User's Manual

72
Antitachycardia Functions
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PMT Prevention
Pacemaker-mediated tachycardia is generally triggered by ventricle
depolarization that is out of synchrony with atrial depolarization, e.g.,
as would be the case in ventricular extrasystoles (VES). The
tachycardia is maintained retrogradely by VA conduction coming from
the ventricle depolarization due to pacing and antegradely by P-wave-
triggered ventricular pacing.
In order to prevent PMT in cases where there is ventricular sensing
without a preceding atrial event, the pacemakers restart the basic
interval and the atrial refractory period (ARP). If an atrial refractory
period extension has been programmed, this is additionally prolonged
even further after a VES. A retrograde P wave with a VA conduction
time shorter than the ARP cannot trigger a ventricular pulse and hence
cannot trigger a PMT (see Figure 14).
Figure 14: VES starts the ARP to prevent pacemaker-mediated tachycardia
Atrial Refractory Period Extension
In the case of a programmed atrial refractory period extension, the
atrial refractory period is extended by the programmed value after a
ventricular event, if the event
• is a ventricular sensed event without a preceding atrial event (VES);
pacing modes: DDD(R), DDT(R), VDD(R), VDT(R),
• is a ventricular pace event that has not been triggered by a P wave;
pacing modes: VDD(R), VDT(R).