What Causes Sudden Cardiac Arrest


Sudden Cardiac Arrest occurs when a heart’s electrical system malfunctions. Sometimes confused with a heart attack, cardiac arrest is caused by an abnormal heart rhythm. Many different factors can cause a change in a person’s heart rhythm, and it isn’t always an underlying, diseased heart or aging.

Irregular Heartbeats

Irregular heartbeats that cause a person to go into cardiac arrest are called arrhythmias. Arrhythmias can be a heart rate that is too fast, too slow or an irregular rhythm. These can originate in the heart’s atria or ventricles and are classified by their origin and heart rate.

Arrhythmias can be categorized as Tachycardia, Bradycardia, and Premature Beat. Tachycardia describes a fast heart rate of 100 beats or more per minute that can originate in the ventricles or atria of the heart. Bradycardia is marked by a slowed heart rate of 60 beats or less per minute. A slower heart rate may be completely normal for an athlete but could be a sign of a heart condition in others. Premature Beat is an extra heartbeat happening too early.

Examples of Tachycardia are:

  • Atrial Fibrillation- chaotic, fast heart rhythm. Risk increases with age.
  • Atrial flutter- a fast heart rate, but not as chaotic as atrial fibrillation
  • Supraventricular tachycardia- originates above the ventricles and last minutes to hours.
  • Premature ventricular contractions- abnormal or extra heartbeats that originate in the ventricles. This is a common abnormality called Premature Ventricular Complex.
  • Ventricular fibrillation- a chaotic and fast heart rhythm where the ventricles quiver rather than pump. This requires immediate medical attention, including CPR and an automated external defibrillator, or AED, to shock the heart back into a normal rhythm.

Examples of Bradycardia are:

  • Sick Sinus Syndrome- failure of the sinus node to produce reliable electrical impulses
  • Heart Block- due to congenital failure, heart disease, or aging. Interruption of the electrical signals moving to the ventricles.
  • Tachy-Brady Syndrome- a heart that sometimes beats too fast, sometimes too slow.

Most people that suffer from sudden cardiac arrest will never notice any forewarning signs or symptoms, but there are a few to watch out for. Since some arrhythmias are diagnosable, it may be worth a visit to your doctor if you ever notice dizziness, fainting (especially during physical activity), a slow or irregular heartbeat, weakness, sweating, shortness of breath, chest pain, or anxiety.

The causes of cardiac arrest could be anything from an underlying, undiagnosed heart condition or an accidental strike to the chest. It can occur in anyone from age 0 to 100+, any race, sex, and at any time. For this reason, AEDs have become a necessity in large public places, at sporting events, gyms, schools, office buildings, and on public transportation.

The causes of Sudden Cardiac Arrest include:

  • Congenital Defects- (all ages affected) include aortic valve stenosis, atrial septal defect, Ebstein’s Anomaly, and single ventricle defects. People are born with these. They are not acquired.
  • Commotio Cordis- (all ages) a structurally normal heart and rhythm is interrupted by a blow to the chest.
  • Myocarditis- (all ages) inflammation of the heart caused by a viral infection, drug reaction, or general inflammatory condition.
  • Atherosclerosis- (older age) hardening of the arteries, usually caused by age in older individuals.
  • Channelopathies- (all ages, usually under 35) are responsible for “autopsy-negative” or undiagnosed deaths. Has a lot to do with the electrical impulses regulated by electrolyte channels and the movement of sodium, potassium, and calcium ions into cardiac cells.
  • Cardiomyopathy- damage to the heart muscle from high blood pressure and heart valve disease. A thickened heart muscle.
  • Scarring of heart tissue- this can occur after a heart attack
  • Recreational drug use- (all ages) can occur to healthy individuals with the use of certain drugs


Sudden cardiac arrest can happen anywhere, at any time. The more people educated about and certified in CPR, the better chance people have of surviving cardiac arrest. It is a proven fact that the use of CPR and an AED, within the first few minutes of sudden cardiac arrest striking someone, will raise the chances of their survival exponentially. For this reason, many states have made it mandatory to have AEDs readily available in gyms, schools, offices, and other public places.  Awareness, education, and preparedness are key factors in the chain of survival.


Blog By Blaire CzarnieckiWritten by Blaire Czarniecki
Customer Service Director

Fact checked by Phillip Woods, BA, NREMT-P, FP-C

Blaire attended the University of Tennessee where she graduated 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 for Coro Medical. 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.

“I know that every day I come to work, I am playing a part in saving someone’s life. I am 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 Jan 12, 2023