Biomedical Engineering Reference
In-Depth Information
The setscrews should be tightened until the wrench starts
skipping. Further tightening is needless because the torque
wrench is set so that it applies the proper force on the set-
screw. In the case of device replacement, an adaptor that
enables connection of a new device to the existing leads might
be needed. Information on available adaptors is also stated in
Clause 7.8 .
After interconnecting the connectors, position the device
into the pocket under the skin or muscle. If dealing with unipo-
lar pacing, it is necessary to ensure creation of permanent con-
tact between the device and the tissue, otherwise the device will
not operate correctly. Before suturing, verify the device func-
tion on the electrocardiogram monitor. Suture the device to the
tissue by means of the eyelets usually placed in the upper part
of the device header. After the implantation of a new device
where a bigger device was placed previously, air bubbles might
be captured in the pocket, the device might move or erode, or
insufficient contact might occur at the device -tissue interface.
The probability of capturing air or of insufficient contact
might be reduced by filling the pocket with a physiological
solution. The possibility of movement or erosion is reduced
by stitching the implant with a fixed suture. Again check the
correct function of the device and correct tightening of the
setscrews before closing the pocket.
(including those that are implanted but not used anymore)
according to their manufacturer, model, and serial number.
As the new device is programmed, consider the mode that
was programmed in the old device and diagnostic data that
were collected by the old device. Before disconnecting the
lead(s), consider the uniqueness of every system. Patients
who are dependent on pacing will have temporary pacing
delivered so that continuous pacing was ensured during the
intervention. In the case of a unipolar configuration,
the patient would not have any pacing pulses delivered after
the device was removed from the pocket. If the selected
replacement device is not compatible with the present leads,
an adaptor must be used or the leads must be replaced. Using
incompatible leads might cause damage to the connector or
it might cause potential adverse consequences such as inad-
equate sensing of heart's activity or failure to apply the
needed therapy. Before exposing the current device, verify
the position of the lead using fluoroscopy. Then proceed
carefully to avoid perforating the lead's insulation or damag-
ing anything during system disassembly.
After incising the pocket, remove the device carefully so
that the leads are not stressed. Change of color on the device's
surface is a consequence of the normal anodic reaction and it
does not influence the device's function. Slacken the set-
screws by means of a calibrated torque wrench. Gently insert
the wrench bit to the central pothole of the seal plug at an
angle less than 90° to unbolt the screw. Apply light down-
ward pressure until the wrench bit gets completely engaged
in the hexagonal pothole in the screw. When the wrench bit is
completely engaged, rotate the wrench slowly counterclock-
wise until the lead connection is dislodged. If the wrench
clicks while being rotated counterclockwise, stop the move-
ment - this means the screw is at the end position. When the
screw is dislodged, catch hold of the lead as close to the con-
nector as possible and pull it out using a light force. Repeat
this procedure for all the leads connected to the device. In
most cases of leads replacement, the leads put up minimal
resistance as they are removed from the header. Occasionally,
the leads might get stuck in the device header, which can
happen for many reasons (e.g., stuck setscrews, fluid in the
header, some glue left over the lead sheath, conglutination of
the lead and header seal plugs, or a small mechanical toler-
ance of the header-lead interface). Recommendations for
how to release the stuck leads are described later.
Check the integrity of the permanently implanted leads at
every replacement of the device. Assess the lead's state
using X-rays and by visually checking the naked insulation
of the lead body, connector, and seal plugs. Using the PSA,
check the electric function of the lead after its disconnection
from the device. Measure the pacing thresholds, intrinsic
amplitudes, and pacing impedances and check whether there
is any noise disturbances at every lead. Insert the lead to
the new device header after the visual check of the set-
screws, which must be sufficiently extended from the device.
12.4
Device Replacements
The device might need to be replaced for various reasons.
The most common reasons for replacement are the end of
battery life or infection of the pocket. Further reasons include
an upgrade to a dual-chambered or biventricular system or
technical problems with the device [ 84 ] .
To a great extent, the success of the procedure is depen-
dent on the preoperative planning and technique. Before the
intervention it is necessary to ensure that all necessary equip-
ment is available for the intervention in case of complications.
The equipment for monitoring and display, temporary pacing,
and external defibrillation of the patient must be in place.
When the patient is connected to the monitor, the defibrillation
therapy of the device must be switched off to avoid unneces-
sary shocks. The electric signals that come to the body from
some external monitoring devices or as the setscrews are
loosened might cause high rate pacing. Consider switching
off all functions that influence the pacing rate because the
sensor's response might be activated by handling the device
as it is being removed from the pocket. Electrosurgical cau-
tery at the leads or in their immediate surroundings might
cause ventricular arrhythmias or fibrillation. Using electro-
cauterization at the device or in its close proximity might be
the cause of temporary incorrect functioning of the device.
Apart from other things, the preoperative planning of the
replacement procedure includes verifying data dealing with
the implant and determining the system parts that are used
