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Sudden Cardiac Arrest: Why It Happens, Types, & Emergency Treatment

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Last updated January 14, 2021

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Sudden cardiac arrest is an emergency condition that is described by when the heart suddenly stops beating. Symptoms include a loss of consciousness, lightheadedness or dizziness, or a lack of pulse or breathing. Treatment includes trying to restore the heartbeat via defibrillation.

Sudden cardiac arrest quiz

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What is sudden cardiac arrest?

Sudden cardiac arrest (SCA) occurs when the heart abruptly stops beating. In media portrayals, SCA classically occurs after a heart attack, also known as a myocardial infarction. While heart attacks are a common cause of SCA, in real life they are just one of many etiologies.

The common feature of almost all causes of SCA is a problem with the heart's electrical conduction system, which is usually responsible for maintaining the organized, coordinated rhythm that ensures all parts of the heart muscle beat properly. Symptoms include a loss of consciousness, lightheadedness or dizziness, pulselessness, and a lack of breathing.

Treatment plans include a variety of measures to restore heart function as well as pulse and consciousness via emergent defibrillation. Other methods will involve medications, implantable devices, and careful monitoring.

You should go to the ER immediately since the longer the heart goes without blood, the worse the irreversible damage will be. Hurry!

Symptoms of a sudden cardiac arrest

As the name would imply, most people who experience SCA have almost no preceding symptoms. However, this depends on the specific cause of the arrest. For example, a heart attack that triggers SCA will likely cause chest pain and shortness of breath. Nausea and profound sweating are also common. If an abnormally fast heart rate (known as a tachyarrhythmia) triggers SCA, symptoms may include the feeling of a pounding or racing heartbeat, also known as palpitations. The symptoms universally seen in all SCA are consequences of impaired blood flow, including the following.

  • Loss of consciousness: Also known as fainting or syncope, this results mainly from insufficient blood flow to the brain.
  • Lightheadedness or dizziness: This may precede the loss of consciousness depending on how rapidly the arrest progresses.
  • Pulselessness: This is a defining feature of all cardiac arrest since without a heartbeat no blood flow can be felt at pulse points such as the neck or wrist.
  • Cessation of breathing: This is not a universal feature but can occur when the muscular function or neurological control of breathing is sufficiently impaired.

Sudden cardiac arrest quiz

Take a quiz to find out if you have sudden cardiac arrest.

Take sudden cardiac arrest quiz

Causes of a sudden cardiac arrest

If you've ever seen a movie or TV character clutch their chest and fall to the floor, chances are they're portraying a heart attack triggering SCA. Disruptions of the heart's rhythm system, collectively known as arrhythmias, prevent the heart from beating correctly. This, in turn, prevents blood from reaching vital organs such as the brain, making SCA an extremely dangerous and serious event.

If blood flow is not restored, death typically occurs within minutes. The term "sudden cardiac death" (SCD) is often used for those events which prove fatal. In the U.S. alone, conservative estimates attribute more than 350,000 deaths each year to SCD.

With rare exceptions, SCA is caused by dysfunction of the heart's conduction system. However, the umbrella term SCA encompasses various types of electrical dysfunction, and each type can have a variety of underlying causes.

Underlying causes and triggers

Underlying cause and triggers that can lead to SCA include the following.

  • Heart attack: This is the single most common trigger for SCA. A heart attack results from impaired blood flow to the heart muscle itself, usually as a result of a blocked coronary artery. While they can occur suddenly, most heart attacks are preceded by many years of coronary artery narrowing known as atherosclerosis. Once blood flow to the heart muscle is interrupted, tissue death can lead to severe disruptions of the electrical pathways within minutes.
  • Structural heart abnormalities: Damaged valves or malformations of the heart muscle are a particularly common cause of SCA in individuals under 30 years old. Hypertrophic obstructive cardiomyopathy, an inherited disease which causes heart tissue to become massively overgrown, is the classic cause of SCA in otherwise healthy young athletes.
  • Underlying conduction defects: This means there is something fundamentally abnormal about the way electricity flows through a person's heart and can even occur in otherwise healthy individuals. The most common disorders include Long QT syndrome, Wolff-Parkinson-White syndrome and Brugada syndrome, though these are just a few examples among a vast spectrum of complex electrophysiological disorders.
  • Severe non-cardiac stressors: This includes a massive pulmonary embolism (blood clot in the lungs), extensive blood loss, drug overdose, and metabolic derangements.

Types of arrest

The following details describe different types of cardiac arrest that may be experienced.

  • Ventricular fibrillation (VF): This is the classic arrhythmia associated with SCA. VF describes a state in which the large chambers of the heart (ventricles) are quivering (fibrillating) in a disorganized manner rather than producing coordinated beats. Defibrillation, colloquially referred to as "shocking" the heart, is primarily used as a way to stop ventricular fibrillation.
  • Pulseless ventricular tachycardia (VT): This is a condition similar to VF, though in VT there is still enough coordination of electrical activity to produce beats, albeit several hundred per minute. Pulseless VT, in which the beats are too weak to create a pulse that can be felt externally, is considered a form of cardiac arrest.
  • Heart block: This describes a failure of the conduction pathway to carry an electrical signal from the heart's internal pacemaker to the rest of the cardiac tissue. Since the heart has a number of backup systems in place, most cases of heart block are mild and never progress to cardiac arrest. When they do cause SCA, it may be preceded by an extremely slow heart rate, known as bradycardia.
  • Pulseless electrical activity (PEA): This refers to any circumstance where there is still electrical activity in the heart but this activity fails to trigger effective beats (and does not fit any specific arrhythmia pattern). PEA arrests are often associated with non-cardiac causes of SCA such as massive trauma.
  • Asystole: This describes the complete cessation of electrical activity within the heart. While we may be used to seeing someone "flatline" on a TV show, this is actually a fairly uncommon mechanism of cardiac arrest in real life.

Treatment options and prevention for sudden cardiac arrest

The ultimate management of any SCA varies depending on the underlying cause, and the subtleties of SCA management remain active topics of research and debate. That said, there are a handful of interventions which will play an important role in most cases of SCA, including the following.

  • Urgent defibrillation: This is the single most important step in treating SCA. Defibrillation works by delivering a "shock" of electricity to "reboot" the heart's electrical system, effectively ending the fibrillation that underlies most cardiac arrest.
  • Implantable cardioverter defibrillator (ICD): These devices allow for the same type of "shock" used by external defibrillators to be delivered to the heart the moment it is needed. Since life-threatening arrhythmias are responsible for most cases of SCA, and urgent defibrillation is the most important step in treatment, ICDs are often the best option available to decrease the chances that any future cardiac arrest would prove fatal. However, like all surgeries and life-sustaining interventions, ICD placement is not without risks. The ability to terminate a serious arrhythmia doesn't always make it the best decision for every person. When deciding whether to have an ICD placed, it is important to carefully discuss with your physician the long-term implications and prognosis.
  • Antiarrhythmic medications: These medications help interrupt or prevent abnormal heart rhythms such as VF or VT. While generally less effective than defibrillation at interrupting SCA, antiarrhythmics often still play an important role. Some of these medications, including beta blockers like metoprolol, have much broader benefits in the treatment of heart disease and will, therefore, be prescribed to most SCA survivors.

Other measures

Other measures often used or necessary for treating SCA include the following.

  • Pacemaker: These devices provide a small signal to trigger heartbeats at the desired rhythm, much as the heart's own pacemaker is supposed to do naturally. Pacemakers are particularly useful for those whose arrest resulted from heart block or other causes of an inappropriately slow heart rate. They are often combined with an ICD, allowing both pacing and defibrillation to be performed as needed by a single device.
  • Cardiopulmonary resuscitation (CPR): Chest compressions, while nowhere near as effective as a genuine heartbeat, can provide a small amount of blood circulation to buy time while attempting more definitive treatment. In rare cases, these compressions can help restart the heart. Sadly though, survival after CPR is far less common than most people believe.
  • Additional cardiovascular support: This is often needed to help maintain adequate blood flow and blood pressure. This can include everything from simple intravenous fluids to medications to mechanical devices which offload some of the heart's function. While these can be helpful, it is important to note that they are only temporary measures to provide support while awaiting a definitive solution.


By definition, SCA occurs suddenly and is therefore difficult to predict or prevent. Many people who suffer SCA have no known history of heart disease.

That said, the known risk factors for SCA overlap strongly with the known risk factors for heart disease in general, and those with known heart disease are at a significantly increased risk of SCA. Steps that can reduce the risk of heart disease in general and SCA specifically include the following.

  • Management of known disease: This includes many non-cardiac conditions and often requires adherence to medications and lifestyle changes needed for the treatment of high cholesterol, high blood pressure, obesity, and diabetes. These measures can significantly reduce the risk of heart disease and SCA, and for many people, appropriately treating these types of conditions can provide substantial improvements in cardiovascular health.
  • Not smoking: This represents one of the biggest single steps someone can take to reduce their risk of heart disease and SCA. For current smokers, quitting is obviously the best option, but even reducing the quantity can provide significant cardiovascular benefits. Even long-time smokers can achieve significant benefits after quitting since rates of SCA among former smokers have been found to eventually even out with rates in those who never smoked.
  • Exercising regularly: Due to the increased stimulation, extremely strenuous exercise can transiently increase the risk of cardiac arrest, but this risk is short-lived and outweighed by the overall improvement in cardiac health. Still, it is important to pace yourself and not overexert. Anyone with a personal or family history of heart disease should consult their physician before initiating a new exercise regimen.
  • Consuming alcohol only in moderation: While very low levels of alcohol consumption (one to two drinks daily) have actually been associated with lower SCA risk, heavy alcohol consumption and binge drinking have both been shown to significantly increase cardiac risk.
  • Heart-healthy diets: Diets favoring fruits, vegetables and whole grains over heavily processed foods have been repeatedly shown to benefit overall cardiovascular health. Some data has suggested that increased consumption of fish or fish oil supplements may be associated with better cardiovascular outcomes, but as with most dietary supplements, the evidence remains limited.

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When to seek further consultation for sudden cardiac arrest

Sudden cardiac arrest is a life-threatening emergency that must be treated as rapidly as humanly possible. If someone you know is experiencing symptoms concerning for a heart problem, please stop reading and call an ambulance immediately. It is also vital to call for any medical providers on hand since CPR and defibrillation in the field offer the best chance of survival. Even if no one with medical training is available, many stores and public buildings are equipped with defibrillators which can automatically determine if a shock is needed. Simply following the instructions included with the machine may be enough to save someone's life. Unfortunately, though, very few people survive SCA even with appropriate care.

Those that have already suffered SCA and were fortunate enough to survive will need close monitoring going forward. Extensive testing of the heart's conduction systems, physical structure and contractile function will likely be required. While the specific management will depend on the underlying cause of a person's arrest, simply having had SCA puts you at higher risk for subsequent arrest. Regardless of the specific management steps required, it is vitally important for anyone with significant heart disease to work closely with a physician who is comfortable handling these conditions.

Questions your doctor may ask to determine sudden cardiac arrest

  • Have you experienced any nausea?
  • Have you been feeling more tired than usual, lethargic or fatigued despite sleeping a normal amount?
  • Do you have a cough?
  • Do you currently smoke?

Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.

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The stories shared below are not written by Buoy employees. Buoy does not endorse any of the information in these stories. Whenever you have questions or concerns about a medical condition, you should always contact your doctor or a healthcare provider.
Dr. Rothschild has been a faculty member at Brigham and Women’s Hospital where he is an Associate Professor of Medicine at Harvard Medical School. He currently practices as a hospitalist at Newton Wellesley Hospital. In 1978, Dr. Rothschild received his MD at the Medical College of Wisconsin and trained in internal medicine followed by a fellowship in critical care medicine. He also received an MP...
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