Atrial Fibrillation

Atrial fibrillation (AF) is one of the most common abnormal rhythms affecting the heart, characterised by an irregularly irregular heart rhythm.

Causes

• Heart failure
• Valvular heart disease
• Ischaemic heart disease
• Infection
• Hypertension
• Hyperthyroidism
• Alcohol intoxication
• Rheumatic heart disease
• Pulmonary embolism
• Pericarditis/Myocarditis
• Idiopathic

Clinical Features

Patients may be asymptomatic, but when symptoms are present, they typically include palpitations, chest pain, dyspnoea, dizziness, syncope and fatigue. Signs include tachycardia and an irregularly irregular pulse.

Investigations

Bedside

• Observations: Once you start working, you'll often see patients coming to hospital in fast AF where they're tachycardic with the AF. Patients can become unstable, particularly when they're very tachycardic and these instances call for DC cardioversion (more on that later)
• ECG:
  • This will show QRS complexes occurring at irregularly irregular intervals and absent P waves.
  • If the AF is not detected by a standard ECG, a 24-hour ECG monitor can be used if episodes are less than 24 hours apart.
  • Where episodes are more than 24 hours apart and not detected on standard ECG, an event recorder can be used. This can be a device such as an implantable loop recorder. These subcutaneous devices have activator buttons which, when pressed, record a portion of the ECG before, during and after. This means patients can press the button when they have symptoms or even after regaining consciousness following syncope, and the recorder will store the portion of the ECG. Remember,

Bloods

• FBC, U&E, LFT, TFT: Baseline and to rule out alternative causes of AF such as thyrotoxicosis/infection

Imaging

• Echocardiogram: For checking for a structural disease or if patients are being considered for rhythm control as some drugs are contraindicated in structural heart disease e.g. fleicanide. This is not typically performed on a routine basis.

Classification

• First Diagnosed: The first episode of AF when it is first identified.
• Acute: AF < 48 hours
• Paroxysmal: Episode of AF ends within 7 days.
• Persistent: Episode of AF is continuous and lasts for more than 7 days.
• Long-standing persistent: Continuous AF for more than 1 year.
• Permanent: Continuous AF and the patient + doctor both agree to cease attempts to return to sinus rhythm.

Assessing Stroke Risk

Due to the irregular beating of the heart, patients with AF are at an increased risk of stroke. This is because the fibrillation of the atria can result in some blood stagnating in the heart, increasing the likelihood of a clot forming. This can then embolise to cause a stroke.

To reduce the risk of a clot forming, we can anticoagulate patients but we must consider anticoagulation in the context of the bleeding risk. If the bleeding risk outweighs the risk of stroke, it may not be worth anticoagulating the patient.

 Thus, a bleeding risk and stroke risk need to be calculated for these patients. Stroke risk is assessed using the CHA2DS2-VASc (pronounced CHADS Vasc) score.

• Congestive Heart Failure
• Hypertension
• Age ≥75
• Diabetes mellitus
• Stroke/Transient ischaemic attack/Thromboembolic event
• Vascular disease e.g. prior myocardial infarction
• Age 65-74
• Sex (Female) 

An age equal to or over 75 and history of a stroke/TIA/TE counts for 2 points, whilst all the other options score 1 point. As the score increases, the risk of stroke increases.

Assessing Bleeding Risk

The HAS-BLED score is a frequently used scoring tool. NICE guidelines suggest using the ORBIT bleeding risk score. The ORBIT score is listed below, with the points scored for each criterion in brackets:

• Females: Haemoglobin <120 g/L or haematocrit <36% OR Males: Haemoglobin <130 g/L or haematocrit <40%  (+2)
• Age >74 (+1)
• History of bleeding e.g. GI bleed/haemorrhagic stroke/intracranial bleeds (+2)
• GFR <60 (+1)
• Currently on antiplatelets (+1)

A score equal to or more than 4 indicates a high-risk patient. The bleeding risk is considered in the context of the stroke risk. If the risk of stroke outweighs the risk of bleeding, patients are usually offered anticoagulation therapy.

Principles of AF Management

There are three main things that need controlling when treating AF:

1. Stroke Risk: We try mitigate this with anticoagulation
2. Heart Rate: Patients can get quite tachycardic with AF, so we usually try control the heart rate
3. Heart Rhythm: In instances where we think we might be able to get a patient back into sinus rhythm, we try and control the rhythm, rather than rate control

Anticoagulation

This is considered in male patients with a CHA2DS2-VASc score of 1, or a CHA2DS2-VASc of 2 in women, but this is taken in the context of the bleeding risk.

Suggested drugs for anticoagulation as per NICE guidelines are the Direct Oral Anticoagulants (DOACs) i.e. apixaban, rivaroxaban, dabigatran or edoxaban. Where DOACs are not tolerated or contraindicated, a vitamin K antagonist such as warfarin can be used (or instances patients are already on warfarin).

Warfarin is less preferable these days due to the need to monitor the INR - patients on warfarin have a target INR they need to be between, so they require frequent blood tests to monitor their INR and dose adjust accordingly.

In patients who cannot tolerate anticoagulation or where anticoagulation is contraindicated, a left atrial appendage occlusion might be considered. However, this is not used in situations where anticoagulation could be given to patients.

Rate Control

Rate control is the first line treatment option in patients with AF, with the exception of a few specific situations e.g. where AF is reversible (see below). Otherwise, the treatment algorithm as per NICE guidelines is as follows:

1. Monotherapy: Either give a beta-blocker other than sotalol or a rate-limiting calcium channel blocker (CCB) as first line. If patient has non-paroxysmal AF and is sedentary, digoxin can also be used.
   1. Examples of beta-blockers: Atenolol, metoprolol, propranolol, bisoprolol. Sotalol isn't recommended as it's an antiarrhythmic i.e. it has a rhythm control effect
   2. Examples of rate limiting CCBs (aka non-dihydropyridine CCBs): Verapamil and diltiazem
       
2. Combination therapy: If monotherapy does not work, a combination of 2 of the following can be used: beta-blocker, diltiazem or digoxin. However, it is important to remember co-prescribing beta-blockers with diltiazem carries a risk of profound bradycardia.

When is Rhythm Control Preferred?

NICE guidelines state that in the following situations, rhythm control is preferred to rate control:

• New-onset AF
• Reversible AF
• Patients who have heart failure which is thought to be caused by AF
• Clinical judgement dictates that rhythm control would be better
• Patient has atrial flutter that could be treated with ablation

Rhythm Control

In select groups of patients, rhythm control may be used as a first-line strategy. Otherwise, it is considered when symptoms persist despite attempts to control the heart rate (other than permanent AF). Rhythm control can be achieved in the following ways:

1. Cardioversion: This is a process used to restore the heart to sinus rhythm. There are two types of cardioversion – electrical (DC) or pharmacological. If cardioversion is successful, patients will be at risk of developing an embolic stroke (when returning back to sinus rhythm, a lodged thromboembolus might be able to escape once the heart starts beating regularly, and can then cause a stroke). Thus, patients need to have either had a short duration of symptoms or be adequately anticoagulated prior to cardioversion.
    
   1. Electrical:
      • Prior to this being performed, an echocardiogram may need to be done to ensure there are no intra-atrial thrombi.
      • Electrical cardioversion is preferred to pharmacological when patients have had AF for more than 48 hours.
      • Amiodarone can be started 4 weeks before electrical cardioversion and continued for up to 1 year following cardioversion to try and maintain sinus rhythm.
         
   2. Pharmacological: This can be with various agents including amiodarone, propafenone or flecainide. The latter two should not be offered to individuals with known ischaemic or structural heart diseases. 
       
   3. Anticoagulation: Patients with AF for more than 48 hours need to be on anticoagulation for at least 3 weeks prior to cardioversion, and this should be continued for 4 weeks after cardioversion, as per 2016 European Society of Cardiology guidelines. This can vary between hospitals so local guidelines should be followed.
       
2. Long-term Drug Treatment: The first line for this is a beta-blocker other than sotalol. If this is unsuitable, other antiarrhythmic drugs can be offered such as flecainide or amiodarone.
    
3. Left Atrial Ablation: This is usually used when drugs have failed or control the AF.

Acute AF

1. Haemodynamic Instability: If there is life-threatening haemodynamic instability, emergency electrical cardioversion is needed.
    
2. <48 Hours: If the patient had onset <48 hours ago, rate or rhythm control can be offered.
   • If rhythm control selected: You can use electrical cardioversion or pharmacological cardioversion.
   • If pharmacological cardioversion selected: Patients with evidence of structural heart disease should be cardioverted with amiodarone. Patients without evidence of ischaemic or structural heart disease can have flecainide or amiodarone.
      
3. >48 Hours/Uncertain: Rate control should be started. If also considering long-term rhythm control with cardioversion, patients need to be anticoagulated for at least 3 weeks – they should be rhythm controlled during this time as well.
    
4. Anticoagulation: New-onset AF patients can be given heparin for anticoagulation (provided there are no contraindications and/or the patient is not already on anticoagulation), until a full assessment of bleeding and stroke risk is conducted.

References

Feather A, Randall D and Waterhouse M (eds). 2020. Kumar and Clark's Clinical Medicine 10th edition, Elsevier, Edinburgh.

Ralston, S. H., Penman, I. D., Strachan, M. W. J., & Hobson, R. (Eds.). (2018). Davidson’s principles and practice of medicine (23rd ed.). Elsevier Health Sciences.

https://emedicine.medscape.com/article/2172597-overview

https://academic.oup.com/eurheartj/article/37/38/2893/2334964#110288881

https://www.whittington.nhs.uk/document.ashx?id=6034

https://www.nice.org.uk/guidance/cg180/chapter/1-recommendations#initial-management-of-stroke-and-atrial-fibrillation

https://doclibrary-rcht.cornwall.nhs.uk/DocumentsLibrary/RoyalCornwallHospitalsTrust/Clinical/Anaesthetics/ManagementOfPostoperativeAtrialFibrillationClinicalGuideline.pdf

https://www.mdcalc.com/orbit-bleeding-risk-score-atrial-fibrillation#why-use 

https://www.aerjournal.com/articles/practical-implementation-anticoagulation-strategy-patients-undergoing-cardioversion-atrial 

https://bnf.nice.org.uk/treatment-summary/arrhythmias.html