Atrial Fibrillation Ablation

General Information

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.

  • 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 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.

  • 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.

DC Shock. 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 back from the top part of the body back to the heart) and infrequently the inferior vena cava (vein draining blood back 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.

Linear Ablation

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.


  • Professor Sanders says...

     
    Atrial fibrillation is a consequence of several reversible risk factors - high blood pressure, diabetes, obesity, sleep apnoea, and excessive alcohol. Your management of atrial fibrillation must include strict control of these risk factors.

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