Biomedical Engineering Reference
In-Depth Information
Fig. 7.10
Various left ventricular endocardial leads
Fig. 7.11
Bipolar and unipolar epimyocardial leads
corresponding to anatomical circumstances, the possibility
of rotation by the entire lead body, resistance to spontaneous
torsion, and good visibility under a skiascope.
Nowadays, there are lots of leads available on the market
for implantation via the coronary sinus (Fig.
7.10
). Modern
leads are positioned by means of the stylet or angiological
wire (over-the-wire). In the optimal case, the lead offers both
possibilities for implantation. Selection of a particular lead is
made with regard to the anatomical arrangement of the coro-
nary veins. Thicker leads with a preformed shape, enabling
good fixation at the required position, are suitable for larger
branches with little curved distance from the trunk [53, 54].
The diameter of the body of bipolar left ventricular leads is
usually about 2 mm. However, at the distal end it decreases to
1.8 mm. Currently, the thinnest left ventricular leads have a
lead body diameter of 1.5 mm, with a diameter of 1.35 mm at
the distal end [ 55- 57 ] . The way left ventricular leads are fi xed
does not require the distal pacing electrode to be completely at
the end; within the left ventricular lead, both electrodes are
shaped as “rings” and there is no contact with tissue at the end
of the lead, which is placed in the vein. Depending on the
design, the surface of pacing electrodes ranges from about 5 to
8 mm
2
. The steroid-eluting ring and X-ray contrasting markers
also are placed at the distal part of the lead.
7.6
Epimyocardial Leads
Permanent epimyocardial leads are used in cases when it is
impossible to introduce the endocardial lead via the venous
route, for example, in the case of central veins emphraxis,
congenital heart disease, and repeated infections, or if posi-
tioning of the left ventricular lead for cardiac resynchroniza-
tion therapy failed. Epimyocardial leads are screwed to the
epimyocardium of the atrium or ventricles (see Fig.
7.11
)
and are sutured on its surface.
Proper fixation of the lead is important for keeping its
excellent long-term electric parameters. Loosely fixed leads
might move excessively or they might sense insufficiently,
irritate epicardium, and cause higher threshold values. The
intervention is usually performed during the cardiac surgery,
most often using laparoscopy. It enables the use of various
surgical approaches, such as the subxiphoid approach, left-
sided thoracotomy, median sternotomy, transsphenoidal
approach, or transmediastinal approach. The lead should be
positioned and fixed at the avascular area without infarction,
fat, and fibrosis. Before implantation, it is possible to use the
epimyocardial lead for mapping by positioning the electrode
in the epicardium [ 58 ] .
