Detection of faults in implanted cardiac pacemakers.

Since 1958, totally implantable pacemakers have been used to stimulate the hearts of patients suffering from chronic heart block. The evidence that such patients have a reduced mortality rate in comparison with unpaced patients (Sowton, 1967) and the ability to return to a normal life have meant that pacemaker implantation for heart block is now accepted practice. There have been increasing numbers of reports on the improved reliability of such pacemakers (Parsonnet, Gilbert, and Zucker, 1966; Forbes et al., 1968; Sowton, 1968), but nevertheless failures do occur and it is most important that continued research into methods of anticipating and diagnosing such failures should continue. Sowton (1968) has emphasized the need for followup arrangements to be carried out at specially equipped clinics. At the same time, it should be appreciated that there is as yet no single test or method which will satisfactorily diagnose all possible faults (Dekker, Biller, and Schuilenburg, 1965). We have made a preliminary announcement of a method of testing the integrity of lead systems (Green et al., 1968) in which an analysis is made of the vector produced in the frontal plane by the pacemaker signal obtained using an oscilloscope and standard surface electrocardiographic electrodes. This paper reports the results of our experience in using this method in three Glasgow pacemaker clnics. As seen in an electrocardiogram, the pacemaker signal has the appearance of a sharp deflection immediately before the QRS complex, usually negative in leads I and II with a bipolar catheter and either positive or negative in lead III (Fig. 1). By excluding the electrocardiogram signal and examining the pacemaker signal on an oscilloscope (preferably a storage oscilloscope), the characteristics of the pacemaker signals can be seen in more detail (Fig. 1). The pacemaker signal is a "square-wave" pulse of electricity, two milliseconds or less in dura-