Atrial fibrillation
Atrial fibrillation is one of the most common cardiac arrhythmias.
It is the result of extremely rapid, disorganized impulses arising
in the upper chambers of the heart. This chaotic electric activity
is not associated with any effective contraction of the upper
chambers. Within the upper chambers, electrical activation
forms at very rapid rates, usually in excess of 350-400 beats
per minute. Attempts to transmit this rapid activity into the
lower chambers is controlled by a structure known as the AV
node, the sole electrical connection between the upper and lower
chambers. Usually, the AV node limits the ability for impulses
to gain access into the lower chambers so that heart rates
remain in a more well-controlled range (60-120 bpm). However,
the transmission of impulses is often poorly controlled and
heart rates can become very fast. This is the primary cause
of symptoms associated with atrial fibrillation. Symptoms
include palpitation, intermittent lightheadedness, shortness
of breath, fatigue or poor exercise tolerance.
Atrial fibrillation is generally classified as being new onset or chronic.
Chronic forms include paroxysmal, persistent and permanent. The
paroxysmal form occurs intermittently with variable frequency and
may not be associated with underlying heart disease. The persistent
form tends to last for much longer periods of time and is more likely
to require drug therapy or electrical cardioversion to restore sinus
rhythm. The permanent form implies that normal sinus rhythm is no
longer achievable. Underlying heart disease is more often present in
the latter two forms.
Atrial fibrillation is generally diagnosed during the recording of an
electrocardiogram. It can also be detected using either a 24-hour
Holter monitor or an event recorder. If episodes are rare and last
for only very brief periods, there may be no specific therapy
prescribed. Specific antiarrhythmic medications are available
to ameliorate symptoms when present or to minimize/prevent
episodes if more frequent or long lasting. Select patients may
be candidates for radiofrequency catheter ablation. In addition to
treating symptoms due to atrial fibrillation, a second major goal
in the treatment of this rhythm disorder is to prevent stroke.
Stroke, or cerebral vascular accident is caused by the dislodgement
of a small blood clot arising from the lining of the upper chambers.
The dislodged blood clot, known as an embolus, travels to the brain
where it can lodge in a small vessel and compromise blood supply to
a specific region of the brain. The consequences may be brief
(transient ischemic attack-TIA) or permanent (stroke). Patients
who are determined to be at increased risk for stroke are placed
on life long medications aimed at thinning the blood.
Atrial flutter
Atrial flutter is also a fairly common rhythm disorder involving
the upper chambers and is very closely related to atrial fibrillation.
The primary difference lies in the fact that atrial flutter is an
organized electrical activity. The rate of this activity is almost
always 300 bpm. Due to the unique properties of the AV node,
every other impulse gains access to the lower chambers and
results in a heart rate of 150 bpm in most instances. As a result,
atrial flutter results in a more regular rhythm in contrast to
trial fibrillation.
While medications are available to treat atrial flutter, this arrhythmia
can now be cured with radiofrequency catheter ablation.
Paroxysmal Supraventricular Tachycardia - PSVT
This is a group of tachycardias arising from the upper chambers
and, like atrial fibrillation and atrial flutter are not life threatening.
They tend to be very regular rhythms with rates in the range of
150-220 bpm. Although they tend to be more common in the
younger age group, these tachycardias can occur in just about
any age group. The three most common forms include AV nodal
reentrant tachycardia, atrioventricular reentrant tachycardia
and ectopic atrial tachycardia. All produce essentially identical
symptoms, which include sustained palpitation or racing heart.
Lightheadedness can also occur, particularly if the tachycardia
is quite rapid or if the patient is slightly dehydrated. Chest dis-
comfort or shortness of breath are less commonly associated
symptoms. Because these tachycardias are generally well tolerated,
patients may experienced many episodes before eventually seeking
medical attention. A diagnosis is confirmed by event recorder techniques
or 24-hour Holter monitoring. Often times, the diagnosis is established
in the emergency room.
While some episodes can be terminated by the patient using either
the Valsalva maneuver (bearing down after taking a large, deep breath)
or submerging ones face in ice water, episodes often require an
emergency room visit. Intravenous injection of a drug known as
Adenosine usually leads to prompt tachycardia termination. Many
antiarrhythmic medications are available to prevent recurrences
of PSVT, but most drugs eventually lose their effectiveness. The
most ideal treatment is curative radiofrequency catheter ablation.
Ventricular Tachycardia
Ventricular tachycardia is a rapid heart rhythm originating from
within one of the lower chambers of the heart. This arrhythmia
is usually considered dangerous, often fatal. It is the tachycardia
responsible for sudden cardiac death or cardiac arrest. It is
usually associated with some form of underlying heart disease,
most commonly a prior heart attack. If the patient survives an
episode of ventricular tachycardia, the usual symptom is syncope.
In a relatively small number of cases, patients can experience
ventricular tachycardia and have symptoms no worse than those
commonly seen with PSVT. Hospitalization is mandatory and the
diagnosis is confirmed by electrophysiologic testing.
The treatment of ventricular tachycardia involves the proper
management of the underlying heart disease, if present, in
addition to efforts aimed at eliminating the rhythm disturbance.
Both antiarrhythmic medications and radiofrequency catheter
ablation are available options. To date, the most effective
means of preventing recurrent sudden death or cardiac arrest
is the implantable cardioverter defibrillator (ICD).
Ventricular fibrillation is another type of ventricular tachycardia
but is uniformly lethal. In contrast to ventricular tachycardia,
ventricular fibrillation is an extremely rapid, disorganized rhythm
arising within the lower chambers. Unlike some cases of ventricular
tachycardia, there is no effective contraction during ventricular
fibrillation under any circumstance. The only effective method
of treatment is the ICD.
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