User Manual

Programming constraint:
The Ventricular Autothreshold function is not programmable when the basic rate is above
85 ppm.
Atrial Autothreshold (for the DR model only)
The Atrial Autothreshold function allows automatic adjustment of the amplitude of atrial
pacing, according to a threshold test performed by the device at regular intervals.
Description:
Once a day (at 2 am by default), ALIZEA searches for the atrial threshold. This search is done
either if the atrium is paced or not. The Atrial autothreshold test is starting only if the rhythm is
not too fast so the cardiac interval must be longer than programmed the atrial autothreshold
max rate interval + 200 ms.
2 types of test are possible: P test in case of stable intrinsic rhythm or AR test in case of stable
AV conduction. A first phase of selection determines the appropriate test. The pacemaker is
pacing at 50 min-1 to search for intrinsic atrial rhythm. If 8 stable P-P intervals are detected,
the P test will be launched. If not, the pacemaker overdrives the atrial rhythm and prolongs
the AV delay to 450ms to promote AV conduction. If 8 stable A-R intervals are detected, the
AR test will be launched. Else, the atrial autothreshold will not start.
Then, a calibration phase, consisting of one pacing pulse at 2 V, determines the starting
amplitude.
When P test is selected, the basic rate is forced to 50 min-1 to promote intrinsic atrial rhythm
and searching for the atrial threshold consists of a series of atrial pacing pulses increasing
from either 2.25 V (if the initial calibration 2V pacing pulse was ineffective) or 0.25V to 4V,
so increasing from ineffective atrial pulse amplitude to effective pulse amplitude. The P test
principle is pacing the atrium 200ms before the expected next P wave on one cardiac cycle
out of three. If the next P wave occurs, it indicates that atrial pacing was not effective and
so atrial amplitude is increased. As soon as next P wave does not occur, it means that atrial
pacing is effective. The threshold search stops and the atrial pacing threshold corresponds to
this atrial pulse amplitude.
When AR test is selected, searching for the atrial threshold consists of a series of atrial pacing
pulses decreasing from either 4V (if the initial calibration 2V pacing pulse was ineffective)
or 1.75V to 0.25 V, so decreasing from effective atrial pulse amplitude to ineffective pulse
amplitude. The AR test principle is looking at a ventricular sensed event after the atrial pacing
on one cardiac cycle out of two. If a ventricular event is sensed, it means that atrial pacing
is effective and so atrial amplitude is decreased. As soon as no ventricular event is sensed,
it means that atrial pacing is ineffective and a atrial back-up is applied. The threshold search
stops and the atrial pacing threshold corresponds to the amplitude of the last effective atrial
pacing pulse.
1. If the Atrial Autothreshold function is programmed to "Auto”, the atrial pacing amplitude is
programmed to twice* the pacing threshold (but not below the programmable “Minimum
Amplitude”).
*as-shipped, programmable “A amplitude safety margin”
If the threshold search is not successful at 4V (the max tested amplitude), the atrial
pacing amplitude is forced to 5V.
If the threshold search is not successful, the atrial pacing amplitude is unchanged,
but after 7 consecutive days with no success, the pacing amplitude is forced to the
programmed Safety amplitude (or the last programmed amplitude if higher) until a new
15.7.4.
15. FUNCTIONS AND PARAMETERS
ALIZEA – UA10414A 49