Treatments for Atrial Fibrillation (AF)
- Rate Control and Rhythm Control for AF
- Pulmonary Vein Isolation
- Catheter ablation for Paroxysmal Atrial Fibrillation
- Pulmonary Vein Isolation (PVI)
- How is Catheter Ablation achieving Pulmonary Vein Isolation performed?
- Point-by-point ablation (3D mapping systems)
- Cryo-ablation for AF
- Laser Balloon Ablation for AF
- Success Rates for Ablation of Paroxysmal AF
Rate Control and Rhythm Control for AF
- Rate control - drugs to slow down heart rate and/or
- Rhythm control, including:-
- Drugs to prevent AF from happening (called anti-arrhythmic drugs)
- Electrical cardioversion (also known as shocking the heart)
- Catheter ablation – to try and cure atrial fibrillation
Unfortunately, medications to prevent or suppress AF (anti-arrhythmic drugs) do not work particularly well. Many drugs have been tried over the years, but the ones currently used most commonly include flecainide, propafenone and sotalol. The most successful drug, amiodarone, causes multiple side-effects with long term use including lung fibrosis, liver and thyroid gland derangement, eye problems, skin sensitivity to sunlight and blue skin discolouration. It is now (or at least should be) rarely used to treat AF and even this drug has a success rate of only 30% at best.
Pulmonary Vein Isolation
It is because drugs work so poorly that doctors sought better alternatives and about 15 years ago worked out how episodes of AF are triggered and how to perform catheter ablation to stop this. This heralded the era of pulmonary vein isolation.
Catheter ablation for Paroxysmal Atrial Fibrillation
Single extra heart beats, known as ectopics, arising from the pulmonary veins (these are the veins at the back of the heart that take blood from the lungs to the heart) trigger AF episodes in the majority of patients. If an electrical barrier is formed around these veins, episodes of AF in the majority of people will fail to start. Pulmonary vein isolation (or PVI for short) is a procedure in which such a barrier is created.
Pulmonary Vein Isolation (PVI)
PVI can be performed using catheters (fine wires) introduced from the top of the leg in a key-hole procedure or surgically, either by endoscope with instruments inserted through small holes in the chest or with open heart surgery by cutting the chest open to expose the heart. There are also techniques in which surgery and key-hole techniques are combined (known as hybrid operations). Once the heart has been accessed, ablation is performed to destroy the tissue around the entrance to the pulmonary veins. There are different options for ablation energy too, including radiofrequency energy (a bit like microwave energy) to cauterise tissue, cryo-ablation (when the tissue is frozen to very low temperatures) and laser (laser energy causes tissue heating just like radiofrequency energy). Catheters are guided by the use of x-rays, 3-dimensional mapping systems (which create computerised 3D images of the left atrium and show the catheters moving in real-time inside them), direct vision (using an endoscope with the laser baloon catheter) and sometimes ultrasound (echo).
There are claims from the manufacturers of the different ablation technologies of superiority over others but it appears, thus far, overall success rates and complication rates are broadly similar. Different physicians favour different methods of pulmonary vein isolation and will have different experience using these methods. The key with any medical procedure is that the physician gets reproducible and reliable results with the methods they use with acceptable levels of complication rates.
How is Catheter Ablation achieving Pulmonary Vein Isolation performed?
This procedure can be performed under local or general anaesthetic. The latter means the patient feels no pain or discomfort. Sedation is given if the former is used. Most physicians will perform a trans-oesophageal echocardiogram (TOE) at the start of the procedure. This involves passing a tube into the oesophagus (gullet) which takes detailed ultrasound pictures of the heart. The images are scrutinised to exclude a pre-existing clot within the heart, particularly the left atrial appendage. The procedure is abandoned if a clot is found and often anticoagulant treatment modified before trying again at a later date.
If the TOE is clear, catheters are inserted (minimum usually two) through the large vein(s) in the groin and are advanced through the veins up to the heart using x-ray guidance. Once in place, access to the left atrium is achieved by a procedure called trans-septal puncture. This involves passing a needle across the wall in the middle of the heart between the atria. This can be guided directly by TOE if general anaesthetic is used.
Point-by-point ablation (3D mapping systems)
Once inside the left atrium, catheters are navigated around the left atrium to create a 3D computerised image of the entire chamber. This also shows the catheters moving in real time inside it. This image shows the pulmonary veins and their entrances and it is then a matter of manipulating the ablation catheter tip around the vein entrances to ablate tissue and create an electrical barrier.
The tip of the ablation catheter is heated using radiofrequency energy but at the same time cooled, using saline irrigation to ensure the heat dissipates into heart tissue and not the blood, thereby reducing the risk of clot formation and stroke. Additional catheters help to confirm that electricity cannot pass from the heart into the vein or vice-versa – known as bidirectional block.
Cryo-ablation for AF
Once inside the left atrium, the cryo-balloon is inflated and advanced into the entrance of each pulmonary vein sequentially. Once inside, dye (contrast medium) is injected into the vein to confirm a tight seal of the balloon. The liquid inside the balloon is then rapidly cooled down to -70°C. This aims to freeze the tissue around the entrance to each vein all in one go, achieving pulmonary vein isolation with a single delivery of ablation (lasting 3-4 minutes).
Care must be taken when freezing the right sided veins due to their proximity to a nerve called the phrenic nerve. This nerve supplies the diaphragm under the right lung and is therefore very important for breathing. It can be inadvertently injured during cryo-ablation and therefore most physicians will pace the phrenic nerve using an additional catheter while cryo-freezing the right veins to monitor phrenic nerve function. Additional catheters help to confirm electricity cannot pass from the heart into the vein or vice-versa as with point-by-point ablation (bidirectional block).
Laser Balloon Ablation for AF
The laser balloon is used in a somewhat similar way to the cryo-balloon. However, rather than deploy a circle of energy around the vein entrance all in one go, a small arc of laser is fired on to a small piece of atrial tissue and slowly moved around each individual vein entrance to create a continuous circle. This process is guided by directly visualising the inside of the heart using a very thin endoscope. As with cryo-ablation, there is a risk of injury to the right sided phrenic nerve and physicians will monitor its function whilst administering laser to this area. Additional catheters help to confirm electricity cannot pass from the heart into the vein or vice-versa as with point-by-point ablation (bidirectional block).
Success Rates for Ablation of Paroxysmal AF
A complete cure of paroxysmal AF can probably be achieved in about 50% of patients at 5 years after ablation without the need to take anti-arrhythmic drugs. However, at least 50% of patients will need 2 (possibly more) procedures to achieve this. Although this sounds rather poor, a much larger proportion of patients will probably remain free of AF, or largely free of any symptoms of AF, for at least 1-2 years after the procedure (80-90%) and many others will be AF free if they take antiarrhythmic medications.
Unfortunately, the ageing process continues after ablation and it is thought this causes recurrences of AF with time. There is no reason ablation cannot be repeated in the future and it is clear some patients require repeat ablation every few years to keep them free of symptoms. Others may be cured after a single procedure and yet others will never achieve a cure despite multiple attempts. The most critical factors in determining whether someone is cured with ablation is how long a person has had AF, the shorter the better, and how big the left atrium is. If the left atrium is only normal sized or only mildly dilated, this bodes well for the success of catheter ablation.
See - Complications from Catheter Ablation for Paroxysmal Atrial Fibrillation (PAF)
