The atrioventricular delay is the interval between an atrial sensed event (sensed AV Delay) or an atrial paced event (paced AV Delay) and the delivery of the ventricular pulse.
- the nominal value of the sensed AV delay is 150 ms
- the nominal value of the paced AV delay is 200 ms
Rate Responsive AV Delay
The rate responsive AV delay parameter increases or decreases the paced or sensed AV delay in relation to the changes in the sensor-indicated rate (AP) or in the sensed intrinsic atrial rate (AS). In the new platforms, the shortening of the AV delay starts from 60 bpm (rather than 90 bpm for the older devices). The shortening of the AV delay continues until the maximal sensor rate, the maximal tracking rate or the shortest AV delay is reached.
- low: AV delay is shortened by 0.5 ms per bpm
- medium: AV delay is shortened by 0.75 ms per bpm
- high: AV delay is shortened by 1.0 ms per bpm
- the value of the shortest AV delay is programmable
Negative AV Hysteresis
The parameter Negative AV hysteresis allows the device to reduce the paced or sensed AV delay when an R wave is sensed to avoid intrinsic conduction and encourage ventricular pacing.
- when Negative AV Hysteresis is active, an R wave sensed during the AV delay triggers the subtraction of the programmed Negative AV Hysteresis delta to the measured A-VS interval
- the shortened AV delay stays active during 32 cycles if no R wave is sensed
- if no R wave is sensed, the paced/sensed AV delay that is programmed permanently becomes active again after 32 cycles
- if another R wave is sensed, the shortened paced/sensed AV delay is maintained during 255 cycles before going back to the programmed value