discharge rate of demand pacemakers may be associated with intermittent fractures and resulting resistance changes in the electrode-lead system. These variations in rate are related to inhibition of the demand circuit of the pacemaker. Most pacemakers produce a biphasic output pulse which results in a low amplitude current during the interval between stimuli. Therefore, sudden changes of resistance in the electrode-lead system will produce a potential change at the pacemaker terminals which is of sufficient magnitude to be interpreted as spontaneous ventricular depolarization and inhibit the demand pacemaker. Such inhibition may occur in the absence of other signs of lead fracture and present a difficult differential diagnostic problem of pacemaker malfunction.