Determining optimal atrial sensitivity settings for single lead VDD pacing: the importance of the P wave histogram

In order to provide atrioventricular synchrony, VDD pacing systems require reliable atrial sensing. Variations in atrial signals with exercise and daily activities may lead to undersensing, with loss of physiological pacing. The aim of this study was to determine, for a single lead VDD pacing system, the maximal variation in atrial signals in order to facilitate optimal programming of atrial sensitivity. Fifteen patients underwent implantation of a Vitatron Saphir VDD pacemaker with a Vitatron Brilliant electrode. At a mean (+/-SD) follow-up of 67.3 +/- 38.8 days, resting P wave amplitude was compared with the P wave amplitude histogram obtained from the pacemaker, which recorded atrial signals over the preceding 30 days. Resting P wave amplitude was also compared with P wave amplitudes during variations in posture, respiration, and during exercise. P wave amplitude showed great variation with changes in posture and respiration, but there was no consistent increase or reduction. During exercise, the mean P wave amplitude fell by 36.6% +/- 31.3% compared with the resting value (P < 0.05). During daily activities, 22.6% of P wave amplitudes recorded on the P wave histogram were < 0.5 mV. The smallest P wave amplitudes were detected by the P wave histogram in 11 (79%) of 14 patients. These data suggest that atrial sensitivity may need to be programmed higher than that indicated by single readings or exercise. The P wave amplitude histogram is the most reliable indicator of the smallest atrial signal and should be used to optimize atrial sensitivity settings.