Atrial fibrillation Flashcards
Atrial fibrillation (AF)
Atrial fibrillation (AF) is a supraventricular arrhythmia of the heart in which there is a lack of co-ordinated conduction in the atria. Electrical impulses are fired off from different parts of the atria and this leads to a reduced functional ability of the atria to pump blood effectively and smoothly. Electrical impulses transmitted from the atria via the AV node cause an irregular transmission to the ventricles leading to an irregular ventricular rate. The ventricles can beat up to 150 beats / minute or higher and it is this rapid and irregular ventricular rate which is the cause of many symptoms of AF. Usually patients with AF who have symptoms have a ventricular rate of greater than 90 beats/minute at rest. This increases to more than 110 beats/minute with mild to moderate exercise or activity.
The type of AF whose underlying cause is not linked to heart valve damage is known as non-valvular AF.
By contrast, valvular AF results from damage to the heart valves as a result of congenital heart disease or structural changes to the valves arising from underlying disease.
Epidemiology
AF is the most common type of ‘sustained’ cardiac arrhythmia and, according to NICE (2014) the condition occurs in approximately 1.6% of the population in England and Wales. Its prevalence increases with age, estimates being 1-2% for those aged 50-59 years and rising to a prevalence of around 24% in those aged 80-89 years. Males are twice as likely to be affected as females.
The condition is thought to be underdiagnosed in the general population.
Risk factors
Common predisposing factors include both non-cardiac and cardiac causes. The list is not exhaustive but includes:
Increasing age Gender Hypertension Ischaemic heart disease Heart failure Diabetes Obesity Thyrotoxicosis Excess alcohol Infection
- The precise underlying mechanisms are unclear however factors including Renin-Angiotensin-Aldosterone-System (RAAS) activation, structural changes to the atria and rapid activation of the atria secondary to other supraventricular tachyarrhythmias are thought to be involved.
Diagnosis
Careful clinical assessment and evaluation of the patient is required. AF is often initially diagnosed in the GP surgery when the patient’s pulse reveals an irregular heartbeat. Not all irregular pulses lead to a diagnosis of AF. AF is confirmed with a 12 lead ECG. A 24 hour ambulatory ECG monitor is used in patients with suspected paroxysmal AF. Transthoracic echocardiogram is also performed when, for example, a rhythm control strategy is being considered or where structural heart abnormalities are suspected.
Symptoms
Many patients are asymptomatic which is why AF can remain undetected. It is also why prevalence of AF in the population is thought to be underestimated.
Symptoms experienced by the patient may include the following:
Shortness of breath Palpitations Chest pain Dizziness / feeling faint Tiredness
Classification
Once diagnosed AF is classified according to timing of onset
- Lone AF
- Paroxysmal
- Persistent
- Permanent
Clinical features and arrhythmia pattern - lone AF
A single episode of AF where the heart is structurally normal and there is normal clinical examination.
Lone AF may or may not recur.
Clinical features and arrhythmia pattern - Paroxysmal
The pattern is recurrent. The AF terminates spontaneously usually within 7 days, but often within 24-48 hours.
Clinical features and arrhythmia pattern - Persistent
The pattern is recurrent. The AF lasts more than 7 days and does not self-terminate.
Clinical features and arrhythmia pattern - Permanent
The pattern is established. The AF is not terminated. Cardioversion has either failed or has not been attempted. Duration is greater than 1 year.
Management
Early diagnosis and treatment of any underlying / predisposing factors.
A risk assessment of the likelihood of developing a thromboembolism is required along with the need for thromboprophylaxis. (See section on Stroke prevention).
The need for either a rate or a rhythm control strategy should then be considered.
Patients should also be offered a personalised package of care to include up-to-date education and information on such facts as stroke awareness and prevention, rate control and assessment of symptoms for rhythm control. Patients should also know who to contact for advice and for psychological support if needed. Pharmacists can make an important contribution in providing education and advice on medicines to patients with AF.
Summary of options for rhythm control strategy are as follows:
- Cardioversion
- Amiodarone can be considered starting 4 weeks before cardioversion and continuing for up to 12 months in order to maintain sinus rhythm. However the benefits and risks of using amiodarone should be discussed with the patient first.
- Drug treatment for long term rhythm control. These include standard beta blockers (not sotalol) as first line treatment and other anti-arrhythmic agents such as dronedarone and amiodarone.
- Left atrial ablation. This can be used when drug therapy fails to control symptoms or is unsuitable.
- Pace and ablate strategy. This can be considered in patients with permanent AF and symptoms or with left ventricular dysfunction thought to be caused by high ventricular rates.
Non-Pharmacological management
Up to 50% of patients with recent onset AF will revert to normal sinus rhythm spontaneously.
In order to convert to normal sinus rhythm either pharmacological or electrical cardioversion is considered. Electrical cardioversion is often quicker and has a high success rate but the procedure requires the need for ‘conscious sedation’ or for anaesthesia.
Pharmacological management
When approaching pharmacological management a choice should first be made between either rate or rhythm control for each individual patient.
Rate control strategy
The aim is to control the ventricular rate (= rate control) promptly. Drug therapy lies between a beta blocker (not sotalol) or a ‘rate-limiting’ calcium channel blocker.
Rate control can be used first line for most patients presenting with AF.
NICE recommends that rate control is ‘offered as the first line strategy’ for patients presenting with AF except in the following:
whose AF has a reversible cause
who have heart failure primarily thought to be caused by AF
who present with new-onset AF
with atrial flutter where ablation strategy is considered suitable to restore sinus rhythm
when clinical judgement considers a rhythm control strategy would be more suitable
Rhythm control strategy
Rhythm control aims to restore and maintain normal sinus rhythm. This can be achieved by using either an anti-arrhythmic agent (= pharmacological therapy) and/or electrical rhythm control (= cardioversion). This strategy is used for patients whose symptoms continue after heart rate has been controlled OR in whom rate control has failed.
NICE recommends that rhythm control strategy may be more appropriate in the following cases i.e. for patients in whom rate control is not recommended:
With new onset AF
Where AF has a reversible cause e.g. infection
Where AF is thought to be caused or worsened by heart failure
With atrial flutter where ablation strategy is considered suitable to restore sinus rhythm
When clinical judgement considers a rhythm control strategy more suitable
‘Pill-in-the-pocket’ Strategy
This strategy is suitable for patients who have paroxysmal AF and who have a history of infrequent symptomatic episodes. They should also have a systolic BP of greater than 100mmHg and a resting heart rate of greater than 70bpm. A history of left ventricular dysfunction, valvular or ischaemic cardiac disease should be ruled out.
Patients should be able to fully understand when and how to take their medication in the event of a paroxysm of AF. Drugs such as flecainide or propafenone are used on a ‘when required’ basis. Known precipitants such as caffeine, alcohol and stress should be avoided where possible.
