5th May 2025

Atrial Arrhythmias

Background

Atrial arrhythmias are arrythmias that are generated above or at the level of the atrioventricular node (AVN) and follow the normal His-Purkinje bundle system to rapidly activate the ventricles. These encompass a wide variety of abnormal heart rhythms caused by a multitude of underlying aetiologies. When assessing and managing atrial arrhythmias, follow the standard resus council guidelines for managing arrhythmias:

• Is there evidence of haemodynamic instability? If so, needs synchronised DC shock
• Is the rhythm fast or slow?
• Are the QRS complexes broad or narrow (i.e. <120ms)? Atrial arrhythmias are generally narrow complex (although beware of atrial tachycardias with variable block/aberrant conduction which may appear broad complex!)
• Is the rhythm regular or irregular?

Image Source: Wikimedia Commons (2017). Cardiac Conduction System, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Cardiac_conduction_system.jpg (Accessed 1 May 2025).

Epidemiology

Narrow complex tachycardias can be divided into:

Table 1: Stratification of narrow complex tachycardias.

Atrial fibrillation is the most common cardiac arrhythmia with a prevalence in England of 2.5%. Approximately 1.4 million people were living with AF in England in 2016 with approximately 425,000 undiagnosed and untreated. Prevalence is higher in men (2.9%) than women (2.0%).

Image Source: Wikimedia Commons (2011). WPW, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:WPW.jpeg (Accessed 1 May 2025)

Aetiology

Atrial arrhythmias are caused by a wide variety of diseases and it is useful to stratify this using a surgical sieve as in the table below. Due to this, a thorough history and examination is of paramount importance in ascertaining the cause of arrhythmia.

Table 2: Causes of atrial arrhythmias.

Diagnosis

Definitive diagnosis of an atrial arrhythmia will be based on ECG evidence, however as with all conditions a detailed history and examination should precede investigations (in a haemodynamically stable, alert patient).

Symptoms (history)

• Palpitations
• Chest pain
• Shortness of breath
• Orthopnoea/paroxysmal nocturnal dyspnoea (evidence of cardiac decompensation)
• Loss of consciousness/blackouts (no warning)
• Dizziness/light-headedness
• Stroke symptoms

Signs (examination)

It is important to look for signs pertaining to possible underlying causes for the arrhythmia (based on history and presentation). Signs may include:

• Fever
• Hypotension
• Loss of consciousness
• Pallor
• Cachexia
• Tachypnoea
• Irregular, fast pulse
• Elevated JVP if in heart failure
• Cardiac murmurs if associated structural disease
• Evidence of thyroid disease – tremor, weight loss, exophthalmos, goitre, anxiety

Investigations

Investigations should be tailored to the suspected underlying cause. Below is a non-exhaustive table of immediate investigations to help ascertain the type of arrhythmia and possible underlying cause.

Table 3: Investigations in patients presenting with cardiac arrhythmias

ECGs

Image Source: Wikimedia Commons (2020). Atrial Fibrillation, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:ECG_Atrial_Fibrillation_98_bpm.jpg (Accessed 1 May 2025).

Image Source: Wikimedia Commons (2012). Cardio Networks ECGpedia, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:E234_(CardioNetworks_ECGpedia).jpg (Accessed 1 May 2025).

Image Source: Wikimedia Commons (2012). WPW 2012, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:WPW2012.jpg (Accessed 1 May 2025).

Image Source: Wikimedia Commons (2014). Junctional Tachycardia, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Junctional_Tachycardia.jpg (Accessed 1 May 2025)

Image Source: Wikimedia Commons (2012). Multifocal Atrial Tachycardia, Licensed under a creative commons licence. Available for free at: 

https://commons.wikimedia.org/wiki/File:Multifocal_atrial_tachycardia_-_MAT.png (Accessed 1 May 2025).

Management

Management of patients presenting with any tachyarrhythmia should be preceded by an immediate ABCDE assessment and then follow the resus council guidelines for adult tachycardia. The primary treatment for any tachycardia is to identify and treat reversible causes e.g. electrolyte abnormalities, hypovolaemia etc.

Life-threatening features

If a patient presenting with an atrial tachycardia has been adequately resuscitated medical and has ongoing evidence of haemodynamic compromise, syncope, myocardial ischaemia or severe heart failure then proceed as below:

1. Deliver up to 3 synchronised DC shocks (sedate patient if conscious)
2. If unsuccessful – give amiodarone 300mg over 10-20 minutes
3. Reattempt synchronised DC cardioversion

Regular narrow-complex tachycardias

For patients who are haemodynamically stable and have a regular narrow-complex tachycardia, follow the steps below:

1. Attempt vagal manoeuvres. This can be sufficient to cardiovert the patient back to sinus rhythm.
2. If unsuccessful and there is no evidence of a pre-excitation syndrome (e.g. WPW), give adenosine under direct ECG monitoring. The doses are 6mg rapid IV bolus, then 12mg if unsuccessful, then 18mg if unsuccessful.
3. If unsuccessful, give verapamil or beta-blocker (metoprolol is the drug of choice in acute situations due to its fast onset of action)
4. If ineffective, attempt DC cardioversion as above (note atrial flutter is unlikely to chemically cardiovert and will often need DC cardioversion if treatment of underlying causes is unsuccessful).

Patients with a pre-excitation syndrome such as Wolff-Parkinson-White should not be given digoxin or verapamil, as these can provoke fatal arrhythmias through blockade of the SA node, encouraging conduction down the aberrant pathway.. If cardioversion is unsuccessful, patients should be referred for consideration of radio-frequency ablation of their aberrant conduction pathway.

Table 4: Vaughan-Williams classification of anti-arrhythmic drugs.

Irregular narrow-complex tachycardias (i.e. atrial fibrillation)

Atrial fibrillation is the most common tachyarrhythmia in the UK. In the acute setting the priority should be on rapid pharmacological rate control of the stable patient, and then subsequent decision regarding rate vs rhythm control. There is no evidence to suggest mortality is any worse following a rate control rather than a rhythm control strategy for patients, if high-risk patients are anticoagulated. However, patients in sinus rhythm may report a better quality of life than those in AF. The mainstay of treatment in AF therefore is rate control and prevention of thromboembolic events.

Atrial fibrillation can be classified as paroxysmal (less than 7 days, then terminating), persistent (greater than 7 days, would last indefinitely unless cardioverted) and permanent (greater than 7 days, sinus rhythm not possible).

• Rate control
  • Usually with a standard beta-blocker (e.g. bisoprolol) or rate-limiting calcium-channel blocker (diltiazem or verapamil)
  • Consider digoxin if above contra-indicated
  • Amiodarone should not be used for long-term rate control
• Anticoagulation
  • Use CHA2DS2VASc and ORBIT scores to assess patient for suitability of anticoagulation
  • First-line anticoagulation for AF is a direct oral anticoagulant (DOAC) such as apixaban, dabigatran, edoxaban or rivaroxaban
  • Vitamin K antagonists such as warfarin can be used if DOACs are contraindicated

Table 6: ORBIT scoring system to assess bleeding risk when considering a patient for anticoagulation. A score of 1-2 is deemed low risk, 3 is medium risk and 4-7 high risk for a significant bleed if started on anticoagulation.

• Cardioversion
  • DCCV may be appropriate for patients presenting with fast AF if onset is within 48 hours of presentation.
  • If the history is suggestive of symptoms beginning earlier than this, or the patient is asymptomatic with no clear time of onset, cardioversion is contraindicated due to the risk of stroke from atrial thrombus formation.  
  • It is important to note that chemical cardioversion with flecainide or amiodarone carries the same risk, and therefore in patients presenting longer than 48 hours after development of AF, the management strategy should focus on rate or rhythm control, as detailed above.

References

1. https://www.uptodate.com/contents/narrow-qrs-complex-tachycardias-clinical-manifestations-diagnosis-and-evaluation?search=atrial%20arryhthmia&topicRef=2118&source=see_link
2. https://litfl.com/arrhythmias/
3. https://cks.nice.org.uk/topics/atrial-fibrillation/
4. Longmore et al. Oxford Handbook of Clinical Medicine. 8th Edition. Oxford University Press 2010.
5. Ramrakha et al. Oxford Handbook of Acute Medicine. 3rd Edition. Oxford University Press 2010.
6. https://www.resus.org.uk/sites/default/files/2021-04/Tachycardia%20Algorithm%202021.pdf