DIRECT AND TELEMETERED LEAD IMPEDANCE

Objectives: We undertook this study to determine whether telemetered l ead impedance measurements (LIM) can be correlated with direct LIM and to determine the stability of LIM over time when measured directly an d via telemetry. Methods: Direct LIM and telemetered LIM were measured in 91 patients; 101 leads during initial implantation and 40 leads du ring pulse generator replacement. Differences in direct LIM measured d uring 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 postoperative ly, at 1 month and 1 year, postimplantation was assessed in 50 patient s (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 t elemetered LIM (r = 0.58), and chronic direct LIM was 670.9 +/- 49.3 O mega versus 607.0 +/- 36.3 Omega for telemetered LIM (r = 0.87). In ve ntricular 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 wa s 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 atria l leads and 10 Omega (P = NS) in ventricular leads. Telemetered LIM fo r atrial leads was 581.0 +/- 27.6 Omega immediately postimplantation c ompared 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 Omeg a 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 betwe en direct and telemetered LIM. Mean direct LIM obtained at initial imp lantation is similar to that measured at pulse generator replacement. The telemetered LIM is stable over the first month postimplantation bu t tends to rise during the first year of follow-up and substantial cha nges in impedance are not uncommon in individuals with normal function . There is a tendency for LIM to rise with lead maturation. If telemet ered LIM is to be followed over time, a baseline telemetered value sho uld be obtained immediately postoperatively.