The aim of this study was to determine whether current of injury can guide adequate placement of active-fixation pacing leads. Active-fixation leads cause injury to the myocardium at the time of fixation, manifested as a current of injury(COI) that may result in acute elevation of pacing thresholds. The relationship of COI to subsequent improvement in pacing thresholds is not clear. Sixty-five patients undergoing active-fixation lead implantation were enrolled. Current of injury was characterized as the duration of the intracardiac electrogram(EGM) and the magnitude of ST-segment elevation. Pacing parameters were measured up to 10 min after fixation. A total of 96 active-fixation leads were studied, and 76 leads had a current of injury. From baseline to the time of fixation, the duration of the intracardiac EGM in ventricular leads increased from 150±31 ms to 200±25 ms(p< 0.001), and the ST-segment increased from 1.5±0.2 mV to 10.0±2.0 mV(p< 0.001), with subsequent improvement in pacing thresholds from 1.5±0.4 V to 0.8±0.3 V(p< 0.001) at 10 min. Atrial leads with a current of injury had similar findings. Of the 20 leads without a COI, 5 dislodged acutely and 15 had high pacing thresholds at 10 min, requiring repositioning. The development of a COI indicates that within 10 min of fixation, pacing threshold will return to an acceptable range even if the initial measurement is high. Conversely,without a COI, lead fixation is not adequate and the lead should be repositioned. The aim of this study was to determine whether current of injury can guide adequate placement of active-fixation pacing leads. Active-fixation leads cause injury to the myocardium at the time of fixation, manifested as a current of injury (COI) that may result in acute elevation of pacing thresholds. The relationship of COI to subsequent improvement in pacing thresholds is not clear. Sixty-five patients undergoing active-fixation lead implantation were enrolled. Current of injury was characterized as the duration of the intracardiac electrogram (EGM) and the magnitude of ST-segment elevation. Pacing parameters were measured up to 10 min after fixation. A total of 96 active-fixation leads were studied, and 76 leads had a current of injury. From baseline to the time of fixation, the duration of the intracardiac EGM in ventricular leads increased from 150 ± 31 ms to 200 ± 25 ms (p <0.001), and the ST-segment increased from 1.5 ± 0.2 mV to 10.0 ± 2.0 mV (p <0.001) with subsequent improvement in p acing thresholds from 1.5 ± 0.4 V to 0.8 ± 0.3 V (p <0.001) at 10 min. Atrial leads with a current of injury had similar findings. Of the 20 leads without a COI, 5 dislodged acutely and 15 had high pacing thresholds at The development of a COI indicates that within 10 min of fixation, pacing threshold will return to an acceptable range even if the initial measurement is high. Conversely, without a COI, lead fixation is not adequate and the lead should be repositioned.