ACUTE CHANGES IN PACING THRESHOLD AND R-WAVE OR P-WAVE AMPLITUDE DURING PERMANENT PACEMAKER IMPLANTATION

This study examines the changes in pacing threshold and R- or P-wave amplitude during the first 30 minutes after implantation of tined and screw-in leads. The leads examined were those of 1 manufacturer (Medtronic) and consisted of 3 ventricular pacing leads (model numbers 6957 unipolar screwin [11 patients], 6961 unipolar tined [12 patients] and 6962 bipolar tined [7 patients]) and 1 atrial lead (model number 6957J unipolar screw-in [10 patients]). After optimal lead position was obtained fluoroscopically in the right ventricular apex or right atrium, the pacing threshold and R- or P-wave amplitudes were measured at 5-minute intervals for 30 minutes. The acute ventricular pacing threshold with the screw-in lead was significantly higher than with the tined lead (0.84 ± 0.17 vs 0.58 ± 0.15 volts; p < 0.001). There was a significant (p < 0.001) acute decrease in the ventricular pacing threshold with both lead types, with the maximum decrease occurring 5 minutes after lead implantation. There was a significant acute increase in R-wave size with the ventricular screw-in lead that peaked 20 minutes after lead implantation (11.9 ± 3.0 to 14.7 ± 4.1 mV; p < 0.001). The atrial screw-in lead behaved in a manner identical to its counterpart in the ventricle. In conclusion, there are acute changes in the pacing threshold and R- or P-wave amplitude obtained with tined and screw-in pacing leads. In some patients, a pacing threshold or R- or P-wave amplitude that is initially unacceptable may improve to an acceptable level over 15 to 20 minutes without further lead manipulation, especially when an atrial screw-in lead is used. © 1990.