Arrhythmias
Arrhythmias are abnormal or irregular patterns of your normal
heart rhythm. They can be totally asymptomatic and without significant
threat to the normal work of the heart, or they can be of a serious
and life-threatening nature. Think of your heart as an electrical
system with the capabilities of creating electrical impulses and
transmitting them through
conduction pathways to generate our heartbeat. An abnormality within
this electrical pathway can produce an abnormal heart rate and
rhythm that can affect the efficiency of the heart as a pump.
The initial electrical impulses are generated within a special
group of cells located in the heart’s right atrium (the right
upper chamber). This cell grouping is referred to as the SA node
(sinoatrial node) and is also known as the natural pacemaker of
the heart. The impulses from the SA node travel from the atria
(the two upper chambers of the heart)
to the AV node (atrioventricular node). The AV node serves as a
relay station to conduct the impulses from the atria to the ventricles.
Specialized conduction fibers (referred to as the His-Purkinje
system) then transmit the electrical impulses throughout the ventricles.
Any interruption that occurs within this conduction process can
result in an abnormal heartbeat.
The heart beats or contracts as the impulses are produced within
the electrical system. The atria (the upper chambers of the heart)
contract first, thus filling the ventricles (the lower chambers
of the heart) with blood. The electrical impulse conduction continues
which results in the contraction of the ventricles.
Normal resting heart rate ranges from 60 to 100 beats per minute.
However, during episodes of exercise or stress, heart rate increases
to supply increased blood flow demand to the body.
Causes Of Arrhythmia
The causes of arrhythmia are variable. Arrhythmia can be of a
congenital nature and already present at birth or can result from
the presence of heart disease, valvular abnormalities, diabetes,
stroke, and high blood pressure.
Lifestyle choices such as smoking, alcohol use, drug abuse, high
caffeine consumption, and even some over-the-counter medications
for cough and cold treatment can result in an abnormal heart rhythm.
Diet medications and some herbal remedies can also precipitate
arrhythmia. However, some arrhythmias have no identifiable cause
and occur with no known reason.
Types of Arrhythmia
Arrhythmias can be categorized based on their location of origin
within the conduction system. Supraventricular arrhythmias originate
in the atria or the two upper chambers of the heart while ventricular
arrhythmias are generated within the ventricular conduction system
(the ventricles or two lower chambers of the heart).
Arrhythmias are also described in terms of their effect on the
heart rate. Bradycardia is generally defined as heart rate less
than 60 beats per minute. Tachycardia is a fast heart rate of more
than 100 beats per minute.
The ventricular arrhythmias are generally more life-threatening
than the supraventricular arrhythmias. This is the case because
ventricular arrhythmias seriously disrupt the ability of the heart
to effectively pump blood to the body.
Premature beats (skipped beats) either from the atria or ventricles
are the most common type of arrhythmia. They can be of no significance,
or they may be the first indicators of underlying heart disease.
Supraventricular arrhythmias include supraventricular tachycardia
(SVT), atrial flutter, and atrial fibrillation. These all result
in rapid heart rates, usually greater than 140 beats per minute.
Atrial fibrillation is the most common of the arrhythmias. The
two upper chambers essentially quiver rather than contract. This
results in an irregularly, irregular, rapid rhythm which, if persistent
and untreated, can result in clot formation with subsequent stroke
or progressive weakening of the heart. More than 2 million people
have atrial fibrillation in the United States. Atrial flutter and
supraventricular tachycardia also
originate with an electrical impulse conduction abnormality in
the atria. They also result in a rapid pulse rate which requires
treatment if persistent.
Ventricular tachycardia causes a very rapid heart rate when the
electrical impulse regulating the heartbeat originates in the ventricles
rather than the SA node (the natural
pacemaker of the heart). Because of the rapidity of the rate and
the heart’s pumping
inefficiency, acute symptoms of palpitations, lightheadedness,
or fainting may occur.
This is a medical emergency requiring immediate treatment. It is
always seen in patients with advanced heart disease. If untreated,
it usually leads to ventricular fibrillation that results in an
extremely rapid and uncoordinated pumping of the heart, a circumstance
which cannot sustain life. This is often referred to as the “sudden
death syndrome.” Immediate cardiopulmonary resuscitation
(CPR) and a 911 call to the emergency medical response team may
result in effective treatment and subsequent full recovery.
Bradycardia, a heart rate less than 60, can be normal especially
in well-conditioned people. It can also be abnormal if the SA node
or AV node stops producing or conducting electrical impulses. These
conditions are commonly referred to as “sick sinus syndrome” or “heart
block.” Here the pulse rate is usually less than 50 beats
per minute and results in symptoms.
Symptoms of Arrhythmia
Symptoms of arrhythmia depend on the nature of the abnormal heartbeat.
The origin of the arrhythmia, its frequency of occurrence, and
its duration will influence the severity of the symptoms demonstrated.
Underlying medical conditions such as advanced heart disease and
valvular disease will also contribute to the extent the symptoms
of arrhythmia are demonstrated.
The arrhythmia’s effect on the heart rate will greatly determine
the symptoms experienced. Bradycardia, or a slow heart rate, will
produce feelings of fatigue and
weakness, dizziness, and fainting spells. Symptoms of tachycardia,
or a fast heart rate,
may include the sensation of skipped beats, fluttering, and of
the heart racing. The rapid pulse rate may produce chest discomfort,
shortness of breath, lightheadedness, weakness, and dizziness.
Indeed, if the rate is fast enough, you may feel your pulse “throbbing” in
your neck.
Symptoms are variable and individual to each patient.
Some arrhythmias are without any symptoms at all
Diagnosis of Arrhythmia
An electrocardiogram (EKG or ECG) is a tracing of the corresponding
electrical activity
of the heart. The wave tracing generated by the electrical impulses
will be assessed by your physician for potential heartbeat abnormalities.
Your physician may suggest that you have ambulatory monitoring.
In this case, you wear electrodes on your chest for a
24 to 48 hour period. This produces a continuous recording of your
heart’s electrical activity and is examined by your physician
for any abnormality.
Event monitors are worn for a much longer period of time in an
effort to detect an arrhythmia. These devices are small, usually
the approximate size of a beeper, and in some cases, they are worn
as wristwatch models. They are capable of automatically recording
the heart rate and rhythm. The patient can activate them with the
onset of symptoms, and the tracing is sent to a monitoring facility
where it is assessed for the
occurrence of an arrhythmia.
Electrophysiology studies are performed by a specially trained
physician in the cardiac catheterization laboratory. In this procedure,
the physician introduces a special catheter
from a major peripheral vessel in the leg through the circulatory
system to the heart. Through this catheter, the physician is able
to establish a mapping of the electrical impulses generated by
the heart’s electrical conduction system. Abnormalities of
this
electrical mapping are assessed. Drugs may be given in an attempt
to reproduce the arrhythmia.
Tilt table testing may be indicated to determine if fainting episodes
or sudden loss of
consciousness may be related to an arrhythmia. During a tilt table
study, the patient lies flat on a table that is slowly raised to
an upright 90 degrees. During this time, blood pressure and pulse
are monitored and the heart’s rate and rhythm are recorded
via electrodes attached to the chest. If the patient experiences
a fainting episode (syncope),
the study is considered positive for what is known as vasovagal
or neurocardiogenic syncope. This occurs when an abnormality of
the central nervous system causes a reduction in the heart rate
and a dilation of the blood vessels with subsequent lowered blood
pressure. These physical responses result in the fainting or syncopal
episode.
Treatment of Arrhythmia
A wide variety of anti-arrhythmic medications are available for
the treatment of arrhythmias. The selection of your anti-arrhythmic
medication is highly individualized.
Electronic pacemakers can be permanently implanted to correct
a slow heart rate. Pacemakers and anti-arrhythmic drugs are frequently
used in combination.
Radiofrequency ablation that uses radio waves to eliminate abnormal
conduction pathways of the heart’s conduction system may
be used to eliminate an arrhythmia if medical therapy is not working
effectively. By applying these high frequency radio waves to the
abnormal pathways, their impulse conduction is eliminated, and
the irregular heartbeat is no longer produced.
Atrial fibrillation, the most common of the supraventricular arrhythmias,
occurs when the atria (the heart’s two upper chambers) do
not produce the normal pattern of electrical impulse conduction
and therefore do not contract effectively to empty blood into the
ventricles. Because residual blood remains in the atria, the danger
of clot formation and subsequent stroke is the most concerning
complication of atrial fibrillation.
Medication therapy to regulate the heart rhythm is indicated in
the treatment of atrial fibrillation along with anticoagulation
therapy to prevent clot formation. If symptoms and heart rate are
not well controlled utilizing medication therapy, electrical shock
(cardioversion) may be used in an attempt to restore normal heart
rhythm.
Radiofrequency ablation may also be used to treat atrial fibrillation.
One option is the use of radiofrequency waves delivered via special
catheters to the area of the
atrioventricular node (AV node) to eliminate its conduction of
the abnormal electrical impulses from the atria. This is called
an atrioventricular nodal ablation. When this occurs, a permanent
pacemaker is placed to assume the work of the AV node in conducting
electrical impulses to the ventricles.
Pulmonary vein isolation is another radiofrequency ablation technique
that uses high intensity radio wave energy. A specially trained
physician uses this energy to map the
conduction pathways of the atria, identify the abnormalities, and
applies the energy to areas of the atria that connect with the
pulmonary vein. This process is repeated until a conduction block
exists, and the atrial fibrillation conduction pattern can no longer
be relayed to the ventricles.
Atrial flutter is another common arrhythmia that originates with
an electrical impulse
conduction abnormality in the atria. The result is a very rapid
contraction of the atria
that may limit the amount of blood which is emptied from the atria
into the ventricles.
Atrial flutter is caused by a more organized conduction pattern
than that of atrial fibrillation.
As with atrial fibrillation, treatment options will include medication
therapies to control and regulate the heart rate and rhythm. If
this management is not sufficient, then electrical cardioversion
may be attempted in which electrical shock is delivered to reestablish
a normal heartbeat. Radiofrequency ablation is also a possibility
to prevent the atrioventricular node (AV node) from conducting
the abnormal impulses from the
atria. If this conduction system is destroyed, then a permanent
pacemaker is placed to ensure normal electrical conduction patterns.
Surgical ablation techniques are now available to treat arrhythmias.
These would include the Maze procedure for atrial fibrillation
in which a series of incisions are created in the atria to eliminate
potential pathways for the random electrical activity produced
in the two upper chambers. Other surgical methods for creation
of similar lesions in the atria
allow disruption in the random abnormal electrical conduction which
causes atrial fibrillation. One is called cryoablation or cryothermy
in which a special probe and extreme cold produce these disruptive
lesions. The treatment option chosen for each patient is individualized
and based on various factors including the patient’s age
and other existing disease conditions.
Ventricular fibrillation occurs when the ventricles contract in
a rapid and uncoordinated manner that prevents them from filling
with adequate amounts of blood that would normally be supplied
to the body. This is a life-threatening emergency and requires
immediate intervention to sustain life. Treatment involves drug
therapy and electrical shock to reestablish safe patterns of electrical
impulse conduction. If treatment is not undertaken, sudden cardiac
death will ensue.
Implantable cardioverter defibrillator (AICD or ICD) placement
is now an option to provide immediate electrical shock to the heart
when ventricular fibrillation is detected by the electronic device.
In patients where heart disease automatically predisposes them
for risk of development of life-threatening arrhythmias, the ICD
constantly monitors for such dangerous irregular heart rhythms
and automatically delivers an electrical shock to the heart to
convert the abnormality. Some ICDs are now programmed to respond
to atrial fibrillation and can be used to trigger an electrical
shock to convert the heart rhythm when atrial fibrillation is experienced.
