Atrial Fibrillation, or AF for short, is the commonest heart rhythm disorder in the world and estimated to affect 1-2 million people in the UK. As people age, and when other conditions such as high blood pressure develop, the heart’s ability to conduct electricity in the atria (the top heart chambers) changes and can become chaotic, called fibrillation. During AF, the atria do not contract at all and blood inside can stagnate and form blood clots. Clots can break off and make their way to the brain resulting in a stroke.
Paroxsymal (or intermittent) AF
AF usually first occurs intermittently, jumping from a normal heart beat to AF unpredictably. This is known as ‘paroxysmal AF’, and typically the heart races very fast and irregularly when the AF occurs causing palpitations, breathlessness, lightheadedness, tiredness or even loss of consciousness. But paroxysmal AF can also occur without causing symptoms in up to 25% of people. Paroxysmal AF is usually triggered by an extra heartbeat, or ectopic, from just inside one of the pulmonary veins. The pulmonary veins, of which there are usually four, carry blood back from the lungs to the left atrium. Episodes can last from seconds or minutes, to hours or days. The flipping in and out of rhythm when episodes occur can be very uncomfortable.
If an AF episode lasts longer than seven days it is called ‘persistent’. When AF lasts this long it means the electrical properties of the atria are sufficiently abnormal that they continue to fibrillate rather than return to normal rhythm. This is more likely if a patient has a history of high blood pressure or cardiac disease. The natural history of AF is for it to start off as paroxysmal and with time become persistent. However, many patients present with persistent AF without a clear history of previous attacks. If AF is persistent, treatments designed to convert and keep patients in normal rhythm are less effective than in paroxysmal AF and the longer AF has persisted, the less effective these treatment become. Although it can cause palpitations, persistent AF commonly causes tiredness, breathlessness and reduced exercise capacity. It also causes no symptoms in up to 25% of people.
Permanent AF is defined as AF that is present all the time (like persistent AF) but no efforts are made to try to restore normal rhythm, or efforts to do so have failed. Sometimes this strategy is chosen as the AF does not cause symptoms, sometimes because treatments to restore normal rhythm are deemed too risky or sometimes because the AF has been present for so long that it’s thought treatments are very unlikely to work.
Risk of stroke
The risk of stroke is the most important adverse effect of atrial fibrillation. The risk is not determined, as one might think, by the length of time you spend or have spent in AF. Rather, it is one’s overall risk for stroke that is important. This risk is calculated by using a scoring system called the CHA2DS2-VASc score.
The CHA2DS2-VASc score is an acronym. It stands for:
- ¥ C = Congestive cardiac failure (or heart failure or impaired left ventricular function)
- ¥ H = Hypertension (or high blood pressure)
- ¥ A2 = Age >75
- ¥ D = Diabetes
- ¥ S2 = Stroke or TIA (transient ischaemic attack, or ‘mini-stroke’)
- ¥ V = Vascular disease (heart attack or other arterial disease)
- ¥ A = Age >65
- ¥ Sc = Sex category (female = 1 point)
If you have or have ever had one of these conditions you score one point for each, except age >75 or stroke/TIA which count as 2 points, hence CHA2DS2VASc score.
If you have a CHA2DS2-VASc score or 1 or more, it is now recommended you take warfarin or a Novel Oral Anticoagulant for life to reduce your risk of stroke. So, if you are 65 or older and have AF, it is now recommended you are treated with an anticoagulant for the rest of your life (and not aspirin which is now known not to help and has been removed from the guidelines). The only exception is if you are female and have no other risk factors.
Control of heart rate
One of the key aspects of treatment is to prevent the heart from beating rapidly when in AF, and different medications can be used to slow the heart. These drugs are especially useful for persistent and permanent AF and often work best in combination. These include:
- ¥ Beta-blockers e.g. bisoprolol, atenolol, carvedilol, metoprolol
- ¥ Calcium channel blockers e.g. verapamil, diltiazem
- ¥ Digoxin
These drugs are also given in combination with drugs such as flecainide or propafenone to treat paroxysmal AF, to prevent AF episodes.
Medications for symptomatic AF
There are numerous medications used to try and prevent AF episodes, most of which have been available for decades. These drugs are known as anti-arrhythmic drugs and include flecainide, propafenone, amiodarone and sotalol. Medications are, unfortunately, not highly effective at maintaining normal rhythm over time, the best being amiodarone with long term success achieved in about 30% of people. Sadly, amiodarone also has the highest number of unwanted and potentially dangerous side effects (including thyroid dysfunction, lung scarring, liver damage, blue skin and excess skin sensitivity to sunlight). Flecainide, propafenone and sotalol have a very tiny risk of causing more serious heart rhythm disturbances and in rare cases dying, particularly if a patient develops heart failure or a heart attack, or exercises very strenuously. For these reasons, and to abolish symptoms, ablation is often considered to try and achieve a cure.
Electrical (DC) cardioversion
Cardioversion is a long-established technique that is designed to immediately restore normal rhythm when patients are in AF. If an electrical charge is applied across the chest when one is in AF, it resets all the cells of the atria allowing the heart’s own pacemaker to take over. This is performed under a light general anaesthetic with gel pads placed on the front and back of the chest and the ‘shock’ applied between the two. The shock only lasts a fraction of a second and is not always successful in restoring normal rhythm. If normal rhythm is restored, the shock has no further effect and the heart can flip back into AF at any time, even seconds, minutes or hours later. The chance of remaining in normal rhythm 6 months after a cardioversion is only 50% and at 5 years is only 5%.
Ablation is a technique of heating or freezing small areas of tissue within the heart to destroy to prevent abnormal heart rhythms from occurring. Although ablation for other arrhythmias was first performed in the early 1980’s, it was only developed for AF using ‘keyhole techniques’ in 1999 and only widespread around the world from the early 2000s. Since then there have been rapid and dramatic improvements in available technologies and the different techniques used with ever-increasing success rates. It is now by far the most commonly performed cardiac ablation procedure in the world. For further information, please visit www.oliversegal.com.
Unfortunately, AF almost always recurs once it has occurred once, although attacks can initially be separated by several years. Although drugs and cardioversion can keep it at bay temporarily, it is only ablation that can offer the chance of a permanent cure.
To read the full article and to see other information about AF, atrial flutter and AF ablation, please visit www.oliversegal.com