Atrial fibrillation

Atrial fibrillation (Afib) is the most important supraventricular arrhythmia, characterised by fibrillation of the atria, and is the most common arrhythmia overall. It’s problematic because of the following:

It increases the risk of thromboembolic stroke
It can cause tachycardia-induced heart failure (= arrhythmia-induced cardiomyopathy)
It can cause symptoms

It’s a highly prevalent condition which becomes more and more common with age.

Etiology

Afib can be multifactorial and idiopathic, but in some cases it’s caused by treatable etiologies:

Alcohol abuse, smoking, and obesity are risk factors for idiopathic Afib.

Classification

We can distinguish three types of Afib:

Paroxysmal Afib – Afib that terminates spontaneously within 48 hours
Persistent Afib – Afib which lasts more than seven days or requires electrical cardioversion to restore sinus rhythm
Permanent Afib – Afib where a decision has been made to no longer try to achieve sinus rhythm, either because cardioversion or drugs have failed, or because a rate-control strategy is used instead

Afib usually progresses from paroxysmal to persistent to permanent with time.

Clinical features

Most patients are asymptomatic, and Afib is discovered incidentally. Patients may also present with palpitations, syncope, dyspnoea, or symptoms of heart failure. Some people with new-onset Afib are haemodynamically unstable. This is a rare presentation.

With longstanding Afib, the atria undergo both structural and electrical remodeling, which further increases susceptibility to Afib, resulting in a vicious cycle.

Diagnosis and evaluation

The characteristic ECG findings of atrial fibrillation is the lack of normal P-waves in all leads, and irregularly irregular ventricular rate. The ventricular rate is often high.

Investigating possible underlying causes is important. All patients with newly diagnosed Afib should undergo echocardiography to assess for structural heart disease. If cardioversion is being considered, transoesophageal echocardiography must be performed to rule out thrombosis in the atria.

Treatment

ESC uses an ABC pathway for the management of Afib:

Anticoagulation/avoid stroke
Better symptom control
Comorbidity management/cardiovascular risk factor reduction

In some cases, Afib is caused by a reversible etiology and does not return when the etiology is treated. However, it's difficult to know whether the Afib actually receded when the assumed underlying etiology was treated or whether the Afib is just paroxysmal and coincidentally went away.

In case of unstable patients, emergency electrical cardioversion is indicated.

Anticoagulation

Stroke risk is increased in patients with atrial fibrillation, due to the Afib’s tendency to form thrombi in the left atrium which can embolise to the brain. All patients with Afib should have the CHA2DS2-VASc score calculated:

Congestive heart failure – 1 point
Hypertension – 1 point
Age > 75 years – 2 points
Diabetes mellitus – 1 point
Stroke, TIA, or thromboembolism – 2 points
Vascular disease (CAD, PAD, etc.) – 1 point
Age 65 – 74 years – 1 point
Sex Category: female – 1 point

A score of 1 or more in men and 2 or more in women is an indication for anticoagulation. A score of 0 in males, or 1 or 0 in females has low risk for stroke and does not require anticoagulation. The bleeding risk (with the HAS-BLED score) should be calculated and considered, and modifiable risk factors for bleeding should be treated if possible. Anticoagulation should be with a DOAC, and it should be continued indefinitely. VKA is the second choice.

Better symptom control

The symptoms of Afib can be controlled with either a rate-control strategy or a rhythm-control strategy. Choosing between them can be difficult. Generally, we use rhythm-control for patients who are young, have heart failure, have significant symptoms, have high cardiovascular risk, or if rate-control has failed. Rate-control is generally used for older or asymptomatic patients.

Rate control

Rate control involves not attempting to convert to sinus rhythm, but to use negative chronotropic drugs to reduce the ventricular rate. This improves symptoms and prevents development of heart failure. The first choice is a beta blocker, often metoprolol. Second choices include verapamil and dilitazem.

Rhythm control and cardioversion

Rhythm control involves restoring and maintaining sinus rhythm. This involves electrical cardioversion, pharmacological cardioversion, or catheter ablation. Chronic antiarrhythmic treatment is usually require to maintain sinus rhythm afterwards.

Indications for cardioversion include if adequate rate control can’t be achieved, or if the onset of the Afib is recent (<2 days). As atrial remodelling occurs early after onset of Afib, cardioversion has a lower chance of being successfull the longer the duration of the Afib.

Cardioversion can be electrical or pharmacological, but it is contraindicated in case of left atrial thrombus, as cardioversion could trigger embolism. Cardioversion can be attempted if:

Afib has lasted <2 days
- (As no thrombus could’ve formed in that time)
Afib has lasted >2 days but the patient has been properly anticoagulated for 3 – 4 weeks
- (As anticoagulation would have dissolved the thrombus)
Afib has lasted >2 days and the patient hasn’t been anticoagulated but a TEE has been performed and excluded the presence of cardiac thrombus

Patients must usually remain on antiarrhythmic drugs after conversion to prevent recurrence.

Electrical cardioversion involves administering synchronised electrical shock under sedation to restore sinus rhythm.

Pharmacological cardioversion involves administering antiarrhythmic drugs which, in some cases, can alone be enough to convert to sinus rhythm. The choice of specific drug depends on whether there is concomitant structural heart disease or not. The most commonly used drugs are flecainide, amiodarone, and vernakalant.

The “pill in the pocket” approach may be appropriate for those with infrequent symptomatic episodes of Afib. These patients may carry oral doses of antiarrhythmics (usually flecainide or propafenone) and take them when an episode occurs, which pharmacologically cardioverts back to sinus rhythm. This is only an option if it’s been confirmed in-hospital that these drugs successfully cardiovert the patients.

Catheter ablation is another option for rhythm control. It’s a well-established, safe, and effective treatment option for rhythm control. It involves electrically isolating the pulmonary veins, which is a common ectopic focus.

Comorbidity management/cardiovascular risk factor reduction

Tachycardia-induced heart failure should be treated like other types of heart failure, with ACEi/ARB, beta blockers, diuretics, etc. Other cardiovascular risk factors, like hypertension, diabetes, atherosclerosis, etc., should be managed as well.