Ventricular fibrillation: what it is, causes, symptoms and treatment

The heart has its own electrical system, which helps it to beat regularly and at the right time. The British Heart Foundation explains that when this system does not work properly the heart can beat too quickly, too slowly or irregularly, which is called an arrhythmia. Not all abnormal heart rhythms are life-threatening, but some mean the heart cannot pump blood around the body.

The BHF lists ventricular fibrillation (VF) among the abnormal heart rhythms that can lead to a cardiac arrest, alongside ventricular tachycardia (VT) and supraventricular tachycardia (SVT). It is therefore treated as a cardiac arrest rhythm rather than as a problem that can be monitored.

VF is different from the more common arrhythmias that people may feel as palpitations. The BHF says most arrhythmias are not dangerous, but some can be. The NHS notes that many people with heart rhythm problems need no treatment or only regular check-ups, and that palpitations with chest pain, shortness of breath, dizziness or fainting are a reason to call 999 or go to A&E.

There is usually no time to diagnose VF by name at the scene. What others see is a cardiac arrest. According to the BHF, the person collapses suddenly and is unconscious, unresponsive and not breathing or not breathing normally; they may make gasping noises. The BHF says a cardiac arrest usually happens without warning and that, without immediate treatment, the person will die.

A cardiac arrest is sometimes mistaken for a heart attack, but the two are different. The NHS says a heart attack happens when blood flow to the heart is blocked, whereas the BHF describes a cardiac arrest as the heart suddenly stopping pumping blood around the body.

• Call 999 immediately and say that someone has collapsed and is not breathing normally.

• Start CPR straight away and follow the instructions given by the 999 call handler until the ambulance crew arrive.

• If someone is with you, ask them to fetch a defibrillator. The BHF says the machine will talk you through the steps and you do not need training to use one.

• Do not stop CPR to wait and see whether the person recovers on their own.

VF is usually the end result of another problem rather than a disease in its own right. The BHF lists heart conditions that can lead to the abnormal rhythms behind cardiac arrest if they are severe or left untreated: diseases of the heart muscle (cardiomyopathies), inherited conditions that affect the electrical system such as Brugada syndrome, congenital heart disease, heart failure, heart valve disease and severe or untreated myocarditis.

It also lists other causes of cardiac arrest: a heart attack, often caused by coronary artery disease; losing a large amount of blood; a sudden drop in oxygen levels; being electrocuted; and a drug overdose. The NHS adds that some medicines, viruses, caffeine, alcohol, smoking and recreational drugs can provoke an abnormal heartbeat, although these are far more often linked to less dangerous rhythm changes.

Inherited conditions deserve a special mention. The BHF notes that where an inherited condition such as long QT syndrome or Brugada syndrome is found, the doctor will talk about testing family members, which can help show whether they need treatment now or in the future.

The BHF explains that after a cardiac arrest you will be looked after in a coronary care or intensive care unit, where close monitoring is possible. You may be kept asleep, sometimes called an induced coma, to allow the body to recover. Many people have no memory of the event.

Once the situation is stable, doctors want to work out why it happened. Tests used to investigate heart rhythm problems in general include an electrocardiogram (ECG), an echocardiogram and an electrophysiological (EP) study, according to the BHF. Which tests you need depends on your history and what is found first.

Treatment aims to reduce the risk of it happening again. The BHF names an implantable cardioverter defibrillator (ICD) and ablation among the options after a cardiac arrest, and the NHS lists medicines to control heart rate and rhythm, ablation, cardioversion and devices fitted under the skin as treatments for heart rhythm problems more broadly. Treatment for any underlying condition, such as coronary artery disease or heart failure, is part of the same plan.

An ICD is a device that the BHF lists among the treatments for arrhythmias and after cardiac arrest. NICE technology appraisal TA314 recommends ICDs as an option for people with a previous serious ventricular arrhythmia, including people who, without a treatable cause, have survived a cardiac arrest caused by VT or VF. It also recommends them for people with a familial cardiac condition that carries a high risk of sudden death, such as long QT syndrome, hypertrophic cardiomyopathy, Brugada syndrome or arrhythmogenic right ventricular dysplasia, and for some people who have had surgical repair of congenital heart disease.

The same guidance sets out when an ICD or cardiac resynchronisation therapy may be considered for people with heart failure and a reduced left ventricular ejection fraction. These decisions are made by specialist teams, and the choice of device depends on individual factors such as heart function and the width of the QRS complex on an ECG.

The BHF says recovery time depends on the cause and on how long it took for the heart to beat on its own again. It can take several weeks, a few months or longer if more rehabilitation is needed, for example to relearn walking or self-care. Cardiac rehabilitation is often offered to help rebuild confidence, fitness and strength.

A lack of oxygen to the brain can sometimes have long-term effects, including memory problems, tiredness, dizziness or balance issues, and changes to speech and language. It is also normal to feel low, angry or confused afterwards, and relatives who witnessed the event may be affected too. The BHF suggests speaking to a doctor about counselling, and NHS talking therapies can be self-referred.

Practical matters such as driving and work need to be discussed with the care team. The BHF notes that if your ability to drive is affected by an arrhythmia you must tell your insurance company and the DVLA, and your GP can tell you whether this applies. Lifestyle measures that doctors may suggest include a healthy diet, stopping smoking, cutting down on alcohol, being active and taking medicines as prescribed.

Emergency treatment for cardiac arrest in the UK is delivered through 999 and NHS ambulance and hospital services. After the event, the BHF says doctors will want to work out what caused it and can recommend medicine and treatment to reduce the risk of it happening again, and may refer you to cardiac rehabilitation.

Some people also choose a private cardiologist for a second opinion or quicker access to tests. Whichever route you use, it helps to ask which team is responsible for your follow-up and device checks, and how information will be shared between hospitals and your GP.