Cardiac arrest

A cardiac arrest (also known as sudden cardiac arrest) is when the heart suddenly stops beating. As a result, blood flow to the brain and other vital organs stops, and the sufferer loses consciousness and stops breathing normally.

A cardiac arrest is a medical emergency and can be fatal without immediate treatment.

The terms “cardiac arrest” and “heart attack” are often used interchangeably, but they are not the same thing.

A heart attack occurs when a blockage stops blood flow to the heart. Blockages can occur when fat and other substances build up and form plaque in the arteries through a process called atherosclerosis. When plaque breaks away from the artery wall, it can form a blood clot (thrombosis) that interrupts the flow of blood around the body. If the clot blocks or stops the flow of oxygen-rich blood to the heart, this can lead to a heart attack, and the heart muscle starts to die due to lack of oxygen.

A cardiac arrest occurs when there is a malfunction in the heart’s electrical system that causes the heart to stop beating properly.

Difference in symptoms of cardiac arrest and heart attack

The symptoms of cardiac arrest and heart attack are different, as well as how they are managed and treated.

In a cardiac arrest, the sufferer will not be conscious or breathing normally, and their heart will have stopped beating.

In a heart attack, the sufferer will usually be awake, breathing and experiencing symptoms of heart attack such as chest pain. The heart continues beating during a heart attack. In some cases, a heart attack can trigger an electrical disturbance that leads to cardiac arrest.

The heart has an electrical system that controls the rate and rhythm of the heartbeat and how it pumps blood around the body. If something goes wrong with this system, the heart can beat too fast, too slow or irregularly (arrhythmia).

A cardiac arrest is usually caused by a malfunction in this electrical system that causes the heart to stop beating. The main causes of this malfunction and cardiac arrest include the following.

• Ventricular fibrillation: The most common cause of cardiac arrest is ventricular fibrillation, a type of arrhythmia where the heart’s lower chambers (ventricles) quiver instead of pumping regularly.
• Coronary heart disease (coronary artery disease): Most cases of cardiac arrest occur in people who have heart conditions like coronary heart disease, where their arteries are clogged, and blood flow to the heart is reduced. If left untreated, coronary heart disease can result in heart failure, which can lead to cardiac arrest.
• Heart attack: Heart attack increases the risk of a cardiac arrest. Cardiac arrest can occur after the heart attack or during the recovery phase.
• Structural changes in the heart and defects: These include defects present from birth, such as congenital heart disease, as well as changes due to disease, such as an enlarged heart (cardiomyopathy).
• Inflammation of the heart muscle (acute myocarditis): Myocarditis can affect the heart’s electrical system, causing an arrhythmia.

Other causes of cardiac arrest include trauma, major blood loss, severe lack of oxygen, electrocution, drowning, allergic reactions and drug overdose. Sometimes the cause of a cardiac arrest cannot be identified.

Reversible causes of cardiac arrest

Some of the causes of cardiac arrest can be reversed with treatment by healthcare professionals. These include the following.

• Heart attack
• Drug overdose
• Fluid build-up around the heart
• Collapsed lung or blood clot in the lung
• Hypoxia (severe lack of oxygen)
• Major loss of blood or other bodily fluids
• Abnormal pH level in the body
• Too low or too high potassium levels
• Too low or too high blood glucose levels
• Hypothermia (low core body temperature)

Cardiac arrest usually happens suddenly and without warning. The person suffering cardiac arrest will:

• suddenly collapse
• lose consciousness
• have no pulse
• stop breathing or will be breathing abnormally, such as gasping for air.

Signs of cardiac arrest: How to recognise if you’re having one

Sometimes cardiac arrest can be preceded by other signs and symptoms. These include:

• chest discomfort
• heart palpitations
• shortness of breath
• weakness.

These are similar to the signs and symptoms of heart attack.

Every year in Australia, more than 25,000 cardiac arrests occur outside of hospitals.¹ The majority occur at home. Sadly, 90 per cent of these people will not survive.

Providing early cardiopulmonary resuscitation (CPR) together with defibrillation within minutes gives the person the best chance of survival. For every minute that passes without CPR and defibrillation, the chance of survival decreases by up to 10 per cent.

Among people who suffer a cardiac arrest outside of hospital, those who receive CPR have a higher survival rate.

The risk of cardiac arrest increases with age, and men are at higher risk than women. The below factors also increase the risk of suffering cardiac arrest.

• Having coronary heart disease
• Having a heart attack
• Having heart failure
• A history of irregular heartbeats (arrhythmia)
• A personal or family history of cardiac arrest or disorders that can cause arrhythmia
• Drug or alcohol abuse

Risk factors for cardiac arrest that can be managed

Due to the link between cardiac arrest and cardiovascular diseases like coronary heart disease, the risk factors for cardiovascular disease are also risks for cardiac arrest. Some of these can be managed to decrease the risk.

• High blood pressure: High blood pressure can speed up atherosclerosis. It can be managed through medication and dietary changes, such as lowering salt intake.
• High cholesterol: High levels of LDL cholesterol, the “bad” cholesterol, can add to the build-up of atherosclerotic plaque. Making dietary changes can help manage high cholesterol. High cholesterol mediations are also available.
• Inactivity: An inactive lifestyle can contribute to being an unhealthy weight and increase the risk of other risk factors like high blood pressure and cholesterol levels. It’s also important to stay active after a cardiac arrest or diagnosis of a cardiovascular disease, under medical guidance.
• Overweight and obesity: Being overweight can increase the risk of health problems, including other risk factors like high blood pressure and high cholesterol. A healthy diet and regular physical activity can help in reaching and maintaining a healthy weight.
• Diabetes: Having diabetes can double the risk of a person developing cardiovascular disease. A healthy lifestyle and dietary changes can help manage diabetes.
• Poor nutrition: A diet high in saturated fat, trans fat, LDL cholesterol, salt and sugar can contribute to being an unhealthy weight. Try to eat a balanced, nutritious diet.
• Smoking: Quit smoking if you smoke. Smoking can increase the risk of atherosclerotic plaque.
• Stress: Long-term stress can damage the arteries and worsen other risk factors for cardiovascular disease.

Call 000 straight away if you suspect a cardiac arrest. Without immediate treatment, cardiac arrest can lead to death. In some cases, cardiac arrest can be reversed if treated immediately.

Performing CPR can temporarily treat cardiac arrest until more advanced emergency treatment is available. In CPR, a person compresses the chest of the cardiac arrest victim to increase blood flow to the organs.

The use of a defibrillator (a device that sends an electric shock to the heart to help it regain function and beat normally) can improve the chances of survival. Paramedics and other emergency personnel will be equipped with defibrillators.

An automated external defibrillator (AED) may be installed in some public places. These are similar to defibrillators, but they are designed to give an electric shock only if they detect a dangerous arrhythmia. They can be used by anyone and do not require prior training, as they provide verbal and visual instructions. An AED will not hurt the person it is used on, even if they are not suffering cardiac arrest.

HRI is conducting critical research to prevent and treat the cardiovascular diseases and heart conditions that can lead to cardiac arrest, such as heart attack, congenital heart disease and heart failure.

Our Coronary Diseases Group is investigating whether the anti-inflammatory drug colchicine can be repurposed to protect against repeat heart attacks.

Our Clinical Research Group is conducting research into congenital heart disease, with a focus on young adults living with congenital heart disease and how to improve their health outcomes.