What is an arrhythmia?
An arrhythmia (also referred to as dysrhythmia) is an abnormal rhythm of
the heart, which can cause the heart to pump less effectively.
Arrhythmias can cause problems with contractions of the heart chambers by:
Not allowing the ventricles (lower chambers) to fill with an adequate amount
of blood because an abnormal electrical signal is causing the heart to
pump too fast.
Not allowing a sufficient amount of blood to be pumped out to the body
because an abnormal electrical signal is causing the heart to pump too
slowly or too irregularly.
In any of these situations, the body's vital organs may not receive
What are the symptoms of arrhythmias?
The effects on the body are often the same, however, whether the heartbeat
is too fast, too slow, or too irregular. Some symptoms of arrhythmias
include, but are not limited to:
The symptoms of arrhythmias may resemble other conditions. Consult your
doctor for a diagnosis.
To better understand arrhythmias, is it helpful to understand the heart's
electrical conduction system.
The heart's electrical system
The heart is, in the simplest terms, a pump made up of muscle tissue. The
heart's pumping action is regulated by an electrical conduction system
that coordinates the contraction of the various chambers of the heart.
How does the heart beat?
An electrical stimulus is generated by the sinus node (also called the
sinoatrial node, or SA node), consisting of a small mass of specialized
tissue located in the right atrium (right upper chamber) of the heart.
The sinus node generates a regular electrical stimulus, which for adults,
is usually 60 to 100 times per minute under normal conditions. This electrical
stimulus travels down through the conduction pathways (similar to the
way electricity flows through power lines from the power plant to your
house) and causes the heart's lower chambers to contract and pump
out blood. The right and left atria (the two upper chambers of the heart)
are stimulated first and contract a short period of time before the right
and left ventricles (the two lower chambers of the heart).
The electrical impulse travels from the sinus node to the atrioventricular
node (also called AV node), where impulses are slowed down for a very
short period, then allowed to continue down the conduction pathway via
an electrical channel called the bundle of His into the ventricles. The
bundle of His divides into right and left pathways to provide electrical
stimulation to the right and left ventricles. Each contraction of the
ventricles represents one heartbeat.
Each day the heart beats about 100,000 times, on average. Any dysfunction
in the heart's electrical conduction system can make the heartbeat
too fast, too slow, or at an uneven rate, thus, causing an arrhythmia.
What is an electrocardiogram (ECG)?
The electrical activity of the heart is measured by an electrocardiogram
(ECG or EKG). By placing electrodes at specific locations on the body
(chest, arms, and legs), a graphic representation, or tracing, of the
electrical activity can be obtained. Changes in an ECG from the normal
tracing can indicate arrhythmias, as well as other heart-related conditions.
What does an ECG mean?
Almost everyone knows what a basic ECG tracing looks like. But what does it mean?
The first little upward notch of the ECG tracing is called the "P
wave." The P wave indicates that the atria (the two upper chambers
of the heart) are electrically stimulated to pump blood to the ventricles.
The next short flat segment is called the "PR interval." The
PR interval represents the delay in the conduction of the electrical signal
from the atria to the ventricles.
The next part of the tracing is a short downward section connected to a
tall upward section. This part is called the "QRS complex."
This part indicates that the ventricles (the two lower chambers of the
heart) are electrically stimulated (undergo depolarization) to pump out
blood to the body.
The next short flat segment is called the "ST segment." The ST
segment indicates that the ventricles are depolarized and that the electrical
signal for ventricular contraction is completed.
The next upward curve is called the "T wave." The T wave indicates
the electrical recovery period of the ventricles (ventricular repolarization)
in preparation for the next electrical depolarization and mechanical contraction.
When your doctor studies your ECG, he or she looks at the size and length
of each part of the ECG. Variations in size and length of the different
parts of the tracing may be significant. The tracing for each lead of
a 12-lead ECG will look different, but will have the same basic components
as described above. Each lead of the 12-lead is "looking" at
a specific part of the heart, so variations in a lead may indicate a problem
with the part of the heart associated with the lead.
What are the different types of arrhythmias?
An atrial arrhythmia is caused by abnormal function of the sinus node or
the atrioventricular node, or by the development of another atrial pacemaker
within the atrium that takes over the function of the sinus node.
A ventricular arrhythmia is caused by an abnormal electrical focus within
the ventricles, resulting in abnormal conduction of electrical signals
within the ventricles. The sinus node and atrioventricular node may function normally.
Arrhythmias can also be classified as slow (bradyarrhythmia) or fast (tachyarrhythmia).
"Brady-" means slow, while "tachy-" means fast.
Listed below are some of the more common arrhythmias:
Sinus arrhythmia. A condition in which the heart rate varies with breathing. Sinus arrhythmia
is commonly found in children; adults may often have it as well. This
is a benign (not dangerous) condition.
Premature ventricular contractions (PVCs). A condition in which an electrical signal originates in the ventricles
and causes the ventricles to contract before receiving the electrical
signal from the atria. PVCs are common and typically do not cause symptoms
or problems. However, if the frequency of the PVCs increases significantly,
symptoms such as weakness, fatigue, dizziness, fainting, or palpitations
may be experienced.
Sinus tachycardia. A condition in which the heart rate is faster than normal because the sinus
node is sending out electrical impulses at a rate faster than usual. Most
commonly, sinus tachycardia occurs as a normal response of the heart to
exercise when the heart rate increases to cope with increased energy requirements.
Sinus tachycardia can be completely appropriate and normal, such as when
a person is exercising vigorously. Sinus tachycardia is often temporary,
also occurring when the body is under stress from strong emotions, infection,
fever, hyperthyroidism, or dehydration, to name a few causes. It may cause
symptoms, such as weakness, fatigue, dizziness, or palpitations, if the
heart rate becomes too fast to pump an adequate supply of blood to the
body. Once the stress is removed, the heart rate will return to its usual rate.
Ventricular tachycardia (VT). A potentially life-threatening condition in which an electrical signal
is sent from the ventricles at a very fast, but often regular rate. If
the heart rate is sustained at a high rate for more than 30 seconds, symptoms,
such as weakness, fatigue, dizziness, fainting, or palpitations, may be
experienced. A person in VT may require an electric shock or medications
to convert the rhythm back to normal sinus rhythm.
Sick sinus syndrome. A condition in which the sinus node sends out electrical signals either
too slowly or too fast. There may be alternation between too-fast and
too-slow rates. This condition may cause symptoms if the rate becomes
too slow or too fast for the body to tolerate.
Ventricular fibrillation (VF). A condition in which many electrical signals are sent from the ventricles
at a very fast and erratic rate. As a result, the ventricles are unable
to fill with blood and pump. This rhythm is life-threatening because there
is no pulse and complete loss of consciousness. A person in VF requires
prompt defibrillation to restore the normal rhythm and function of the
heart. It will result in sudden cardiac death if not treated within seconds.
Premature supraventricular contractions or premature atrial contractions (PAC). A condition in which an atrial pacemaker site above the ventricles sends
out an electrical signal early. The ventricles are usually able to respond
to this signal, but the result is an irregular heart rhythm, which is
typically benign. PACs are common and may occur as the result of stimulants
such as coffee, tea, alcohol, cigarettes, or medications.
Supraventricular tachycardia (SVT). A condition in which the heart rate speeds up due to a series of early
beats from an atrial or junctional pacemaker site above the ventricles.
There are several different forms of SVT arrhythmias. A couple of the
more common examples include arrhythmias caused by an abnormal electrical
connection between the top and bottom chambers of the heart, such as atrioventricular
node reentry tachycardia also referred to as paroxysmal SVT, or atrioventricular
reentry tachycardia with an accessory pathway sometimes referred to as
Wolff-Parkinson-White Syndrome. Another common SVT form can be caused
by an irritated site in the atria that fires rapidly called atrial tachycardia.
SVT arrhythmias usually begin and end rapidly, occurring in repeated periods.
These arrhythmias can cause symptoms, such as weakness, fatigue, dizziness,
fainting, or palpitations if the heart rate becomes too fast.
Atrial flutter. A condition in which the electrical signals come from the atria at a fast
but regular rate, often causing the ventricles to contract faster and
increase the heart rate. When the signals from the atria are coming at
a faster rate than the ventricles can respond to, the ECG pattern develops
a signature "sawtooth" pattern, showing two or more flutter
waves between each QRS complex. The number of waves between each QRS complex
is expressed as a ratio, for example, a two-to-one atrial flutter means
that two waves are occurring between each QRS.
Atrial fibrillation. A condition in which the electrical signals come from the atria at a very
fast and erratic rate. The ventricles contract in an irregular manner
because of the erratic signals coming from the atria.
The symptoms of various arrhythmias may resemble other medical conditions.
Consult your doctor for a diagnosis.
How are arrhythmias diagnosed?
There are several different types of procedures that may be used to diagnose
arrhythmias. Some of these procedures include the following:
Electrocardiogram (ECG or EKG). An electrocardiogram is a measurement of the electrical activity of the
heart. By placing electrodes at specific locations on the body (chest,
arms, and legs), a graphic representation, or tracing, of the electrical
activity can be obtained as the electrical activity is received and interpreted
by an ECG machine. An ECG can indicate the presence of arrhythmias, damage
to the heart caused by ischemia (lack of oxygen to the heart muscle) or
myocardial infarction (MI, or heart attack), a problem with one or more
of the heart valves, or other types of heart conditions.
There are several variations of the ECG test:
Resting ECG. For this procedure, the clothing on the upper body is removed and small
sticky patches called electrodes are attached to the chest, arms, and
legs. These electrodes are connected to the ECG machine by wires. The
ECG machine is then started and records the heart's electrical activity
for a minute or so. The patient is lying down during this ECG.
Exercise ECG, or stress test. The patient is attached to the ECG machine as described above. However,
rather than lying down, the patient exercises by walking on a treadmill
or pedaling a stationary bicycle while the ECG is recorded. This test
is done to assess changes in the ECG during stress, such as exercise.
Signal-averaged ECG. This procedure is done in the same manner as a resting ECG, except that
the heart's electrical activity is recorded over a longer period of
time, usually 15 to 20 minutes. Signal-averaged ECGs are done when arrhythmia
is suspected but not seen on a resting ECG. The signal-averaged ECG has
increased sensitivity to abnormal ventricular activity called "late
potentials." Signal-averaged ECG is used in research and seldom used
in clinical practice.
Electrophysiologic studies (EPS). An invasive test in which a small, thin tube (catheter) is inserted in
a large blood vessel in the leg or arm and advanced to the heart. This
gives the doctor the capability of finding the site of the arrhythmia's
origin within the heart tissue, thus determining how to best treat it.
Another procedure called an esophageal electrophysiologic study may be
ordered where a soft, thin flexible plastic tube is inserted in the nostril
and placed in the esophagus (close to the atria) to provide a more precise
Holter monitor. A continuous ECG recording done over a period of 24 or more hours. Electrodes
are attached to the patient's chest and connected to a small portable
ECG recorder by lead wires. The patient goes about his or her usual daily
activities (except for activities such as taking a shower, swimming, or
any activity causing an excessive amount of sweating that would cause
the electrodes to become loose or fall off) during this procedure.
Holter monitoring may be done when an arrhythmia is suspected but not
seen on a resting ECG, since arrhythmias may be transient in nature and
not seen during the shorter recording times of the resting ECG.
Event monitor. This is similar to a Holter monitor, but the ECG is recorded only when
the patient starts the recording when symptoms are felt. Event monitors
are typically worn longer than Holter monitors. The monitor can be removed
to allow for showering or bathing.
Mobile cardiac monitoring. This is similar to both a Holter and event monitor. The ECG is monitored
constantly to allow for detection of arrhythmias, which are recorded and
sent to your doctor regardless of whether symptoms are experienced. Recordings
can also be initiated by the patient when symptoms are felt. These monitors
can be worn up to 30 days.
How are arrhythmias treated?
Some arrhythmias may be present but cause few, if any, problems. In this
case, the doctor may elect not to treat the arrhythmia. However, when
the arrhythmia causes symptoms, there are several different options for
treatment. The doctor will choose an arrhythmia treatment based on the
type of arrhythmia, the severity of symptoms being experienced, and the
presence of other conditions (diabetes, kidney failure, heart failure,
etc.) which can affect the course of the treatment.
Some treatments for arrhythmias include:
Lifestyle modification. Factors, such as stress, caffeine, or alcohol, can cause arrhythmias. The
doctor may order the elimination of caffeine, alcohol, or any other substances
believed to be causing the problem. If stress is suspected as a cause,
the doctor may recommend stress-reduction measures, such as meditation,
stress-management classes, an exercise program, or psychotherapy.
Medication. There are various types of medications that may be used to treat arrhythmias.
If the doctor chooses to use medication, the decision of which medication
to use will be determined by the type of arrhythmia, other conditions
which may be present, and other medications already being taken by the patient.
Cardioversion. In this procedure, an electrical shock is delivered to the heart through
the chest to stop certain very fast arrhythmias such as atrial fibrillation,
supraventricular tachycardia, or atrial flutter. The patient is connected
to an ECG monitor which is also connected to the defibrillator. The electrical
shock is delivered at a precise point during the ECG cycle to convert
the rhythm to a normal one.
Ablation. This is an invasive procedure done in the electrophysiology laboratory,
which means that a catheter (a very thin, flexible hollow tube) is inserted
into the heart through a vessel in the groin or arm. The procedure is
done in a manner similar to the electrophysiology studies (EPS) described
above. Once the site of the arrhythmia has been determined by EPS, the
catheter is moved to the site. By use of a technique, such as radiofrequency
ablation (very high frequency radio waves are applied to the site, heating
the tissue until the site is destroyed) or cryoablation (an ultra-cold
substance is applied to the site, freezing the tissue and destroying the
site), the site of the arrhythmia may be destroyed.
Pacemaker. A permanent pacemaker is a small device that is implanted under the skin
(most often in the shoulder area just under the collar bone), and sends
electrical signals to start or regulate a slow heart beat. A permanent
pacemaker may be used to make the heart beat if the heart's natural
pacemaker (the SA node) is not functioning properly and has developed
an abnormal heart rate or rhythm or if the electrical pathways are blocked.
Pacemakers are typically used for slow arrhythmias such as sinus bradycardia,
sick sinus syndrome, or heart block.
Implantable cardioverter defibrillator. An implantable cardioverter defibrillator (ICD) is a small device, similar
to a pacemaker, that is implanted under the skin, often in the shoulder
area just under the collarbone. An ICD senses the rate of the heartbeat.
When the heart rate exceeds a rate programmed into the device, it delivers
a small, electrical shock to the heart in order to shock the heart back
to a slower more normal heart rhythm. Newer ICDs are combined with a pacemaker
to deliver an electrical signal to regulate a heart rate that is too slow.
ICDs are used for life-threatening fast arrhythmias such as ventricular
tachycardia or ventricular fibrillation.
Surgery. Surgical treatment for arrhythmias is usually done only when all other
appropriate options have failed. Surgical ablation is a major surgical
procedure requiring general anesthesia. The chest is opened, exposing
the heart. The site of the arrhythmia is located, the tissue is destroyed
or removed in order to eliminate the source of the arrhythmia.