FIRST EXPERIENCE WITH AN AUTOMATIC SENSING ALGORITHM IN SINGLE-LEAD VDD STIMULATION

An ''Autosensing'' algorithm available in SSI(R) and DDD(R) pacemakers automatically adapts the device's sensitivity to changing intracardia c signals. The atrial sensing function of this algorithm was tested fo r the first time with a VDD pacing system in which large variations of the atrial signal may occur because the atrial electrodes float in th e atrial blood pool. Methods: 15 patients with a VDD pacing system wer e studied (Unity 292-07 lead 425; Sulzer Intermedics). The atrial sens ing threshold was measured, and the atrial sensitivity was programmed with a 2:1 safety margin. The autosensing algorithm and sensitivity pr ofile were temporarily activated, and an ambulatory ECG with continuou s marker annotation was recorded. All patients underwent a 30-minute d aily life activities protocol. A beat-to-beat analysis of the ambulato ry ECG was correlated with the changes in atrial sensitivity. Results: The algorithm changed the baseline sensitivity from 0.57 +/- 0.23 mV during the test to 0.39 +/- 0.20 mV after the final rest period (P < 0 .05). During the test 12.6 +/- 10.2 adaptations of the sensitivity occ urred (range 0-33). In eight patients atrial undersensing occurred in 4.4% +/- 7.5% of the cycles (4-458 unsensed P waves). In these patient s, the algorithm continuously adjusted the sensitivity towards more se nsitive values, operating 19.1 +/- 18.3 changes compared with 5.4 +/- 7.3 changes in patients without undersensing (P = 0.009). Over-sensing did not occur. Conclusion: The autosensing algorithm effectively opti mized atrial sensitivity in VDD pacing. In patients with atrial unders ensing the algorithm continuously remained near the most sensitive set tings, thus reacting as intended. A faster sensitivity adjustment of t he system would be desirable.