What is the difference between a heart attack and cardiac arrest?

A heart attack is a circulation problem. One of the coronary arteries that supplies the heart muscle becomes blocked, usually by a blood clot, and part of the muscle starts to lose its blood supply. A cardiac arrest is an electrical problem. The heart's rhythm suddenly becomes chaotic or stops, the heart stops pumping blood, and the person collapses and stops breathing normally. Someone having a heart attack is usually awake and talking. Someone in cardiac arrest is unconscious and will die within minutes without help.

The two are connected, because a heart attack is one of the most common triggers of a cardiac arrest. Both are emergencies, and in both cases the first step is to call 999. For a heart attack, that call gets the person to treatment that can unblock the artery and save heart muscle. For a cardiac arrest, it must be followed immediately by CPR and, as soon as one is available, a defibrillator.

What happens during a heart attack

Most heart attacks happen when a fatty plaque inside a coronary artery cracks open. A blood clot forms on the surface, blocking the artery either completely or partly. The heart muscle beyond the blockage is starved of oxygen, and the longer the artery stays blocked, the more muscle is permanently damaged.

The British Heart Foundation reports around 100,000 hospital admissions for heart attacks in the UK each year, which is roughly one every five minutes.

Symptoms of a heart attack include the following.

• Chest pain, pressure or tightness, often described as a heaviness or squeezing.
• Pain that spreads to the arms, neck, jaw, back or stomach.
• Shortness of breath.
• Sweating, feeling sick or being sick.
• Feeling lightheaded or an overwhelming sense of anxiety.

The pain is not always severe. Some people describe it as indigestion or a dull ache, and some have no chest pain at all. Heart attacks with few or no symptoms are more common than many people realise, particularly in older people and those with diabetes.

What happens during a cardiac arrest

In a cardiac arrest, the heart's electrical system fails. The most common rhythm is ventricular fibrillation, where the main pumping chambers quiver rather than contract. No blood reaches the brain, so the person collapses within seconds. They will not respond to you and will not be breathing normally. Some people make occasional gasping noises in the first minutes, and these can be mistaken for breathing.

Survival depends almost entirely on what bystanders do in the first few minutes. According to the BHF, there are more than 40,000 out-of-hospital cardiac arrests in the UK each year, and fewer than 1 in 10 people survive. Every minute without CPR and defibrillation sharply reduces the chance of survival.

A heart attack is the most common cause of cardiac arrest in adults, but there are others. These include cardiomyopathy, inherited heart rhythm conditions, severe valve disease, inflammation of the heart muscle and serious electrolyte imbalances. In younger people who collapse suddenly, an inherited condition is often the cause.

The difference at a glance

Heart attack

Cardiac arrest

Type of problem

Blocked blood supply to the heart muscle

Electrical failure, the heart stops pumping

Is the person conscious?

Usually yes

No

Are they breathing?

Yes

No, or only gasping

Typical symptoms

Chest pain, breathlessness, sweating, nausea

Sudden collapse with no pulse

What to do

Call 999, sit them down, keep them calm

Call 999, start CPR, use a defibrillator

What to do if someone is having a heart attack

Call 999 straight away. Help the person sit down and rest, and stay with them. The NHS advises that if they are not allergic to aspirin, they should slowly chew a 300mg tablet while waiting for the ambulance. If they have been prescribed a GTN spray for angina, they can use it.

In my experience, calling an ambulance works better than driving to A&E because paramedics can record an ECG at the scene and send it ahead. If it shows the most serious type of heart attack, the patient can be taken directly to a specialist heart attack centre for an emergency coronary angiogram and stent, bypassing A&E altogether. That can save valuable time, and every minute counts for the heart muscle.

During my years at Kingston Hospital NHS Trust, I was closely involved in setting up its cardiac angiography services. That work showed me how much the speed of diagnosis matters. Patients who arrived early and went straight for treatment consistently did better than those who waited at home hoping the pain would pass.

What to do if someone has a cardiac arrest

If someone collapses and is not responding or breathing normally, act immediately.

1. Call 999. Put the phone on speaker so the call handler can guide you.
2. Start CPR. Push hard and fast in the centre of the chest, at a rate of 100 to 120 compressions a minute, letting the chest come back up between each push. The BHF explains hands-only CPR step by step.
3. Get a defibrillator. Send someone to find the nearest one. The 999 call handler can tell you where it is, as most public access defibrillators are registered on The Circuit, the national defibrillator network.
4. Follow the defibrillator's instructions. You do not need training. The machine talks you through every step and will only deliver a shock if one is needed.

Learning CPR takes very little time. The BHF's free online tool, RevivR, teaches it in around 15 minutes, and I recommend it to every patient and family member I see.

How doctors tell which has happened

For a heart attack, the key tests are an ECG and a blood test for troponin, a protein released when the heart muscle is damaged. An ECG can show whether an artery is completely blocked, and an echocardiogram shows which part of the heart is not moving properly. A coronary angiogram then shows exactly where the blockage is, and it can usually be treated during the same procedure with a balloon and stent.

For someone who survives a cardiac arrest, the investigation focuses on finding the cause. If a heart attack triggered it, the artery is treated. If not, tests such as a cardiac MRI, genetic testing and prolonged heart rhythm monitoring look for another explanation. Some survivors are fitted with an implantable cardioverter defibrillator to protect against another arrest.

If you would like to understand more about the tests involved, including the ECG and coronary angiogram, I describe each of them on my heart tests page.

Reducing the risk of both

Because coronary heart disease underlies most heart attacks and many cardiac arrests, the same steps reduce the risk of both. Controlling blood pressure and cholesterol, stopping smoking, staying active and managing diabetes all make a real difference. The most effective ways to lower your risk are mostly simple, but they need to be kept up over many years.

From working with patients, I've found that many people only think about their heart after a friend or family member has a heart attack or collapses suddenly. If that has happened to someone close to you, it is a sensible moment to have your own risk factors assessed. That is especially true if a relative under 50 had a cardiac arrest or died suddenly, as some inherited conditions can be detected and treated before they cause problems.

Warning signs worth getting checked include chest pain on exertion, unexplained fainting, palpitations with dizziness, and breathlessness that is new or getting worse.

Speak to a cardiologist

If you are worried about your heart, or you would like a full assessment of your risk after a family history of heart attack or sudden death, please contact me, Dr Arvind Vasudeva. I have worked as a Consultant Cardiologist for more than 20 years and see patients at Parkside Hospital in Wimbledon, The New Victoria Hospital in Kingston, Cleveland Clinic London and Heartsure in Kingston. You can book an appointment at whichever location is most convenient for you.