Atrial Fibrillation (AF)

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19/Feb/2019

Introduction:

Atrial fibrillation (AF) is the most common recurrent arrhythmia seen in clinical practice with substantial associated morbidity and mortality. It has a strong association with other diseases particularly heart failure, valvular disease, diabetes mellitus, hypertension, obesity, chronic kidney disease and coronary artery disease. It is difficult to estimate exact prevalence of atrial fibrillation because of subclinical atrial fibrillation is frequent, however, current estimates put the prevalence of AF in Australia between 2% to 4%. The risk particularly increases with increasing age. AF is particularly associated with increased risk of embolic stroke and heart failure. The introduction of newer Oral anticoagulants (OAC’s) compared to warfarin in non-valvular AF has led to significant reduction in thromboembolic risk. I will try and focus on management of non-valvular atrial fibrillation and reduction in stroke and thromboembolic risk. 

Definition:

Atrial Fibrillation (AF) is an irregular and often rapid heart rate that can cause in increased risk of stroke and heart failure. The diagnosis of atrial fibrillation requires rhythm documentation using an electrocardiogram (ECG) demonstrating irregular RR intervals and absence of distinct p-waves. For the purpose of stroke reduction, it is divided into valvular and non-valvular AF (N-AF). N-AF refers to AF in the absence of significant mitral stenosis or mechanical heart valves.

Classification:

• Paroxysmal Atrial fibrillation is defined as AF were episodes terminate spontaneously or are cardioverted within 7 days of onset.
• Persistent Atrial fibrillation is defined as episodes of AF lasting > 7 days and do not self-terminate or are cardioverted after 7 days or more
• Long- standing persistent atrial fibrillation is defined as AF lasting > 1 year and it is decided to adopt a rhythm controlling strategy
• Permanent atrial fibrillation is defined as atrial fibrillation when a decision has been made accept the presence of AF and stop further attempts to restore or maintain sinus rhythm

Symptoms and signs:

The clinical presentation is variable, ranging from asymptomatic ‘subclinical’ atrial fibrillation to cardiogenic shock or an embolic cerebrovascular accident (CVA). Common clinical presentations include:

• Palpitations
• Fatigue and reduced exercise tolerance
• Dizziness
• Presyncope or Syncope
• Decompensated heart failure
• Hypotension
• Uncontrolled angina, particular in the setting of rapid ventricular rate
• Transient ischaemic attack (TIA) or Cerebrovascular accident (CVA)

In addition to eliciting symptoms in the clinical history, it is important to elicit history related to relevant precipitating factors. These include dehydration, infection, alcohol use, thyroid dysfunction, known underlying heart or lung disease, etc. A history of reduced exercise, sleep apnoea and obesity are important assessments for long term management of AF.

The clinical examination demonstrates an irregularly irregular pulse, often but not always, with a rapid ventricular response. Patients who have cardiac decompensation might present with hypotension or signs cardiogenic shock. Jugular venous pulse might be elevated and typically demonstrates absence of ‘a’ waves. Cardiac examination may demonstrate various signs depending on any underlying cardiac issues. In addition, the examination should focus on pulmonary, abdominal and neurological examination.

Diagnostic work up:

The following investigations should be considered in patients with atrial fibrillation.

• 12-lead electrocardiogram (ECG) to confirm the diagnosis and to demonstrate the ventricular rate. (Fig 1)

• The laboratory studies usually need to include a full blood count (FBC), Electrolytes, Renal functions, Liver functions, thyroid functions, etc.
• Echocardiography is an important part of the atrial fibrillation evaluation. Transthoracic echocardiography (TTE) can assist in identifying left ventricular function, valvular heart disease, atrial size and volume. Transoesophageal echocardiography (TOE) may be considered in patients requiring electrical or pharmacological cardioversion, particularly in acute setting.
• Cardiac CT is useful in evaluating cardiac anatomy particularly in patients planned for AF ablation. Imaging data from a cardiac CT is used to create 3D maps of the left atrium and pulmonary veins. Cardiac CT is also a useful investigation to rule out left atrial appendage thrombus (Fig 2).

• Other investigations to be considered in patients with AF include cardiac MRI, Holter monitors and EP studies.

Management:

AF management can be divided into:

• Management of risk or precipitation factors
• Acute management of atrial fibrillation
• Long term management of atrial fibrillation
• Reduction of thromboembolic and stroke risk

Precipitating or risk factor management:

The aggressive risk factor management treatment targets included:

• Weight loss of at least 10% or final BMI less than 27 kg/m2, with avoidance of weight fluctuation.
• Exercise to improve aerobic capacity for up to 210 minutes/week.
• Blood pressure of less than or equal to 130/80 mm Hg at rest, and less than or equal to 200/100 mm Hg on exercise.
• Maximal compliance with continuous positive airway pressure (CPAP) therapy if the apnoea–hypopnea index was equal to or greater than 15/hour.
• An HbA1c of less than or equal to 6.5%.
• Lipid targets per overall cardiovascular risk profile.
• Smoking cessation.
• Limitation of alcohol consumption to less than or equal to three standard drinks per week.

Acute management of AF:

One of the most important decisions in acute management of AF is the strategy of rhythm control vs rate control. Factors favouring rhythm control vs rate control include:

• Patient choice
• Highly symptomatic patient
• Active and young patients
• Difficulty in achieving adequate rate control
• Acute AF (duration < 48 hrs)
• LV dysfunction (mortality benefit)
• Absence of severe left atrial enlargement
• Paroxysmal or early persistent AF

If rhythm control strategy is chosen, this can be achieved either with electrical cardioversion or pharmacological cardioversion. Electrical cardioversion is considered in haemodynamically unstable patients with AF. Electrical cardioversion can also be considered in haemodynamically stable patients after consideration of thromboembolic risk or in patients with failed pharmacological cardioversion. The agents used for pharmacological cardioversion include Flecanide and Amiodarone. The evidence for Sotalol in acute cardioversion is limited. Sotalol though can be used in long term maintenance of sinus rhythm once sinus rhythm is restored.  AV nodal blocking agents can be added to Flecanide or Amiodarone to facilitate cardioversion. Flecanide is used in patients without LV dysfunction, significant coronary artery disease or left ventricular hypertrophy.

Catheter ablation should be considered for symptomatic paroxysmal or persistent AF refractory to or intolerant at least one antiarrhythmic medication. Catheter ablation can be considered in considered for symptomatic paroxysmal or persistent AF before initiation of antiarrhythmics. It can also be considered in patients with paroxysmal or persistent AF with heart failure with reduced ejection fraction. Surgical ablation is considered in context of concomitant cardiac surgery.

Long Term management of AF:

Long-term management of atrial fibrillation (AF) is focused on reducing the likelihood of AF recurrence, reducing AF-related symptoms, control of ventricular rate, and reducing stroke risk. Appropriate management of precipitating or risk factors, as mentioned above, is important in reduction of recurrent episodes of AF. The considerations for agents in long term management of AF again depends on rate vs rhythm control strategy.

Long term rhythm control:

• Flecainide can be considered in the maintenance of sinus rhythm in patients without left ventricular systolic dysfunction, moderate left ventricular hypertrophy, or coronary artery disease.
• AV nodal blocking medication is recommended for patients treated with flecainide.
• Amiodarone can be considered for maintenance of sinus rhythm as a second-line agent or as a first-line agent in patients with left ventricular systolic dysfunction, moderate left ventricular hypertrophy, or coronary artery disease.
• Sotalol may be considered for maintenance of sinus rhythm but requires close monitoring of QT interval.
• Beta adrenoceptor antagonists may be considered for the maintenance of sinus rhythm.

Long term rate control:

• Beta adrenoceptor antagonists or nondihydropyridine calcium channel antagonists should be the first-line agents used for long-term control of the ventricular rate.
• Digoxin can be considered for control of the ventricular rate in patients with suboptimal rate control on, or with contraindications to, first-line agents. Serum concentration should be maintained to levels < 1.2 ng/ml.
• Calcium channel antagonists should be avoided in patients with left ventricular systolic dys-function (ejection fraction <40%).
• Amiodarone should not be administered as a first-line agent for chronic rate control, given its toxicity profile.
• Membrane-active antiarrhythmic agents (e.g., sotalol or flecainide) should not be used in patients managed with a rate-control strategy.
• Regular clinical surveillance for emergent cardiomyopathy or overt heart failure should be performed during long-term follow-up because heart failure may develop even in the presence of apparently adequate ventricular rate control.
• Documentation of the adequacy of ventricular rate control at (<110 bpm) at rest and with moderate exertion should be performed at regular intervals in asymptomatic patients without heart failure.
• If pharmacological rate control fails, catheter ablation of the AV node should be considered after a permanent pacing device has been implanted.

Reduction of thromboembolic risk:

AF has been known to be a potent, independent risk factor for embolic stroke. The risk of stroke varies from 1% to 15% depending on presence of associated risk factors. Currently CHA₂DS₂VA score is used to assess the risk of thromboembolic stroke in patient with AF.

CHA₂DS₂VA score

Score	Points	Definition
C	1	Congestive heart failure—recent signs, symptoms or admission for decompensated heart failure; this includes both HFrEF and HFpEF, or moderately to severely reduced systolic left ventricular function, whether or not there is a history of heart failure
H	1	Hypertension
A2	2	Age > or =75 years
D	1	Diabetes
S2	2	History of prior stroke or TIA
V	1	Vascular disease
A	1	Age  65-74years
AF, atrial fibrillation; BP, blood pressure; HFpEF, heart failure with preserved ejection fraction; HFrEF, heart failure with reduced ejection fraction; TIA, transient ischaemic attack.

The benefits of anticoagulation have to be weighed against the risk of bleeding associated with the use of anticoagulants. There are many risk scores to assess the risk of bleeding including HAS-BLED, ATRIA, ORBIT, GARFIELD and HEMOR-R₂HAGES. The risk of bleeding with warfarin is estimated to be about 1.3% in patients with INR of 2 to 3. NOACs also known as direct-acting oral anticoagulants (DOACs) have slightly reduced major bleeding risk compared to warfarin.

Guidelines and Recommendations:

• Oral anticoagulation therapy to prevent stroke and systemic embolism is recommended in patients with N-VAF whose CHA2DS2-VA score is 2 or more, unless there are contraindications to anticoagulation.
• Oral anticoagulation therapy to prevent stroke and systemic embolism should be considered in patients with N-VAF whose CHA2DS2-VA score is 1.
• Oral anticoagulation therapy to prevent thromboembolism and systemic embolism is not recommended in patients with N-VAF whose CHA2DS2- VA score is 0.
• In asymptomatic patients with atrial lead pacemakers, anticoagulation should be considered in device-detected and EGM-confirmed AF of 24 hours or more in patients with a CHA2DS2-VA score of 2 or more.
• When oral anticoagulation is initiated in a patient with N-VAF, an NOAC—apixaban, dabigatran, or rivaroxaban is recommended in preference to warfarin.
• Warfarin is recommended and NOACs should not be used in patients with valvular AF.
• Antiplatelet therapy is not recommended for stroke prevention in N-VAF patients, regardless of stroke risk.
• LAA occlusion may be considered for stroke prevention in patients with N-VAF at moderate to high risk of stroke and with contraindications to oral anticoagulation therapy.