Atrial fibrillation

Atrial fibrillation (AF) is the most common type of arrhythmia with irregular and often fast heart beat, affecting 500,000 people in the UK. Normally, heart beats approximately 60-100 times per minute whereas in untreated AF the pulse is often 100-150 beats per minute. Depending upon the duration and severity, AF can be classified in several categories:


  • Paroxysmal atrial fibrillation - Occasional episodes of irregular heart beat lasting usually minutes or hours. Paroxysmal AF lasts not more than 7 days (usually around 48 hours) and terminates spontaneously without any treatment.

  • Persistent atrial fibrillation - Persisten AF lasts for more than 7 days and does not revert back to normal heart rhythm spontaneously without treatment. It may recur after successful treatment.

  • Permanent atrial fibrillation - The heart rate remains irregular, does not revert back to normal sinus rhythm and there are no further attempts on cardioversion.

Mechanism of AF

In AF, atria (the upper two chambers of the heart) contract randomly and erratically which does not allow proper filling of the heart with blood affecting the pumping function similarly to an engine running half-empty. Symptoms of AF include dizziness, tiredness, shortness of breath and sometimes unpleasant awareness of heart beats (palpitations). However, many patients may remain asymptomatic and AF is often diagnosed incidentally during a routine medical check.

Why it happens

AF occurs when abnormal electrical impulses override the heart's natural pacemaker (sinus node) which then loses control over the heart leaving it to beat irregularly. Gradually, over time the electric and mechanical properties of the heart muscle change (remodeling) perpetuating the arrhythmia.

Who is at risk?

AF can affect any adult at any age but it is more common in men and in the elderly. AF affects 10% of population above 75 years of age. AF is common in people with high blood pressure, valve disease and coronary artery disease. AF can triggered by hyperactive thyroid and by excessive alcohol intake especially in combination with heavy physical exercise. Interestingly, AF is also relatively common among endurance sportsmen.

complications

The most feared complication of AF is a stroke. Irregular heart beat in AF leads to sluggish blood flow in the upper heart chambers. The stagnation of blood predisposes to the formation of small bloods clots. If the blood clots get dislodged from heart, they may end up stuck in the small vessels of the brain. The blood clots then block off oxygen supply to the brain and lead to ischaemic stroke.
The risk of stroke can be quantified with CHA2DS2-VASc score. This acronym is made up of risk factors: congestive heart failure, age>75 years, diabetes, stroke/TIA, vascular disease, age>65 and sex category, i.e. female gender. Each risk factor counts for 1 point, only age>75 and history of stroke/TIA count for 2 points. Treatment with blood thinning medication (anticoagulation) is usually recommended in CHA2DS2-VASc score 1 or more in men and 2 or more in women.
AF may also precipitate heart failure and angina through the uncoordinated contraction of the heart muscle and reduced cardiac output. 

Prognosis

AF is not an immediately life-threatening condition; however, it causes unpleasant symptoms, increases risk of stroke and long-term mortality. Patients with atrial fibrillation need basic blood tests to rule out low blood count (anaemia), infection, impaired kidney function and hyperactive thyroid. Echocardiogram (heart ultrasound) is usually carried out to exclude an underlying structural problem. 
Medication in AF is used to control heart rate (beta blockers, calcium channel blockers, digoxin), heart rhythm (antiarrhythmics, e.g. flecainide, dronedarone, amiodarone) and to reduce risk of stroke (anticoagulants, i.e. blood thinning medicines, i.e. warfarin or one of new oral anticoagulant drugs, NOACs, such as apixaban, rivaroxaban, edoxaban and dabigatran).

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