User Manual

Lumax Technical Manual 77
Cardiac signals vary in amplitude; therefore detection thresholds
cannot be static. With the Automatic Sensitivity Control (ASC)
every paced/sensed event is measured, and the upper and lower
thresholds are re-set accordingly (also known as beat-by-beat
adaptation). The ASC begins by tracking the cardiac signals (R
and P-waves) during the sensed refractory periods. The peak
values measured during this time are used to set the sensing
thresholds during the active detection periods.
2.3.1 Right Ventricular Sensitivity Settings
There are three programmable preset options for setting the
sensitivity of the right ventricular input stage. The sensitivity
selections are designed to adapt the parameters of the input
stage to various signal conditions. The predefined parameter sets
are described in Table 27
.
Table 27: Sensitivity Settings
Setting Definition for Use
Standard This setting is recommended for most
patients, especially for those with
measured R-wave amplitude of 3 mV.
Enhanced
T Wave
Suppression
This setting offers suppression of T-wave
oversensing. This mode should not be
used on patients with the following
conditions:
 Sinus rhythms with small signal
amplitudes, R-waves 4 mV
 VF with highly fluctuating signal
amplitudes.
Enhanced
VF Sensitivity
This setting enhances VF detection, in
cases of highly fluctuating signal
amplitudes. It is not to be used for patients
that have sinus rhythms containing large
amplitude T-waves.
Typically, the upper threshold is reset with each sensed R-wave,
but in order to ensure that pacing does not occur during an
episode of VF, the ASC behaves differently with paced events.
Each paced event is followed by a paced refractory period after
which the ventricular threshold is set to the minimum
programmed value.