Search AV +

Tracing

N° 3

Manufacturer Boston Scientific Device PM Field AV delays, refractory periods management of tachycardia

Patient

Graph and trace

Atrial sensing and ventricular pacing with programmed AV delay
Prolongation of the AV delay in order to search for intrinsic conduction (AV delay hysteresis)
A sensed ventricular complex (Vs-Hy) is systematically observed

Comments

Once the device has switched to DDD(R) mode, the device uses the AV Search+ algorithm to periodically search for the return of intrinsic conduction
The AV Search + algorithm promotes intrinsic AV by periodically extending the AV delay
It is therefore necessary to program this algorithm in combination with Rythmiq
If the AV Search+ is programmed OFF, the device permanently remains in DDD mode after the first switch in DDD mode without possibility of returning to ADI/VVI backup mode until the next interrogation
It is essential to deprogram the 2 algorithms simultaneously if the patient has a complete and permanent atrioventricular block in order to avoid the repetition of intrinsic conduction searches
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)

When the AV Search Interval is reached, the AV delay is extended to the programmed AV Search + value
Failed Search: the device maintains DDD(R) pacing and the AV Search + interval is restarted if no intrinsic conduction is detected within the 8 cycle search period or 3 out of the last 10 ventricular events are paced
Successful Search: if a V-sense is detected within the 8 cycle period of AV search hysteresis, hysteresis continues: each ventricular sensed event is marked as VS-Hy (Hysteresis), AV Conduction Counter is incremented with each VS-Hy beat; when the AV Conduction Counter is ≥ 25, sustained conduction is detected and the device switches back to AAI(R) mode with VVI back-up

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