First Experience with an Automatic Sensing Algorithm in Single‐Lead VDD Stimulation

An “Autosensing” algorithm available in SSI(B) and DDD(R) pacemakers automatically adapts the device's sensitivity to changing intracardiac signals. The atrial sensing function of this algorithm was tested for the first time with a VDD pacing system in which large variations of the atrial signal may occur because the atrial electrodes float in the atrial blood pool. Methods: 15 patients with a VDD pacing system were studied (Unity 292–07, lead 425; Sulzer Intermedics). The atrial sensing threshold was measured, and the atrial sensitivity was programmed with a 2:1 safety margin. The autosensing algorithm and sensitivity profile were temporarily activated, and an ambulatory ECG with continuous marker annotation was recorded. All patients underwent a 30-minute daily life activities protocol. A beat-to-beat analysis of the ambulatory 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 occurred (range 0–33). In eight patients atrial undersensing occurred in 4.4%± 7.5% of the cycles (4–458 unsensed P waves]. In these patients, the algorithm continuously adjusted the sensitivity towards more sensitive values, operating 19.1 ± 18.3 changes compared with 5.4 ± 7.3 changes in patients without undersensing (P = 0.009). Oversensing did not occur. Conclusion: The autosensing algorithm effectively optimized atrial sensitivity in VDD pacing. In patients with atrial undersensing the algorithm continuously remained near the most sensitive settings, thus reacting as intended. A faster sensitivity adjustment of the system would be desirable.