BIOTRONIK Lumax DR ICD Series, Technical Manual, Page: 111 / 176

Lumax Technical Manual 103
2.10.3 Shock Impedance Measurements
The Lumax ICDs/CRT-Ds have the ability to perform automatic
and manual painless shock impedance measurements. The
devices can measure the shock impedance by delivering an
undetectable 3 nJ shock by applying 1 ma of current. The device
then measures the resulting voltage drop and calculates the
resulting shock impedance. This impedance measurement is tied
to the pacing impedance measurement, meaning that the pacing
impedance measurement is done daily, and shock impedance is
done (concurrently with pacing impedance measurement) every
fourth day. The results of these impedance measurements are
available through the devices statistics function.
2.10.4 Testing for Retrograde Conduction
Retrograde conduction from the ventricles to the atrium can be
assumed when a 1:1 relationship between the ventricular
stimulation and atrial depolarization has been obtained with a
constant coupling interval during ventricular stimulation. The
ICD/CRT-D features a test for measuring retrograde conduction
time. During operation of this test, the patient is paced (in VDI
mode) at an increased ventricular rate over several cycles while
the retrograde conduction time is measured. Therefore, the
pacing
Rate must be programmed at a rate higher than the
patient’s intrinsic rhythm.
This measurement can be made for both the right and left
ventricles, but only one at a time. The ventricle being tested,
pacing rate, voltage and pulse width are all programmable. In
addition, the pacing polarity of the left ventricle is also
programmable as described in Section 2.1. Both the programmer
display and printout provide measured retrograde conduction
times. The duration of time that the test is conducted is based on
how long the Measure button is depressed. The paper speed for
the test printout is also programmable for this test.
To prevent retrograde P-waves from triggering ventricular pulses,
thereby mediating a “re-entry” tachycardia (pacemaker mediated
tachycardia, PMT), it is recommended that the programmed post-
ventricular atrial refractory period be programmed longer than the
retrograde conduction time.