User's Manual

Antitachycardia Functions

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If these two conditions are met, the pacemaker automatically extends

or shortens the AV delay by a defined value. If the resulting V

-A

interval remains constant, the PMT is considered confirmed. The

algorithm for terminating the PMT is automatically started.

Note: In cases where a low upper tracking rate and long

AV delays have been programmed, pacing rates

slightly above the UTR may occur for a few cycles.

PMT Termination

The PMT is terminated by extending the total atrial refractory period

(TARP) for a pacing cycle. This interrupts the retrograde conduction

loop and hence the PMT. Consequently, the PVARP must be longer

than the retrograde conduction period after ventricular pacing or

sensing. The duration of the PVARP depends on the duration of the

TARP used in the systems and on the AV delay (PVARP = TARP minus

the AV delay).

Note: A safety interval of 300 ms protects against

competitive pacing and prevents the atrial pulse

from reaching refractory and/or vulnerable tissue.

This safety interval cannot be programmed and is only active when the

PMT function is active.

Preventive Overdrive Pacing

Atrial overdrive pacing is a preventive measure to reduce the incidence

of atrial tachycardias. Numerous clinical studies and publications

indicate a decreased risk of developing atrial tachycardias. The

overdrive algorithm effects atrial overdrive pacing and ensures pacing

at a rate that is slightly above the intrinsic sinus rate. Atrial overdrive

pacing thereby minimizes the number of detected atrial events. The

overdrive mode is available in the modes DDD(R)

, DDT/A(R)

DDT/V(R)

, AAI(R)

and AAT(R)