Sudden Cardiac Arrest

1 What is Sudden Cardiac Arrest?

Sudden cardiac arrest is a medical emergency in which your heart stops pumping blood to your body parts. As your heart suddenly stops pumping, there occurs cessation of breathing and loss of consciousness.

It is usually caused by problems in your heart’s electric impulse conduction. A heart attack and sudden cardiac arrest are different conditions. However, the latter could result from a heart attack.

Death ensues within a few minutes if the condition is not immediately treated. Immediate medical care may increase survival rates. Before the arrival of emergency care team, sudden cardiac arrest can be primarily managed by cardiopulmonary resuscitation (CPR), use of a defibrillator or simple technique like compression on the chest.

2 Causes

Irregular heart rhythms (arrhythmias) caused by abnormal electrical impulses in your heart are the most obvious cause of a sudden cardiac arrest.

Your heart pumps through its own electric stimulation that starts at sinus node, a cluster of specialized cells in the upper right chamber of your heart. Your heart rate and pumping action are optimally maintained by electric impulses from the sinus node. Problems in sinus node or transmission of electric flow can cause either too slow or too fast heartbeats.

Though usually temporary and harmless, some of these irregular heartbeats can cause sudden cardiac arrest. A cardiac arrest is often caused by an abnormal vibration in your ventricles called ventricular fibrillation. Generally, serious irregular heart rhythms occur due to triggers like an electric shock, consumption of illegal drugs or blow to the chest at critical time of the heart's cycle (commotio cordis).

Sudden cardiac arrest can also occur due to other heart conditions like:

  • Coronary artery disease: Sudden cardiac arrest is common in people with coronary artery disease. Narrowed arteries can cause problems with flow of electric impulses through your heart.
  • Heart attack: A heart attack may trigger ventricular fibrillation, the most common cause of a sudden cardiac arrest. Moreover, scar tissues after a heart attack can also disrupt normal electric conduction in your heart.
  • Enlarged heart (cardiomyopathy): Damages to heart muscles can also cause arrhythmias.
  • Disease of heart valves: Diseased valves can cause damages to heart muscles which may result in cardiac arrhythmias.
  • Congenital heart disease: Heart conditions that you are born with, can also increase risk of sudden cardiac arrest.
  • In conditions called primary heart rhythm abnormalities, arrhythmias are caused by problems in the heart's electrical system itself, for example in Brugada's syndrome and long QT syndrome.

3 Making a Diagnosis

If you survive a sudden cardiac arrest, your doctor will perform various tests to diagnose the causes and prevent future attacks. Some of the tests include:

  • Electrocardiogram (ECG): An ECG measures and records electrical activity of your heart through electrodes attached commonly to your chest. Using ECG after cardiac arrest is a common practice. Abnormal patterns in your ECG indicate potential risks such as prolonged QT interval.
  • Blood tests: Blood levels of various substances that influence functions of your heart, such as potassium, magnesium, hormones and others can be measured. Your doctor may also test your blood sample to detect recent heart injury and heart attacks.
  • Imaging tests:
    • Chest X-ray: A chest X-ray shows your heart’s size and shape, and its blood vessels may be useful in detecting heart failure.
    • Echocardiogram: Using sound waves to produce an image of your heart, an echocardiogram helps to locate damages caused by a heart attack, and detect heart’s pumping activity or abnormal heart valves.
    • Nuclear scan: This test detects flow of an injected radioactive material (thallium) through your heart and lungs. Combined with a stress test, it can help detect problems with blood flow. 

Some other tests used for the diagnosis include:

  • Testing your heart’s electrical activities and electrical pathways: An electrophysiology test involves threading a number of electrode-tipped catheters to your heart and measuring electrical activities inside your heart. In some cases, your doctor may use a pacemaker to induce controlled arrhythmia. 
  • Coronary catheterization (angiogram): A catheter is inserted into arteries in your leg and gently guided to your heart. Then, a liquid dye is passed through the catheters. As the dye moves through the arteries, blockages are detected using X-rays. Your doctor may also treat the blockage during this procedure, by performing an angioplasty and using a stent to keep the artery open.
  • Ejection fraction testing: This test which measures your heart’s pumping capacity is important one in diagnosing heart failure. This shows what percentage of blood is pumped out of a ventricle in one heartbeat. Its normal value is 55 to 70 while a value less than 40 percent means you are more likely to have sudden cardiac arrest. An ejection fraction can be measured by an echocardiogram, magnetic resonance imaging (MRI), a nuclear medicine scan (multiple gated acquisition, or MUGA), a computerized tomography (CT) scan or a cardiac catheterization.

4 Treatment

An immediate treatment of sudden cardiac arrest increases chances of survival.

Emergency treatment

  • CPR: An immediate cardiopulmonary resuscitation (CPR) is the most important primary treatment for sudden cardiac arrest which can save life by maintaining a blood flow to vital organs before the arrival of professional medical care. If you are not trained in CPR, call 911 or emergency medical assistance as soon as you see an unconscious person. Perform chest compression and aim for 100 to 120 compressions per minute. Continue doing this until medical team arrives.

How to perform CPR?

Before performing a CPR, make sure if the person is conscious and call 911 or local emergency number. If you have access to an AED, deliver one shock before starting CPR.

Place heel of one hand on the center of victim’s chest and cover the first hand with the other hand. Push down hard and fast while keeping your elbows straight. Aim for 100 to 120 compressions per minute.

After every 30 compressions, open the airway by gently tilting the head back and lifting the chin up. Check if the person is breathing.

If you cannot detect breathing for 10 seconds, give two rescue breaths. Remember that when you are giving the breaths, the victim’s chest should rise. 

Shut the nostrils by pinching and give first rescue breath. If the chest rises, give the second breath. If it doesn't rise, give the second breath by tilting the head back and lifting the chin.

If the victim does not move after five cycles (about 2 minutes) and you have access to an AED. Deliver one shock and resume CPR. 

After 2 minutes, deliver a second shock. 

If you don’t know how to use an AED, call a 911 or emergency medical to get directions.  

Continue CPR or chest compressions till the person regains consciousness and breathing is normal, or till emergency medical help arrives.

  • Defibrillation: Defibrillation is a procedure in which abnormal heart rhythm is stopped by administering an electrical shock to the heart. The device that delivers the shock only when needed, is called a defibrillator. A defibrillator may be used by an emergency personnel or by a citizen if the device is available. Nowadays, portable defibrillators are installed in various public places, such as, shopping malls, casinos, health clubs, and community and senior citizen centers.

Treatment at the emergency room: Treatment at the emergency room involves medications to normalize heart rhythms and treat a possible heart attack, heart failure or electrolyte imbalances. 

Long-term treatment

Once stable, you may have to undergo some extra tests to determine the underlying cause. You may also be recommended measures to prevent future attacks. Treatments may include:

  • Medications: Drugs used in the treatment of cardiac arrhythmia are called anti-arrhythmic drugs. A range of medications such as beta blockers, angiotensin-converting enzyme (ACE) inhibitors, calcium channel blockers or a drug called amiodarone are used for treating arrhythmias or potential complications. The most serious side effect of an anti-arrhythmic drug is its ability to increase frequency of an existing arrhythmia or cause a new arrhythmia.
  • Implantable cardioverter-defibrillator (ICD): An ICD is a heart rhythm monitor that’s implanted near your collarbone. It works as a pacemaker and regulates your heart rhythm to keep it normal. 
  • Coronary angioplasty: A balloon tipped catheter is inserted into an artery in your leg and is guided to your heart. As it reaches a blocked artery in the heart, the balloon is inflated to open the artery. The artery may be held open by using a stent.
  • Coronary bypass surgery: The blocked artery is skipped by creating a graft, which allows normal blood flow to your heart. It is also called coronary artery bypass grafting. 
  • Radiofrequency catheter ablation:  It involves using radiofrequency energy to destroy a tiny portion of heart tissue to block electrical pathways responsible for irregular heart rhythms.
  • Corrective heart surgery: Surgery may be carried out to correct an abnormal heart valve or structural abnormalities in your heart.

5 Prevention

Risk minimization is the key to prevent events of sudden cardiac arrest. Here are some tips:

  • Don't smoke, and drink in moderation.
  • Focus on a balanced diet.
  • Exercise
  • Manage other risk factors such as high cholesterol or diabetes.
  • You may take anti-arrhythmic drugs or have an implantable cardioverter-defibrillator (ICD), if required.
  • Get an automated external defibrillator (AED) for household use. 
  • If you wish, you may learn CPR. Learn about courses in CPR and defibrillator use, from The American Red Cross and other organizations.

6 Risks and Complications

There are several risks and complications associated with sudden cardiac arrest.


  • A family history of cardiac disorders such as coronary artery disease, cardiac arrest or a previous heart attack
  • Smoking
  • High blood pressure
  • High level of cholesterol in blood
  • Obesity
  • Diabetes
  • Lack of physical activity
  • Heavy alcohol consumption
  • Increasing age
  • Sex: Males are two to three times more vulnerable
  • Consumption of drugs, such as cocaine or amphetamines
  • Electrolyte imbalance, such as low levels of potassium or magnesium 


Brain damage is a life-threatening complication of a sudden cardiac arrest. Loss of consciousness occurs due to reduced blood flow to your brain. Brain damage, if not corrected early, leads to death within minutes. If a person has sudden cardiac arrest lasting more than 8 minutes, there is a very little chance of survival. Even with survival, signs of brain damage cannot be prevented.

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