CLINICAL-EVALUATION OF A THIN BIPOLAR PACING LEAD

The main disadvantages of bipolar pacing leads have traditionally been related to their relative thickness and stiffness compared to unipola r leads. In a new ''drawn filled tube'' plus ''coated wire'' technolog y, each conductor strand is composed of MP35N tubing filled with silve r core and coated with a thin ETFE polymer insulation material. This a nd parallel winding of single anode and cathode conductors into a sing le bifilar coil resulted in a bipolar lead (ThinLine, Intermedics) wit h a body diameter and flexibility similar to unipolar leads. The lead is tined, polyurethane, with the cathode and the anode made of iridium -oxide-coated titanium (IROX). The slotted 8-mm(2) cathode tip is coat ed with polyethylene glycol, a blood soluble material. We present the clinical evaluation results from four pacemaker clinics, where 47 lead s (23 atrial-J model 432-04 and 24 ventricular model 430-10) were impl anted in 25 patients and followed for up to 2 years. The lead handling characteristics were found to be very satisfactory. Electrical parame ters of the leads were measured at implant and noninvasively on postop erative days 1, 2, 21, 42, and months 3, 6, 12, and 24. Mean chronic p ulse width thresholds at 2.5 V were 0.14 +/- 0.05 ms in the atrium and 0.10 +/- 0.02 ms in the ventricle, pacing impedances 443 +/- 104 Omeg a and 520 +/- Omega, while median electrogram amplitudes were greater than or equal to 3.5 mV and greater than or equal to 7 mV, respectivel y. Pacing impedances and thresholds were found to be slightly but stat istically significantly higher in unipolar than in bipolar configurati on-the findings are explainable by the lead construction. One of 47 le ads failed 3 weeks after implant; the conductors were short circuited due to an error during the manufacturing process. We conclude that the new lead thus far has demonstrated appropriate mechanical and electri cal characteristics.