Background: Active-fixation screw-in leads are associated with initially high thresholds. However, pacing thresholds have been shown to improve within several minutes after screwin. The aim of this study is to investigate the long-term stability of rapidly improved pacing thresholds following the implantation of active-fixation screw-in leads.Methods: We performed a prospective observational study on 68 consecutive patients, who were referred for an initial pacemaker or implantable cardioverter defibrillator implantation. Pacing thresholds, sensing amplitudes, and lead impedances were measured immediately after screw-in. If the initial pacing threshold was higher than 2.0 volts, lead reposition was performed. If the initial pacing threshold was lower than 1.0 volts, the lead position was considered adequate. If the initial pacing threshold was slightly high, i.e., between 1.0 and 2.0 volts, all parameters were measured again 5 minutes after screw-in without lead repositioning, and 1 week, 1 month, 6 months, and 1 year after the procedure.Results: Fifty-three atrial leads and 59 ventricular leads were implanted using activefixation screw-in leads. The initial pacing threshold was slightly high, i.e., between 1.0 and 2.0 volts in 16 (30%) atrial leads and 28 (47%) ventricular leads. Pacing thresholds significantly improved after 5 minutes in both atrial and ventricular leads as follows: 1:5 AE 0:2 to 0:9 AE 0:3 volts (p < 0:05) in atrial leads and 1:5 AE 0:3 to 0:9 AE 0:3 volts (p < 0:05) in ventricular leads. These improved pacing thresholds remained stable during the first year and were 0:8 AE 0:3 volts in atrial leads and 0:8 AE 0:2 volts in ventricular leads after the initial year. P-and R-wave amplitudes did not change significantly during the follow-up. Lead impedances decreased 1 week after the procedure and remained stable in both atrial and ventricular leads.Conclusions: Slightly high pacing thresholds using active-fixation screw-in leads improved rapidly and remained stable in the long term. An acute pacing threshold of <2:0 volts immediately after screw-in may change to an acceptable value without lead repositioning. (J Arrhythmia 2010; 26: 244-249)
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