User's Manual

66
Antitachycardia Functions
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Tachycardia Behavior
Cylos offers a choice of two algorithms that effectively suppress atrial
tachycardia from being conducted to the ventricle. At the start of a
tachycardic episode, the pacemaker automatically switches from an
atrial-controlled to a ventricular-controlled mode.
The following functions are available:
• Automatic Mode Conversion
• X/Z-out-of-8 Mode Switching
Automatic Mode Conversion
This option is available in the atrial modes DDD(R) and VDD(R) as well
as in DDT(R)/A and DDT(R)/V modes. In the case of atrial tachycardias
-- when the P-P interval is shorter than the ARP (the atrial refractory
period) – there is an automatic conversion to a mode without atrial
control. If the pacemaker is in DDD(R), DDT(R)/A, or DDT(R)/V mode,
it converts to DVI(R); if it is operating in VDD(R) mode, it converts to
VVI(R). This procedure prevents P-wave-triggered ventricular pacing
during tachycardia.
When mode conversion is disabled, an atrial sensed event within the
refractory period does not trigger an interval. In activated mode
conversion, however, an atrial sensed event within the refractory period
triggers a restart of the refractory period. The basic interval and the AV
delay are not restarted. If the coupling interval between the consecutive
P waves becomes shorter than the atrial refractory period, the atrial
refractory period will be continuously restarted. This means that the
pacemaker remains refractory in the atrium during the entire basic
interval (see Figure 13).