Atrial Fibrillation (AF)

Introduction

Atrial Fibrillation (AF) is the most common heart rhythm disturbance and is increasingly common with increasing age. It often affects hearts that otherwise quite normal. 

It generally exists in one of two forms:

1. Recurrent episodes that stop on their own (Paroxysmal)

2. Episodes that will continue incessantly once they have started (Persistent)

Subclinical atrial fibrillation

Subclinical AF refers to episodes in a patient has without symptoms and without a prior history of AF, which are detected only by monitoring techniques. 

Aetiology / causes

AF is caused by extra beats arising from the mouths of the 4 veins that connect into the left atrium – the heart chamber from which the fibrillation arises. These 4 pulmonary veins have sleeves of electrical tissue that are the sources of the triggers of atrial fibrillation which once started continues as rapid, random electrical activity (fibrillation) around the whole atrium.

Significant structural heart disease is associated with AF, in particular affecting the heart valves. Hearts affected by 'Ischaemic Heart Disease' and hypertension can also be prone to AF.

Diseases which affect conduction in the Atria (chambers of the heart) or the size of the atria also predispose to AF.

Temporary or reversible causes of AF include cardiac surgery, hypertension, alcohol, theophylline or other stimulant toxicity, pericarditis, MI and hormonal problems (hypothyroidism, hyperthyroidism, pheochromocytoma.

AF which has occurred in the absence of any structural heart problems is called 'Lone AF'.

Differential diagnosis

Other forms of irregular heart rate should be considered and excluded with tests and monitoring.

Diagnostic approach

The basic diagnosis is made on the basis of an ECG (EKG). The hallmark of AF is an irregular, fluctuating baseline to the ECG. The ventricles (main pumping chambers of the heart) may well also be beating irregularly and fast (>100 beats per minute).

Hormonal (endocrine) issues can diagnosed on blood tests and structural heart disease is investigated by echocardiogram/ CT or MRI.

Epidemiology

Age

AF is uncommon in children. Healthy young adults are also at low risk (1). The prevalence of AF increases with age (2-5). The ATRIA study in America showed the overall prevalence of AF was 1 percent; 70 percent were at least 65 years old and 45 percent were ≥75 years old (5). The STROKESTOP study in Sweden showed the prevalence of AF in a 75- to 76-year-old population to be 12 percent (6). Another European study of 6808 people ≥ 55 years of age showed an overall prevalence of 5.5 percent, ranging from 0.7 percent in those aged 55 to 59 years and 17.8 percent for those ≥85 years of age (4).

Sex

The prevalence was higher in men than women (1.1 versus 0.8 percent). This difference was seen in every age group. Another study, reported the rates were 6 versus 5.1 percent, respectively (5).

Race

In one study, AF was more frequent in whites than blacks over the age of 50 years (2.2 versus 1.5 percent) (6). 

Geography

The age-adjusted prevalence rate (per 100,000 population) was reported highest in North America (700 to 775) and lowest in Japan and South Korea (250 to 325) (7). The rate in China was also relatively low (325 to 400).

Time period

The prevalence of AF in the population is increasing. In a community-based study of 1.4 million patients in England and Wales, the age-standardized prevalence of AF between 1994 and 1998 increased by 22 and 14 percent in men and women, respectively (2). 

Treatment

Overall, atrial fibrillation can be treated by either trying to restore and maintain normal rhythm (rhythm control) or by leaving the heart in atrial fibrillation but controlling the rate (rate control). Rhythm control, if it can be achieved, is generally preferable unless the atrial fibrillation is particularly longstanding, causing no symptoms or has proved impossible to control by other means.

Blood thinning with medicines (anticoagulation) is also important for patients in AF. The risk versus benefits of anticoagulation are weighed up by a number of factors which are often combined into a score. Rhythm control is achieved by: 1. antiarrhythmic medication (such as Flecainide, Amiodarone, Sotalol) with or without: 2. DC cardioversion (an electrical shock under anaesthetic which abruptly terminates atrial fibrillation) 3. Ablation therapy

This is currently considered appropriate in patients who have a significant burden of atrial fibrillation from which they have symptoms not controlled by antiarrhythmic tablets. Ablation can cure AF in many patients but is a challenging procedure that usually needs repeating, with moderately good success rates and small but significant and important risks.