Atrial Fibrillation

AF is the most common sustained cardiac arrhythmia you will encounter. In this article, we focus on the management of it. Identification of atrial fibrillation is usually fairly easy due to the irregularly irregular pattern (using the RR intervals), typically narrow QRS complexes & the lack of P waves. If you need a quick refresher on how to identify it, then do check out LITFL.

Introduction

As part of your assessment of a patient with breathlessness, palpitations, dizziness/syncope, chest discomfort or stroke/TIA, you will obtain an ECG and will often identify atrial fibrillation. Usually, this is not a new diagnosis. AF is often paroxysmal – that is to say, it occurs and terminates randomly – but it may also be persistent.

In AF, there is uncoordinated electrical activity in the atria which results in them not contracting properly. As a result, blood stagnates resulting in thrombus formation and an increased risk of stroke. Depending on how much of this electrical activity passes through to the ventricles, the ventricular rate may be raised (AF with rapid ventricular response) or not.

The principles of management include:

  • Emergency management
  • Identification of the trigger
  • Short-term control (rate vs rhythm)
  • Rate Control
  • Anticoagulation
  • Long-term Control

Emergency Management

As with all supraventricular tachycardias, if the patient has any adverse features: shock, syncope, new heart failure, chest pain/myocardial ischaemia (or if you’re worried) then put out a peri-arrest call & ask a nurse to bring the crash trolley! For more details see the resus council’s tachyarrhythmia protocol.

It is also important to use an ABCDE approach, initially approaching the patient as any patient with tachycardia. AF with RVR (rapid ventricular response/tachycardia) may be completely appropriate due to infection or shock. In this context, resuscitation is key rather than b blockers which could make things worse.

Identify the trigger

Ensure you assess for the onset & potential causes of atrial fibrillation by obtaining relevant history & examination features. Addressing these are much more likely to be successful at treating and preventing further recurrence of atrial fibrillation. These include:

Investigations

  • Bloods: FBC, U&Es, CRP, Bone Profile, Magnesium, TFTs & Troponin. If new onset, consider clotting studies before anticoagulation is started
  • Echocardiogram: structural disease, valvular disease & regional wall motion abnormalities to help identify the underlying cause

Short-term Control (Rate vs Rhythm)

Initially, most patients are treated with rate control. The risk of rhythm control is that if the AF suddenly corrects, there is a risk this might dislodge a clot. Whilst on rate control strategies, if appropriate the patient is then prepared for rhythm control.

You should refer the patient to cardiology if there are indications for rhythm control such as:

  • Acute onset (<48 hours)
  • Paroxysmal AF (as this is more likely to reverse)
  • If the patient is young (e.g. less than 65 years old)
  • Structurally normal heart
  • Heart failure
  • If you’re unsure whether rate or rhythm control is appropriate

Rate Control

We aim to reduce the HR to below 100. Not all patients need medication to control this as some have rate controlled AF or it will settle with treating their underlying condition causing tachycardia e.g. dehydration, infection or anaemia. They should be on a cardiac monitor for you to be able to judge the response to therapy (& to monitor for bradycardia).

Use local guidelines & your senior’s advice to initiate the correct therapy but for illustration, I have included some examples below.

Metoprolol

Used if the heart rate is very high (≥150) or if the patient is very symptomatic for rapid reduction in heart rate. It works much quicker than bisoprolol, but lasts for a shorter amount of time. Ensure you check for contraindications (e.g. bronchospasm in asthma).

Intravenously it’ll start working within minutes and can be repeated within 5-10 minutes as per the BNF. Usually, around 2 mg IV will be used with the heart rate and blood pressure carefully monitored.

Orally, it will start working within around 2 hours but requires three doses per day (often 50 mg TDS to begin with).

Bisoprolol

Used in all other cases unless there are contraindications. Often 1.25 mg or 2.5 mg will be used initially, but the onset of action can take a few hours and reaches a steady state after a few days. Once again, do ensure you review if there are any contraindications. Avoid using both metoprolol & bisoprolol as it may result in profound bradycardia.

Calcium channel blockers

Verapamil (or diltiazem) is typically used in patients where b blockers are contraindicated such as asthma. They are not as frequently used. Dosing would be as per the BNF.

Digoxin

Digoxin is used in patients who are usually immobile or have multiple comorbidities/frailty. It may also be added in if b blockers or calcium channel blockers are not enough. Before you start digoxin, ensure the patient is potassium replete. Hypokalaemia can potentiate digoxin toxicity.

In hospitals, we usually load digoxin intravenously as we want to rapidly improve a patient’s heart rate. The patient has some response within 30 minutes, but digoxin takes at least a week to exert its full effect.

In a young patient with normal renal function: IV 500 mcg followed by another 500 mcg 6 hours later (if the patient remains tachycardic). After this, an oral maintenance dosing of 125 mcg once daily is used.

In an elderly patient or those with impaired renal function: IV 250 mcg followed by another 250 mcg 6 hours later (if the patient remains tachycardic). After this, an oral maintenance dosing of 62.5 mcg once daily is used.

Amiodarone

This is very effective, but usually reserved as a third-line agent because it can cause a lot of adverse effects. The use of amiodarone should be senior-led.

Anticoagulation

We use the CHA₂DS₂-VASc & HAS-BLED scores to work out the percentage risk of stroke vs their risk of major bleeding. This allows you to directly compare the benefits and risks. Usually, those with a CHADVASC of >2 are anticoagulated but for scores lower than this, people vary in their approach and you should therefore discuss this with your seniors. These days DOACs (e.g. apixaban, rivaroxaban) tend to be preferred over warfarin. DOACs don’t require loading or bridging with LMWH, usually, they can just be started.

You can read more about anticoagulation here.

Long-term management

In appropriate patients as described above, the cardiology team may consider rhythm control with cardioversion or catheter ablation. Whilst this is very specialist, the thing you can do to really help reduce the risk recurrence of atrial fibrillation is supporting patients in their management of risk factors e.g. alcohol or hypertension.

References & Resources

Original article written by Dr Elsa Barbosa (Registrar)
Updated by Dr Akash Doshi ST3 (June 2021)

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