Biomedical Engineering Reference
In-Depth Information
Table 4.2 Continued
Components
Selected
Primary
Applicable standards
materials
tissue
contacts
Fixation
Silicone,
Blood, cardiac
ISO 10993
polyether
tissues
ISO 14708-1 (CEN EN 45502-1)
polyurethane,
ISO 14708-2
or lead
ISO 14708-3
electrode
CENELEC EN 45502-2-1
metals
ISO 14708-6 (CENELEC EN
45502-2-2)
Guidance for Industry (12)
Drug release
Silicone or
Blood, cardiac
ISO 10993
components
polyether
tissues
ISO 14708-1 (CEN EN 45502-1)
polyurethane
ISO 14708-2
ISO 14708-3
CENELEC EN 45502-2-1
ISO 14708-6 (CENELEC EN
45502-2-2)
Guidance for Industry (12)
pulses also travel through special conduction pathways to a second specialized
group of cells localized between the atria and ventricles. These cells are referred
to as the atrioventricular (AV) node. The time delays in the signal conducting
from the SA node and the AV node synchronize the beating rhythms of the atria
and ventricles for optimum blood outputs. Pacemakers are used if a heart beats
too slowly (bradycardia) because of diseases in the heart's own pacemaker or
electrical conduction system (such as the AV node or HIS±Purkinje system
abnormalities).
A pacemaker is implanted just under the skin either over or under the
pectoral muscle. The pacemaker is connected to the heart via a lead (or leads)
that is inserted through a vein and positioned in the heart muscle. Leads may be
inserted in the muscle of the right atrium, right ventricle, or indirectly to regions
of the left ventricle via cardiac veins accessible from the right side of the heart,
i.e., the coronary sinus. A schematic of an implantable pacemaker and leads is
shown in Fig. 4.1. The lead carries both the electrical impulse generated by the
pacemaker to the heart and the heart's electrical signals back to the pacemaker
for analysis. The pacemaker contains a battery and a tiny computer that
interprets the heart's signals and formulates pulses to stimulate the heart to
contract.
A pacemaker may have one, two, or three leads, depending on the type of
heart problem diagnosed. A single chamber pacemaker uses one lead, either in
the right atrium or right ventricle, to increase the heart rate. A dual chamber
pacemaker paces both the right atrium and right ventricle. A biventricular
