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 ARRHYTHMIAin which the
HEARTrate 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 stan-
dard pacemaker has two components: the pacing
lead and the computerized control unit. The pac-
ing lead extends through a BLOODvessel 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 gener-
ate 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

aware. The “on demand” feature of current pace-

makers 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 sensi-

tive to electromagnetic interference from house-

hold 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 pace-

maker. There is some question about the potential

of interference from cellular and portable tele-

phones. To be safe, cardiologists recommend keep-

ing 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 HEARTis racing,

pounding, or skipping beats. Palpitations are may

represent signs of underlying cardiovascular con-

ditions such as ARRHYTHMIAthough frequently sig-

nal high stress, anxiety, or excessive consumption

of STIMULANTSsuch as CAFFEINEor NICOTINE(via ciga-

rette smoking). When palpitations do suggest

arrhythmia, they tend to occur along with other

symptoms such as weakness and SYNCOPE(faint-

ing). Awareness of the heartbeat is common dur-

ing or immediately following strenuous exercise,

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