User's Manual

Timing Functions

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Figure 7: Basic rate and rate hysteresis in DDD mode

In pacing modes DDD(R), DDT(R)/A, DDT(R)/V, DDT(R), VDD(R),

VDT(R), AAT(R), and AAI(R) the hysteresis interval starts with an atrial

sense event. In the modes DDI(R), VVI(R), VVT(R) and VDI(R) it starts

with a ventricular sense event. In modes DDD(R), DDT(R)/A, DDT(R)/V,

DDT(R), VDD(R) and VDT(R) it also starts with a ventricular

extrasystole.

The rate hysteresis is specified as the difference from the basic rate. In

rate-adaptive pacing, the hysteresis remains constant while the

hysteresis rate follows the variable (sensor-controlled) basic rate.

Note: If the rate hysteresis is to be used in the DDI

mode, the AV delay must be programmed shorter

than the spontaneous conduction time. Otherwise,

the pacemaker paces at the hysteresis rate instead

of the basic rate even in the absence of

spontaneous activity.

Repetitive Rate Hysteresis

The repetitive rate hysteresis helps to maintain the spontaneous

rhythm and avoid unnecessary pacing in situations that exceed the

basic hysteresis, such as post-extrasystolic pauses.

If such a pause occurs, the pacemaker continues to pace at the

hysteresis rate for a programmable number of cycles instead of

immediately reverting to the basic rate (See Figure 8).