Chapter 1 - What is AF?

Key points

  • AF is the most common sustained heart rhythm disorder
  • Having AF doubles the risk of death, regardless of age
  • In symptomatic patients, AF is frequently associated with a highly significant reduction in quality of life
  • In all AF patients, the risk of suffering a stroke is increased nearly 500%
  • AF can be detected with a simple pulse check but approximately half of all patients remain undiagnosed
  • AF, and AF related illness, costs the NHS over £2.2 billion each year
  • AF affects nearly 2% of the population, a number that is rising fast
  • Between 100,000 and 200,000 people in the UK develop AF every 12 months

Atrial fibrillation (AF) is a common heart rhythm disorder associated with deadly and debilitating consequences including heart failure, stroke, poor mental health, reduced quality of life and death.71

AF is also the most prevalent sustained heart rhythm disorder.193  Today, approaching a million Britons are diagnosed with AF,61 yet experts suggest that between one third and a half of all AF patients have not yet been detected.  Today, everyone aged 40 or over has a life time risk of developing AF of at least one in four.24  For context, this compares with one in eight for breast cancer in women of the same age.25 

Among many damaging and debilitating consequences, AF increases an individual’s risk of suffering a stroke by five times.68 This effect alone results in considerable disability and death,193,4 not to mention avoidable millions in healthcare expenditure61 that the National Health Service (NHS) cannot afford.

What is AF?

Atrial: pertaining to the atria (pleural of atrium) the top two chambers of the heart

Fibrillation: the rapid, irregular and unsynchronised contraction of muscle fibres

AF is a heart rhythm disorder (a cardiac arrhythmia) of the atria.  The normal beat of the heart (called sinus rhythm) is managed by a sophisticated electrical control system.  This system matches heart rate with physiological demands and ensures that the four chambers of the heart contract and relax in time with one another to maintain a steady and efficient rhythm to pump blood.

The heart’s natural pacemaker is a cluster of special cells in the atria called the sinus node.  The sinus node controls the rate at which the atria contract and relax.  In AF, chaotic electrical activity develops in the walls of the atria, over-riding the sinus node.  The normal, steady rhythm of the atria is disrupted and they instead begin to fibrillate; quivering with a shallow but very fast rhythm as their muscular walls fail to contract with regularity and coordination.

An irregular pulse

This atrial fibrillation disrupts the electrical signals that trigger the contraction of the heart’s main pumping chambers, the ventricles.  Consequently, the ventricles beat faster and their rhythm becomes irregular as the electrical conduction system is over-run by the fast and chaotic impulses from the fibrillating atria.  This altered ventricular beating can be detected as an irregular pulse, a valuable yet simple test for AF.

A progressive condition

Initially for most patients, AF is an electrical problem in the heart that can be addressed by therapies which treat the rate and rhythm of the heartbeat, or which can immediately return the heart to normal sinus rhythm – a procedure called cardioversion.

Over time, AF which is untreated, or which fails to respond to treatment, begins to change the anatomy of the heart muscle, interfering further with the electrical conduction necessary for a normal heart beat.  Eventually, all treatments to correct the electrical system become ineffective, leading to therapy that aims only to prevent the consequences of AF.

Deadly consequences

Atrial fibrillation disrupts the efficient pumping of blood through the heart and around the body.  The disturbance in flow can allow clots to form where the blood moves too slowly.  The blood stream can then carry these clots to vessels in the brain causing deadly blockages that result in stroke.

Massive NHS burden

AF is a significant and growing drain on the NHS.  During the past 20 years there has been a 60% increase in the number of patients being admitted to hospitals as a result of AF.26  In 2008, there were an estimated 850,000 GP visits because of AF in the UK.61  When including AF as a causative secondary diagnosis, the total cost of AF to the NHS has been calculated to be nearly £2.2 billion a year.61  Some authoritative estimates predict a three-fold increase in AF over the next 50 years.12,27

Signs, symptoms and consequences of AF

There are many negative consequences of AF frequently leading sufferers into a life of confusion and despair.28  AF is associated with a significant increase in risk of stroke, heart failure and death.71  It has also been found that approximately one third of AF patients suffer persistent anxiety or depression.  From the same research, depression was also noted to have considerable negative impact on future quality of life.29  Other symptoms include palpitations, shortness of breath, light-headedness, fainting, fatigue and chest pain.33  For emergency admissions to hospital, AF most often presents as difficulty with breathing, chest pain and palpitations.64

A simple and easily identifiable sign of AF is an irregular pulse.  For this reason, many AF experts and patient advocacy groups are calling for pulse checks to become a free, swift and routine part of every GP visit.

However, AF is frequently intermittent and many people with AF have no or non-specific symptoms.8  These combine to make detection and diagnosis difficult; often, AF is not apparent until a person goes to see their doctor with a serious complication such as stroke, a blood clot in the leg or heart failure.64

Yet, even patients who do experience symptoms of AF are not always diagnosed immediately. In a recent international survey, there was an average delay of 2.6 years between the onset of symptoms and the diagnosis of AF.30  In another piece of research, among patients with documented chronic AF, it was found that more than a third were not aware of their diagnosis and up to half were unaware of why they were being treated.31  This indicates that many patients with AF are not being detected or managed effectively and that many are at risk of serious long-term consequences such as stroke.

Efforts have already begun to increase the rates of diagnosis and effective management of AF.  For example, the National Institute for Health and Clinical Excellence (NICE) recommends that doctors make assessments for the presence of AF in all people presenting with breathlessness, palpitations, fainting/dizziness, chest discomfort, stroke or mini-stroke (TIA).32

How does AF lead to stroke?

AF results in a fivefold increase in the risk of stroke, making it the most powerful independent risk factor for stroke.68  Moreover, strokes in patients with AF tend to be more severe than in non-AF patients.72  The below chart illustrates the impact that AF has on the likelihood of suffering a stroke compared to other stroke risk factors such as high blood pressure, heart disease and heart failure.

AF increases the risk of stroke by nearly five times, more than any other cardiovascular risk factor

The risk of stroke increases because AF is associated with the formation of clots inside the heart.  During AF, blood can slow as fibrillation prevents the normal high-pressure flow of blood through the heart and out to the arteries.  When blood is allowed to travel slowly the natural formation of clots can begin.  This is usually a safety mechanism to help prevent excessive bleeding at sites of injury. 

In stark contrast, clots forming within the heart and arteries can be deadly.  As clots travel downsteam into increasingly smaller arteries, even small clots can cause blockages that prevent oxygen and nutrients reaching the tissues.  If such a blockage occurs in the brain, the damage done by the lack of blood flow results in a stroke.  AF is estimated to be responsible for approximately 15%-20% of all strokes. 63,4

Who gets AF?

It is difficult to overstate just how big a problem AF presents.  To provide some perspective, one authoritative and recent study from the Mayo clinic in the US concluded that, for anyone aged 40 or above, the lifetime risk of AF exceeds 25%;24 meaning that one in four adults can expect to develop AF.  This compares to the lifetime risk of breast cancer in women of the same age, which is one in eight.25  However, because of improved detection methods, each new study of the prevalence of AF reports an increase for the same point in time.  For example, the Mayo clinic study above was published in 2004 when AF was thought to affect less than 1% of the population they were studying.34

We now know that around 2% of the population in 2004 had AF.  It is predicted that by 2050, over 4% of the population will have it.12  Consequently, it is very likely that, for those aged 40 today, the lifetime risk of developing AF in fact higher than one in four .

Given the number of people who have or will develop AF, it is not easy to define a typical AF patient.  Men and women of all ages can be affected.  In general terms, the likelihood of developing AF increases with age.193

However, some people appear to be at a higher genetic risk.  This predisposition to AF is most often seen in young patients.191,199  In addition, some studies suggest that the incidence of AF is higher than normal in athletes and others who engage in frequent, vigorous exercise regardless of age.35,36 For all these reasons, AF is not just a condition of the elderly.

What causes AF?

The most common underlying causes of AF are high blood pressure, thyroid disease and, to a lesser extent, coronary artery disease and diabetes.195,178  Dietary, lifestyle and other factors that contribute to the risk of AF include emotional and physical stress and excessive caffeine, alcohol or illicit drug intake.64

The main causes of AF are different than they were 20 years ago.  At that time, rheumatic disease commonly resulted in the hardening and narrowing of the heart’s mitral valve (mitral stenosis) and was an important cause of AF.  The incidence of rheumatic disease in European patients has diminished considerably in recent decades due mainly to improved living conditions.  Today, AF as a result of mitral stenosis is relatively rare.  The term ‘non-valvular AF’ is used to describe cases where rhythm disturbance is not associated with these problems.8  This report is concerned only with non-valvular AF, which is that most frequently encountered in the UK.

How many people suffer from AF?

As we have seen, AF is responsible for many hundreds of thousands of GP visits61 despite estimates that nearly between one third and a half of those affected are yet to be diagnosed.  Over 800,000 patients in the UK are known to have AF.61  As symptoms are not always specific, and because there is no routine screening for early detection, experts estimate that the total number with AF in the UK might exceed 1.5 million.

The numbers of people affected by a condition are generally measured in two ways.  Prevalence is the proportion of a population affected at any given time; usually as a percentage.  The other measure is incidence, which measures just the newly affected patients in the population over a given time span, usually 12 months. 

Growing and under-detected prevalence of AF

As seen in the example above from the Mayo clinic in the US, the proportion of the UK population with diagnosed AF is also growing.  Today we believe the prevalence of AF in the UK to be near 2% and increasing.27  Between 1994 and 2006, the UK prevalence of AF rose from 0.78% to 1.42%.27  This increase appears to reflect increasing life expectancy as well as the impact of medical science that enables more people to survive conditions such as heart attacks that can add to the likelihood of developing AF. 66  There is also the very real likelihood that an improved focus on AF, and improved methods of detection, will uncover greater numbers still.

Independent of this increase in prevalence of AF over time in our society, the number of people with AF has been shown to double with each advancing decade of age, from 0.5% at age 50-59 years to almost 9% at age 80-89 years.193  Not surprisingly, the incidence of AF also increases with age, contributing to the growing prevalence.193

As all these factors combine, it has been predicted that the total number of people affected by AF is likely to triple by 2050.12,27

Incidence of AF in the UK

The most recently published data on the number of people in the UK who develop AF is from 2002.  This research reported that the incidence of AF in the UK was 1.7 per 1,000 patient years.37  With today’s population this would mean that 105,000 people develop AF every year.  If, however, the number of people developing AF has been increasing each year since 2002, similar to the increase observed above, then it could be that approaching 200,000 people in the UK are now developing AF every 12 months.37,12

The number affected by AF is predicted to double by 2050