Sudden Cardiac Arrest: What It Is & What Causes It

Doing CPR first aid to man with heart attack part of the resuscitation process, Close up shot with vintage picture style.

Sudden Cardiac Arrest (SCA) is a medical emergency that often strikes without warning and can lead to devastating consequences if not promptly addressed. In this blog, we’ll explore the underlying causes of SCA, its relationship with various heart conditions, and some critical facts highlighting the importance of understanding and responding to this life-threatening event. By comprehensively understanding SCA, its causes, and its impact, we can better prepare ourselves to recognize the warning signs and take appropriate action to save lives.

What is Sudden Cardiac Arrest?

Sudden cardiac arrest occurs when the heart stops abruptly and unexpectedly. When this happens, blood flow to the brain and other organs stops, and the person collapses. Within seconds, they lose consciousness and stop breathing. Without immediate CPR and medical treatment, sudden cardiac arrest can be fatal.

What Causes Sudden Cardiac Arrest

Various heart conditions and factors can trigger cardiac arrest. Most cardiac arrests happen when the heart’s electrical system malfunctions due to a diseased heart. This malfunction leads to abnormal heart rhythms like ventricular tachycardia or ventricular fibrillation. Ventricular fibrillation is the most common cause and occurs when the electrical impulses that control heartbeats become erratic, causing the heart to beat erratically and chaotically. In some cases, cardiac arrests are also caused by an extremely slow heart rhythm (bradycardia). These irregular heartbeats can be life-threatening.

Other causes of SCA include:

  • Scarred heart tissue – This can result from a previous heart attack or other causes. A heart with scarring or enlargement is at risk of developing life-threatening ventricular arrhythmias. The initial six months following a heart attack represent a high-risk period for sudden cardiac arrest in patients with atherosclerotic heart disease.
  • Thickened heart muscle (cardiomyopathy) – Heart muscle damage may stem from high blood pressure, heart valve disease, or other factors. A damaged heart muscle increases the risk of sudden cardiac arrest, mainly if heart failure is also present. For more information, explore cardiomyopathy.
  • Heart medications – In some situations, certain heart medications can predispose individuals to arrhythmias that lead to sudden cardiac arrest. Interestingly, antiarrhythmic drugs designed to treat arrhythmias can occasionally cause ventricular arrhythmias even at normal doses, a phenomenon known as a
  • “proarrhythmic” effect. Drastic fluctuations in blood potassium and magnesium levels (potentially due to diuretic use) can also lead to life-threatening arrhythmias and cardiac arrest.
  • Electrical abnormalities – Conditions such as Wolff-Parkinson-White syndrome and Long QT syndrome can provoke sudden cardiac arrest in children and young adults.
  • Blood vessel abnormalities – These uncommon cases typically involve the coronary arteries and aorta. Intense physical activity, which causes adrenaline release, can trigger sudden cardiac arrest in the presence of such abnormalities.
  • Recreational drug use – can occur to healthy individuals abusing stimulants or opiates.
  • Other potential causes include electrical shock, drowning, suffocation, extreme emotional stress, and physical exertion.

Sudden Cardiac Arrest Statistics

1. Around 356,000 out-of-hospital cardiac arrests occur annually in the United States. SCA is a leading cause of death in the country.

2. According to the American Heart Association, approximately 10% of people who experience an out-of-hospital cardiac arrest survive. However, when a bystander performs CPR and utilizes an AED (Automated External Defibrillator) promptly, the chances of survival can double or even triple.

3. A victim’s chances of survival are reduced by 7-10% with every minute without CPR and defibrillation.

4. Approximately 50% of SCA victims initially require defibrillation. All require CPR. If you perform CPR immediately and use an AED within minutes, you can significantly increase a person’s chance of survival.

5. Bystander intervention plays a significant role in improving survival rates. According to the American Heart Association, bystander CPR is performed in only 39% of out-of-hospital cardiac arrests.

6. Sudden Cardiac Arrest can affect people of all ages, including children and young adults. However, the risk of SCA increases with age, particularly in individuals over 45 years old.


In conclusion, understanding the nature and causes of Sudden Cardiac Arrest is crucial in raising awareness and improving survival rates. By recognizing the various factors contributing to SCA, such as abnormal heart rhythms, heart conditions, and other potential triggers, we can take proactive measures to minimize risks and enhance our ability to respond effectively during emergencies. Education on SCA and proper training in CPR and AED use empower individuals to make a difference in critical moments, potentially saving lives and reducing the impact of this life-threatening event.

Written by BlaireWritten by Blaire Czarniecki
Customer Service Director

Blaire graduated from the University of Tennessee with a Bachelor of Science in Human Ecology- Child and Family Studies. She has been in the Automated External Defibrillator (AED) industry for over eight years and is the Director of Customer Service. Blaire is also an American Red Cross certified CPR/AED/First Aid Instructor, highly trained by each manufacturer on their specific AEDs, and knowledgeable regarding ALL State AED regulations and legislation.“Every day I come to work, I know I am playing a part in saving someone’s life. I’m passionate about these devices and am always looking for new and innovative ways to spread awareness and knowledge about Sudden Cardiac Arrest (SCA). I look forward to the day when everywhere I go, I will see an AED—when SCA will no longer take any lives.”

Last updated April 13th, 2023