Atrial Fibrillation (AF)

In atrial fibrillation (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 atria fibrillate they often beat at ≥400 beats a minute and these very rapid impulses are conducted down to the hearts lower chambers to produce an irregular and often rapid heart beat (pulse). Some patients may have both atrial fibrillation and atrial flutter (see the section on 'Atrial Flutter') at different times.

Symptoms and Treatment

Atrial fibrillation may cause a persons heart rate to be increased (tachycardia) and 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 AF the top chambers of the heart 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.

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. An ablation procedure can lead to freedom form 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). More recent studies such as CASTLE-AF and CAMERA-MRI (on patients with AF and heart failure with impaired ejection fraction) have suggested that AF ablation can lead to improvements in heart failure and mortality as well.

An Atrial Fibrillation (AF) Ablation

An atrial fibrillation (AF) ablation may take between 1.5 and 4 hours depending on the technique used 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. Pulmonary vein isolation (PVI for short) electrically isolates these veins and can be performed by either freezing the tissue (Cryoballoon ablation) or cauterising the tissue (radiofrequency of RF ablation) around the veins. Both 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 (1). Since then the technology has advanced further and due to shorter and less complicated procedures we favour cryoballoon ablation for initial procedures in patients with AF.

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 cryoballoon ablation). 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 or rarely vagal nerve injury with cryoballoon ablation (2,3).

Following an ablation it is important to continue to maintain good cardiovascular health to reduce the chances of developing further AF in to the future. This includes keeping active (≥30 minutes of exercise a day), maintaining a healthy weight, a healthy blood pressure (≤130/80mmHg), not smoking, not drinking alcohol excessively (≤2 standard drinks on ≤5 days a week) and treating obstructive sleep apnoea (if applicable). 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:

1. 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.
2. 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.
3. 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. AF 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 either freeze or cauterize around these pulmonary veins to isolate them electrically. The short circuit that causes atrial flutter is shown in blue (see the separate section entitled 'Atrial Flutter').

The picture above shows an Arctic Front Cryoballoon® positioned against the left upper pulmonary vein with contrast injected 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 image at the top left is an X-Ray showing catheters positioned within the left atrium. The circular pulmonary vein catheter sits inside the pulmonary vein and the ablation catheter cauterises (ablates) carefully around this to electrically isolate each vein in turn. The top right is a corresponding image of the left atrium created with an electro-anatomic mapping system (guidance system for catheters). This system continuously shows the position of the catheters (without X-Ray) and every time ablation is performed a red dot is recorded to ensure the ablation is complete (there are no gaps). In the bottom left picture the left atrium is shown in an anterior view (from the front). Here ablation lesions (red dots) have been created at sites away from the pulmonary veins to treat different electrical short circuits causing atrial fibrillation (AF). The bottom right hand image shows a voltage map (or scar map) of the left atrium from behind. Healthy atrial muscle is shown in purple with scarred regions shown in red and regions with intermediate voltage shown in other colours. Left atria that have extensive scarring make AF ablation more difficult as regions of scar can contain multiple short circuits capable of causing AF.