[Incomplete lead fracture as a cause of bradyarrhythmia in patients with artificial pacemakers (author's transl)]

The fracture of a permanent cardiac pacing lead may be complete or incomplete. In the first case, the function of the pacemaker system will completely cease. An incomplete fracture, however, is defined as a capillary interruption of the wire and will lead to a loose connexion between both parts of the electrode. This, in turn, may result in sudden changes of the electrical resistance of the lead and, therefore, in alterations of the electrode voltage during the second part of the biphasic current wave delivered by the pacemaker; this voltage change--in the 10-mV-range--will inhibit a blocking demand pacemaker with an intermittent, irregular increase of the pacemaker escape interval as the corresponding ECG finding. Usually, this "oversensing" phenomenon can be eliminated by turning the pacemaker function to the fixed rate mode with a test magnet applied. -- Although this malfunction is more often seen with bipolar pacemaker systems and with epicardial wires, it may also occur in a unipolar, transvenous system. -- Among 2100 patients, we have seen this malfunction in 6 cases in whom other, even more rare causes--such as a defect of the electronic circuit of the pulse generator, muscle potentials, etc.--could be ruled out. The x-ray findings revealed no evidence of a lead fracture in any case. The diagnosis was established on the ECG, the examination of the surgically removed electrode in 2 cases, and the finding, that only the implantation of a new lead abolished the malfunction, whereas the implantation of a new pacemaker alone ws ineffective.