Variation in P wave amplitude immediately after pacemaker implantation: possible mechanism and implications for early...

The P wave amplitude (PWA) plays an important role in determining atrial sensing capabilities. To assess early PWA change, we compared the unipolar PWA in 43 patients at the time of atrial lead placement, measured by a pacing systems analyzer, to the unipolar PWA recorded at the end of pacemaker surgery, from telemetered atrial endocardial electrograms. Individual PWA varied from a decrease of 5.2 mV to an increase of 2 mV (-63% to 267%). In 33 patients with active fixation leads, the implant PWA was 1.96 +/- 0.99 mV versus 2.4 +/- 1.4 mV after surgery. In 11 patients with passive fixation leads, the implant PWA was 2.8 +/- 1.9 mV versus 1.9 +/- 0.8 mV after surgery. The PWA change, measured as the difference between the postsurgical and implant PWA was 0.43 +/- 0.8 mV in active versus -0.86 +/- 1.6 mV in the passive fixation lead groups (P less than 0.05). Considerable change in individual P wave amplitude can therefore occur very early after pacemaker implantation. The direction differs significantly between active (predominantly positive) and passive fixation groups (predominantly negative). These data suggest that an adequate margin of safety is important when initially programming atrial sensitivity, particularly when using passive fixation leads.