IN-LINE BIPOLAR, STEROID-ELUTING, HIGH IMPEDANCE, EPIMYOCARDIAL PACING LEAD

Recent advances in electrode surface designs have eliminated tradition al threshold differences between endo- and epicardial pacing leads. Si nce the epicardial approach offers the potential of direct left ventri cular pacing and the transvenous approach may not be feasible or warra nted in all instances, more advanced leads are being designed to optim ize epicardial pacing capabilities. This study was conducted to evalua te a bipolar epimyocardial lead. Six immature canines (age 3 months) w ere instrumented. The lead (Medtronic model 10389) is a single-pass, ' 'in-line'' bipolar electrode with low current drain and high impedance , with an intramyocardial steroid-eluting cathode and nonsteroid epica rdial anode. Twelve ventricular leads were implanted (two per animal) and the animals followed for 6 months with weekly analysis of pacing a nd sensing capabilities. Results at explant were compared with implant values and showed no significant differences between sensed R waves o r in R wave slew rates in unipolar or bipolar modes. Explant lead impe dances remained high in both modes: bipolar, 1658 +/- 331; and unipola r, 1327 +/- 308 Ohm (P < 0.05). Chronic voltage (V) threshold at 0.5 m s showed no significant change from implant values during the study: u nipolar, 0.3 +/- 0.06 versus 1.0 +/- 0.8; and bipolar, 0.4 +/- 0.06 ve rsus 1.6 +/- 1.2. Histologic review showed negligible fibrous reaction at the electrode-tissue interface. This study introduces a high imped ance, low threshold, ''in-line'' bipolar pacing lead design capable of stable chronic pacing with implant facilitated by a single suture tec hnique.