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76 Stratos LV/LV-T Technical Manual
2.3.6 Refractory Periods
Sensed events that occur during the refractory period have no
effect on pacemaker timing. These atrial or ventricular sensed
events are classified as “unused” for normal CRT-P timing.
In the Stratos CRT-Ps, the total atrial refractory period has been
subdivided into an atrial refractory period (ARP), atrial far-field
protection (FFP) and a PMT protection window (PMT). In terms
of priority FFP is first, ARP second and PMT third.
When mode switching is turned ON, the atrial events in the atrial
refractory period and the PMT protection window are used as the
criteria in order to sense atrial tachyarrhythmias and to ensure
high atrial rates are not transmitted to the ventricle.
The behavior of BIOTRONIK CRT-Ps reacts differently
depending on the timing interval in which the atrial event occurs.
The behavior is summarized in Table 20.
Table 20. Response to Atrial Sense Events in Different
Timing Intervals in Stratos CRT-Ps
Timing Interval Response
A
s
occurs during
the far-field
protection (FFP)
No consequence. A
s
is ignored (unused).
Neither the AV delay nor the ARP is
started. There is no influence on mode
switching.
A
s
occurs during
the Atrial
Refractory
Period (ARP)
The event influences mode switching.
A
s
occurs in the
PMT protection
window
The AUI (atrial upper interval) starts. The
AV delay is not restarted. Post-AES
pacing is started if the atrial sense is
classified as an AES.
2.3.6.1 Atrial Refractory Period
In all modes in which atrial depolarization can be sensed, the
Stratos CRT-Ps will start an atrial refractory period upon each
atrial depolarization (programmable: AUTO, 225…(25)…775). In
standard “Auto” setting, the atrial refractory period (ARP) is
automatically preset to a minimum value of 225 ms and is
automatically extended if the AV delay is longer.