User Manual

2. For the DR model, when the Overdrive function is activated, the atrial Autosensing
function is not programmable.
Ventricular Autothreshold (automatic adjustment of ventricular pacing amplitude)
The Ventricular Autothreshold function allows automatic adjustment of the amplitude of
ventricular pacing, according to a threshold test performed by the device at regular intervals.
Description:
ALIZEA searches for the ventricular threshold daily at 0am, 6am, 12am and 6pm. This search
is done only if the rhythm is below 95 bpm in dual chamber modes out of fallback mode switch
and below 80 bpm for single chamber modes or in case of Fallback Mode Switch.
It is based on the measurement of negative sensing signal deflection during the 65 ms
following ventricular pacing. In order to avoid the risks of ventricular fusion, in dual chamber
modes, the AV delay is forced to 39 ms after a P wave or 63 ms after an atrial pacing pulse.
In single chamber modes or Fallback mode switch, the escape interval is decreased by 109
ms while searching for the threshold. Following the AV delay or escape interval reduction, the
calibration phase is starting only if 4 consecutive cycles are paced.
Calibration phase, consisting of 3 ventricular pacing pulses at 4 V and 3 ventricular pacing
pulses at 2 V (followed, after 65 ms, by a back-up safety pulse at 4 V and 1 ms) and 2
ventricular pacing at 0 V (followed, after 65 ms, by a back-up safety pulse at 4 V and 1 ms),
determines the capture criterion.
Searching for the ventricular threshold consists of a series of ventricular pacing pulses
decreasing from 1.75V to 0.25 V by step of 0.25V.
This search stops as soon as a pacing pulse is ineffective (then followed, after 65 ms, by
back-up pacing at 2.5 V and 1 ms). The ventricular pacing threshold corresponds to the
amplitude of the last effective pacing pulse.
If the Ventricular Auto-threshold function is programmed to Auto, the ventricular pacing
amplitude is programmed to twice* the pacing threshold limited to a programmed minimal
value (2.5V**). This value is set until the next threshold search.
*as-shipped, programmable “RV amplitude safety margin”
**as-shipped, programmable “RV min amplitude”
If the threshold search is not successful, the ventricular pacing amplitude is forced to a safe
amplitude (either the programmable “Maximum Amplitude” or “Safety Amplitude”).
Whenever Ventricular Auto-threshold is programmed to Monitor, the programmed ventricular
pacing amplitude is maintained
When Ventricular Auto-threshold is programmed to Monitor or Auto, the programmable pulse
widths are limited to values between 0.12 ms and 0.50 ms
NOTE: : For optimal operation of the Ventricular Auto-threshold function, it is advisable to
avoid using high polarization leads.
WARNING: Certain drugs can greatly increase the pacing threshold. The Ventricular
Autothreshold function should be used with caution, properly adjusting the minimal
ventricular pacing amplitude.
15.7.3.
15. FUNCTIONS AND PARAMETERS
48 ALIZEA – UA10414A