Arrhythmias
© Copyright 1999 Dialog Medical, Inc. All rights reserved.
Facts About Arrhythmias/Rhythm Disorders
What is an arrhythmia?
An arrhythmia is a change in the regular beat of the heart. The
heart may seem to skip a beat or beat irregularly or very fast
or very slowly.
Does having an arrhythmia mean that a person has heart disease?
No, not necessarily. Many arrhythmias occur in people who do
not have underlying heart disease.
What causes arrhythmias?
Many times, there is no recognizable cause of an arrhythmia.
Heart disease may cause arrhythmias. Other causes include: stress,
caffeine, tobacco, alcohol, diet pills, and cough and cold medicines.
Are arrhythmias serious?
The vast majority of people with arrhythmias have nothing to
fear. They do not need extensive exams or special treatments for
their condition. In some people, arrhythmias are associated with
heart disease. In these cases, heart disease, not the arrhythmia,
poses the greatest risk to the patient.
In a very small number of people with serious symptoms, arrhythmias
themselves are dangerous. These arrhythmias require medical treatment
to keep the heartbeat regular. For example, a few people have
a very slow heartbeat (bradycardia), causing them to feel lightheaded
or faint. Some people may have very rapid heart rhythms from the
bottom part of the heart (ventricular tachycardia). If left untreated,
this type of heart rhythm can be dangerous and the risk it poses
should be assessed by a physician.
How common are arrhythmias?
Arrhythmias occur commonly in middle-age adults. As people get
older, they are more likely to experience an arrhythmia.
What are the symptoms of an arrhythmia?
Most people have felt their heart beat very fast, experienced
a fluttering in their chest, or noticed that their heart skipped
a beat. Almost everyone has also felt dizzy, faint, or out of
breath or had chest pains at one time or another. One of the most
common arrhythmias is sinus arrhythmia, the change in heart rate
that can occur normally when we take a breath. Experiencing irregular
heart beats may cause anxiety, but for the majority of people,
they are completely harmless.
You should not panic if you experience a few flutters or your
heart races occasionally. But if you have questions about your
heart rhythm or symptoms, check with your doctor.
Arrhythmia Types
Originating in the Atria
Sinus arrhythmia. Cyclic changes in the heart rate during breathing.
Common in children and often found in adults. This is normal.
Sinus tachycardia. The sinus node sends out electrical signals
faster than usual, speeding up the heart rate. Causes include exercise,
fever, excitement, certain medications, dehydration and an overly
active thyroid gland.
Sick sinus syndrome. The sinus node does not fire its signals
properly, so that the heart rate slows down. Sometimes the rate
changes back and forth between a slow (bradycardia) and fast (tachycardia)
rate.
Premature supraventricular contractions or premature
atrial contractions (PAC). A beat occurs early in the atria,
causing the heart to beat before the next regular heartbeat.
Supraventricular tachycardia (SVT), paroxysmal atrial tachycardia
(PAT). A series of early beats in the atria speed up the heart
rate (the number of times a heart beats per minute). In paroxysmal
tachycardia, repeated periods of very fast heartbeats begin and
end suddenly. Heart rates are generally in the 160 to 220 beat per
minute range.
Atrial flutter. A rapid short circuit rhythm in the top
part of the heart. The atria contract at 300 beats per minute. The
lower chambers (the ventricles) contract at multiples of this (150,
100, or 75 beats per minute). The usual rate is 150 beats per minute.
Atrial fibrillation. Electrical signals in the atria are
fired in a very fast and uncontrolled manner. Electrical signals
arrive in the ventricles in a completely irregular fashion, so the
heart beat is completely irregular.
Wolff-Parkinson-White syndrome. Abnormal pathways between
the atria and ventricles cause the electrical signal to arrive at
the ventricles too soon and to be transmitted back into the atria.
Very fast heart rates may develop as the electrical signal ricochets
between the atria and ventricles.
Originating in the Ventricles
Premature ventricular complexes (PVC). An electrical signal
from the ventricles causes an early heart beat that generally goes
unnoticed. The heart then seems to pause until the next beat of
the ventricle occurs in a regular fashion.
Ventricular tachycardia. The heart beats fast due to electrical
signals arising from the ventricles (rather than from the atria).
Ventricular fibrillation. Electrical signals in the ventricles
are fired in a very fast and uncontrolled manner, causing the heart
to quiver rather than beat and pump blood.
What happens in the heart during an arrhythmia?
Describing how the heart beats normally helps to explain what
happens during an arrhythmia. The heart is a muscular pump divided
into four chambers--two atria located on the top and two ventricles
located on the bottom.
Normally each heartbeat starts in the right atrium. Here, a specialized
group of cells called the sinus node, or natural pacemaker, sends
an electrical signal. The signal spreads throughout the atria
to the area between the atria called the atrioventricular (AV)
node.
The AV node connects to a group of special pathways that conduct
the signal to the ventricles below. As the signal travels through
the heart, the heart contracts. First the atria contract, pumping
blood into the ventricles. A fraction of a second later, the ventricles
contract, sending blood throughout the body.
Usually the whole heart contracts between 60 and 100 times per
minute. Each contraction equals one heartbeat.
An arrhythmia may occur for one of several reasons:
- Instead of beginning in the sinus node, the heartbeat begins
in another part of the heart.
- The sinus node develops an abnormal rate or rhythm.
- A patient has a heart block.
What is a heart block?
Heart block is a condition in which the electrical signal cannot
travel normally down the special pathways to the ventricles. For
example, the signal from the atria to the ventricle may be (1)
delayed, but each one conducted; (2) delayed with only some getting
through; or (3) completely interrupted. If there is no conduction,
the beat generally originates from the ventricles and is very
slow.
What are the different types of an arrhythmias?
There are many types of arrhythmias. Arrhythmias are identified
by where they occur in the heart (atria or ventricles) and by
what happens to the heart's rhythm when they occur.
Arrhythmias arising in the atria are called atrial or supraventricular
(above the ventricles) arrhythmias. Ventricular arrhythmias begin
in the ventricles. In general, ventricular arrhythmias caused
by heart disease are the most serious.
How does the doctor know that I have an arrhythmia?
Sometimes an arrhythmia can be detected by listening to the heart
with a stethoscope. However, the electrocardiogram is the most
precise method for diagnosing the arrhythmia.
An arrhythmia may not occur at the time of the exam even though
symptoms are present at other times. In such cases, tests will
be done if necessary to find out whether an arrhythmia is causing
the symptoms.
What tests can be done?
First the doctor will take a medical history and do a thorough
physical exam. Then one or more tests may be used to check for
an arrhythmia and to decide whether it is caused by heart disease.
Tests for Detecting Arrhythmias:
Electrocardiogram (ECG or EKG). A record of the electrical
activity of the heart. Disks are placed on the chest and connected
by wires to a recording machine. The heart's electrical signals
cause a pen to draw lines across a strip of graph paper in the
ECG machine. The doctor studies the shapes of these lines to check
for any changes in the normal rhythm.
The types of ECGs are:
Resting ECG. The patient lies down for a few minutes while
a record is made. In this type of ECG, disks are attached to the
patient's arms and legs as well as to the chest.
Exercise ECG (stress test). The patient exercises either
on a treadmill machine or bicycle while connected to the ECG machine.
This test tells whether exercise causes arrhythmias or makes them
worse or whether there is evidence of inadequate blood flow to
the heart muscle ("ischemia").
24-hour ECG (Holter) monitoring. The patient goes about
his or her usual daily activities while wearing a small, portable
tape recorder that connects to the disks on the patient's chest.
Over time, this test shows changes in rhythm (or "ischemia")
that may not be detected during a resting or exercise ECG.
Transtelephonic monitoring. The patient wears the tape
recorder and disks over a period of a few days to several weeks.
When the patient feels an arrhythmia, he or she telephones a monitoring
station where the record is made. If access to a telephone is
not possible, the patient has the option of activating the monitor's
memory function. Later, when a telephone is accessible, the patient
can transmit the recorded information from the memory to the monitoring
station. Transtelephonic monitoring can reveal arrhythmias that
occur only once every few days or weeks.
Electrophysiologic study (EPS). A test for arrhythmias
that involves cardiac catheterization. Very thin, flexible tubes
(catheters) are placed in a vein of an arm or leg and advanced
to the right atrium and ventricle. This procedure allows doctors
to find the site and type of arrhythmia and how it responds to
treatment.
How are arrhythmias treated?
Many arrhythmias require no treatment whatsoever. Serious arrhythmias
are treated in several ways depending on what is causing the arrhythmia.
Sometimes the heart disease is treated to control the arrhythmia.
Or, the arrhythmia itself may be treated using one or more of
the following treatments.
Drugs
There are several kinds of drugs used to treat arrhythmias. One
or more drugs may be used. Drugs are carefully chosen because
they can cause side effects. In some cases, they can cause arrhythmias
or make arrhythmias worse. For this reason, the benefits of the
drug are carefully weighed against any risks associated with taking
it. It is important not to change the dose or type of your medication
unless you check with your doctor first.
If you are taking drugs for an arrhythmia, one of the following
tests will probably be used to see whether treatment is working:
a 24-hour electrocardiogram (ECG) while you are on drug therapy,
an exercise ECG, or a special technique to see how easily the
arrhythmia can be caused. Blood levels of antiarrhythmic drugs
may also be checked.
Cardioversion
To quickly restore a heart to its normal rhythm, the doctor may
apply an electrical shock to the chest wall. Called cardioversion,
this treatment is most often used in emergency situations. After
cardioversion, drugs are usually prescribed to prevent the arrhythmia
from recurring. This treatment is performed while the patient
is sedated.
Automatic implantable defibrillators
These devices are used to correct serious ventricular arrhythmias
that can lead to sudden death. The defibrillator is surgically
placed inside the patient's chest. There, it monitors the heart's
rhythm and quickly identifies serious arrhythmias. With an electrical
shock, it immediately disrupts a deadly arrhythmia.
Artificial pacemaker
An artificial pacemaker can take charge of sending electrical
signals to make the heart beat if the heart's natural pacemaker
is not working properly or its electrical pathway is blocked.
During a simple operation, this electrical device is placed under
the skin. Insulated electrical wires are placed into the heart
through a vein under the collar bone. The pacemaker monitors the
heart's electrical activity and provides electrical impulses to
the heart as needed.
Ablation
When an arrhythmia cannot be controlled by other treatments, doctors
may perform ablation therapy by inserting catheters into the heart,
localizing areas responsible for the arrhythmia, then destroying
those areas using radiofrequency waves.
How can arrhythmias be prevented?
If heart disease is not causing the arrhythmia, the doctor may
suggest that you avoid what is causing it. For example, if caffeine
or alcohol is the cause, the doctor may ask you not to drink coffee,
tea, colas, or alcoholic beverages.
Is research on arrhythmias being done?
The National Heart, Lung, and Blood Institute (NHLBI) supports
basic research on normal and abnormal electrical activity in the
heart to understand how arrhythmias develop. Clinical studies
with patients aim to improve the diagnosis and management of different
arrhythmias. These studies will someday lead to better diagnostic
and treatment strategies.
Where can I find publications about heart disease?
To obtain publications about heart disease, you may want to contact
your:
Local American Heart Association chapter.
Local or state health department.
The National Heart, Lung, and Blood Institute also has publications
about heart disease. For more information, contact:
NHLBI Information Center
P.O. Box 30105
Bethesda, MD 20892-0105
Telephone: (301) 251-1222
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service
National Institutes of Health
National Heart, Lung, and Blood Institute
NIH Publication No. 95-2264
Reprinted September 1995
Edited October 1998
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