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The radio frequency catheter
ablation procedure
The
need for radio frequency catheter ablation is assessed on an individual basis,
according to the type of lesion in the heart; the risk to the patient; the
patient's age; and the kinds of symptoms the patient has displayed.
Just
before the radio frequency catheter ablation procedure, patients usually stop taking
medications used to try and control their condition (such
as beta-blockers, calcium channel blockers, digoxin and antiarrhythmia drugs).
This is because on the day of the procedure, the electrophysiology (EP)
doctor often needs to trigger an episode of the electrical
disturbance in order to determine what type it is and where it is
coming from.
After
discussing the procedure and giving informed consent, the
patient is brought to the EP laboratory. Local anaesthetic (or in a few cases, general
anaesthetic) is used before the catheters (long wires) are inserted in the groin and perhaps
also the side of
the neck, the elbow, or the area under the collarbone. 3 to 5
catheters are often used simultaneously, in order to trigger and map electrical
disturbances in the heart.
Once
catheters are in the veins or artery, x-ray is used as they are
moved toward the heart and positioned in strategic locations. With
the catheters in place, recordings
of the heart’s electrical activity can be made from inside the heart.
By deliberately triggering an electrical disturbance, and then analysing the
recordings of this disturbance, it is possible to locate which tissues in the
heart are responsible for the electrical disturbance. This process is
called mapping. A special ablation catheter is then maneuvered
so that an electrode at its tip is in contact with the abnormal tissue.
At
this point, radio frequency energy is turned on and, if the special
ablation catheter
location is correct, the abnormal heart tissue is eliminated (ablated). The
delivery of radio frequency energy causes the tissue in direct contact with the electrode at the tip of the
special ablation catheter to be heated. Deeper tissues are also
heated by conduction of heat from this region. The size of the area to be
eliminated (ablated) is determined by the balance between conduction of heat
through the tissue and convective heat loss to the blood pool. The temperature
at the electrode must be approximately 50°C or higher to destroy the tissue.
After
ablation of tissue, testing
is performed to see if the problematic electrical disturbance can be triggered
again by the catheters. If it is still present, the process of mapping
continues to locate further abnormal tissue, which is in turn eliminated
(ablated). This 'mapping and ablation' continues until the
electrical disturbance can no longer be triggered by the catheters, whereupon
the catheters are withdrawn from the body. The procedure usually
takes 2 to 4 hours.
After
the radio frequency catheter ablation procedure
Patients
are observed for a few hours for symptoms, rhythm problems, and
bleeding from the areas where tissue ablation took place. In many cases, at
the end of this observation period they may be discharged. Others
stay overnight in the hospital. Aspirin is often prescribed for 2 to
4 weeks to minimize risk of clot formation at ablation sites.
Patients can perform light activity (e.g. walking, stairs) almost
immediately in most cases, with resumption of full work or school
activities within a few days. A follow-up visit to the doctor is
often useful to check the ablation sites and review the procedure.
Possible
complications of radio frequency catheter ablation
Radio
frequency catheter ablation has an extremely high success rate of around 90-95%
for SVT, WPW, atrial flutter and VT. Because the procedure uses x-ray,
there is a certain amount of exposure to radiation. However, the x-ray
part of radio frequency catheter ablation is often less than 60 minutes, and the
radiation risk is considered to be low - almost as negligible as the radiation
risk from x-ray procedures for broken bones. Complications occur
in about 3% of ablation procedures, though this rarely results in the death of
the patient.
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