Interference with cardiac pacemaker function

A survey is given of the factors affecting cardiac pacemaker function. Whereas it was earlier considered that external interference was a frequent cause of a pacemaker failure, more recent studies indicate that this is of minor importance. It would appear that failure of pacemaker function due to changes in the QRS-complex, i.e. voltage change, intraventricular conduction defects and frequency changes, intraventricular conduction defects and frequency changes, are more important. A lesser known cause of failure in demand function is the inhibition which arises from skeletal muscle postentials. This appears to be a major problem in some types of pacemaker. Manufacturing defects are unavoidable, and it can still be assumed that electronic component defects may develop in 1 of 1000 pulse generators. Cases with the problem of early run-away pacemaker are still being reported and two such cases are discussed. In one of the patients the run-away phenomenon was intermittent, and was accompanied by a variation in run-away frequency. This possibility should thus always be taken into consideration in a pacemaker patient presenting with snycope. In a patient with a QRS-inhibited pacemaker a double stimulation phenomanen has been observed.