ATRIAL SENSING IN A NEW VDD SYSTEM

VDD stimulation is an alternative to DDD pacing due to the possibility of p-wave synchronous ventricular pacing without the need of an atria l lead. Mainly, the reliability of the system depends on the atrial se nsing. In 22 patients the intraoperative atrial amplitude and, postope ratively, the atrial sensing threshold were measured. Furthermore, the stability of the atrial sensing threshold during followup was proven. The mean atrial amplitude was intraoperative by 2.4 +/- 1.2 (1.0-6.8) mV. The measurement of the atrial sensing threshold in the first 5 po stoperative days showed a mean value of 1.02 +/- 0.49 (0.3-1.6) mV. Th e measurements of the mean atrial sensing threshold after 30, 90, and 180 days showed no statistical differences. Intraindividual variance w as shown in 17/20 patients (0.55 +/- 0,42; 0.15-1.05 mV). Seventeen of the 22 patients were programmed with an atrial sensing threshold of 0 .3 mV. In five patients the atrial sensing threshold was programmed at less than 0.3 mV in order to reach a twofold atrial sensitivity. Desp ite a programmed atrial sensitivity of 0.1 mV and isometric conditions no atrial oversensing occurred. The postoperative atrial sensing thre sholds of the VDD system investigated were significantly lower than th e intraoperatively measured atrial amplitudes. The mean atrial sensing threshold did not change during the followup period. The variation wh ich did occur was within individual variation at different return visi ts.