Datasheet

ADAS1000/ADAS1000-1/ADAS1000-2 Data Sheet
Rev. A | Page 42 of 80
Pace Amplitude Threshold
This register (Address 0x07, see Table 32) can be used to set the
minimum valid pace pulse amplitude:
PACEAMPTH setting =
16
2×
×
GAIN
VREFN
, (corresponds to a
range of 20 µV to 5 mV in the ×1.4 gain setting (GAIN 0))
where:
N = 0 to 255 (8 bits), register default N = 0x24, (PACEAMPTH
= 706 μV in the ×1.4 gain setting)
GAIN = 1.4, 2.1, 2.8, or 4.2 (programmable).
VREF = 1.8 V.
This level would typically be set to be the minimum expected
pace amplitude.
For best results under most operating conditions for both
biventricular and unipolar pacing, it is suggested to set the
pace amplitude threshold to a value of approximately 700 μV
to 1 mV. It is not recommended to set the threshold below
250 μV to avoid 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 Edge Threshold
This programmable level (Address 0x0E, see Table 39) is used to
find a leading edge, signifying the start of a pace pulse:
PACEEDGETH setting =
16
2×
×
GAIN
VREFN
(corresponds to a
range of 20 µV to 5 mV in the ×1.4 gain setting)
where:
If N = 0, PACEEDGETH = PACEAMPTH/2, then N = 0 to 255
(8 bits).
GAIN = 1.4, 2.1, 2.8 or 4.2 (programmable).
VREF = 1.8 V.
Pace Level Threshold
This programmable level (Address 0x0F, see Table 40) is used to
find the leading edge peak:
PACELVLTH setting =
16
2×
×
GAIN
VREFN
, signed (FF = −1,
01 = +1), default = 0
where:
N = 0 to 255 (8 bits).
GAIN = 1.4, 2.1, 2.8 or 4.2 (programmable).
VREF = 1.8 V.
Pace Validation Filter 1
This filter is used to reject sub threshold pulses such as minute
ventilation (MV) pulses and inductive coupled implantable
telemetry systems. It is typically enabled and is controlled via
the PACECTL register, Bit 9 (see Table 29) register. Filter 1
applies to all leads enabled for pace detection.
Pace Validation Filter 2
This filter is also used to reject sub threshold pulses such as
MV pulses and inductive implantable telemetry systems. It is
normally enabled and is controlled via the PACECTL register,
Bit 10 (see Table 29). Filter 2 applies to all leads enabled for pace
detection.
Pace Width Filter
When enabled, this filter searches for an edge of opposite polarity
to the leading edge with a magnitude of at least half the original
trigger. The second edge must be between 100 µs to 2 ms from the
original edge. When a valid pace width is detected, the width is
stored. When disabled only the minimum pulse width of 100 μs
is disabled. This filter is controlled by the PACECTL register, Bit 11
(see
Table 29).
BIVENTRICULAR PACERS
As described previously, the pace algorithm expects the pace
pulse to be less than 2 ms wide. In a pacer where both ventricles
are paced, they can be paced simultaneously. Where they fall
within the width and height limits programmed into the
algorithm, a valid pace will be flagged, but only one pace pulse
may be visible.
With the pace width filter enabled, the pace algorithm seeks
pace pulse widths within a 100 μs to 2 ms window. Assuming
that this filter is enabled and in a scenario where two ventricle
pacer pulses fire at slightly different times, resulting in the pulse
showing in the lead as one large, wider pulse, a valid pace is
flagged so long as the total width does not exceed 2 ms.
PACE DETECTION MEASUREMENTS
Design verification of the ADAS1000 digital pace algorithm
includes detection of a range of simulated pace signals in
addition to using the ADAS1000 and evaluation board with
one pacemaker device connected to various simulated loads
(approximately 200 Ω to over 2 kΩ) and covering the following
4 waveform corners.
• Minimum pulse width (100 μs), minimum height (to
<300 μV)
• Minimum pulse width (100 μs), maximum height (up to
1.0 V)
• Maximum pulse width (2 ms), minimum height (to
<300 μV)
• Maximum pulse width (2 ms), maximum height (up to
1.0 V)
These scenarios passed with acceptable results. The use of the
ac lead-off function had no obvious impact on the recorded
pace height, width, or the ability of the pace detection algorithm
to identify a pace pulse. The pace algorithm was also evaluated
with the respiration carrier enabled; again, no differences in the
threshold or pacer detect were noted from the carrier.