Biomedical Engineering Reference
In-Depth Information
Fig. 13.1 Flow chart for
ambulatory device
follow-ups
Question
about mean
time
Any palpitations,
pain, dyspnea,
shocks?
Physical
examination
Blood pressure,
ECG, incision, pocket
Device
interrogation
Automatic device
messages? Warnings?
Battery
check-up
Assumed longevity?
ERI?
Manual ICD capacitor
reformation
EGM analysis-check
therapy adequacy,
counters reset
Device
diagnostic
evaluation
Stored EGM,
counters, histograms,
ATR, PMT, etc.
Check and set
pacing safety
margin, consider
configuration
Electrical
parameters
measuring
P and R waves,
impedance, pacing
thresholds
Print out,
saving to
disk
Next follow-
up
scheduling
memory (since the previous follow-up) and long-term
memory (since implantation). Overall, the follow-up proce-
dure may be described as shown in Fig. 13.1 .
The range of electrical parameter values follows from the
manufacturer's recommendations. The usual minimum value
of intrinsic activity is 1-2 mV for the P wave and 5 mV for
the R wave. Pacing impedance usually ranges from 300 to
1,200
13.1
Measuring Lead Pacing Thresholds
A temporary pacing mode, in which the pacing thresholds are
measured, depends on the heart chamber in which the thresh-
old is to be measured. In general, thresholds can be measured
using a programmer in a comprehensive DDD mode, but for
the sake of good visibility on a surface ECG record, it is rec-
ommended that a single-chamber mode be used; that is, AAI
or A00 for the right atrium and VVI or V00 for the right and
left ventricles. Optimally, a temporary LRL for measuring
threshold must be set approximately 20/min higher than the
patient's actual intrinsic heart rate; for that reason, the differ-
ence between asynchronous or inhibition modes should not
be of any significance. For the sake of safety, the inhibition
mode should be used because of the possible occurrence of
ventricular extrasystoles. Usually, a voltage pacing threshold
is measured while gradually decreasing the amplitude at a
; the value for the left ventricular lead can be even
higher - up to 1,800
W
. Depending on the lead type, imped-
ance of the defibrillation circuit reaches approximately
35-60
W
; provided that only a lead distal shock electrode is
used, it is usually higher - up to 90
W
. The optimum voltage
pacing threshold is below 1.0 V at a pacing pulse width of
0.5 ms. The pacing threshold slightly increases after implan-
tation and then decreases again. This phenomenon is sup-
pressed by steroids. Long-term monitoring should prove all
the electrical parameters to be more or less on the same level
throughout the system's longevity.
W
 
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