- the device provides AAI(R) pacing at the lower rate limit and/or sensor indicated rate
- the device provides backup VVI pacing at a rate of 15 bpm slower than the programmed lower rate limit
- the backup VVI pacing rate is limited to no slower than 30 bpm and no faster than 60 bpm
- switch from ADI/VVI backup to DDD mode is not based on the presence of blocked P waves but on the presence of slow ventricular beats
- two types of ventricular beats are considered slow: a paced ventricle and a sensed ventricular event with an interval greater than 150 ms relative to the programmed lower rate limit or current rate response
- the device automatically switches to DDD(R) mode if 3 ventricular beats are considered slow in a rolling window of 11 consecutive ventricular beats
- after a switch to DDD(R) mode, the device uses the AV Search+ algorithm to periodically search for the return of intrinsic conduction
- the AV Search+ algorithm corresponds to an AV delay hysteresis with different programmable parameters: (Search AV delay: 30-400 ms and Search Interval: 32-1024 intervals)
- failed Search: no intrinsic conduction is detected within the initial search period (8 cycles) or 3 out of the last 10 ventricular events are paced
- successful Search: if a V-sense is detected during the initial search period, hysteresis continues; each ventricular sensed event is marked as VS-Hy and AV Conduction Counter is incremented with each VS-Hy beat; when the AV Conduction Counter is ≥ 25, the device switches to AAI(R) mode with VVI back-up
10 things you need to know about RYTHMIQ (Boston Scientific)
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