Atrial fibrillation (AF) is a common heart rhythm disturbance. Instead of a coordinated electrical wave there is chaotic electrical activity with individual or small groups of fibres discharging electrical pulses which do not lead to organised contraction of the atria. The heart rate is much faster than usual and completely irregular.
The atria are uneven in shape and have an area on the outer edge – the appendage- where blood flow can stagnate if the atria are not contracting. The blood clot can then leave the heart into the circulation, either during AF or when rhythm and contraction is restored, blocking blood vessels to important organs such as the brain (stroke), kidneys, bowel, or limbs. This is more likely to happen in hearts which have other forms of heart disease such as valve disease or heart failure.
Atrial fibrillation can be triggered by stimulating the vagus (vagal AF) or sympathetic nerves (adrenergic AF). Common vagal triggers include gut disturbances such as drinking cold drinks, nausea, vomiting, indigestion or abdominal pain. Athletes with high vagal nerve activity are prone to it. It is commoner in sleep when the heart rate is slower due to the effect of the vagus nerve on it. Adrenergic triggers include exercise or emotional stress and adrenergic AF is more likely during the day. We commonly see AF triggered by stresses such as infection and major surgery. Sleep apnoea is an increasingly recognised trigger of AF.
Treatment of atrial fibrillation is directed at controlling the rhythm and preventing serious consequences such as worsening heart failure or stroke. Treatments include: drugs, electrical cardioversion and curative procedures.
The two common types of rhythm treatment are intended either to keep the heart in normal rhythm – rhythm control – or slow the heart rate when in atrial fibrillation to a more normal range – rate control. The types of drugs used vary.
There are two types of drugs which lower the risk of stroke: anti-platelet (aspirin, clopidogrel) and anti-coagulant (warfarin or dabigatran) drugs. These drugs can cause bleeding as a side-effect so the type recommended depends on the relative balance of the risks of clotting versus bleeding in individual patients.
Provided there is a low chance of clot inside the heart, we commonly shock the heart back into rhythm (cardioversion) under a short general anaesthetic.
Increasingly electrical (electrophysiology) procedures are being used to prevent or cure atrial fibrillation (‘pulmonary vein isolation’ or PVI) when AF causes disabling symptoms. These relatively time consuming procedures may need to be repeated to achieve success. These may also be performed at the time of heart surgery.
Another novel procedure uses a device which is used to reduce the risk of stroke by filling the atrial appendage and avoid the need for anti-coagulant drugs (Watchman™).