Encyclopedia of Health and Medicine

P
pacemaker A small, implanted electronic device
that emits electrical impulses to maintain a regular
HEART RATE. The most frequent use of a pacemaker is
to treat bradycardia, an ARRHYTHMIA in which the
HEART rate is persistently below 60 beats per minute.
A pacemaker may also be an effective treatment for
obstructive CARDIOMYOPATHY, in which thickening of
the heart wall interferes with the ability of the
myocardial cells to convey electrical impulses.
Implanting the Pacemaker
The cardiologist implants the pacemaker during a
brief procedure, with local anesthetic and a mild
sedative to make the person comfortable. A standard
pacemaker has two components: the pacing
lead and the computerized control unit. The pacing
lead extends through a BLOOD vessel into the
heart, where the cardiologist positions it against
the wall of the heart, usually the right ventricle or
the right atrium. Some pacemakers may have two
pacing leads, with one going into the right atrium
and the other to the right ventricle.
The cardiologist then makes a small incision just
below the collarbone to create a pocket that holds
the control unit, and connects the pacing lead to
the control unit. The cardiologist then programs the
control unit to deliver an electrical impulse, a very
mild electrical shock, when the heart rate falls
below a specific threshold. Most pacemakers are set
to respond “on demand,” which means they emit
pacing impulses only when the heart fails to generate
them itself. The incision over the pacemaker
control unit heals in about two or three weeks,
leaving a barely noticeable protrusion.
Living with a Pacemaker
Some people notice when the pacemaker releases
an electrical impulse, though most people are not
93
aware. The “on demand” feature of current pacemakers
allows the heart to accelerate its rhythm
during physical exercise, sexual activity, and other
situations in which the heart would naturally beat
faster. Certain medical and dental equipment,
such as MAGNETIC RESONANCE IMAGING (MRI),
machines that deliver RADIATION THERAPY, and some
dental drills also can interfere with pacemakers.
Though earlier models of pacemakers were sensitive
to electromagnetic interference from household
appliances and other electronic devices, this
is no longer the case. Only high-power devices
such as welding equipment or power tools emit
enough electromagnetic energy to disrupt a pacemaker.
There is some question about the potential
of interference from cellular and portable telephones.
To be safe, cardiologists recommend keeping
the phone at least six inches from, and holding
it to the ear opposite, the pacemaker’s control
unit. Pacemakers run on lithium batteries and can
function for about seven years before they need to
be replaced.
See also CARDIAC RESYNCHRONIZATION THERAPY
(CRT); IMPLANTABLE CARDIOVERTER DEFIBRILLATOR (ICD);
MEDICATIONS TO TREAT CARDIOVASCULAR DISEASE;
RADIOFREQUENCY ABLATION.
palpitations Perception that the HEART is racing,
pounding, or skipping beats. Palpitations are may
represent signs of underlying cardiovascular conditions
such as ARRHYTHMIA though frequently signal
high stress, anxiety, or excessive consumption
of STIMULANTS such as CAFFEINE or NICOTINE (via cigarette
smoking). When palpitations do suggest
arrhythmia, they tend to occur along with other
symptoms such as weakness and SYNCOPE (fainting).
Awareness of the heartbeat is common during
or immediately following strenuous exercise,