User's Manual

39
Timing Functions
The beginning and end of the night, as well as the basic night rate, can
be programmed. At the beginning of the night period, the basic rate
and the hysteresis rate are gradually reduced to the night values. If
rate adaptation is enabled, the sensor threshold during the night is
increased by one increment (less sensitive). This prevents undesirable
rate increases even in patients who do not sleep soundly. After the
night has ended, the pacemaker resumes its daytime pacing values.
Note: Please take into consideration that the patient may
travel to other time zones. If this is expected, the
night duration should be programmed accordingly
shorter or even deactivated.
Note: The internal clock of the pacemaker is
automatically adjusted to the clock of the
programmer at every follow-up. Ensure that the
time displayed by the programmer is correct.
Refractory Period
Sensed events that occur during the refractory period do not affect the
timing. The functions related to tachycardia behavior are an exception:
automatic mode conversion and mode switching. In these functions,
sensed events within the refractory period are utilized for arrhythmia
detection.
In DDD(R) and VDD(R) modes with automatic mode conversion, the
atrial refractory period (ARP) can be triggered, i.e., a sensed event
occurring in the atrial refractory period can restart it.
In the DDD mode the ARP not only starts after atrial sensing or pacing,
but also with ventricular extrasystoles (VES). This is to prevent
pacemaker-mediated tachycardia. For the same reason, the ARP also
begins in the VDD mode upon ventricular pacing that was not triggered
by an atrial event, and upon VES. In the DDI mode, the ARP starts only
after an atrial sensed or paced event.