An unusual cause of pacemaker current leakage causing muscle stimulation

Body surface isopotential mapping of permanent cardiac pacemaker spike amplitudes: a noninvasive method for detecting and localizing insulation failure

Cardiac pacing systems produce cardiac contractions by delivering electrical charges to the myocardium. Reliable cardiac pacing, and the longevity of pacemakers depends on the absence of electrical leaks. Electrical leaks often do not cause symptoms and if suspected, there are few methods which are able to identify their location and none suited to small or intermittent leaks. We surface mapped the pacemaker spike amplitudes over the pockets of 29 patients with unipolar pacemakers, several of which had suspected pacemaker leaks. For each patient, pacer voltage spikes were recorded with an optical ECG recorder from sixty-three positions on the skin over the pacemaker. The spike voltages were interpolated with a 2-D Fourier transform, contoured, and plotted by a computer. Electrical leaks were readily detected and their positions indicated by the resulting maps. The operative findings confirmed the map guided prediction in all six patients sent for pacemaker revision. Pacemaker spike amplitude surface mapping detects and locates pacing system insulation failures.

Noninvasive detection of insulation break

The electric current leak through an unsealed connector or insulation break can be a source of problems in cardiac pacing. This study describes a method of leak detection. The underdrive inhibition test--chest wall stimulation with external stimulator (ES)--was used for this purpose. Three cutaneous electrodes (CE) were applied: the first one above the indifferent electrode, the second one above the suspected leak location, and the third one above the active electrode. Two inhibition thresholds (IT) were measured: the first one connecting ES on first CE and second CE, and the second one connecting ES on first CE and third CE. The inhibition threshold is the value of ES output charge at which the inhibition of implanted pacemaker occurs. The relation between two ITs, not the absolute value, is significant for leak estimation. The former should be at least five times higher than the latter, if there is no current leak. During the two years of follow-up of 541 patients, 272 measurements were performed. In 52 cases the connector leak was found-both ITs were approximately equal. Twenty-seven cases were confirmed by surgery for EOL pacemaker replacement; the intrusion of body fluid was evident. Five operations were indicated because of the leak problem: two--muscle twitching, one--loss of capture, one-undersensing, and one--insulation break with lead fracture. The method, although approximate, is a reliable qualitative estimation of leak.