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Chapter 5 Programmable Parameters
Evia HF / HF-T Technical Manual
PAGE 34
5.5.4.4 AV Scan Hysteresis
With AV Scan Hysteresis enabled, after 180 consecutive pacing cycles, the AV delay is extended for the
programmed number of pacing cycles. (1 … 10). If an intrinsic rhythm is detected within the extended
AV delay, the longer AV delay remains in effect. If an intrinsic rhythm is not detected within the number
of scan cycles, the original AV delay value resumes.
Figure 17: AV Scan Hysteresis
5.5.4.5 Negative AV Delay Hysteresis
With Negative AV Delay Hysteresis, the AV delay is decreased by a defined value after a ventricular event
is sensed, thereby promoting ventricular pacing. The Negative AV Delay Hysteresis value corresponds to
the programmed AV delay, multiplied by approximately 2/3, limited to a minimum of 15 ms.
The normal AV delay resumes after the programmed number of consecutive ventricular paced events
(Repetitive Negative AV Delay Hysteresis) elapses.
Figure 18: Negative Hysteresis
CAUTION
Negative AV Delay Hysteresis This feature insures ventricular
pacing, a technique which has been used in patients with hypertrophic
obstructive cardiomyopathy (HOCM) with normal AV conduction in order
to replace intrinsic ventricular activation. No clinical study was conducted
to evaluate this feature, and there is conflicting evidence regarding
the potential benefit of ventricular pacing therapy for HOCM patients.
In addition, there is evidence with other patient groups to suggest that
inhibiting the intrinsic ventricular activation sequence by right ventricular
pacing may impair hemodynamic function and/or survival.