A heart arrhythmia
is an abnormal heart rhythm. Arrhythmias can be a
byproduct of damage to the heart from disease or
age. Heart rhythm problems (arrhythmias) occur when
the electrical impulses in your heart that
coordinate your heartbeats don't function properly,
causing your heart to beat too fast, too slow or
Most people have experienced occasional, brief,
usually harmless arrhythmias, such as the feeling of
a skipped, fluttering or racing heartbeat. However,
more than 4 million, mainly older Americans
experience heart arrhythmias that may cause
bothersome - sometimes even dangerous - signs or
symptoms. These may include shortness of breath,
fainting or even sudden cardiac death - an
unexpected loss of heart function, breathing and
consciousness that leads to death within minutes
without emergency medical treatment.
Advances in medical technology have added new
treatment methods to the array of procedures that
doctors may use to try to control or eliminate
arrhythmias. In addition, because troublesome
arrhythmias are often made worse - or even caused -
by a heart weakened or damaged by
disease (CAD), you may be able to reduce your
arrhythmia risk by adopting a heart-healthy
Signs and symptoms
Arrhythmias may not produce any symptoms. In fact, your doctor might
detect them before you do during a routine examination. But often,
abnormal heart rhythms cause noticeable signs and symptoms, which may
Your heart is divided into four hollow chambers. Divided top to bottom,
the chambers on either half of your heart form two adjoining pumps with
an upper chamber (atrium) and a lower chamber (ventricle). During a
single heartbeat, the pumps operate in a two-phase cycle. First, the
smaller, less muscular atria contract and fill the relaxed ventricles
with blood. A split second later, the powerful ventricles contract and
discharge blood as the atria relax and fill. Efficient blood circulation
requires rhythmic coordination of this priming and pumping system. In
addition, it requires proper heart rate control, which, in a normal
heart, is 60 to 100 beats a minute when the body is at rest.
Orchestration of these two factors is performed by the heart's
electrical system. Ideally, this system operates in the following
Each heartbeat normally originates within a specialized group of
cells called the sinus node. Located in the upper-right atrium, the
sinus node is your heart's natural pacemaker. It has the ability to
spontaneously produce the electrical impulses that initiate
heartbeats. Other cells within the heart have a similar ability, but
they're normally inactive when the sinus node is doing its job of
setting your heart's pace. Doctors refer to normal heart rhythm as
normal sinus rhythm.
From the sinus node, electrical impulses travel through the heart.
As an impulse travels, the heart muscle contracts. In a normal
heartbeat, the impulse first spreads across the right, then left
atrium. After activating the atria from top to bottom, the impulse
proceeds to the atrioventricular (AV) node, located at the center of
the heart. The AV node normally is the only electrical path between
the atria and ventricles. Within it, the impulse slows for a split
second to allow the atria to fill the ventricles with blood. Exiting
the AV node, the impulse is conducted along two electrical pathways
(right and left bundles), which spread impulses throughout the right
and left ventricles.
Each cell in the heart that helps to conduct the heart's electrical
impulses has two electrical states a poised (polarized) state and
a relaxed (refractory) state. In a polarized state, heart cells are
ready and able to conduct the electrical impulse that will cause a
heartbeat. After a heartbeat, the cells are momentarily in a
refractory state before recharging to a polarized state for the next
heartbeat. While it's in the refractory state, a heart cell is
unable to conduct an impulse.
In a healthy person with a normal, healthy heart, it's unlikely for a
sustained arrhythmia to develop without some outside trigger such as an
electrical shock or the use of illicit drugs. That's primarily because
his or her heart is free from any abnormal elements such as a spot of
scarred tissue. Scarring can result from numerous forms of disease
most commonly, from a previous heart attack and may disrupt the
initiation or conduction of electrical impulses. In addition, the
inability of heart cells to conduct electrical impulses during the
refractory period acts as a buffer, preventing the occasional offbeat
electrical impulse from developing into an arrhythmia.
However, in a heart with some form of disease or deformity, the
initiation or conduction of the heart's electrical impulses may be
destabilized, which makes arrhythmias more likely to develop.
Conditions that may lead to arrhythmias
pre-existing structural heart condition can lead to arrhythmia
development due to:
If blood supply to the heart is somehow reduced, it can alter the
ability of heart tissue including the cells that conduct
electrical impulses to function properly.
Damage or death
of heart tissue.
When heart tissue becomes damaged or dies, it can affect the way
electrical impulses spread in the heart.
These pre-existing heart conditions may include:
Although it has been linked to many arrhythmias, CAD is most closely
associated with ventricular arrhythmias and sudden cardiac death.
Narrowing of the arteries that occurs with CAD can progress until a
portion of your heart dies from lack of blood flow (heart attack).
An old heart attack leaves behind a scar. Electrical short circuits
around the scar can prevent normal heart function by causing the
heart to beat dangerously fast (ventricular tachycardia) or to
quiver (ventricular fibrillation).
This occurs primarily when your ventricle walls stretch and enlarge
(dilated cardiomyopathy) or when your left ventricle wall thickens
and constricts (hypertrophic cardiomyopathy). In either case,
cardiomyopathy decreases your heart's blood-pumping efficiency and
often leads to heart tissue damage.
Leaking or narrowing of your heart valves can lead to stretching and
thickening of your muscle (myocardium). When the chambers become
enlarged or weakened due to the added stress caused by the tight or
leaking valve, there's an increased risk of developing arrhythmia.
Types of arrhythmias
Heart arrhythmias may occur when any phase in the heart's electrical
system malfunctions. Doctors classify arrhythmias by where they
originate (atria or ventricles) and by the speed of heart rate they
cause. Tachycardia refers to a fast heartbeat a
heart rate greater than 100 beats a minute. Bradycardia
refers to a slow heartbeat a resting heart rate less than 60 beats a
minute. Not all tachycardias or bradycardias indicate disease. For
example, during exercise, it's normal to develop sinus tachycardia as
the heart speeds up to provide your tissues with more oxygen-rich blood.
Athletes at rest often have a heartbeat less than 60 beats a minute
because their hearts are so efficient.
Tachycardias originating in the atria include:
This fast and chaotic beating of the atrial chambers is the most
common arrhythmia. It affects about 2 million, mainly older
Americans. Your risk of developing atrial fibrillation increases
past age 65 mainly due to the wear and tear that may affect your
heart's function as you age. During atrial fibrillation, the
electrical activity of the atria becomes uncoordinated. The atria
beat so rapidly as fast as 300 to 400 beats a minute that they
quiver (fibrillate). The electrical waves have the same chaotic
activity that you would see if you threw a handful of pebbles into a
quiet pond. Fortunately, not all of these atrial impulses reach the
ventricles. The AV node between the atria and ventricles acts as a
gatekeeper, usually letting only a portion of the impulses through.
Still, extra impulses often get through the AV node. This may
accelerate your pulse (ventricular contractions) during atrial
fibrillation to 150 beats a minute or more. In addition, the atrial
impulses that reach the ventricles often arrive at irregular
intervals. This may cause an irregular heart rhythm. Atrial
fibrillation can be intermittent (paroxysmal), lasting a few minutes
to an hour or more before returning to a regular heart rhythm. It
can also be chronic, causing an ongoing problem. Atrial fibrillation
is seldom a life-threatening arrhythmia, but over time it can be the
cause of more serious conditions such as stroke.
Although atrial flutter is less common than atrial fibrillation, the
arrhythmias are in some ways similar. In fact, both can coexist in
your heart, coming and going in an alternating fashion. The key
distinction is that more-organized and more-rhythmic electrical
impulses cause atrial flutter. These occur because atrial flutter,
unlike atrial fibrillation, arises from a short circuit. In typical
atrial flutter, this short circuit exists in the right atrium. This
is an important distinction because typical right atrial flutter is
more amenable to some forms of treatment, such as catheter ablation.
Supraventricular tachycardia (SVT).
SVT is a broad term that includes many forms of arrhythmia
originating above the ventricles (supraventricular). SVTs usually
cause a burst of rapid heartbeats that begin and end suddenly and
can last from seconds to days. These often start when the electrical
impulse from a premature heartbeat begins to circle repeatedly
through an extra pathway. SVT may cause your heart to beat 140 to
200 times a minute. Although generally not life-threatening in an
otherwise normal heart, symptoms from the racing heart may feel
Wolff-Parkinson-White syndrome (WPW).
One type of SVT is known as Wolff-Parkinson-White syndrome (WPW).
This arrhythmia may, rarely, run in families and is caused by an
extra electrical pathway between the atria and the ventricles. This
pathway may allow electrical current to pass between the atria and
the ventricles without passing through the AV node, leading to short
circuits and rapid heartbeats.
Tachycardias occurring in the ventricles include:
This fast, regular beating of the heart is caused by abnormal
electrical impulses originating in the ventricles. Most often, these
are due to a short circuit around a scar from an old heart attack
and can cause the ventricles to contract more than 200 beats a
minute. Most VT occurs in people with some form of heart-related
problem such as scars or damage within the ventricle muscle from
coronary artery disease or a heart attack. Sometimes, VTs last for
30 seconds or less (unsustained) and are usually harmless, although
they cause inefficient heartbeats. Still, an unsustained VT may be a
predictor for more serious ventricular arrhythmias such as
longer-lasting (sustained) VT. An episode of sustained VT is a
medical emergency. It may be associated with palpitations,
dizziness, fainting, or possibly death. Without prompt medical
treatment, sustained VT often degenerates into ventricular
fibrillation. Rarely, VT occurs in an otherwise normal heart. In
this setting, it's far less dangerous, but the condition still needs
the attention of a doctor.
With ventricular fibrillation, rapid, chaotic electrical impulses
cause your ventricles to quiver uselessly instead of pumping blood.
Without an effective heartbeat, your blood pressure plummets,
instantly cutting off blood supply to your vital organs including
your brain. Most people lose consciousness within seconds and
require immediate medical assistance such as cardiopulmonary
resuscitation (CPR). Your chances of survival may be prolonged if
CPR is delivered until your heart can be shocked back into a normal
rhythm with a device called a defibrillator. Without CPR or
defibrillation, death results in minutes. As with VT, most cases of
ventricular fibrillation are linked to some form of heart disease.
Ventricular fibrillation is frequently triggered by a heart attack.
However, ventricular fibrillation may also be your first indication
of heart problems.
This syndrome may be either an acquired or an inherited condition.
In older adults, this rare arrhythmia may be triggered by one or a
combination of more than 50 drugs, many of them commonly used.
These drugs affect the heart's electrical function. Less commonly,
long QT may be an inherited condition in which an abnormality in the
microscopic channels on the surface of the heart cells causes them
to function improperly. On an electrocardiogram, the letter Q marks
the point where an electrical impulse signals the ventricles to
contract. The letter T marks the point where the cells of your
ventricles have electrically recharged for the next heartbeat. When
the QT interval is prolonged, ventricle cells may not be recovered
in time to properly conduct the next heartbeat. People with long QT
syndrome are prone to palpitations and fainting spells, and may have
an increased risk of sudden death.
Although a heart rate below 60 beats a minute while at rest is
considered a bradycardia, a low resting heart rate doesn't always signal
a problem. If you're physically fit, you may have an efficient heart
capable of pumping an adequate supply of blood with fewer than 60 beats
a minute at rest. However, if you have a slow heartbeat that isn't
pumping enough blood, you may have one of several bradycardias
If your pacemaking sinus node isn't sending impulses properly, your
heart rate may be too slow, or it may speed up and slow down
intermittently. If your sinus node is functioning properly, sick
sinus can be caused by an impulse block near the sinus node that's
slowing, disrupting or completely blocking conduction.
A block of your heart's electrical pathways can occur in or near the
AV node or along the bundle branches that conduct impulses to each
ventricle. Depending on the location and type of block, the impulses
between your atria and ventricles may be slowed or partially or
completely blocked. If the signal is completely blocked, certain
cells in the AV node or ventricles are capable of initiating a
steady, although usually slower, heartbeat. Some blocks may cause no
signs or symptoms, and others may cause skipped beats or bradycardia.
Even without signs or symptoms, a conduction block is usually
detectable on an electrocardiogram (ECG). Since some blocks are
caused by heart disease, an ECG showing a block may be an early sign
of heart problems.
Premature atrial contractions and premature ventricular
Although it often feels like a skipped heartbeat, a premature heartbeat
is actually an extra beat between two normal heartbeats. Premature
heartbeats occurring in the ventricles come before the ventricles have
had time to fill with blood following a regular heartbeat.
Thus, the beat feels weak if it's felt at all. This premature beat is
usually followed by a pause, during which time the ventricles fill with
more than the usual amount of blood. The ejection of more blood from the
ventricle causes the next regular heartbeat to feel stronger than
Although you may feel an occasional premature beat, they seldom indicate
a more serious problem. Still, a premature beat can trigger a
longer-lasting arrhythmia especially in people with heart disease.
Certain factors may increase your risk of developing an arrhythmia.
With age, your heart muscle naturally weakens and loses some of its
suppleness. This may affect how electrical impulses are conducted.
Being born with a heart abnormality such as the extra electrical
pathway that occurs with Wolff-Parkinson-White syndrome may affect
your heart's electrical function.
Narrowed heart arteries, heart attack or other heart damage are risk
factors for almost any kind of arrhythmia.
Your metabolism speeds up when your thyroid gland releases excess
hormones. This may cause fast or irregular heartbeats and is most
commonly associated with atrial fibrillation. Your metabolism slows
when your thyroid gland releases too few hormones, which may cause a bradycardia.
Over-the-counter cough and cold medicines containing pseudoephedrine,
the herbal supplement ephedra (ma-huang) and certain prescription
drugs may contribute to arrhythmia development.
This increases your risk of developing coronary artery disease. It
may also cause the walls of your left ventricle to thicken, possibly
altering how your heart's electrical impulses are conducted.
Your risk of developing coronary artery disease and hypertension
greatly increase with uncontrolled diabetes. In addition, episodes
of low blood sugar (hypoglycemia) can trigger an arrhythmia.
This disorder can cause bradycardia and bursts of atrial
Electrolyte minerals such as potassium, sodium, calcium and
magnesium help trigger and conduct the electrical impulses in your
heart. Electrolyte levels that are too high or too low can affect
your heart's electrical impulses and contribute to arrhythmia
Drinking too much alcohol can affect factors that alter the
conduction of electrical impulses in your heart or increase the
chance of developing atrial fibrillation. In fact, development of
atrial fibrillation after an episode of heavy alcohol intake is
sometimes called holiday heart. Chronic alcohol abuse may depress
the function of your heart and can lead to cardiomyopathy. Both are
factors in arrhythmia development.
Stimulants such as caffeine and nicotine can cause premature
heartbeats and may contribute to the development of more serious
arrhythmias. Illicit drugs such as amphetamines and cocaine may
profoundly affect the heart and lead to many types of arrhythmias or
to sudden death due to ventricular fibrillation.
When to seek medical advice
Arrhythmias may cause you to feel premature beats, or you may feel that
your heart is racing or beating too slowly. Other signs and symptoms may
be related to diminished blood output from your heart. These include
shortness of breath or wheezing, weakness, dizziness, lightheadedness,
fainting or near fainting and chest pain or discomfort. Seek urgent
medical care if you suddenly or frequently experience any of these signs
and symptoms at a time when you wouldn't expect to feel them.
With little or no blood being pumped through the body, a person with
ventricular fibrillation will collapse within seconds and soon won't be
breathing or have a pulse. If this occurs, follow these steps:
for the emergency number in your area.
If you or someone
nearby knows cardiopulmonary resuscitation (CPR), administer it if
it's needed. CPR can help maintain blood flow to the organs until an
electrical shock (defibrillation) can be given.
Portable defibrillators are available in an increasing number of places,
such as airplanes, police cars and shopping malls. These automated
external defibrillators come with built-in instructions on their use.
They are programmed to allow a shock only when appropriate.
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