Sudden cardiac arrest: causes, CPR and recovery

The British Heart Foundation (BHF) says a cardiac arrest is when your heart suddenly stops pumping blood around your body. It is sometimes mistaken for a heart attack, but the two are different.

In a heart attack the heart muscle is short of blood because an artery is blocked. The NHS says people are usually awake and may have chest pain, breathlessness and sweating. In a cardiac arrest the heart stops pumping effectively, usually because its electrical system fails, and the person collapses and stops responding.

Heart attack is one of the causes of cardiac arrest, which is why the two are linked in people's minds.

The BHF describes a sudden collapse with the person unconscious, unresponsive and either not breathing or not breathing normally. Gasping noises can occur. St John Ambulance advises ignoring occasional irregular gasps, which are common in the early stages of cardiac arrest.

The advice from both organisations is to call 999 and start CPR straight away. Chest compressions keep blood and oxygen moving to the brain while help comes.

St John Ambulance describes pressing in the centre of the chest with the heel of the hand, arms straight, to a depth of about 5 to 6 cm, at 100 to 120 compressions a minute. If trained and willing, give two rescue breaths after every 30 compressions. If not, continuous compressions are fine. The 999 call handler will guide you.

A defibrillator delivers a controlled electric shock to try to restore a normal rhythm. The BHF says that if someone is with you, ask them to go and get one. St John Ambulance adds that you should not leave the person to look for one if you are alone, and that the ambulance controller can say where the nearest is.

Not every rhythm responds to a shock. The BHF explains that in non-shockable rhythms, the electrical activity does not respond to a defibrillator and you continue CPR. The machine decides whether a shock is advised.

The BHF says a cardiac arrest happens when the heart's electrical system does not work properly and the heart beats too quickly, too slowly or irregularly. Rhythms that can lead to it include ventricular fibrillation, ventricular tachycardia and supraventricular tachycardia.

Conditions that can trigger dangerous rhythms if severe or untreated include cardiomyopathies, inherited heart conditions such as Brugada syndrome, congenital heart disease, heart failure, heart valve disease and myocarditis. Other causes listed are heart attack, major blood loss, a sudden drop in oxygen, electrocution and drug overdose.

The BHF explains that inherited conditions are caused by changes in genes, and that for many families the first sign is when someone dies suddenly with no obvious cause, known as sudden arrhythmic death syndrome (SADS). Warning signs in others can include dizzy spells, palpitations, blackouts, breathlessness and chest pain, which should be discussed with a GP.

The BHF says people are looked after in a coronary care or intensive care unit and may be kept asleep in an induced coma to allow recovery. Doctors then work out the cause so they can recommend medicine or treatment to reduce the risk of a repeat.

Treatments may include an implantable cardioverter defibrillator (ICD), a device that can detect and correct dangerous rhythms, or ablation. Referral to cardiac rehabilitation can help rebuild confidence, fitness and strength.

Because of the lack of oxygen to the brain, some people have lasting effects such as memory problems, tiredness, dizziness, balance issues, speech and language difficulty, or involuntary muscle movements. Speech and language therapists and occupational therapists can help.

The BHF says it is normal to have no memory of the arrest, and to feel low, angry or confused. Family members who saw it happen may also be affected. It suggests speaking to a doctor, who may refer for counselling, and notes that you can refer yourself for NHS talking therapies. Sudden Cardiac Arrest UK is named as a peer support group.

Relatives may be offered testing. The BHF says that when a family member has an inherited heart condition or there has been an unexplained death, tests can include an ECG, echocardiogram, 24-hour heart monitor, exercise test or MRI, and relatives may be referred to a specialist centre for genetic testing, with genetic counselling to explain the results.

Emergency treatment is delivered by ambulance services and hospital cardiac teams through 999. Survivors are followed up by NHS cardiology, with ICD implantation, rehabilitation and genetic services arranged through the same pathway.

Private cardiology may be sought for heart rhythm assessment, screening of family members, or a second opinion. For inherited conditions, specialist inherited cardiac condition services are the usual route, and results should be shared with your GP and cardiologist.