I

implantable cardioverter defibrillator (ICD) A
small, battery-operated electronic device, similar
to a PACEMAKER, that monitors the heart’s electrical
activity for certain patterns of ARRHYTHMIA and
administers a moderate electrical shock when the
HEARTstays in the pattern beyond the programmed
length of time. One or two wires, called leads,
extend from the ICD’s PULSEgenerator to the inte-
rior of the heart, threaded through a BLOODvessel
during a procedure similar to a CARDIAC CATHETERI-
ZATION. The cardiologist creates a small pocket in
the tissues near the shoulder or in the abdomen to
implant the pulse generator, a tiny computer.
Once placed, the leads and the ICD are perma-
nent. The cardiologist then programs the ICD to
maintain the appropriate heart rhythm.
ICD is a treatment option for ventricular tachy-
cardia and VENTRICULAR FIBRILLATION, arrhythmia
disorders that affect the ability of the ventricles to
contract to expel blood from the heart. Ventricular
tachycardia, in which the ventricles contract rap-
idly but regularly, is exhausting for the heart and
does not generate adequate CARDIAC OUTPUT to
meet the body’s needs. Ventricular fibrillation, in
which the ventricles contract rapidly and irregu-
larly, is life-threatening. An ICD can initiate pac-
ing impulses when the heart’s rate becomes too
slow or a stronger electrical impulse to shock the
heart from a harmful to a normal rhythm (CAR-
DIOVERSION). Most people do not feel the pacing
impulses though do feel a jolt with cardioversion
impulses. People who have ICDs need to be cau-
tious around electrical devices because they gener-
ate magnetic fields that can interfere with an ICD’s
operation and programming.
See also CARDIAC RESYNCHRONIZATION THERAPY
(CRT); MEDICATIONS TO TREAT CARDIOVASCULAR DISEASE;
RADIOFREQUENCY ABLATION.

intermittent claudication PAINin the lower legs

that occurs with physical activity such as walking.

Intermittent claudication is the primary symptom

of PERIPHERAL VASCULAR DISEASE(PVD), which is ATH-

EROSCLEROSISthat affects the arteries of the legs.

The atherosclerotic accumulations of PVD occlude

(block) BLOODflow through the arteries, limiting

their ability to respond to the increased oxygen

need of the leg muscles during exercise. The insuf-

ficient oxygen causes pain that is typically severe

enough to stop the activity. Resting relieves the

pain and the person can resume the activity.

People who have intermittent claudication typ-

ically develop a pattern of walking and resting

that accommodates their symptoms. About 60

percent of people who have intermittent claudica-

tion have it in both legs. Cigarette smoking, DIA-

BETES, and lack of physical exercise are the leading

causes of PVD and intermittent claudication. The

PVD that causes intermittent claudication most

often affects the popliteal ARTERY, which branches

from the femoral artery and drops behind the

knee to supply the lower leg with blood.

The most effective treatment is consistent exer-

cise such as walking. Doctors recommend a pro-

gressive approach that begins with walking until

pain forces rest, several times every day, and try-

ing to extend the time by a few minutes every

week. The regular physical activity conditions the

leg muscles, improving the efficiency with which

they use oxygen and decreasing oxygen demand.

Most people who have PVD and intermittent clau-

dication also take medications to decrease the

blood’s clotting tendencies, such as ASPIRIN THERAPY

or anticoagulation medications such as clopidogrel

(Plavix) or warfarin (Coumadin). These methods

cannot eliminate intermittent claudication though

they can reduce its severity.

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