Atrial Fibrillation Ablation

What is Atrial Fibrillation (AF)?

Atrial fibrillation (AF) is the most common sustained arrhythmia in humans. It is increasing in its prevalence and affects around 1% of the population at age 50 and up to 5-10% of the population by age 80. In AF, the electrical activity in the atria (hearts upper chambers) is disorganised and multiple short circuits swirl around a bit like mini-tornados across the atria. When the heart is in AF the top chambers beat so quickly that they do not effectively pump blood and blood clots can develop. For this reason an anticoagulant or ‘blood thinner’ is often recommended to reduce the risk of blood clots and stroke.

AF will cause a persons heart beat (pulse) to be irregular and will often make it very rapid (tachycardia). This can lead to symptoms such as palpitations (the sometimes unpleasant awareness of a persons heart beat), shortness of breath, dizziness, chest pain or sometimes lethargy. In patients with symptoms from AF a trial of antiarrhythmic medication is generally recommended (medications include sotalol, flecainide or amiodarone) and if this is ineffective then an ablation procedure can be performed. Studies show an ablation procedure can lead to freedom from recurrent AF in up to 80% of patients in the medium term for paroxysmal AF (episodes of AF last less than a week) and up to 60-70% for patients with persistent AF (episodes last for more than a week at a time). Some people with AF can also have other 'short circuits' such as atrial flutter (see the section on atrial flutter).

An atrial fibrillation (AF) ablation may take from 1-4 hours (usually 1.5-2 hours) depending on the technique used, whether prior ablations have been performed and the targets of the ablation. It involves access to the left atrium (via a fine needle which is passed through the inter-atrial septum under guidance) and then electrical isolation of the four pulmonary veins that return oxygen rich blood back to the heart from the lungs. Numerous studies have shown that AF is most commonly started by ectopic (extra) beats that originate in these veins. Electrical isolation of the pulmonary veins (PVI for short) can be performed by either freezing the tissue (Cryoballoon ablation), cauterising the tissue (radiofrequency of RF ablation) or Pulsed Field ablation (which uses very short bursts of current to disrupt atrial cells from conducting electricity). All of these techniques allow the pulmonary veins to function normally but no longer conduct electricity. The doctors at Hunter Heart performed the largest initial study of cryoballoon ablation in Australia on 200 patients with AF and have since performed some of the first Australian cases of Pulsed Field ablation.

In patients with persistent AF (episodes of AF last more than a week) there may be more scar tissue within the atrium itself and the AF may be started by ectopic beats outside of the pulmonary veins themselves. The use of radiofrequency ablation allows for a more flexible approach to target these areas and may be preferred in patients with persistent AF or in patients requiring a repeat procedure to adequately control their AF. The risks of an AF ablation are specific to the technique used but include a 1-2% risk of a potentially serious complication that could include a heart attack (<1:2,500), stroke (<1:400), bleeding around the heart (1:200) or atrio-oesophageal fistula (1:2,500 with radiofrequency and <1:10,000 with the cryoballoon). There is a 1-2% risk of bruising or bleeding in the groin where catheters are passed into the femoral vein to gain access to the heart and a 3% risk of phrenic nerve injury with cryoballoon ablation.

Studies such as the EAST-AFNET 4 trial (NEJM, 2020) have shown the importance of maintaining sinus rhythm (normal rhythm) in people with atrial fibrillation and studies such as CASTLE-AF (NEJM, 2018) and CAMERA-MRI (JACC, 2017) have provided strong evidence for a symptomatic and a survival benefit for maintaining normal rhythm in patients with AF and heart failure.

Managing Atrial Fibrillation Long Term

Over time it is possible to develop further scar tissue or 'short circuits' in the heart and AF can return. These episodes may be more brief and infrequent but sometimes they can be sustained as well. To reduce the risk of further AF in the future it is important to manage cardiac risk factors well such as good blood pressure control (≤130/80mmHg), achieve and maintain a healthy weight (seeing a dietitian can help with this), keep active with exercise for at least 30 minutes a day for 5 days a week, if you choose to drink then keep alcohol to a minimum (≤2 standard drinks a day for no more than 5 days a week) and look for and treat obstructive sleep apnoea with a sleep study in particular. Monitoring your blood pressure and pulse with a blood pressure monitor at home or monitoring your pulse with a smart watch that records heart rhythm traces can be useful for managing AF as well.

For further reading about atrial fibrillation (AF) please visit www.hrsonline.org/Patient-Resources or read the articles below. The Heart Rhythm Society video on youtube.com entitled ‘What is Atrial Fibrillation? Chapter 1 (HRS Patient Video)’ is also a very good patient resource.

References:

Jackson N, Barlow M, Leitch J, Attia J. Treating atrial fibrillation: pulmonary vein isolation with the cryoballoon technique. Heart Lung Circ Aug 2012;21:427-432.
Kuck KH, Brugada J, Furnkranz A, et al. Cryoballoon or Radiofrequency Ablation for Paroxysmal Atrial Fibrillation. The New England journal of medicine Jun 9 2016;374:2235-2245.
Cappato R, Calkins H, Chen SA, et al. Updated worldwide survey on the methods, efficacy and safety of catheter ablation for human atrial fibrillation. Circulation Arrhythmia and electrophysiology Feb 2010;3:32-38.

The diagram above shows a normal heart with four chambers (right and left atria at the top and right and left ventricles at the bottom). The hearts normal electrical system is shown in yellow. Electrical activity during atrial fibrillation (AF) is shown in green. It is usually started by extra beats coming from the pulmonary veins (shown in grey) and these extra beats lead to very rapid and disorganised electrical activity in the atria. The most effective treatment for AF is to electrically isolate these pulmonary veins. A related short circuit known as atrial flutter in shown in blue (see the section on atrial flutter).

The picture above shows an Arctic Front Cryoballoon® positioned against the left upper pulmonary vein with contrast injected down the catheter lumen to outline this vein. After positioning, the Cryoballoon then fills with super cool nitrous oxide down to -40 to -50 degrees to electrically isolate this vein. This process is then repeated for the other three pulmonary veins in turn.

The picture above shows X-Ray images of an atrial fibrillation ablation being performed with the Farapulse® Pulsed Field Ablation system. This is the newest technology for AF ablation and it uses multiple very short, high energy electrical pulses to disrupt the electrical conduction of the heart cells around the pulmonary veins. This technique makes AF ablation faster and more straightforward. It may also avoid injury to nearby structures around the heart such as nerves or the oesophagus.

The final picture shows how AF ablation is performed with radio-frequency (RF) energy (like cauterisation). This is the most studied ablation energy and remains the most flexible as any short circuit can be identified and targeted. For this reason the doctors at Hunter Heart favour radio-frequency ablation for repeat AF ablation procedures as the short circuits are often outside of the pulmonary veins. The top right image shows how RF energy is used to encircle the pulmonary veins (each ablation is shown as a red dot), the bottom left image shows how RF energy can be used to draw lines to block short circuits and the bottom right image shows how scar tissue can develop outside the pulmonary veins and these areas can often be treated/ablated with RF energy.