Mechanical failure causing current leakage with unipolar pacemakers: significance and detection

Pacemaker malfunction caused by mechanical failure at the site of electrode generator connection has been observed in 5 patients fitted with unipolar pacemakers. Intermittent failure to capture occurred in one patient. The fault was the same in each case and resulted from fracture of a plastic screw designed to hold an insulating cap in place over the electrode generator connection. Changes in impulse amplitude, relative pacing threshold, and distortion of the shape of the pacemaker impulse (overshoot of the leading and trailing limbs and prolongation of the plateau length) occurred in each case, and are helpful in making the diagnosis. In contrast no significant change occurred in the frontal plane axis of the pacemaker impulse. It is concluded that current leaks in unipolar pacemakers can be of sufficient magnitude to cause failure to capture. Early detection is important and is best achieved by examination of the pacemaker signal for amplitude and shape, and assessment of pacing threshold where possible.