There are four main types of arrhythmia: premature
(extra) beats, supraventricular arrhythmias, ventricular arrhythmias, and
bradyarrhythmias.
Premature (Extra) Beats
Premature beats are the most common type of
arrhythmia. They are harmless most of the time and often dont cause any
symptoms. When symptoms do occur, they usually feel like a fluttering in the
chest or a sensation of a skipped beat. Most of the time, premature beats need
no treatment, especially in healthy people.
Premature beats that occur in the atria are called
premature atrial contractions, or PACs. Premature beats that occur in the
ventricles are called premature ventricular contractions, or PVCs.
In most cases, premature beats occur naturally, not
due to any heart disease. But certain heart diseases can cause premature beats.
They also can happen because of stress, too much exercise, or too much caffeine
or nicotine.
Supraventricular Arrhythmias
Supraventricular arrhythmias are tachycardias (fast
heart rates) that start in the atria or the atrioventricular node (cells
located between the atria and the ventricles). Types of supraventricular
arrhythmias include atrial fibrillation (AF), atrial flutter, paroxysmal
supraventricular tachycardia (PSVT), and Wolff-Parkinson-White (WPW)
syndrome.
Atrial Fibrillation
AF is the most common type of serious arrhythmia.
Its a very fast and irregular contraction of the atria. AF occurs when
the hearts electrical signal begins in a different part of the atrium
than the sinoatrial (SA) node or when the signal is conducted abnormally. When
this happens, the electrical signal doesnt travel through the normal
pathways in the atria, but instead may spread throughout the atria in a fast
and disorganized manner. This causes the walls of the atria to quiver very fast
(fibrillate) instead of beating normally. As a result, the atria arent
able to pump blood into the ventricles the way they should.
The animation below shows atrial fibrillation. Click
the "start" button to play the animation. Written and spoken explanations are
provided with each frame. Use the buttons in the lower right corner to pause,
restart, or replay the animation, or use the scroll bar below the buttons to
move through the frames.
The animation shows how the
hearts electrical signal begins in a different place in the heart,
causing the atria to beat very fast and irregularly.
In AF, electrical signals can travel through the
atria at a rate of more than 300 per minute. Some of these abnormal electrical
signals can travel to the ventricles, causing them to beat too fast and with an
irregular rhythm. AF is not usually life threatening, although it can be
dangerous when it causes the ventricles to beat very fast.
The two most serious complications of chronic
(long-term) AF are
stroke and
heart
failure. Stroke can happen when a blood clot travels to an artery in the
brain, blocking off blood flow. In AF, blood clots can form in the atria
because some of the blood pools in the fibrillating atria instead
of flowing into the ventricles. If a piece of a blood clot in the left atrium
breaks off, it can travel to the brain, causing a stroke. People with AF are
often treated with blood-thinning medicines to reduce the chances of developing
blood clots.
Heart failure is when the heart cant pump
enough blood to meet the needs of the body. AF can cause heart failure when the
ventricles beat too fast and dont have enough time to fill with blood to
pump out to the body. Heart failure causes tiredness, leg swelling, and
shortness of breath.
AF and other supraventricular arrhythmias can occur
for no apparent reason. Most of the time, however, they are caused by an
underlying condition that damages the heart muscle and its ability to conduct
electrical impulses. These conditions include
high
blood pressure (hypertension),
coronary
artery disease, heart failure, or rheumatic heart disease.
Other conditions also can lead to AF, including
overactive thyroid gland (too much thyroid hormone produced) and heavy alcohol
use. AF also becomes more common as people get older.
Atrial Flutter
Atrial flutter is similar to atrial fibrillation,
but instead of the electrical signals spreading through the atria in a fast and
irregular rhythm, they travel in a fast and regular rhythm. Atrial flutter is
much less common than atrial fibrillation, but has similar symptoms and
complications.
Paroxysmal Supraventricular Tachycardia
PSVT is a very fast heart rate that begins and ends
suddenly. PSVT occurs due to problems with the electrical connection between
the atria and the ventricles. In PSVT, electrical signals that begin in the
atria and travel to the ventricles can reenter the atria, causing extra
heartbeats. This type of arrhythmia is not usually dangerous and tends to occur
in young people. It can happen during vigorous exercise.
A special type of PSVT is called
Wolff-Parkinson-White syndrome. WPW syndrome is a condition in which the
hearts electrical signals travel along an extra pathway from the atria to
the ventricles. This extra pathway disrupts the timing of the hearts
electrical signals and can cause the ventricles to beat very fast. This type of
arrhythmia can be life threatening.
The animation below shows Wolff-Parkinson-White
syndrome. Click the "start" button to play the animation. Written and spoken
explanations are provided with each frame. Use the buttons in the lower right
corner to pause, restart, or replay the animation, or use the scroll bar below
the buttons to move through the frames.
The animation shows how an extra,
abnormal electrical pathway in the heart disrupts the normal timing of the
hearts electrical signal, causing the atria and ventricles to beat too
fast.
Ventricular Arrhythmias
These are arrhythmias that start in the ventricles.
They can be very dangerous and usually need immediate medical attention.
Ventricular arrhythmias include ventricular tachycardia and ventricular
fibrillation (v-fib). Coronary artery disease,
heart
attack, weakened heart muscle, and other problems can cause ventricular
arrhythmias.
Ventricular Tachycardia
Ventricular tachycardia is a fast, regular beating
of the ventricles that may last for only a few seconds or for much longer. A
few beats of ventricular tachycardia often dont cause problems, but
ventricular tachycardia episodes that last for more than just a few seconds can
be dangerous. Ventricular tachycardia can turn into other, more dangerous
arrhythmias, such as v-fib.
Ventricular Fibrillation
V-fib occurs when disorganized electrical signals
make the ventricles quiver instead of pump normally. Without the ventricles
pumping blood out to the body, a person will lose consciousness within seconds
and will die within minutes if not treated. To prevent death, the condition
must be treated immediately with defibrillation, an electric shock to the
heart. V-fib may happen during or after a heart attack, or in a heart that is
already weak because of another condition. Health experts think that most of
the
sudden
cardiac deaths that occur every year (about 335,000) are due to v-fib.
The animation below shows ventricular fibrillation.
Click the "start" button to play the animation. Written and spoken explanations
are provided with each frame. Use the buttons in the lower right corner to
pause, restart, or replay the animation, or use the scroll bar below the
buttons to move through the frames.
The animation shows how disorganized
electrical signals in the hearts ventricles can cause them to pump
abnormally and quiver.
Torsades de pointes (torsades) is a specific form of
v-fib with a unique pattern on an
EKG
(electrocardiogram). Certain medicines and imbalanced amounts of potassium,
calcium, or magnesium in the bloodstream can cause this condition. People with
a particular finding on an EKG test, called prolonged QT interval, are at
increased risk of developing torsades. People with prolonged QT interval need
to be careful about taking certain antibiotics, heart medicines, and
over-the-counter medicines.
Bradyarrhythmias
Bradyarrhythmias are arrhythmias in which the heart
rate is slower than normal. If the heart rate is too slow, not enough blood
reaches the brain, and the person can lose consciousness. In adults, a heart
rate slower than 60 beats per minute is considered a bradyarrhythmia. Some
people normally have slow heart rates, especially people who are very
physically fit. For them, a heartbeat slower than 60 beats per minute is not
dangerous and doesnt cause symptoms. But in other people, bradyarrhythmia
can be due to a serious disease or other condition.
Bradyarrhythmias can be caused by heart attack,
conditions that harm or change the hearts electrical system (such as
underactive thyroid gland or aging), an imbalance of chemicals or other
substances (such as potassium) in the blood, or even some medicines (such as
beta blockers).
Bradyarrhythmias also can happen as a result of
severe bundle branch block. Bundle branch block is a condition in which the
electrical signal traveling down either or both of the bundle branches is
delayed or blocked. When this happens, the ventricles dont contract at
exactly the same time, as they should, and the heart has to work harder to pump
blood to the body. The cause of bundle branch block is often an existing heart
condition.
Arrhythmias in Children
Normally, a childs heart beats between 70 and
100 times a minute. A newborns heart beats about 140 times a minute. A
baby or childs heart can beat faster or slower than normal for many
reasons. As is true for adults, when children are active, their hearts will
beat faster. When they are sleeping, their heart will beats slower. Their heart
rates can speed up and slow down as they breathe in and out. All of these
changes are normal.
Some children are born with heart defects that cause
arrhythmias. In other children, arrhythmias can develop later in childhood.
Doctors do the same kinds of tests in children and adults to diagnose
arrhythmias.
Treatments for children with arrhythmias include
medicines, electric shock (defibrillation), surgically implanted devices that
control the heartbeat, and other procedures that fix distorted electrical
signals in the heart.