Biomedical Engineering Reference
In-Depth Information
4.2 Internal viewof a pacemaker. The component at the top is referred to as the
connector module (courtesy of Medtronic, Inc.).
These features provide the crucial sensing and pacing functions and opportunity
for remote monitoring and reprogramming by physicians.
Figure 4.2 shows an implantable pacemaker with one half of the shield
removed to show internal components, including integrated circuits (ICs),
discrete components, electrical feedthroughs, and the battery. These
components are housed inside titanium shields which are welded shut to
prevent moisture ingress into the electronics. The transference of signals
between the inside and the outside of the cans is completed by the wires leading
out of the cans through special components called feedthroughs. These
feedthroughs are highly insulated, sealed against moisture permeation, and
mechanically fixed to the cans.
Epoxy resin and stainless steel were used in some of the earlier pulse
generators. Today, titanium is the most commonly used material. Titanium has
been proven to be well accepted upon implantation in the human body (bio-
compatible) and quite stable against corrosion under biological environments
(biostable). It is lighter than stainless steel, yet rigid and strong enough to protect
the electric components inside the cans from mechanical damage. Its good
electric conductivity allows it to function, when needed, as an additional elec-
trode, e.g., in unipolar systems. In certain cases, a Parylene coating (poly-
paraxylylene) is partially applied to the surface of cans to further improve its
biocompatibility and biostability.
One complication with pacemaker pulse generators is bacterial infection. The
rate of infection has been low (1±7%) (Darouiche, 2001). However, if infection
happens, the device is often replaced even though its function is intact. This is
because the bacteria aggregate and form a biofilm on the surface or corners of
the implant, making treatment with antibiotics often poor or ineffective.
