Atrial Fibrillation (cont.)
Procedures for treating and preventing atrial fibrillation
After successful cardioversion many patients (up to 75%) may experience
recurrence of AF within 12 months. Therefore, many patients will need long-term
treatment with medications to prevent a recurrence of AF; however, medication(s)
are effective only 50%-75% of the time in preventing recurrence. Moreover, many
patients cannot tolerate the side effects of long-term medication. For these
reasons, several procedures have been developed to treat and prevent recurrence
of AF; they include:
- Ablation of the AV node with implantation of a
pacemaker
- Implantation of a pacemaker
- Implantation of an atrial defibrillator
- Maze procedure
- Isolation of the pulmonary vein
Ablation of the AV node with implantation of a pacemaker. Ablation of
the AV node is a procedure that destroys the AV node so that the atrial
electrical discharges cannot pass through the AV node to activate the
ventricles. The procedure usually is performed in a cardiac catheterization unit
or an electrophysiology unit of a hospital.
1) Procedure. For ablation of the AV node, patients are given a local
anesthetic to minimize pain and are mildly sedated with intravenous medications.
Using x-ray guidance, a wire (catheter) is inserted through a vein in the groin
to reach the heart. Electrical recordings from inside the heart help to locate
the AV node. The AV node is destroyed (ablated) using heat delivered by the
catheter. After successful ablation of the AV node, electrical discharges from
the atria can no longer reach the ventricles. Destruction of the AV node
(whether by catheter ablation or by disease that occurs with age) can lead to an
excessively slow rate of ventricular contractions (slow heart rate). Therefore,
a pacemaker is implanted in order to provide the heart with a minimum safe heart
rate.
2) Benefits of ablation of the AV node. The benefits of ablation of
the AV node and implantation of a pacemaker include:
- resumption of a regular heart rate (even though a
pacemaker may be determining the heart rate)
- relief from palpitations, fainting, dizziness, and
shortness of breath
- ability to stop medications and avoid their potentially serious side
effects
3) Risks of ablation of the AV node. Potential complications of
ablation of the AV node and permanent implantation of a pacemaker
include bleeding, infection, heart attack, stroke, introduction of air into the space
between the lung and chest wall, and death. Still, this technique has helped
many patients with severe symptoms to live normally.
4) Candidates for ablation of the AV node. Candidates for ablation of the AV
node are patients with AF who respond poorly to both chemical and electrical
cardioversion. These patients experience repeated relapses of AF, often with
rapid rates of ventricular contractions despite medications. Ablation also may
be an option for patients who develop serious side effects from the medications
that are used for treating and preventing AF.
5) Limitations of ablation of the AV node. Ablation of the AV node only
controls the rate with which the ventricles beat. It does not convert AF to
normal rhythm. Therefore, blood clots still can form in the atria and patients
are still at risk of strokes. Thus, there is a need for long-term
anticoagulation in addition to the permanent pacemaker.
Pacemakers. Permanent pacemakers are battery-operated devices
that generate electrical discharges that cause the heart to beat more rapidly
when the heart is beating too slowly. Recent studies suggest that some patients
with recurrent paroxysmal AF can benefit from the implantation of a
permanent pacemaker. Although the reasons for this benefit are unknown, regular
electrical pulses from the pacemakers may prevent the recurrence of AF. Furthermore,
newer pacemakers that can stimulate two different sites within the atria (dual
site atrial pacing) may be even more effective than standard pacemakers in
preventing AF. Nevertheless, permanent pacemaker implantation cannot be
considered as standard non-medication treatment for AF.
Implantable atrial defibrillators. Implantable atrial defibrillators
can detect and convert AF back to a normal rhythm by using high-energy shocks.
By detecting AF and terminating it quickly, doctors hope that these devices will
prevent recurrences of AF over the long term.
Atrial defibrillators are surgically implanted within the chest under local
anesthesia. These devices deliver high-energy shocks to the heart that are
somewhat painful. Atrial defibrillators are not useful in patients with chronic
sustained AF and are suitable only for patients with infrequent episodic attacks
of AF.
Maze procedure. Many doctors believe that the atria cannot fibrillate
if they are sectioned into small pieces so that the conduction of the electrical
current through the atria is interrupted. During the Maze procedure, numerous
incisions are made in the atria to control the irregular heartbeat and restore a
regular rhythm to the heart.
1) Procedure. The Maze
procedure is most commonly performed via open-heart surgery.
Some electrophysiologists (doctors specially trained to treat abnormalities
of rhythm) are now attempting to perform the Maze procedure using
catheters inside the heart that are passed through a vein in the groin
without open-heart surgery. Unfortunately, the success rate using the catheter
is below 50% and complications (such as strokes) may occur.
2) Effectiveness of the Maze procedure. The Maze procedure done
surgically (using open heart surgery) has been reported to correct AF in
90-99% of patients. Only 15-20% of the patients need a pacemaker after
surgery, and there is only a 30% chance of requiring long-term medications to
maintain a normal rhythm.
3) Risks of the Maze procedure. The surgical maze procedure involves
open-heart surgery and the pumping of blood by an external bypass pump while
the surgery is performed, much like patients undergoing cardiac bypass
surgery. The complications are not insignificant and include stroke, bleeding,
infection, and death. Therefore, doctors usually do not recommend a surgical
Maze procedure for the treatment of AF unless the patient is undergoing
open-heart surgery for another condition (such as for coronary artery bypass
or replacement or repair of a diseased heart valve).
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