ADAS1000-4BSTZ datasheet(44/80 Pages) AD

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ADAS1000-3/ADAS1000-4

Data Sheet

Pace Edge Threshold

This programmable level (Address 0x0E, see Table 41) is used to

find a leading edge, signifying the start of a potential pace pulse. A

candidate edge is one in which the leading edge crosses a threshold

PACEEDGETH from the recent baseline. PACEEDGETH can

be assigned any value between 0 and 255. Setting PACEEDGETH

to 0 forces it to the value PACEAMPTH/2 (see the following

equation). Non-zero values give the following:

PACEEDGETH setting =

GAIN

VREF

where:

N is the 8-bit programmed PACEEDGETH value (1 ≤ N ≤ 255).

VREF is the ADAS1000-4 reference voltage of 1.8 V.

GAIN is the programmed gain of the ECG channel.

The minimum threshold for ×1.4 gain is 19.6 µV, while the

maximum for the same gain setting is 5.00 mV.

Pace Level Threshold

This programmable level (Address 0x0F, see Table 42) is used to

detect when the leading edge of a candidate pulse ends. In general,

a pace pulse is not perfectly square, and the top, meaning the

portion after the leading edge, may continue to increase slightly

or droop back towards the baseline. PACELVLTH defines an

allowable slope for this portion of the candidate pulse, where

the slope is defined as the change in value over an internally-

fixed interval after the pace edge is qualified.

PACELVLTH is an 8-bit, twos complement number. Positive

values represent movement away from the baseline (pulse

amplitude is still increasing) while negative values represent

droop back towards the baseline.

PACELVLTH setting =

GAIN

VREF

where:

N is the 8-bit programmed PACELVLTH value (−128 ≤ N ≤ 127).

VREF is the ADAS1000-4 reference voltage of 1.8 V.

GAIN is the programmed gain of the ECG channel.

The minimum value for ×1.4 gain is 9.8 µV, while the maximum

for the same gain setting is 2.50 mV.

An additional qualification step, performed after PACELVLTH

is satisfied, rejects pulses with a leading edge transition time greater

than about 156 µs. This filter improves immunity to motion and

other artifacts and cannot be disabled. Overly aggressive ESIS

filtering causes this filter to disqualify valid pace pulses. In such

cases, increasing the value of PACEEDGETH provides more

robust pace pulse detection. Although counterintuitive, this

change forces a larger initial deviation from the recent baseline

before the pace detection algorithm starts, reducing the time

until PACELVLTH comes into play and shortening the apparent

leading edge transition. Increasing the value of PACEEDGETH

may require a reduction in PACEAMPTH.

Pace Amplitude Threshold

This register (Address 0x07, see Table 34) sets the minimum

valid pace pulse amplitude. PACEAMPTH is an unsigned 8-bit

number. The programmed height is given by:

PACEAMPTH setting =

GAIN

VREF

where:

N is the 8-bit programmed PACEAMPTH value (1 ≤ N ≤ 255).

VREF is the ADAS1000-4 reference voltage of 1.8 V.

GAIN is the programmed gain of the ECG channel.

The minimum threshold for ×1.4 gain is 19.6 µV, while the

maximum for the same gain setting is 5.00 mV. PACEAMPTH

is typically set to the minimum expected pace amplitude and

must be larger than the value of PACEEDGETH.

The default register setting of N = 0x24 results in 706 μV for a

gain = 1 setting. An initial PACEAMPTH setting between

700 µV and 1 mV provides a good starting point for both

unipolar and biventricular pacing detection. Values below

250 µV are not recommended because they greatly increase

sensitivity to ambient noise from the patient. The amplitude

may need to be adjusted much higher than 1 mV when other

medical devices are connected to the patient.

Pace Validation Filters

A candidate pulse that successfully passes the combined tests of

PACEEDGETH, PACELVLTH, and PACEAMPTH is next passed

through two optional validation filters. These filters are used to

reject sub-threshold pulses such as minute ventilation (MV) pulse

and signals from inductively coupled implantable telemetry

systems. These filters perform different tests of pulse shape

using a number of samples. Both filters are enabled by default;

Filter 1 is controlled by Bit 9 in the PACECTL register (see

Table 31) and Filter 2 is controlled by Bit 10 in the same register.

These filters are not available on a lead by lead basis; if enabled,

they are applied to all leads being used for pace detection.

Pace Width Filter

A candidate pulse that successfully passes the edge, amplitude, and

noise filters is finally checked for width. When this final filter is

enabled, it checks that the candidate pulse is between 100 μs

and 2 ms wide. When a valid pace width is detected, the width

is stored. Disabling this filter affects only the minimum width

(100 µs) determination; the maximum width detection portion

of the filter is always active. This filter is controlled by the

PACECTL register, Bit 11 (see Table 31).

Rev. B | Page 44 of 80

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