|
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 the
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 the electrical
signal is causing the heart to pump too slowly or
too irregularly.
In any of these situations, the body may not receive
enough blood because the heart cannot pump out an adequate
amount with each beat as a result of the arrhythmia's
effects on the heart rate.
What are the symptoms of arrhythmias?
The effects on the body are often the same, whether
the heartbeat is too fast, too slow, or too irregular.
Some symptoms of arrhythmias include, but are not limited
to:
• weakness
• fatigue
• palpitations
• low blood pressure
• dizziness
• fainting
The
symptoms of arrhythmias may resemble other conditions.
Consult your physician 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. Like all pumps, the heart requires
a source of energy in order to function. The heart's
pumping action comes from an intrinsic electrical conduction
system.
How does the heart beat?
An
electrical stimulus is generated by the sinus node (also
called the sinoatrial node, or SA node), which is a
small mass of specialized tissue located in the right
atrium (right upper chamber) of the heart. The sinus
node generates an electrical stimulus periodically (60-100
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
(AV) node, where impulses are slowed down for a very
short period, then continues down the conduction pathway
via the bundle of His (also known as the AV bundle or atrioventricular bundle)
into the ventricles. The bundle of His divides into
right and left pathways to provide electrical stimulation
to both ventricles.
Normally, as the electrical impulse moves through the
heart, the heart contracts about 60 to 100 times a minute.
Each contraction of the ventricles represents one heartbeat.
The atria contract a fraction of a second before the
ventricles so their blood empties into the ventricles
before the ventricles contract.
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.
How does the physician know what an ECG means?
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 part of the tracing is a short downward
section connected to a tall upward section. This next
part is called the "QRS complex." This part
indicates that the ventricles (the two lower chambers
of the heart) are electrically stimulated to pump
out blood.
• The next short flat segment is called the
"ST segment." The ST segment indicates the
amount of time from the end of the contraction of
the ventricles to the beginning of the "T wave."
• The next upward curve is the T wave. The T
wave indicates the recovery period of the ventricles.
When your physician studies your ECG, he/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 that lead.
What are the different types of arrhythmias?
An atrial arrhythmia is an arrhythmia caused by a dysfunction
of the sinus node or the development of another atrial
pacemaker within the heart tissue that takes over the
function of the sinus node. A ventricular arrhythmia is an arrhythmia caused by a dysfunction of the sinus
node, an interruption in the conduction pathways, or
the development of another pacemaker within the heart
tissue that takes over the function of the sinus node.
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:
ATRIAL 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 usually a benign condition - there
may be no symptoms or problems associated with sinus arrhythmias.
Sinus tachycardia: A condition in
which the heart rate is faster than 100 beats per minute
because the sinus node is sending out electrical impulses
at a rate faster than usual. This condition 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. Sinus tachycardia is often
transient, occurring when the body is under stress from
exercise, strong emotions, fever, or dehydration, to
name a few causes. Once the stress is removed, the heart
rate will usually return to its normal rate.
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.
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. PACs are common
and may occur as the result of stimulants such as caffeine,
alcohol, cigarettes, or medications.
Supraventricular tachycardia (SVT), paroxysmal atrial
tachycardia (PAT): 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. PAT usually begins and ends rapidly, occurring
in repeated periods. This condition 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 even 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, i.e., 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.
VENTRICULAR ARRHYTHMIAS
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 fairly common and often do not cause symptoms
or problems. However, if the frequency of the PVCs increases
to several per minute, symptoms such as weakness, fatigue,
dizziness, fainting, or palpitations may be experienced.
Ventricular tachycardia (VT): A 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, symptoms such as weakness,
fatigue, dizziness, fainting, or palpitations may be
experienced. A person in VT may require an electric
shock to "convert" the rhythm to a regular
one.
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 a
complete loss of consciousness. A person in VF requires
prompt defibrillation to restore the normal rhythm and
function of the heart. It may cause sudden cardiac death.
The symptoms of various arrhythmias may resemble other
medical conditions. Consult your physician 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-average 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
15-20 minutes. Signal-average ECG is done when arrhythmia
is suspected but not seen on a resting ECG, since
arrhythmias may be transient in nature and not seen
during the short recording time of the resting ECG.
Electrophysiologic studies (EPS)
This is an invasive test in which a small catheter
(hollow tube) is inserted through the groin or neck
into the heart. This gives the physician the capability
of finding the site of the arrhythmia's origin within
the heart tissue, thus, determining how to best treat
it.
Holter monitor
A Holter monitor is an ECG recording done over a period
of 24 or more hours. Three electrodes are attached
to the patient's chest and connected to a small portable
ECG recorder by lead wires. The patient goes about
his/her usual daily activities (except for activities
such as taking a shower, swimming, or any activity
causing an excessive amount of sweating which would
cause the electrodes to become loose or fall off.)
There are 2 types of Holter monitoring:
» continuous recording - the ECG is recorded
continuously during the entire testing period.
» event monitor, or loop recording - the ECG
is recorded only when the patient starts the recording
when symptoms are felt.
Holter monitoring may be done when an arrhythmia
is suspected but not seen on a resting or signal-average
ECG, since arrhythmias may be transient in nature
and not seen during the shorter recording times of
the resting or signal-average ECG.
How are arrhythmias treated?
Arrhythmias may be present but cause few, if any, problems.
In this case, the physician may elect not to treat the
arrhythmia. However, when the arrhythmia causes symptoms,
there are several different options for treatment. The
physician 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. Your physician 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 physician may recommend stress-reduction
measures such as meditation, stress-management classes,
an exercise program, or psychotherapy.
• medication
There are various types of medications which may be
used to treat arrhythmias. If the physician 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 sinus tachycardia. 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 (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, most 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 to slow the heart rate. Many newer ICDs
can also function as a pacemaker by delivering an
electrical signal to regulate a heart rate that is
too slow. ICDs are typically used for fast arrhythmias
such as ventricular tachycardia.
• 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.
|
