Five-year performance of the Medtronic 6971 polyurethane endocardial electrode

There is a considerable debate over the long-term performance of polyurethane electrodes. Observation to date has demonstrated surface cracking and some clinical failures in patients. Since 1978 we have implanted about 82 6971 Unipolar Medtronic electrodes in the ventricle. In 33 patients, lead integrity was assessed by chronic thresholds determined by decreasing pulse width and pulse amplitude. Sensing functions were assessed by electrocardiographic rhythm analysis. At a follow-up between 7 and 67 months, chronic thresholds at 2.50 volts were 0.08 +/- 0.04 milliseconds in 26 patients with Medtronic Pulse generators (Models 8423, 5985, and 7000). In two patients with similar units, no loss of capture was seen even at 0.05 milliseconds. Three patients, one with Cordis Unit (233F) showed loss of capture at 0.20 milliseconds at 2.00 MA, the other with a Pacesetter unit (255-6) showed loss of capture at 0.20 milliseconds, at 2.50 volts. One patient with Intermedics unit (283) lost capture at 0.07 milliseconds at 2.70 volts. Insulation breaks seen in two patients were demonstrated by pectoral stimulation and pacemaker oversensing. In addition, 24-hour long-term electrocardiographic monitoring was performed in 22 patients between 23 to 70 months. Appropriate pacemaker function was seen except in one patient who demonstrated oversensing. Interruption in insulation was demonstrated at the ligature site at exploration. Thus, in this series of patients who were paced in the ventricle by the 6971 Medtronic electrode, only two patients have demonstrated insulation failure. The incidence of insulation break in this polyurethane unipolar electrode is uncommon and occurs at further stress points.