User's Manual

Timing Functions

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Timing Functions

Basic Rate

The basic rate is the rate at which the pacemaker delivers pulses in the

absence of a spontaneous rhythm or if sensing is deactivated. The

corresponding interval is called the "basic interval" - the interval

between two pacing pulses.

In the atrial-controlled modes, the basic interval is started by an atrial

event. In the atrial-controlled dual-chamber modes, the basic interval is

also started by a ventricular extrasystole.

In the ventricular-controlled modes, the basic rate is started by a

ventricular event.

Rate Hysteresis

To preserve a spontaneous rhythm once it occurs, a rate hysteresis can

be programmed in the modes DDD(R), DDT(R), DDT(R)/A, DDT(R)/V,

DDI(R), VDD(R), VDT(R), VDI(R), VVI(R), VV T(R), AAI(R) and AAT(R). In

this case, the pacemaker, after detecting a sense event, “waits” not

only for the duration of the basic interval for a new sense event, but

also for the duration of the longer hysteresis interval before pacing

occurs. This means that the pacemaker tolerates a spontaneous

rhythm whose rate lies below the basic rate. However, the intrinsic rate

must be higher than the rate that corresponds to the hysteresis

interval. If a sensed event does not occur within the hysteresis interval,

a pacing pulse is delivered at the end of the hysteresis interval. The

next interval then conforms to that of the basic rate or the interval

determined by the sensor (See Figure 7).