Sudden Cardiac Arrest

December 4, 2023

Sudden cardiac arrest (SCA) occurs when the heart abruptly stops beating, often without warning, leading to a sudden collapse. Recognizing SCA is crucial, as immediate action can be lifesaving.

If you suspect SCA, call for emergency support and commence CPR promptly. Without intervention, death can occur within minutes. Employing an automated external defibrillator (AED), if available, is vital. AEDs, found in various locations, can detect harmful heart rhythm changes and administer an electric shock (defibrillation).

If someone else is present, ask them to locate an AED. Acting swiftly with CPR and AED application within the initial minutes of SCA significantly enhances the likelihood of survival.

During a heart attack … During sudden cardiac arrest …
Blood supply to the heart muscle is reduced or blocked, but the heart keeps beating; however, there may be damage to the heart muscle. The electrical system of the heart goes wrong (think of the way the lights flash before the power goes out), and the heart stops pumping blood.
Usually, the person knows something is happening, and can talk about his or her symptoms. Usually, the person is unconscious, and a pulse may not be found.


While a heart attack may, in certain instances, trigger the electrical abnormalities leading to sudden cardiac arrest, it’s important to note that these events don’t necessarily occur simultaneously.

Sudden cardiac arrest can occur in individuals without a history of heart disease. Although approximately 80% of cases are attributed to pre-existing coronary artery disease, in many instances, SCA serves as the initial indication of a heart issue. This means that those affected may be unaware of their heart disease until experiencing sudden cardiac arrest.

What Increases Your Risk?

The precise cause of sudden cardiac arrest (SCA) is not fully understood, but it is often attributed to a dangerous heart rhythm known as ventricular fibrillation.

SCA can occur in individuals of any age, although certain groups are at a higher risk. For instance, the likelihood increases if someone has previously experienced SCA or if there is a family history of SCA among parents, children, or siblings. Men and African Americans also face an elevated risk.

Specific diseases or conditions can disrupt the heart’s electrical system, leading to SCA. These include:

  • Coronary heart disease
  • Structural alterations in the heart, such as a thickened heart muscle or enlarged heart
  • Heart failure with reduced pumping function, characterized by a low ejection fraction (less than 35%)
  • Heart attack – 75% of SCA cases are associated with a prior heart attack, with many going undiagnosed; survivors of heart attacks are 4 to 6 times more likely to experience SCA than the general population
  • Physical stress, such as trauma, blood loss, dehydration/electrolyte imbalance, or, in rare cases, very intense physical activity
  • Congenital heart problems that make individuals more susceptible to heart rhythm issues.

Signs and Symptoms

Sudden cardiac arrest (SCA) typically occurs without warning, often marked by the sudden onset of fainting, collapsing, or appearing lifeless. You may not be able to feel a pulse, it’s critical to call an ambulance right away.

Recent studies involving SCA survivors reveal that, in certain instances, people recollect sensing that something was amiss before the event. These pre-SCA indicators include:

  • Dizziness
  • Unexplained shortness of breath
  • Chest pains
  • Seizures, typically affecting the arms and legs
  • Feeling nauseous or vomiting approximately an hour before the event

Another study highlights that half of patients aged 35 to 65 experienced warning signs, primarily chest pain and shortness of breath, within the 24 hours leading up to the SCA. In some cases, individuals reported having warning signs for weeks before the event.


The only effective treatment for SCA is to promptly restore the heart’s normal rhythm, typically achieved by using an automated external defibrillator (AED) to administer a shock to the heart. Every passing minute without intervention reduces the chance of survival by 7% to 10%.

People present at the scene during an SCA episode play a pivotal role in saving lives, and their swift actions can be the determining factor between life and death.

What to Do:

  1. Call an ambulance or instruct someone else to do so if others are available.
  2. Initiate CPR immediately while awaiting emergency assistance.
  3. Request another person to locate the nearest AED. AEDs, found in EMS vehicles and public places, provide clear instructions and are programmed to identify electrical issues and administer a shock to the heart.

People who survive an SCA require advanced emergency and cardiac care. Doctors employ basic cardiac testing to identify the cause of SCA and adjust treatment accordingly.

For certain patients, an implantable cardioverter-defibrillator (ICD) may be necessary. Implanted beneath the skin, ICDs can detect abnormal rhythms and deliver mild shocks to restore a normal heartbeat.


Since most instances of SCA occur in people who have experienced a heart attack or have hearts with reduced pumping ability (low ejection fraction) or heart failure, healthcare teams can take preventive measures to avoid repeat events.

It is crucial for SCA survivors to adhere to their treatment plans. The best approach is to adopt a healthy lifestyle by:

  1. Maintaining a diet low in saturated and trans fats, and high in soluble fiber, fruits, and vegetables.
  2. Regular exercise.
  3. Achieving and maintaining a healthy weight.
  4. Managing stress.
  5. Quitting smoking.

What Else You Can Do:

  1. Be knowledgeable about how to respond during sudden cardiac arrest. Survival rates could significantly increase if more people take prompt action and know what steps to follow.
  2. Recognize the warning signs of an SCA.
  3. Act swiftly, as the chances of survival reduce with each minute of delayed treatment. Avoid debating whether it’s an SCA and seek help immediately.
  4. Take a CPR class or refresh your skills if you’ve previously taken one.
  5. Learn how to use an automated external defibrillator (AED) and be aware of their locations.

Keep in mind:

  • AEDs may not be available in all places. Do not postpone CPR or calling an ambulance if an AED is not present.
  • AEDs at home may not significantly impact survival rates, possibly due to many SCA incidents at home occurring when individuals are alone.