Clinical Notes : Cardiovascular Disease

174. Atrial Fibrillation

 

Overview

Atrial Fibrillation (AF) is the most common sustained arrhythmia.

Atrial fibrillation (AF) is a supraventricular tachyarrhythmia.

It is characterised by uncoordinated atrial activity on the surface ECG, with fibrillatory waves of varying shapes, amplitudes, and timing associated with an irregularly irregular ventricular response when atrioventricular (AV) conduction is intact.

New-onset AF is defined as a new onset or a first detectable episode of AF, whether symptomatic or not.

The lifetime risk over the age of 40 years is ~25%.

It affects almost 5% of the population older than 69 years of age.

Complications of AF include haemodynamic instability, cardiomyopathy, cardiac failure, and embolic events such as stroke.

 

Anatomy and pathophysiology

  • AF is associated with electrophysical and/or structural abnormalities of the atria. The autonomic nervous system may also play a role in some cases.

  • The 'triggers' for AF are rapidly firing foci, most commonly within the pulmonary vein. These triggers cause propagating wavelets, which may lead to re-entrant circuits in abnormal atrial myocardium. 

  • When the atrioventricular node receives more electrical impulses than it can conduct, an irregular ventricular rhythm results. The ventricular rate of untreated AF often averages between 160–180 beats per minute, although this is typically slower in older people.

  • Sustained AF results from structural remodelling of atrial tissue (most notably fibrosis)

 

Causes of Atrial Fibrillation

  • Cardiac or valve conditions, such as:

    • Congestive heart failure.

    • Rheumatic valvular disease.

    • Atrial or ventricular dilation or hypertrophy.

    • Pre-excitation syndromes (such as Wolff–Parkinson–White syndrome).

    • Sick sinus syndrome.

    • Congenital heart disease.

    • Inflammatory or infiltrative disease (such as pericarditis, amyloidosis, or myocarditis).

  • Non-cardiac conditions, such as:

    • Acute infection.

    • Autonomic neuronal dysfunction (such as vagally induced AF). 

    • Electrolyte depletion (such as hypokalemia and hyponatremia). 

    • Cancer (such as primary lung cancer involving the pleura and pericardium, and cancers such as breast cancer and malignant melanoma metastasising to the pericardium).

    • Pulmonary embolism.

    • Thyrotoxicosis.

    • Diabetes mellitus.

  • Dietary and lifestyle factors, such as:

    • Excessive caffeine intake.

    • Alcohol abuse (especially in susceptible individuals such as those with structural heart disease).

    • Obesity.

    • Smoking.

    • Medication exposure (such as thyroxine or bronchodilators).

 

Classification of Atrial Fibrillation

Classification is dependent on the presentation and duration of atrial fibrillation as below:

  • First episode – initial detection of AF regardless of symptoms or duration

  • Recurrent AF – More than 2 episodes of AF

  • Paroxysmal AF – Self terminating episode < 7 days

  • Persistent AF – Not self terminating, duration > 7 days

  • Long-standing persistent AF – > 1 year

  • Permanent (Accepted) AF – Duration > 1 yr in which rhythm control interventions are not pursued or are unsuccessful

Commonly AF is associated with a ventricular rate 110 – 160.

AF is often described as having ‘rapid ventricular response’ once the ventricular rate is > 100 bpm.

‘Slow’ AF is a term often used to describe AF with a ventricular rate < 60 bpm.

Causes of ‘slow’ AF include hypothermia, digoxin toxicity, medications, and sinus node dysfunction.

 

Diagnosis of Atrial Fibrillation

  • Suspect atrial fibrillation (AF) in people with an irregular pulse, with or without any of the following:

    • Breathlessness.

    • Palpitations.

    • Chest discomfort.

    • Syncope or dizziness.

    • Reduced exercise tolerance, malaise/listlessness, decrease in mentation, or polyuria.

    • A potential complication of AF, such as stroke, transient ischaemic attack, or heart failure.

  • Assess pulse

    • An accurate assessment of pulse rate and regularity may require palpation of the carotids or auscultation, since palpation of other sites may cause decreased perfusion which potentially influences the findings.

    • Additionally, it can be difficult to detect irregularity if the pulse rate is very fast or slow. 

    • Absence of an irregular pulse makes a diagnosis of AF unlikely, but its presence does not reliably indicate AF

  • Past medical history of risk factors

  • Suspect paroxysmal AF if symptoms are episodic and last less than 48 hours.

 

  • Be aware of the differential diagnoses of an irregular pulse.

 

  • Confirm diagnosis of AF, 

    •  electrocardiogram (ECG):

      • If AF is present, the ECG will have no P-waves, a chaotic baseline, and an irregular ventricular rate. 

      • The ventricular rate is often 160–180 beats per minute but can be lower, especially in people who are asymptomatic.

      • The ventricular complexes look normal unless there is a ventricular conduction defect.

    • ambulatory electrocardiography:

      • If paroxysmal AF is suspected and AF is not detected on standard electrocardiography

        • A 24-hour ambulatory ECG monitor is normally used in people with suspected asymptomatic episodes of paroxysmal AF (incidental finding of an intermittent irregular pulse) or symptomatic episodes that are less than 24 hours apart.

        • An event recorder ECG is normally used in people who have symptomatic episodes more than 24 hours apart.

          • In some centres, a 7-day Holter monitor is used as an alternative to an event recorder, especially when asymptomatic paroxysms of AF are suspected.

 

Management of Atrial Fibrillation

Management of atrial fibrillation is complex depending on duration of atrial fibrillation, co-morbidities, underlying cause, symptoms, and age. Management of atrial fibrillation can be considered in a step-wise manner:

  • Diagnosis of atrial fibrillation.

  • Assessment of duration.

  • Assessment for anticoagulation.

  • Rate or rhythm control.

  • Treatment of underlying / associated diseases.

When to refer

In the OOH setting :

  • If the onset of atrial fibrillation (AF) was within the last 48 hours:

  • Urgently admit to an acute medical unit for emergency electrical cardioversion if the person is exhibiting signs and symptoms of haemodynamic instability, such as a rapid pulse (greater than 150 beats per minute) and/or low blood pressure (systolic blood pressure less than 90 mmHg), loss of consciousness, severe dizziness or syncope, ongoing chest pain, or increasing breathlessness.

  • If the person is not exhibiting signs of haemodynamic instability, consider management in primary care  (if appropriate) or refer the person to an acute medical unit for immediate cardioversion, depending on the person's preferences and clinical judgement. ​

  • For all other people with AF (including paroxysmal AF):

    • Admit or refer with urgency dependent on clinical judgement, if the person exhibits any of the following:

      • Signs and symptoms of haemodynamic instability 

      • Signs suggestive of a stroke or another serious associated or underlying condition such as severe heart failure, pulmonary embolism, pneumonia, or thyrotoxicosis

    • Where an underlying cause for AF is identified, manage where possible, or refer as appropriate (using clinical judgement to determine urgency

 

Patient education

Patients with AF should receive information about (refer back to own GP if required for action) :

  • Atrial fibrillation (AF)

    • Written information on the causes, effects, possible complications, and management of AF. 

    • Details of when and where to seek further medical advice (such as if symptoms worsen).

  • Stroke awareness and how to prevent stroke. 

  • Flying

    • there are no flying restrictions provided AF is stable and has not recently worsened or become more symptomatic.

 

  • Driving

    • in Ireland it is the patient's responsibility to inform the National Driver License Service (NDLS) of any condition that may affect their ability to drive.

      • For group 1 entitlement (cars, motorcycles), the NDLS's medical rules regarding AF are that driving :

        • Must cease after an acute episode that caused dizziness or fainting.

        • May resume when the underlying cause has been identified and controlled for at least 4 weeks.

        • NDLS need not be notified unless there are distracting or disabling symptoms

      • For group 2 entitlement (lorries, buses), the NDSL's medical rules regarding AF are that driving :

        • Must cease if the arrhythmia has caused or is likely to cause incapacity.

        • May resume when the arrhythmia is controlled for at least 3 months and there are no other disqualifying condition.

        • NDLS need not be notified unless there are distracting/disabling symptoms.​

      • Advise the person to check with their insurer that they are still covered for driving.

      • Consult local latest NDSL rules

 

  • Support groups 

    • contact details

 

  • Review any person with an established AF diagnosis at least annually.

 
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Atrial Fibrillation

Dr Ed Burns,

Life in the Fast Lane

last update March 16, 2019

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Atrial Fibrillation

CSK

NICE guidelines

View/Access

New-onset atrial fibrillation

BMJ Best Practice

Last reviewed: June 2019

Last updated: June  2018

View/Access

 

Guidelines for the management of atrial fibrillation

Canadian Cardiovascular Society

2016.

View/Access

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