The heart has its own electrical conduction system. The electrical system usually sends an impulse from the upper chambers of the heart (atria) to the lower chambers (ventricles) to allow it to beat in a regular rhythm. Atrial fibrillation (AF) is an abnormality within the electrical system of the heart In AF, smaller chaotic impulses originating from the left atrium override the normal electrical signals within the heart leading to an irregular heart rhythm,
One in four people will develop atrial fibrillation; it affects an estimated 1.5 million across the UK and in excess of 16 million worldwide. Every 15 seconds someone suffers an AF-related stroke. AF is the most powerful single risk factor for stroke and AF-related strokes tend to be more debilitating with a higher mortality rate.
In AF the upper chambers of the heart, the atria, are not contracting properly to squeeze blood out. Blood can therefore stagnate within the heart and this may lead to the formation of a blood clot. This clot can then be carried to the small blood vessels in the brain where it may block the blood flow and causes a stroke. Not all patients with AF have an increased risk of stroke. This depends on your age and other risk factors. All patients with AF need an assessment of their stroke risk to decide whether or not blood thinners (anticoagulants) need to be started. If blood thinners are started these can dramatically reduce the risk of stroke. Aspirin has no benefit in preventing strokes in AF but does increase bleeding risk.
Some patients may spontaneously return to normal (sinus) rhythm after a short period of time. However, others may find they alternate between these two rhythms. This is called paroxysmal atrial fibrillation. In other patients if paroxysmal AF is left untreated the episodes may become more frequent and over time may evolve into persistent AF when AF is present all the time. AF is considered to be persistent if it is present for more than 7 days. However, given that up to a quarter of people with AF have no symptoms, initial presentation may be with persistent AF.
Finally permanent AF is when no further attempts to achieve a normal rhythm are considered. This may be when attempts at treatments to restore a normal rhythm have failed or there are no symptoms. All types of AF confer the same risk of stroke. Even if you have no symptoms the risk of stroke remains the same.
Atrial fibrillation can present in many different ways. In paroxysmal AF, the most common symptoms are palpitations which are often rapid and irregular. Some people may also experience dizziness and shortness of breath.
Patients with persistent AF may simply be aware of not feeling ‘quite right’, have increased fatigue or inability to perform daily activities. As the onset of persistent AF may be insidious, it is often only when patients are back in a normal rhythm that they realise how much better they feel. In some patients, there are no symptoms and the discovery of AF can be an incidental finding during a health check or when being assessed for another condition
If you experience any symptoms, you should seek medical advice. If your pulse is irregular you are likely to be sent for an electrocardiogram (ECG), which records the electrical activity of the heart. You may also be sent for blood tests and an echocardiogram- an ultrasound scan of the heart that shows how well it is working. These tests are important to look for other conditions which may have caused the AF, such as thyroid problems or heart valve abnormalities. In addition you may be fitted with a continuous ECG monitor which checks your heart through the day and night whilst you continue with your normal activities. The continuous monitoring may record episodes of AF not identified on a standard ECG.
In paroxysmal atrial fibrillation, common triggers include caffeine, alcohol, stress and lack of sleep. However many patients may experience symptoms without any particular trigger.
The priority in treatment of AF is to start blood thinners,if appropriate, to reduce the risk of stroke. AF itself is not life threatening but can be uncomfortable and often needs treatment. There are a number of different approaches, so assessment by a specialist is required to determine which approach is likely to be the most suitable for you.
Medication to control the heart rate or rhythm may be the most suitable treatment for some patients. Medications are currently still recommended as first line treatment for AF, in the UK. Almost all medications may cause side effects, but these may vary from individual to individual. Most side effects will resolve on discontinuation of the treatment. However, the side effects of certain drugs (also the most effective) may remain despite discontinuing the medication. Commonly used drugs for AF are beta blockers, flecainide, amiodarone, diltiazem and digoxin.
In patients with persistent AF, an electrical cardioversion may be useful. A cardioversion involves delivering a small electrical shock across the heart which will often restore the heart to a normal rhythm. This is done via pads on the chest and/or back under a light general anaesthesia. The procedure is very quick and safe and takes a few minutes. However a cardioversion is not a long-term treatment and most patients will revert to AF at some point. It is not possible to predict how long the heart will stay in rhythm. A cardioversion can be useful in patients who have persistent AF, to see if they notice an improvement in their symptoms when they are back in a normal rhythm. If this is the case then an ablation procedure may be appropriate.
Catheter ablation was first introduced as a treatment for AF in 1999. Since then considerable advances in technology means that it is the most common ablation procedure now performed.
Catheter ablation is a minimally invasive treatment option for patients who continue to have symptoms of atrial fibrillation despite medication, or for those patients who do not wish to take regular heart rhythm or rate controlling medications. Catheter ablation offers the prospect to improve quality of life and is the only potentially curative treatment for AF. The results of large clinical trials to establish whether ablation therapy improves outcomes and mortality in patients with AF are awaited.
In catheter ablation for AF, catheters, or fine wires, are introduced from a vein at the top of the leg and advanced to the heart. There are electrodes at the tip of the wires which detect electrical signals from different parts of the heart. Radio frequency waves are used to create heat which prevent the electrical signals that trigger AF (ectopics) from entering the heart. In persistent AF further treatment may be required in the heart chamber itself. An alternative to radio-frequency ablation is the cryoballoon. This is a technology which uses a ‘freezing balloon’ to prevent the signals that trigger AF from entering the heart.
The procedure can be performed under local anaesthetic with sedation or a general anaesthetic. It is usually performed as a day case procedure or with an overnight stay.
The success rates for AF ablation depend on the type of AF you have. Currently success rates for paroxysmal AF are approximately 80-90% and for persistent AF 60-70%. The success rates for persistent AF are lower than for paroxysmal AF as the disease process is usually more advanced.
Achieving these success rates may require more than one procedure. The ablation procedure is now performed on un-interrupted blood thinners, as we have established that this is the safest way to perform the procedure.
The ablation procedure for AF is generally very safe. The overall risks of serious complications are generally accepted to be in the region of 2-3%. These risks include, bleeding in the leg, bleeding around the heart and a very small risk of stroke (less than 1:1000). Very occasionally bleeding in the leg or around the heart requires emergency surgery. With the cryoballoon (freezing) there is a risk of damaging the phrenic nerve that supplies the breathing muscle known as the diaphragm (2%). The risk of death from an ablation procedure is very rare (less than 1:10000)