Atrial Fibrillation (cont.)
Converting atrial fibrillation to a normal rhythm
Converting AF to a normal rhythm can be accomplished with medications (chemical
cardioversion) or by electrical shocks (electrical cardioversion). Doctors
usually recommend that all patients with chronic sustained AF undergo at least
one attempt at cardioversion, chemical or electrical. Successful cardioversion
can alleviate symptoms, improve exercise tolerance, improve quality of life, and
lower the risk of strokes. Doctors usually try medical cardioversion first, and, if
medications fail, then try electrical cardioversion.
Patients who are more likely to attain and maintain a normal heart rhythm
with either chemical or electrical cardioversion include:
- Patients younger than 65 years of age
- Patients who have had AF for a short time (less than
12 months)
- Patients with normal-sized atria and ventricles
- Patients who are having their first episode of AF
Cardioversion with medications. Before prescribing medications for cardioversion, the doctor usually
controls the rate of ventricular contractions and thins the blood, usually with
warfarin.
1) Available Medications. Medications used in
cardioversion usually work by blocking the channels in the walls of cells through which ions
travel (sodium channels, potassium channels, beta adrenergic channels, and calcium
channels). Some examples of these medications include:
- quinidine (Quinaglute)
- procainamide (Procan SR)
- disopyramide (Norpace)
- flecainide (Tambocor)
- sotalol (Betapace)
- flecainide (Tambocor)
- amiodarone (Cordarone)
These medications are capable of converting AF to normal rhythm in about 50%
of patients. They often are used long-term to maintain a normal rhythm and
prevent recurrences of AF.
2) Disadvantages of using medications. Medications used for
converting AF carry a small risk of causing other abnormal heart rhythms--they
are said to be pro-arrhythmic--especially in patients with diseases of the
heart muscle or coronary arteries. These abnormal heart rhythms can be more
life-threatening than AF. Therefore, treatment with these medications often is
initiated in the hospital while the patient's rhythm is continuously
monitored for 24-72 hours.
These medications may not be effective in the longer-term. Many patients
eventually develop a recurrence of AF despite the medications.
Medications used in treating atrial fibrillation often have important side effects.
Many patients discontinue them because they cannot tolerate these side
effects. For example, amiodarone is commonly used in treating AF because it
is less pro-arrhythmic and has been shown to maintain a normal rhythm in up to
75% of patients. However, amiodarone frequently causes side effects and drug
interactions. About 7 out of every 10 patients taking amiodarone experience
some type of side effect, and between 1 in 5 and 1 in 20 experience side
effects that are severe enough that the amiodarone must be stopped. Amiodarone
can interact with other medications such as tricyclic antidepressants,
e.g., amitriptyline (Elavil) or phenothiazine antipsychotics, e.g.,
chlorpromazine (Thorazine) and cause abnormal heart rhythms. Amiodarone interacts with
warfarin and increases the risk of bleeding. This interaction with warfarin can
occur as early as 4-6 days after the start of both drugs or can
be delayed by a few weeks. Thus, doctors prescribing both warfarin and amiodarone will adjust
the dose of warfarin to avoid excessive blood thinning. Amiodarone also can
cause thyroid disturbances in the fetus when administered orally to the
mother during pregnancy. Amiodarone also may affect thyroid function in adults.
The most severe side effect of amiodarone is lung toxicity that potentially
can be fatal. Because of this lung toxicity, patients should report any
symptoms of cough, fever, or painful breathing to their doctors.
Electrical cardioversion.
Electrical cardioversion is a procedure used by doctors
to convert an abnormal heart rhythm (such as AF) to a normal rhythm (sinus
rhythm). Electrical cardioversion requires the administration of an electrical shock over the
chest. This electrical shock stops the abnormal electrical activity of the heart
for a brief moment and allows the normal heart rhythm to take over. Although
electrical cardioversion can be used to treat almost any abnormal fast heartbeat
(such as atrial flutter and ventricular tachycardia), it is used most frequently
to convert AF to a normal rhythm.
Warfarin usually is given for 3 to 4 weeks prior to cardioversion to minimize
the risk of stroke that can occur during or shortly after cardioversion.
Warfarin is continued for four to six weeks after successful cardioversion. For
some patients requiring urgent electrical cardioversion, warfarin may not work
fast enough to thin the blood. Therefore, these patients may be given heparin prior to
electrical cardioversion. Heparin is a faster-acting blood thinner than
warfarin, but it must be administered as a continuous intravenous infusion or as
injections under the skin. After successful cardioversion, these patients can be
switched from heparin to warfarin.
1) Method of cardioversion. Electrical cardioversions (urgent and
elective) usually are performed in a hospital. For elective (non-urgent)
electrical cardioversion, patients usually arrive at the hospital without
eating in the morning. Necessary medications can be taken with small sips of
water. Patients are given supplemental oxygen via nasal catheters, and an
intravenous infusion of fluids is started. Electrodes (pads) are placed on the
skin over the chest to continuously monitor the heart rhythm. Paddles then are
placed over the chest and the upper back. Patients are sedated (anesthetized)
intravenously with medications. This is followed by a strong electric shock
through the paddles. The shock converts the AF to a normal rhythm. After
cardioversion, patients are observed for several hours or overnight to make
sure that their normal heart rhythm is stable.
2) Effectiveness of electrical cardioversion. Electrical
cardioversion is more effective than medications alone in terminating AF and
restoring a normal heart rhythm. Electrical cardioversion successfully
restores a normal heart rhythm in over 95% of patients.
3) Limitations of electrical cardioversion. While electrical
cardioversion is effective in converting AF to a normal heart rhythm, the
normal rhythm may not continue for long. Approximately 75% of patients
successfully treated with electrical cardioversion experience a recurrence of
AF within 12-24 months. Older patients with enlarged atria and ventricles who
have had AF for a long time are especially prone to recurrences. Thus, most
patients who undergo successful cardioversion are placed on oral medications
to prevent recurrences of AF.
4) Risks of electrical cardioversion. The risks of electrical
cardioversion include stroke, heart attack, burns of the skin, and in rare
instances, death.
5) Candidates for electrical cardioversion. Doctors usually
recommend that all patients with chronic, sustained AF undergo at least one
attempt at cardioversion. Cardioversion usually is attempted with medications
first. If medications fail, electrical cardioversion can be considered.
Sometimes a doctor may choose to use electrical cardioversion first if AF is
of short duration (onset within 48 hours) and the transesophageal
echocardiography shows no blood clots in the atria.
Electrical cardioversion is performed urgently (on an emergency basis) on
patients with severe and potentially life-threatening symptoms caused by AF.
For example, some patients with rapid AF can develop chest pain, shortness of
breath, and dizziness or fainting. (Chest pain in these patients is due to an
insufficient supply of blood to the heart muscles. Shortness of breath
indicates ineffective pumping of blood by the ventricles. Fainting or
dizziness usually is due to dangerously low blood pressure.)
Rate control therapy. Recent
studies have shown that an acceptable alternative
to cardioversion (chemical or electrical) is rate-control therapy. In
rate-control therapy, the doctor will leave the patients in AF provided their rate
of ventricular contractions is under good control, the output of blood from the
heart is adequate, and their blood is adequately thinned by warfarin to prevent
strokes. Heart rate in these patients can be controlled using medications
such as beta-blockers, calcium channel blockers, or digoxin or AV node
ablation with pacemaker implantation. Rate-control therapy is used to simplify
therapy and avoid the side effects of anti-arrhythmic medications (medications
used to treat and prevent AF).
Over long periods of observation, patients treated with rate-control therapy
have similar survival and quality of life as compared to patients who undergo
repeated electrical or chemical cardioversions.
Suitable candidates for rate-control therapy include:
- Patients who have had AF for more than one year
- Patients with significant disease of the heart valves
- Patients with enlarged hearts as a result of heart
failure or cardiomyopathy (heart muscle weakness)
- Patients with significant or intolerable side effects with medications for
AF
Next: Procedures for treating and preventing atrial fibrillation »
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