Sudden cardiac arrest

What is sudden cardiac arrest?

Sudden cardiac arrest (SCA) is a condition in which the heart suddenly and unexpectedly stops beating due to a malfunction in the heart’s electrical system. The malfunction that causes SCA is a life-threatening abnormal rhythm, or arrhythmia. Anyone can suffer a sudden cardiac arrest; it is unpredictable and can strike anytime, anywhere and without warning. During SCA a victim first loses his or her pulse, then consciousness and finally the ability to breathe. All of this can happen in a matter of seconds.

View our SCA and Heart Attack - Understanding the Difference information sheet here 


Sudden cardiac arrest is caused by an abnormal heart rhythm (e.g. ventricular tachycardia). There is rarely a warning and the patient always loses consciousness.

SCA is not the same as a heart attack, although a person suffering a heart attack has an increased risk of SCA. A heart attack can be thought of as a problem with the plumbing of the heart, a SCA is a problem with the electrical system within the heart.

A heart attack is caused by a blockage in an artery that supplies blood to the heart. The affected heart muscle then begins to die due to lack of oxygen.

Symptoms include central ‘crushing’ chest pain, often radiating to arms and jaw. The patient usually remains awake and alert.


In cases of SCA, there is rarely a warning and the patient always loses consciousness.

The common symptoms are:

  • Unresponsiveness
  • Loss of consciousness
  • Lack of pulse
  • Cessation of breathing
  • Abnormal Heart Rhythm (an arrhythmia)

Risk factors

Risk factors include a previous heart attack, previous SCA event, fast rhythm in the lower part of the heart (ventricles), family history of SCA and heart failure. Although pre-existing heart disease is a common cause of cardiac arrest, many victims have never had a heart problem.


When someone suffers a sudden cardiac arrest, defibrillation (the administration of an electric shock) together with cardiopulmonary resuscitation (CPR) is the only way to re-establish the heart’s natural rhythm. For every minute that defibrillation is delayed, the victim’s chance of survival decreases by 10%.

CPR alone will not restart a heart following a sudden cardiac arrest. CPR is a temporary measure used to continue a minimal supply of oxygen to the brain and other organs.

  • CPR alone     = 5% Survival?
  • CPR + Early Defibrillation     = 50% Survival

Automated External Defibrillator (AED)

An AED is a small, portable device that analyses the heart’s rhythm and prompts the user to de- liver a shock only if it is needed. Once activated, the AED guides the user through each step of the defibrillation process by providing voice and/or visual prompts.

The device is failsafe as it will only shock the patient if defibrillation is required.

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