Atrial Fibrillation

Cardiology (12%) Core Clinical Conditions

1B: Able to identify the condition as a possible diagnosis: may not have the knowledge or resources to confirm the diagnosis or to manage the condition safely, but can take measures to avoid immediate deterioration and refer appropriately

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Definition Aetiology Pathophysiology Risk factor Sign and Symptoms Investigations Diagnosis Management

Atrial fibrillation (AF) is an irregular and frequently very rapid heart rhythm (arrhythmia) that can cause blood clots. When you are at rest, a typical heart rate should be between 60 and 100 beats per minute. AF increases the likelihood of strokes, heart failure, and other heart-related conditions

AF episodes could be intermittent or persistent. Even though AF is not usually fatal, it is a serious medical problem that must be addressed properly in order to avoid a stroke

• Myocardial infarction (MI)

• Atherosclerosis

• Congenital heart disease 

• Cardiomyopathy 

• Hypertension

• Pulmonary disease 

• Previous heart surgery

• Sleep apnea

• hyperthyroidism

• Asthma and COPD

The heart has two upper chambers (atria) and two lower chambers (ventricles). The sinoatrial or sinus node (SAN) is a collection of cells found in the right atrium, the upper right chamber of the heart; it is the natural pacemaker of the heart (see Figure 1)

Normal heart rhythm: 

• The signal orignates from the sinus node

• The signal travels to the atrioventricular (AV) node, which connects the upper and lower chambers

• The heart contracts as a result of the signal's movement, pumping blood to the body and heart

In AF, the signals of the heart are disorganised. This causes the following: 

• Tachycardia: the heart rate may range from 100 to 175 beats a minute. The normal range for a heart rate is 60 to 100 beats a minute

• Irregular ventricular contraction  

• Increased risk of stroke: this can be caused by a blood clot (emboli) in the atrial which can travel to the brain and cause an ischaemic stroke

• Eventually if not controlled, heart failure

• Age

• Heart disease: previous MI, previous heart surgery, congenital heart defects and HF

• Hypertension 

• Thyroid disease

• Obesity

• Family history 

• Alcohol consumption 

• Other medical conditions: Diabetes, metabolic disorders, chronic kidney disease, lung disease etc.

Patients are frequently picked up without any apparent symptoms while being seen for other purposes

Common symptoms are:

• Palpitations

• Chest pain 

• Shortness of breath

• Dizziness

• Tiredness

• 12 lead ECG (see Figure 2)

• Blood tests

• 24 hr ECG

• Echocardiogram

• Chest X-ray - to check heart size and diagnose/rule out HF

Physical examination, irregular pulse rate + history

For AF sufferers, anticoagulation is the top priority. The treatment of AF can thus be roughly divided into rate control and rhythm control

Rate Control

1. Beta blocker for example bisoprolol or atenolol 

2. Calcium-channel blocker (e.g. diltiazem or verapamil) 

3. Digoxin is only used for patients with a sedentary lifestyle. Can be used as a second line when the patient is at maximum dose of beta-blocker or calcium channel blocker

Rhythm Control

When a patient has new-onset AF (defined as lasting less than 48 hours), rhythm control is the best course of action

Cardioversion: 

If acutely unwell, cardioversion needs to be initiated immediately. This can be done in the following manner: 

• Pharmacological cardioversion: Flecainide (oral or IV) or amiodarone

• Electrical cardioversion: the heart is quickly shocked into sinus rhythm. This entails sedation or general anaesthesia, followed by the controlled delivery of shocks from a cardiac defibrillator machine in an effort to restore sinus rhythm

Long term rhythm control:

• Beta-blockers are first line

• Dronedarone second line 

• Amiodarone can be used for patients with HF

Paroxysmal Atrial Fibrillation

Paroxysmal AF is characterised by intermittent AF that typically lasts no longer than 48 hours. Based on the CHADSVASc score, patients should continue to take anticoagulants

Patients will be advised to take their medication only when they begin to experience the symptoms of atrial fibrillation.  However, they must not have any underlying heart disease

The standard treatment is Flecanide

CHA2DS2VASc 

Patients with AF are more likely to develop a blood clot. Therefore, anticoagulation must be considered to lower their risk of TIA and stroke

The risk of stroke in AF can be determined using the CHA2DS2VASc algorithm (see Table 1). It helps determine whether to provide anticoagulant medication to a patient

Table 1

The decision to initiate anticoagulant therapy can then be made using the total CHA2DS2VASc score (see table 2)

Table 2

A patient should be given the option of either a direct-acting oral anticoagulant (DOAC) or a vitamin K antagonist like warfarin

DOAC or Novel AntiCoagulants (NOACs)

Apixaban, edoxaban, rivaroxaban and dabigatran are common DOACs used for the treatment of AF. They work by inhibiting the clotting cascade of factor Xa which stops thrombus formation

Warfarin

Warfarin is a vitamin K antagonist. Warfarin works by prolonging the prothrombin time, which is the time it takes for blood to clot

We measure INR (international normalised ratio), to assess how anticoagulated the patient is by warfarin. An INR of 1 indicates a normal prothrombin time. An INR of 2 indicates that the patient has a prothrombin time twice that of a normal healthy adult (it takes them twice as long to form a blood clot)

The target INR for AF is 2 – 3

Bleeding Risk

Bleeding risk can be calculated using the HAS-BLED score: 

• H – Hypertension (BP >160 mmHg)

• A – Abnormal renal and liver function (chronic dialysis, renal transplant, creatinine >2.3)

• S – Stroke

• B – Bleeding history 

• L – Labile INRs (whilst on warfarin)

• E – Elderly older than 65 year old

• D – Drugs or alcohol

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