Biomedical Engineering Reference
In-Depth Information
a programmer. For each episode, the data stored includes
information on episode time, electrograms with annotated
markers, cardiac intervals, etc. The information comprises
an episode number, date, time, a type (VF, VT, spontaneous/
commanded), average atrial and ventricular rates, the type of
therapy delivered and its parameters, and episode duration.
The device stores the maximum number of episodes of indi-
vidual types until the memory is full. As soon as the memory
capacity available for storing episode data is filled, the device
rewrites older stored episodes according to their priority.
The trend function provides graphical representation of
bradycardia counters and histograms. This data can be useful
for the evaluation of a patient's condition and efficacy of
programmed parameters. Atrial and ventricular markers, the
patient's daily activity rate, time of the ATR mode switching,
PMT, daily breathing rhythms, intrinsic signal amplitudes,
and pacing and defibrillation circuit impedances are dis-
played, depending on the type of device.
Histograms contain the total number and percentage of
paced and sensed events for the respective heart chamber.
Histogram data can provide clinical information, such as fre-
quency distribution of the patient's intrinsic heart rhythm
and the proportion of paced and sensed events according to
heart rate.
A patient may commence recording electrograms, inter-
vals, and annotated markers during a symptomatic episode by
placing a magnet on the device. If the function is activated, the
device stores a record of arrhythmia from a certain interval
before the recording is started. This is made possible because
electrograms are moved in the register so they are still avail-
able in the memory after the magnet is applied. The data stored
include an episode number, atrial and ventricular action at the
time of magnet application, and the time and date of the begin-
ning of magnet application. However, upon the activation of
this function, all other functions of the magnet, and primarily
the inhibition of therapy, are deactivated. Before the magnet is
given to a patient, it must be evaluated carefully to determine
whether the function of recording is really activated. If the
magnet function remained set to therapy inhibition uninten-
tionally, it could have serious consequences later.
10.5
Electrophysiologic Testing Using an ICD
Electrophysiologic testing functions allow noninvasive
induction and termination of arrhythmia. They are com-
monly used during ICD implantation to test the efficacy of
set detection and therapy.
Common methods of VT induction include the following:
A T wave shock
•
•
Programmed electrical stimulation (PES)
•
A burst
Some systems also allow large-amplitude pacing pulses
(9 or 15 V) applied via lead shock electrodes. The functions
(PES, a burst) can also be available in an atrium with back-
up ventricular pacing.
During electrophysiologic testing, the status of ICD detec-
tion and therapy processes is displayed in real time on the
programmer. If an episode is in progress, the zone in which
the respective detection condition is met is indicated. During
induction, the device detection is switched off automatically;
after termination of induction, the detection is switched on
again automatically. When applying any type of induction,
the ICD stops performing other activities until the end of the
induction, after which the detection is applied and the ICD
responds in an appropriate way. A patient may be medicated
before the induction. During electrophysiologic testing,
patients must be carefully monitored, and an external
defibrillator must be available because induced VT may
degenerate to VF. Once induction is commenced by any
method, the application does not stop, even in the case of
dropped telemetric communication.
When inducting tachycardia by means of a T wave shock
(Fig.
10.6
), relevant programmable parameters must be set.
Coupling interval
S1 Interval
400
400
400
400
400
400
Shock
S1
S1
S1
S1
S1
S1
Synchronization pacing pulses
Fig. 10.6
Shock on T-induction method
