Atrial fibrillation (AF) refers to irregular atrial contraction, caused by chaotic impulses.
AF is increasingly common, NHS studies indicate a prevalence of 1-2% in the UK. It is a major cause of morbidity, in particular stroke, which is largely preventable with appropriate anticoagulation.
AF can be classified as paroxysmal, persistent or permanent:
A large number of conditions may predispose too AF.
Despite the range of risk factors and causative conditions, common changes to the electrophysiology of the heart may occur.
Atrial myocardium has a number of interesting electrophysiological properties. It possesses a short action potential with a refractory period that reduces with an increasing rate.
These properties permit rapid contraction.
As mentioned, AF is caused by disruption of the electrophysiology in the atrial myocardium. Many mechanisms have been proposed with varying degrees of evidence to support their existence. Most likely, they occur simultaneously.
Two of the most commonly discussed mechanisms are:
Ultimately, the physiological sinoatrial node rhythm is superseded by these rapid and chaotic impulses.
The only sign of AF may be an irregularly irregular pulse.
Always consider the clinical features of potential underlying causes. AF may also present with an embolic event (stroke or mesenteric ischaemia) or signs of heart failure.
Patients should be investigated for AF if clinically suspected or if presenting with possible complications of AF (e.g. syncope, strokes, TIA).
Atrial fibrillation is characterised by an irregularly irregular rhythm, absent P waves and fibrillating baseline.
The CHA2DS2-VASc score assesses stroke risk in patients with AF.
NICE categorise CHA2DS2-VASc scores as:
NICE CG 180 recommend anticoagulation in all patients with a score of 2 or more. It should be considered in men with a score of 1. In women with a score of 1 due to gender, NICE do no consider this an indication for treatment.
The HAS-BLED score helps the identification of those at risk of significant bleeding on anticoagulation therapy.
A point is given for each of the following factors shown. HAS-BLED can be used to remember the factors though this does combine drugs and alcohol, as well as abnormal liver function and abnormal renal function to make it fit. The prescence of each of these factors scores an individual point.
Management of AF may be achieved with rate or rhythm control.
Underlying causes should be identified and treated. Patients may be anticoagulated to reduce the risk of thrombo-embolic events.
Most common type of management. Aimed at controlling rapid heart rate.
First line therapies:
Cardioversion is aimed at reverting the heart back to a normal (sinus) rhythm.
Decision made by specialists, may be indicated when:
There are two forms of cardioversion:
In new-onset AF establishing time of onset is important. Firstly, ventricular rate should be appropriately controlled. If onset < 48hrs, immediate cardioversion can take place. If > 48hrs or timing is uncertain, anticoagulation (for at least three weeks) is required before cardioversion. This is due to potential thrombus generation in the atrial appendage.
Anticoagulation may take two main forms:
If the above are contraindicated dual anti-platelet therapy (aspirin and clopidogrel) may be used. Aspirin or clopidogrel monotherapy is no longer advised.
Catheter and surgical ablation therapy offers an additional treatment option. NICE recommends its use when drug treatment has failed. The potential risks and benefits should be discussed with the patient. It is a complex procedure requiring mapping of circuits and can fail.
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