AAIsafeR2 mode will be activated with a basic rate of 60 bpm. The single-chamber arm will be programmed to optimal detection with Acceleration (Onset), Stability and Long Cycle Search (VTLC) activated. A VT zone is requested in this group, with the same programming procedures as described above. Therapies will be set according to the clinical judgment of the participating investigators but a Slow VT-zone with TDI 500 ms in monitoring setting at least is required.