Encyclopedia of Health and Medicine

arrhythmia 17
damage to the HEART MUSCLE. Elevated apoB100
levels convey an increased risk for ATHEROSCLEROSIS
and CAD.
See also CARDIOVASCULAR DISEASE PREVENTION;
CHOLESTEROL BLOOD LEVELS; HYPERLIPIDEMIA; RISK FAC-
TORS FOR CARDIOVASCULAR DISEASE.
arrhythmia Irregularity or abnormality of the
heart’s contractions. Arrhythmias can result from
numerous causes including electrical disturbances
of the heart’s pacing mechanisms, physical damage
to the HEART such as might occur with HEART
ATTACK, interruptions of the heart’s BLOOD supply
that cause myocardial HYPOXIA (oxygen depletion),
severe electrolyte imbalances, and medication side
effects. COCAINE use can initiate sudden and fatal
arrhythmias. Because all myocardial cells have the
ability to initiate electrical impulses, it is sometimes
difficult for cardiologists to determine what
causes an arrhythmia.
The most common kinds of arrhythmias are
• bradycardia, in which contractions are slower
than normal (typically fewer than 60 beats per
minute at rest in a person whose level of routine
physical activity is low)
• tachycardia, in which contractions are faster
than normal (typically greater than 100 beats
per minute at rest in a person whose level of
routine physical activity is low)
• fibrillation, in which contractions are rapid,
erratic, and nonproductive
• premature or extra beats, in which contractions
occur in addition to the heart’s regular contractions
The seriousness of an arrhythmia depends
largely on whether it is atrial or ventricular. Typically
ventricular arrhythmias are more significant
and potentially hazardous than atrial arrhythmias.
The most common arrhythmia that requires treatment
is ATRIAL FIBRILLATION, which health experts
estimate affects about one in five American adults
over age 60 and which accounts for about 15 percent
of strokes. The most deadly arrhythmia is
VENTRICULAR FIBRILLATION, which results in seriously
slowing or even halting the flow of blood to the
body because the ventricles cannot pump in a
coordinated manner. Some arrhythmias are transient
(come and go), and others cause no symptoms
or effect on cardiovascular function.
VENTRICULAR FIBRILLATION is a medical
emergency that can result in death
within minutes without appropriate
treatment (DEFIBRILLATION).
Symptoms and Diagnostic Path
Arrhythmias may cause a range of symptoms or no
symptoms at all. The most common symptoms are
• PALPITATIONS, which feel like the heart is thumping
or “skipping” a beat
• weakness, lightheadedness, or fainting
• shortness of breath with exertion (DYSPNEA)
• CHEST PAIN
It is not possible to know only from the symptoms
what kind of arrhythmia is present. Only an
ELECTROCARDIOGRAM (ECG), a test that records the
heart’s electrical activity, can present the information
a cardiologist needs to determine the diagnosis.
The cardiologist may desire further diagnostic procedures
to identify any underlying causes, as the
findings may influence treatment options and decisions.
Arrhythmias resulting from CORONARY ARTERY
DISEASE (CAD) or HEART FAILURE, for example, require
different treatment than those resulting from idiopathic
electrical disturbances (problems with the
heart’s pacing mechanisms that have no apparent
cause). Occasionally the doctor detects an arrhythmia
during examination for other health concerns,
which requires subsequent evaluation to determine
whether, as it is not causing symptoms, it is a
condition that warrants treatment.
Treatment Options and Outlook
CAFFEINE and ALCOHOL consumption can cause palpitations
and other minor, benign arrhythmias, as
can intense stress. Making lifestyle changes to
reduce or eliminate these factors typically ends the
arrhythmias related to them. Arrhythmias that are
not clinically significant (those that cause no
symptoms or disruptions of cardiovascular function)
do not require treatment, though cardiologists
generally want to monitor them to make sure