Arrhythmias
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.
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:
- 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.
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 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.
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.
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 the lead.
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 |
VENTRICULAR
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 sinus 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. |
| 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 usual rate. |
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. |
| 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 may cause sudden cardiac death.
|
| 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 coffee, tea, 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. |
|
The
symptoms of various arrhythmias may resemble other
medical conditions. Consult your physician for
a diagnosis.
There
are several different types of procedures that
may be used to diagnose arrhythmias. Some of these
procedures include the following:
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. The 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 converter 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.
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