Objectives: We undertook this study to determine whether telemetered lead impedance measurements (LIM) can be correlated with direct LIM and to determine the stability of LIM over time when measured directly and via telemetry. Methods: Direct LIM and telemetered LIM were measured in 91 patients; 101 leads during initial implantation and 40 leads during pulse generator replacement. Differences in direct LIM measured during initial implant and pulse generator replacement (direct-direct) were compared in 41 patients (28 atrial leads and 37 ventricular leads). The stability of telemetered LIM obtained immediately postoperatively, at 1 month and 1 year, postimplantation was assessed in 50 patients (23 atrial and 49 ventricular leads). Results: In atrial leads acute direct LIM was 633.9 +/- 18.4 Omega versus 575.8 +/- 18.5 Omega for telemetered LIM (r = 0.58), and chronic direct LIM was 670.9 +/- 49.3 Omega versus 607.0 +/- 36.3 Omega for telemetered LIM (r = 0.87). In ventricular leads acute direct LIM was 747.3 +/- 16.9 Omega and 684.7 +/- 16.4 Omega for telemetered LIM (r = 0.69), and chronic direct LIM was 674.8 +/- 29.9 Omega and 625.2 +/- 28.5 Omega for telemetered LIM (r 0.68). The mean direct-direct LIM rose 124 Omega (P < 0.001) in atrial leads and 10 Omega (P = NS) in ventricular leads. Telemetered LIM for atrial leads was 581.0 +/- 27.6 Omega immediately postimplantation compared to 625.7 +/- 34.8 Omega at 1 month and 754.1 +/- 43.0 Omega at 1 year. Telemetered LIM for ventricular leads was 661.3 +/- 17.5 Omega at implant, 684.6 +/- 20.7 Omega at 1 month and 724.7 +/- 22.7 Omega at 1 year. Conclusions: There is a good but limited correlation between direct and telemetered LIM. Mean direct LIM obtained at initial implantation is similar to that measured at pulse generator replacement. The telemetered LIM is stable over the first month postimplantation but tends to rise during the first year of follow-up and substantial changes in impedance are not uncommon in individuals with normal function. There is a tendency for LIM to rise with lead maturation. If telemetered LIM is to be followed over time, a baseline telemetered value should be obtained immediately postoperatively.
