RESUMO
UNLABELLED: An "Autosensing" algorithm available in SSI(R) and DDR(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.