Biomedical Engineering Reference
In-Depth Information
4.2.3
Pacemaker connector modules
A connector module is the component that physically and electrically connects
the pulse generators with leads (Fig. 4.2). It has a metal scaffold, typically made
of stainless steel, embedded into a molded polymeric block, usually made of
rigid polyether polyurethane or epoxy. The connector module is bonded to the
can directly on top of the feedthroughs. The metal scaffold connects the wires
from the feedthroughs to the electrodes of the leads inserted into the module.
The connector module contacts host tissue with its polyether polyurethane
surface. A critical feature for the connector to properly function is its bonding
with the pulse generator. Surface cleaning and treatment to promote adhesion
are necessary steps in manufacturing. Electric insulation between the multiple
electrodes and conducting wires is also critical for the device function and
reliability. The stability of conductor modules, especially chronic stability
associated with chemical degradation and mechanical creep, must be carefully
considered.
4.2.4 Pacemaker leads
Pacing leads are `wires' that carry the electricity from the pacemaker to the
heart. Pacemaker leads are implanted through a vein in the chest and fixed to the
inside of the heart chamber. The functions of leads are simple, but they have a
number of components to ensure proper performance. Maintaining proper
functionality of leads relates in part to a constant relative movement between the
heart and lead(s) as the heart beats. A heart beats approximately 32 million times
a year (at 60 beats/minute). Along with being biocompatible and biostable, the
various components of the lead must withstand these cyclical mechanical
interactions. At the heart itself, lead fixation to the endocardial surface of the
heart is critical, and is made possible with a tip fixation component. At the
opposite end is the critical connector that allows the lead to be fastened to the
connector module of the pacemaker. The other crucial lead components are: an
electrical conductor that carries electric signals between the can and the pacing
site; insulation material that isolates the conductors; and the important electrode
tip that senses and delivers the electrical therapy. A picture of a whole lead is
shown in Fig. 4.3.
Lead fixation
Once inside the heart, a pacing lead must be affixed to the heart muscle to
provide proper electrical pacing pulse. Fixation is either active (traumatic
fixation), achieved from an extendible/retractable screw-in electrode, or passive
(atraumatic), accomplished by using tines that can be trapped in the trabeculae
of the heart (Fig. 4.4). Tines are made of flexible polymers such as polyether
polyurethane. Proper fixation is critical to prevent dislodging of electrodes
