User Manual Part 1

3-34

TACHYARRHYTHMIA DETECTION

VENTRICULAR DETECTION

When a detection window becomes satisﬁed, the pulse generator begins

calculating for sudden Onset in a two-stage sequence.

• Stage 1 measures the ventricular intervals prior to the start of the episode

and locates the pair of adjacent intervals (pivot point) where the cycle

length decreased the most. If the decrease in cycle length is equal to or

greater than the programmed Onset value, stage 1 declares sudden Onset.

• Stage 2 then compares additional interva ls. If the difference b et we en the

average interval before the pivot point and 3 out of the ﬁrst 4 intervals

following the pivot point is equal to or greater than the programmed Onset

Threshold, stage 2 declares sudden Onset.

If both stages declare the rhythm sudden, therapy will be initiated. If either

stage indicates a gradual onset, initial ventricular therapy will be inhibited in the

lowest zone. Therapy will not be inhibited by Onset if:

• The rate accelerates to a higher ventricular zone

• Information from the atrial lead determines that the RV rate is faster than

theatrialrate(VRate>ARateprogrammedtoOn)

• The SRD timer expires

Onset is measured using RV intervals only. It can be programmed as a

percentage of cycle length or as an interval length (in ms). It is limited to the

lowest therapy zone of a multi-zone conﬁguration. The selected Onset value

represents the minimum d ifference that must exist bet we en intervals t hat are

above and below the lowest programmed rate threshold. The pulse generator

performs Onset calculations (even when the feature is programmed to Off) for

all episodes except induced or commanded episodes. The m easured Onset

results from a two-stage calculation are stored in therapy history. This stored

data may be used to program an appropriate Onset value.

Sustained Rate Duration (SRD)

Sustained Rate Duration allows delivery of the programmed ventricular therapy

when a tachyc ardia is sustained for a programmed period beyond D urat ion , but

the programmed therapy inhibitors (Vector Timing and Correlation, AFib Rate

Threshold, Onset, and/or Stab ility) indicate to withhold therapy (Figure 3-21 on

page 3-35).

- DRAFT -