Atrial Fibrillation Ablation
How does Atrial Fibrillation occur?
Atrial fibrillation is due to the development of electrical short circuits inside the top chambers of the heart. Usually these short circuits begin in the top chamber on the left (left atrium). These rapid short circuits have several consequences:
The short circuits drive the pumping chambers very rapidly and erratically. This produces palpitations, shortness of breath, and tiredness. In some people it can also cause dizziness and chest pain. Occasionally, these may result in blackouts or heart failure.
The short circuits result in ineffective pumping of the upper chambers. This leads to slow blood flow in both of these upper chambers (the left and right atria). This can rarely cause blood clots and possibly stroke. The reason you are taking warfarin is to thin the blood to prevent a stroke. If you were not taking warfarin, the risk of stroke would be 5-8 fold greater than a person your age without atrial fibrillation.
This risk may be even greater if you have some form of heart disease. Warfarin is to date the most effective drug available for reducing your risk of stroke by 60-70%. It is important that your INR is maintained between 2 and 4. You will need to see your General Practitioner for regular blood tests to ensure that your warfarin is maintained within these limits.
WHY DOES ATRIAL FIBRILLATION OCCUR?
In the majority of people who develop atrial fibrillation the cause is not known. Usually the heart is otherwise sound. In some people, atrial fibrillation can develop due to other conditions such as high blood pressure, prior heart attack or leaky heart valves. Increasingly newer risk factors for the development of atrial fibrillation are emerging.
WHAT TREATMENTS ARE AVAILABLE FOR ATRIAL FIBRILLATION?
There are essentially 2 strategies for the treatment of atrial fibrillation.
(1) Rate Control: To control the ventricular rate to prevent deterioration in the functioning of the bottom chambers (main pumping chambers) of your heart and maintain blood thinners (warfarin). This can involve:
- various medications that can slow the ventricular rate down.
- An ablation procedure whereby the AV node is ablated (destroyed) and a pacemaker is inserted. Due to the risk that atrial fibrillation may cause blood clots in the heart, most patients with this heart rhythm disturbance will require blood-thinning medication to prevent blood clots forming. At your doctor’s discretion this may either be with aspirin or warfarin.
(2) Rhythm Control: Therapies aimed at trying to maintain normal rhythm. This may involve medication. In some people these medicines can be very effective. In others however, the medications are ineffective and may produce side effects. If you elect to take medication, your doctor will discuss the different options and the possible side effects of these medications.
When the heart is in fibrillation it can be reverted to the normal rhythm with a “shock on the chest”. You receive a short general anaesthetic and the shock reverts the rhythm to normal in the majority of cases. With this approach the possibility of the fibrillation returning remains present (approximately 50% of patients will have another episode of atrial fibrillation over the next year). In addition, most patients will also require medication to try to prevent the fibrillation coming back. Increasingly, procedures are being developed and used for the cure of atrial fibrillation. However, these do have several associated risks and are not suitable for all patients. You should have had this option discussed. This information sheet is primarily related to information on this procedure.
PRIMARY ABLATION OF ATRIAL FIBRILLATION
For many years it was considered that there could be no effective means to permanently eliminate atrial fibrillation and restore normal rhythm (sinus rhythm). However, in the early 90’s, surgical teams demonstrated that by “slicing and dicing” the atria and then sewing it back together that they could effectively eliminate atrial fibrillation. However, the procedure itself was extremely invasive and resulted in significant morbidity that it could not be routinely used in patients. In the late 90’s further hope was provided with the recognition that activity from the pulmonary veins (veins at the back of the heart bringing blood back to the heart from the lungs) were the ones that initiated atrial fibrillation in most situations (>90% of cases). This has led to ablation strategies targeting the pulmonary veins in a bid to cure atrial fibrillation.
There have been a variety of ablation strategies that have been proposed but effectively they have all merged into quite a similar procedure. It has also become clear that while pulmonary vein ablation alone is highly effective in a select group of patients with short episodes of atrial fibrillation and normal hearts, further ablation – called substrate modification – needs to be performed in the remainder to achieve a similar degree of success.
WHAT IS RADIOFREQUENCY ABLATION (RFA)?
Radiofrequency ablation is the most common means of ablation used around the world today. It is a low power, high frequency energy that causes a tiny region of the heart near the tip of the catheter to increase in temperature, thus ablating (or cauterising) a small area of abnormal tissue. Radiofrequency energy has been used for decades by surgeons to cut tissue or to stop bleeding. For the treatment of palpitations, a much lower power of radio-frequency energy is used.
THE ABLATION STRATEGY
Pulmonary Vein Isolation
Ablation is performed around the entire circumference of the pulmonary vein to disconnect all the electrical connections between the vein and the heart. Effectively it creates a layer of insulation that prevents any abnormal electrical impulses from the pulmonary vein interacting with the heart to initiate or maintain atrial fibrillation. This step is performed in all patients undergoing ablation of atrial fibrillation.
Isolation of Other Thoracic Veins
While the pulmonary veins are recognised to be the main source of electrical activity that initiates and maintains atrial fibrillation, the other veins that lead into the heart can also be involved. This is increasingly recognised as potential sites that maintain longer episodes of atrial fibrillation particularly in those with other heart disease. These veins are the coronary sinus (the main vein of the heart), the superior vena cava (vein draining blood from the top part of the body back to the heart) and infrequently the inferior vena cava (vein draining blood from the bottom part of the body back to the heart). These veins can be isolated in a similar manner to the pulmonary veins, effectively insulating these regions from the heart. These steps are performed if we observed extra beats from these structures or if you have longer episodes of atrial fibrillation or have other heart abnormalities.
This is probably the most common form of substrate modification performed to date. Essentially ablation is performed joining anatomical structures (such as two pulmonary veins or the pulmonary vein to the mitral valve). This results in an obstruction to electrical conduction and encourages atrial fibrillation to terminate. There may also be other potential reasons why such ablation works. Linear ablation will be performed if you have longer episodes of atrial fibrillation or in those with other heart abnormalities.
Other Forms of Substrate Modification
Several other forms of substrate modification methods have been suggested and may be variably used during your procedure. You may have read about some of these, which include ablation of complex and fractionated atrial electrograms (CFAE ablation), ablation of dominant frequency sites (DF ablation), and ablation at sites eliciting a vagal response. There is a variable amount of information supporting each of these techniques, but they are used in many patients with longer durations of atrial fibrillation and those with other heart abnormalities.
WHAT HAPPENS DURING THE ABLATION PROCEDURE?
You will usually be admitted to hospital on the day of your procedure. You will be required to fast for at least six hours before the procedure. Prior to the procedure you will be required to have an ECG. Once in the Electrophysiology Laboratory (EP lab) you will be given a light sedative and your groin will be shaved. The EP lab has a patient table, X-Ray tube, ECG monitors and various equipment. The staff in the lab will all be dressed in hospital theatre clothes. Many ECG monitoring electrodes will be attached to your chest area and patches to your chest and back. These patches may momentarily feel cool on your skin.
A nurse or doctor will insert an intravenous line usually into the back of your hand. This is needed as a reliable way to give you medications during the procedure without further injections. You will also be given further sedation if and as required. You will also have a blood-pressure cuff attached to your arm that will automatically inflate at various times throughout the procedure. The oxygen level of your blood will also be measured during the EP study and a small plastic device will be fitted on your finger for this purpose. Your groin area and possibly your neck will be washed with an antiseptic cleansing liquid and you will be covered with sterile sheets leaving these areas exposed.
In general, the ablation procedure is performed under conscious sedation. There are many advantages to this as it allows evaluation for the presence of rare complications such as stroke (which is crucial to detect as early as possible). However, it means that we must adjust the degree of pain relief and sedation based on how you are feeling. A nurse will be checking with you on the degree of discomfort that you may be experiencing. It is important that you mention any discomfort to them. Occasionally, for medical reasons or at your preference, the procedure is performed under general anaesthesia. This will be discussed with you before the procedure.
If the procedure is performed under local anaesthetic, the doctor will inject the anaesthetic to the area in the groin where the catheters are to be placed. After that, you may feel pressure as the doctor inserts the catheters but you should not feel pain. If there is any discomfort you should tell the nursing staff so that more local anaesthetic and sedative medication can be given. Occasionally it is also necessary to place a catheter in a vein in the side of the neck.
The catheters are positioned in your heart using X-Ray guidance. Once the catheters are in place you may feel your heart being stimulated and usually your abnormal heart rhythm will be induced. Radiofrequency ablation will be applied to the regions discussed above.
The duration of the procedure is quite variable. In general, pulmonary vein isolation takes between 1 and 3 hours while additional ablation will prolong the procedure further. In cases of permanent AF this may be considerably longer.
WHAT IS THE SUCCESS RATE OF THE PROCEDURE?
The success rates of ablation are variably described around the world. In general, the success rate of the procedure at present is approximately 70% having no arrhythmia and without using antiarrhythmic drugs at 12 months after the procedure. These figures are much better in patients with short episodes of atrial fibrillation and normal hearts where it is between 85% and 90% and slightly worse in patients with permanent atrial fibrillation. It should be noted that approximately 1/3 of patients will require more than 1 ablation session and this improves the success further. This is either because there is recovery of previously ablated regions or that a crucial region was not ablated during the previous session. We will not know for certain whether the procedure has been successful until several months afterwards.
Sometimes it is necessary to perform a second or more procedures in order to cure the problem. This will obviously be decided later on after further discussion with you.
Ablation of paroxysmal atrial fibrillation has been undertaken in its current form since 2000. The group that pioneered the techniques has only presented long-term data out to 5 years. This data suggests that if you remain without any arrhythmia over the first 12 months you had a good chance of remaining in normal rhythm at 5 years.
To date there have been two studies that have suggested that this procedure improves survival compared to using medications. These studies need to be interpreted with caution in that they were both single centre experiences and were not randomised study designs. Similarly, there has been no data on stroke risk reduction after an ablation procedure. The cessation of warfarin will be discussed on an individual basis with you after the procedure. With this in mind, the decision to undertake atrial fibrillation ablation is primarily for symptom control.
WHAT ARE THE RISKS OF AN ATRIAL FIBRILLATION ABLATION PROCEDURE?
Radiofrequency ablation for atrial fibrillation has been developed since 2000. It is therefore quite a new procedure and techniques are continuing to improve. Although most people undergoing radiofrequency ablation do not experience any complications, you should be aware of the following possible risks (all of these will be discussed with you). In general, it has been estimated that the risk of any complication is between 4% and 6%. While much of this is related to complications related to access into the vein (local bleeding, blood clot or haematoma – large bruise), there can be more serious complications (1-2%). Some of these are listed below.
- Damage to the heart wall or artery (this may require urgent open heart surgery to correct)
- Pulmonary vein stenosis (narrowing the blood vessels that enter the left atrium)
- Heart attack
- Damage to the oesophagus (the swallowing tube) as it passes next to the heart. This is thought to be a very rare complication but is often fatal.
- Damage to the gastric nerve or phrenic nerve
- Direct trauma to the lung or airways
- Death – the risk is not known. The risk would be estimated at approximately 1 in 1000
- Rapid abnormal heart rhythm – in some cases a small electric shock may be required to restore your normal rhythm
- Pacemaker – there is a very small chance of damage occurring to the heart’s normal electrical system. This may be temporary, but permanent damage would result in a pacemaker being inserted at the time of the procedure. This would be very unlikely during this type of procedure.
DO I NEED TO UNDERGO THIS PROCEDURE?
Atrial fibrillation ablation is designed to cure your symptoms and improve your quality of life. However, because the procedure carries a small risk of a major complication we recommend it only to those people having frequent episodes of atrial fibrillation that are having a major impact on their quality of life. We do not recommend the procedure for people who have minor or no symptoms or who feel that the condition represents only a relative minor nuisance. We would also always recommend a trial of medications first as some people will be well controlled on tablets.
If there is any chance you may be pregnant, please notify the Cardiovascular Centre and the hospital before your procedure. The procedure is associated with additional risks if you are pregnant.