Cardiac Arrest

(Also known as: Sudden cardiac death)

Cardiac arrest is a sudden loss of heart function, breathing and consciousness, usually caused by disruptions to the normal electrical activity within the heart. This leads to a complete collapse and usually requires emergency measures in order to prevent death. Often, people who experience sudden cardiac death have no warning symptoms. Some people may experience a feeling of lightheadedness or a feeling that their heart is racing. Emergency resuscitation measures must be started right away followed by immediate transport to the hospital for more comprehensive tests and treatment.

What Is Cardiac Arrest?

Cardiac arrest is a sudden loss of heart function, breathing and consciousness. It is a medical emergency and can strike without warning to people of any age and fitness level.

A normal, healthy heart is a muscle that works as a pump. Its main job is to pump a regular supply of blood, oxygen, and nutrients through a series of pipes called arteries to all the structures and organs throughout the body. The pumping of the heart is regulated by an electrical current or impulse which is generated and starts in a specific area of the heart. This impulse fires off at regular intervals to keep the heart beating at a steady rate.

The most common cause of cardiac arrest is a heart attack due to blockages in one or more of the coronary arteries. These arteries are the blood vessels which supply the heart with blood, oxygen and nutrients. Blockages prevent proper blood flow to the heart which can cause damage to the heart muscle itself, as well as electrical disturbances which disrupt the heartbeat.

Malfunctions of the electrical system of the heart can result in a lethal arrhythmia (irregular heart beat) and loss of pumping action of the heart. This may result in the heart stopping suddenly (sudden cardiac arrest) and requiring immediate, emergency resuscitation.  


Cardiac arrest is almost always caused by lethal heart arrhythmias. The most common one is an abnormal rhythm called ventricular fibrillation.

Ventricular fibrillation is a rapid, chaotic rhythm originating in the lower chambers of the heart resulting in the heart not being able to pump blood to the rest of the body.

Death occurs within minutes unless emergency treatment is begun. Emergency treatment includes CPR and defibrillation (a controlled electric shock used to try to return the heart to its normal rhythm).

There are many factors that increase the risk of sudden cardiac arrest. These include:

  • Previous heart attack in which a large part of the heart was damaged
  • History of coronary artery disease
  • Low ejection fraction (<40%) especially in combination with the abnormal heart rhythm called ventricular tachycardia
  • Prior episode of sudden cardiac arrest
  • Family history of sudden cardiac arrest or death
  • Patient or family history of certain types of heart arrhythmias
  • History of congenital heart or blood vessel abnormalities
  • History of syncope (fainting) episodes that do not have a known cause
  • History of heart failure
  • History of dilated cardiomyopathy or hypertrophic cardiomyopathy
  • Significant changes in certain blood electrolytes, potassium and magnesium

Other contributing risk factors are obesity, diabetes, recreational drug abuse, or taking drugs that can affect the regular heart rhythm.


Often patients have mild or no symptoms prior to the event. Symptoms may include some of the following:

  • Feelings of lightheadedness
  • Sensation of  a racing heart (which may herald the beginning of the arrhythmia)
  • Chest pain.

Any person who suddenly collapses and is not responsive is considered to be having a cardiac arrest and needs immediate care. If you see someone collapse, call 911 immediately and start CPR. If one is available, use an automated external defibrillator (AED) but make sure you follow the prompts.

A more definite diagnosis is made through use of an electrocardiogram (ECG) or cardiac monitoring strip showing the arrhythmia. Once transported to the hospital, investigation as to the cause of the arrhythmia is then undertaken.


Patients who experience sudden cardiac arrest and are successfully resuscitated are generally taken to the heart catheterization laboratory to determine if a heart blood vessel blockage is what caused the heart to beat irregularly.

If the heart resumes proper electrical function and is beating correctly, but the patient remains minimally or unresponsive, a treatment called therapeutic hypothermia may be started.

Therapeutic Hypothermia

Hypothermia means the body temperature is below normal. Therapeutic hypothermia is a deliberate but temporary lowering of the body’s temperature to reduce injury or damage to vital body organs.

This treatment protects the brain and other vital organs by lowering their oxygen needs. It also decreases swelling, and limits the release of toxins which can cause brain cell death.  Hypothermia has been shown to improve neurological outcomes and increase survival after a cardiac arrest.


Throughout the recovery period, further testing may be done to help determine the reason why a patient experienced a potentially lethal arrhythmia.

Treatments depend on exactly what caused the cardiac arrest and will be tailored to each individual patient.

Because there are many risk factors for sudden cardiac arrest or death, it is important to speak to your doctor about what you can do to reduce your risk for future events.

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