Atrial fibrillation

Atrial fibrillation is the most commonly encountered abnormal heart rhythm. It is known to occur in 1% of the population but this is an underestimate as in many people it is intermittent and it frequently doesn't cause symptoms. It is more likely to occur as people get older. At least one in 200 over the age of 60 and one in 10 over the age of 80 are in atrial fibrillation all the time.

As the name suggests, atrial fibrillation is an abnormality affecting the atriums, the smaller, top chambers in the heart that receive blood when it returns from the body or lungs and then pump that blood through the tricuspid and mitral valves into the ventricles. During atrial fibrillation there is complete electrical chaos in the atriums, with each individual muscle fibre twitching like mad at 300 to 500 beats a minute. This means that the atriums quiver and shake and don't contract or squeeze effectively, so they don't help to pump blood into the ventricles. This loss of contractility means that there is a reduction in cardiac output (the amount of blood pumped out of the ventricles and around the body).

All of the electrical impulses bombard the atrioventricular node and try to get into the ventricles. The AV node however is able to filter some of them out, stopping the ventricles from going dangerously fast. This filtering is variable so that the impulses getting through and telling the ventricles to beat are random and chaotic, leading to the classic "irregular pulse" that can be felt. The amount of filtering determines how fast the ventricles pump. If there is not much filtering (often the case in younger people) the pulse will be faster than necessary, e.g. more than 100bpm at rest. Exercise and activity will decrease th efiltering, allowing the ventricles to go even faster even shooting up to 160-170 bpm at times. It is also possible to have too much filtering and end up with a slow pulse rate.

Atrial fibrillation has traditionally been classified by how long attacks last. Paroxysmal atrial fibrillation will stop on its own, usually lasting minutes or hours but in some instances up to 7 days. Persistent atrial fibrillation will go on and on until something is done to restore normal sinus rhythm, such as a cardioversion or ablation. Permanent atrial fibrillation is when it has been accepted that atrial fibrillation will remain forever and no attempt at restoring a normal rhythm will be made.

Atrial fibrillation often occurs in otherwise normal hearts. Some medical conditions are linked with the development of atrial fibrillation, including hypertension (high blood pressure), heart failure and thyrotoxicosis (an overactive thyroid gland). Atrial fibrillation may be precipitated by a chest infection or operation, particularly heart surgery. Some people notice an association with alcohol, particularly binge drinking, others with caffeine. Many wonder whether it is associated with stress. Often trying to avoid these potential precipitants does little good and if they are involved they are merely revealing an underlying predisposition to atrial fibrillation and are not the sole cause. There may be patterns to paroxysms in that they occur more often at night or with exercise. The genetics of atrial fibrillation are complex. If one family member has it, particularly at a young age, others may be slightly more likely to develop it but it is not considered to be an inherited condition.

The assessment and treatment of atrial fibrillation should take into account three seperate issues: symptoms, the risk of stroke and the risk of developing heart failure from tachycardia cardiomyopathy. Assessment therefore requires a history and physical examination, a 12 lead ECG and an echocardiogram. Other investigations such as a 24 hour Holter monitor, exercise test and blood tests may be necessary. Click on the buttons below to learn more about assessing and treating atrial fibrillation.

Tachycardia cardiomyopathy is a rare consequence of atrial fibrillation. It can only happen if the ventricles beat faster than 110 bpm constantly, day and night. In some people this constant rapid rate can gradually waer out the ventricular muscle, causing the left ventricle to dilate, enlarge and weaken. After a few weeks it can weaken so much that heart failure develops, with breathlessness, difficulty lying flat at night, fatigue and water retention. To get to this state, people are usually unaware of the arrhythmia and have no palpitations or other atrial fibrillation symptoms. Eventually they see their doctor for the heart failure symptoms and then the atrial fibrillation is diagnosed. Fortunately the heart failure and heart muscle weakness can be reversed and returned to normal by slowing down the heart ratem, ideally by restoring normal sinus rhythm. This can be done using rate controling drugs, cardioversion or ablation.

For most people the two main issues to address are symptoms and stroke prevention. Click on each button below to find out more.

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