Biomedical Engineering Reference
In-Depth Information
pacemakers and defibrillators are provided with an identifier
located on the device head that is visible on a radiographic
image or under a skiascope. This identifier serves as noninva-
sive confirmation of the manufacturer and the necessary
applications of the programmer. Older devices used to be
marked with a numeric code. Nowadays, codes using letters
to identify manufacturers are used more often, together with
numeric identification of the necessary software of the pro-
grammer or identification of the determined pacing mode.
failure. The failure is described in the interaction window and
a solution is proposed. To continue programming changes, it
is necessary to make a correction of the influenced parameter
first. If it is necessary to make a permanent record of the data
interrogated at a follow-up, the programmer offers printed
reports containing actual values of parameters, data on ther-
apy history, information on the device's battery status, and
programmed data about a patient (date of implantation, type
of leads, indication for device implantation, etc.).
2.5
Programmer Usage
2.6
Magnet Usage
Communication with an implanted device is realized by means
of a specialized device called the programmer. It enables pro-
gramming of parameters of electric stimuli, measurement of
sensed signals of the heart's beat and electrical features of the
system, and selection of all other parameters. Data transfer
between the programmer and the device occurs by means of
telemetric inductive coupling or a wireless radio signal.
Programmers are computerized devices with their own
operating system. They contain general service software and
special applications for particular devices or groups of devices.
The user interface is a touch screen that includes buttons for
sending data to the implanted device, for diverting the therapy,
or for selection of paper advance speed in a case of electrogram
(EGM) or electrocardiogram (ECG) records. Furthermore,
the built-in parts include an ECG monitor; an internal printer;
a device for data disc input (diskettes, flash drive); slots for
connecting an external printer, monitor, or keyboard; and
inputs from electrophysiological monitoring systems.
On the main screen of the system, cross-referenced entries
are available, enabling access to information on the set func-
tions before input to application software, as well as language
selection, an easy-to-use diagnostic ECG monitor, a mode for
a quick automatic interrogation of the device, and others are
available. Regarding the ECG monitor, it is possible to change
the speed of motion, to set an input amplifier or an input filter
of the surface ECG, or to display electric stimuli spikes.
Identification of the implanted device by means of a telemet-
ric sensor positioned over the pacemaker and downloading
data from it is designated as reading, or
interrogation
. The
interrogation is the first step of all sessions during follow-up.
At the initial interrogation, the information on, for example,
the parameter settings, patient data, diagnostic data, and bat-
tery status, are copied from the device memory.
Parameter values might be changed by touching the pointer
to the appropriate parameter window and by lifting the pointer
off the screen. After execution of changes to parameter val-
ues, the change will appear in the window until it is pro-
grammed into the device. After a new parameter is defined,
its interactions with the other parameters are evaluated imme-
diately. If a new value breaks the limits of interaction within
the application, an icon will appear that reports parameter
Because of the possibility of an emergency effect on the
behavior of the implantable devices when a programmer is
unavailable, the implantable devices are equipped with a mag-
netic switch (called a reed switch). Technically, it deals with a
reed relay. Its contacts usually are disconnected in a resting
state. For making contact with this relay, a magnet with induc-
tion of more than 1 mT is used. According to the valid stan-
dards [17], the devices must be resistant to magnetic fields up
to 1 mT. In practice, small permanent magnets in the shape of
a horseshoe, an annular ring, or a prism are used. Some manu-
facturers supply a magnet as a part of the telemetric wand of
the programmer. In general, every pacemaker has a designated
response when a magnet is positioned over the device. For
pacemakers, it deals with switching to the asynchronous mode
and pacing using a defined paced rate according to the battery
status. Because the magnet switches off the sensing input
amplifier, in this way it is possible, for example, to interrupt
pacemaker-mediated tachycardia. Regarding defibrillators, it
deals with elimination of tachycardia therapy (shocks or anti-
tachycardia pacing). After the magnet is lifted off the device -
after repeated disconnection of the reed relay - the device
returns to its normal, originally programmed mode.
A setting determining the response to a magnet might be
programmed, depending on the type of the device and the
manufacturer. For example, the following settings of
de fi brillators are available:
Off (no response when the magnet is positioned over the
•
device),
Save EGM (it saves an actual EGM),
•
•
Inhibit tachytherapy (therapy application is stopped; or
de fi brillator mode is switched over).
Some previous systems were equipped with certain pos-
sibilities for the measurement of pacing threshold during
application of a magnet. For example, the first three pulses
were asynchronous, with a paced rate of 100 pulses/min.
They were followed by asynchronous pacing at a pro-
grammed paced rate. The first and second electric stimuli
had the programmed width, whereas the third one had only
75 % of the programmed width. Loss of the paced rate with
the third stimulus meant a small safety reserve. Another sys-
tem applied 16 asynchronous stimuli with a paced rate of
