User's Manual

Antitachycardia Functions

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Mode Switching with X/Z-out-of-8 Algorithm

This X/Z-out-of-8 algorithm can be used to program activation and

deactivation criteria. This prevents, for example, unnecessary mode

oscillations in the case of atrial extrasystoles or unstable atrial signals.

In addition, this algorithm can be employed to determine the speed at

which a de- and resynchronization of ventricular depolarization takes

place. This intervention rate can be programmed within a range from

100… (10)... 250 ppm.

The postventricular atrial blanking (PVAB) period after a ventricular

event can be programmed in a range from 50 – 200 ms. This prevents

any ventricular events from being registered in the atrial channel.

When an atrial tachycardia is detected, the pacemaker automatically

switches to a non-atrial-controlled mode: from DDD(R) to DDI(R), from

DDD(R)

to DDI(R), or from VDD(R) to VDI(R) as well as from DDT(R)/A

and DDT(R)/V to DDI(R).

The mode switch can be programmed so that you can switch from a

non-rate-adaptive mode to a rate-adaptive mode, and vice versa. This

serves to prevent an undesirable rate drop to the basic rate in case of

physical stress.

An atrial tachycardia is considered sensed when the so-called X-out-of-

8 conversion criterion has been fulfilled. The X value can be

programmed in the value range (X = 3... (1)...8).

Detection is based on the continual evaluation of the last 8 atrial

intervals. When X out of 8 intervals reveal an atrial rate that lies above

the programmed intervention rate, then the conversion criterion is

fulfilled and mode switching automatically follows.

The pacemaker works in the programmed non-atrial mode until the

switch-off criterion (Z out of 8) has been fulfilled. The Z value can be

programmed in the value range (Z = 3... (1)...8). Likewise, the last 8

consecutive atrial intervals are continuously evaluated. When Z out of 8

intervals lie below the programmed intervention rate, the atrial

tachycardia is considered to be over, and the pacemaker automatically

switches to the originally programmed atrial-controlled mode.

The X or Z counter is reset to zero after every completed switching.