In the UK, over 30,000 people experience an out-of-hospital cardiac arrest (OHCA) each year - which works out to be around 82 people per day.
A cardiac arrest is different to a heart attack. It's when the heart suddenly and unexpectedly stops pumping blood which can cause problems in your brain and other vital organs.
Read more: Difference between a heart attack and cardiac arrest (Yahoo Life UK, 5-min read)
A new study has found that up to half of all people who have a cardiac arrest will feel symptoms up to 24 hours before it occurs - and the first symptoms are different for men and women.
A cardiac arrest can be fatal and, according to the British Heart Foundation (BHF), less than one in 10 people survive an OHCA, so it's important to know the early warning signs.
"Harnessing warning symptoms to perform effective triage for those who need to make a 999 call could lead to early intervention and prevention of imminent death," senior study author Dr Sumeet Chugh said. "Our findings could lead to a new paradigm for prevention of sudden cardiac death."
Difference between a heart attack and cardiac arrest
A cardiac arrest is caused by a dangerous abnormal heart rhythm (arrhythmia) that means your heart stops beating unexpectedly and suddenly.
A heart attack is when the blood supply to the heart is cut off, often caused by a blood clot. Blood is still pumping around the body during a heart attack and you will be conscious and breathing. You will not be conscious or breathing during a cardiac arrest.
A heart attack can lead to a cardiac arrest if proper medical help isn't sought.
Early cardiac arrest signs for women
According to the study, which has been published in the Lancet Digital Health, women are more likely to experience a shortness of breath in the 24 hours before cardiac arrest.
A 2019 study published in the European Heart Journal found that women are more likely to die from a cardiac arrest if they have one in public because just 68% of women are likely to receive CPR from a bystander compared to 73% of men.
Early cardiac arrest signs for men
Men will feel chest pains as the first warning sign of a cardiac arrest, the research from the Cedars-Sinai Medical Center in the US found.
Cardiac arrest signs and symptoms
While the new study Cedars-Sinai Medical Center has found that the initial cardiac arrest symptoms can occur 24 hours before it happens, most of the time a cardiac arrest will happen without warning.
Signs of someone having a cardiac arrest include:
Not breathing or making gasping sounds
If someone near your is exhibiting any of these signs, call 999 and immediately start performing CPR.
Cardiac arrest: read more
North East mum who lost son after cardiac arrest campaigns for defibrillator access (The Northern Echo, 3-min read)
Neighbour saves life of dad who had cardiac arrest in front of his children (Yahoo Life UK, 6-min read)
Cardiac arrest causes
A cardiac arrest can be caused by abnormal heart rhythms such as cardiomyopathies (disease of the heart muscle), congenital heart disease, heart valve disease and myocarditis, which is inflammation of the heart muscle.
Other causes can be a heart attack, hypoxia (a sudden drop in oxygen levels), a severe haemorrhage, electrocution or a drug overdose.
You are at a higher risk of having a cardiac arrest if you:
Have a family history of coronary artery disease
Have high blood pressure
Have an inactive lifestyle
Have had a heart attack
Use drugs like cocaine
Have low potassium or magnesium levels
Have sleep apnoea
Have chronic kidney disease
Cardiac arrest treatment
A cardiac arrest can only be treated by performing CPR, using a defibrillator, or getting the patient to an emergency room as soon as possible.
The BHF says starting CPR immediately is vital to keep blood and oxygen moving to the brain. Public defibrillators can usually be found in train stations or shopping centres.
Call 999 if you see someone collapse and who is unresponsive and the operator can give you further instructions.