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Stratos LV/LV-T Technical Manual  87 
Wenckebach Behavior 
If the end of the AV delay falls within the upper threshold rate 
interval, ventricular pacing occurs at the end of the upper 
tracking interval. 
2:1 Behavior 
If the high-rate atrial event occurs in the ARP, the FFP or PMT 
protection window, an AV delay is not started. 
In Wenckebach mode, the CRT-P switches to ventricular timing.  
This means that a VA delay is started after a ventricular event to 
avoid the atrial basic interval extend the duration of the 
Wenckebach mode.  The VA delay is calculated from the basic 
(hysteresis) interval minus the AV delay (or the AV safety 
interval). 
The timing of the Stratos CRT-Ps ensures that the ventricular 
paced event (Vp) following the VA delay allows atrial pacing at 
the end of the AV delay; thus, terminating the Wenckebach 
cycle.  
The CRT-P counts the number of Wenckebach cycles.  In more 
than four Wenckebach cycles are detected, a shortened VA 
delay is started after a right or left ventricular paced event to 
guarantee constancy of the ventricular rate.  The short VA delay 
is in this instance calculated from the ventricular interval of the 
upper tacking interval minus the AV delay (or the AV safety 
interval).  If the Wenckebach mode has been terminated, the 
counter of the CRT-P is reset.