What is Sudden Cardiac Death?

Sudden cardiac death (SCD) is defined as death due to the sudden and unexpected cessation of the heartbeat. This is called sudden cardiac arrest (SCA) and leads to a cut-off of the blood flow to vital organs such as the brain. In most cases, death results in minutes. SCA is more common during or after a heart attack, but can also occur in otherwise healthy people.

With SCA, the person usually loses consciousness, and there is no heartbeat. In a few cases, the person suddenly feels that their heart is racing, in addition to also feeling dizzy, nauseated, or breathless before collapsing.

Symptoms of Sudden Cardiac Arrest | Cedars-Sinai


SCD may be due to severe bodily fatigue, which rapidly increases adrenaline levels to dangerous levels. Electrolyte imbalances and a lack of oxygen are other potential causes of SCA in s patients. SCA can also be due to certain heart abnormalities, or inherited conditions, that interfere with normal electrical transmission in the heart. These are more often associated with SCA in childhood.

SCA in adult life is most common in people who have coronary heart disease, whether symptomatic or silent. Almost 90% of people with SCA were found to have coronary heart disease. Some people may even have had silent heart attacks before SCD occurs.

Notably, SCA is often the first, and only, symptom or sign of heart disease. To this end, SCA accounts for more than half of the deaths from this cause.

SCA is more common in the first 6 months of recovery from a heart attack, silent or not. This is because the affected areas of the heart have an abnormal blood supply as a result of blockage in the coronary arteries. When the damaged area includes the pacemaker area of the heart, which initiates the heartbeat, it results in abnormal heart rhythms that may lead to cardiac arrest.

SCA also occurs more commonly when the heart structure is anomalous, either as a result of chronic heart disease or severe hypertension.

The most common arrhythmia that causes SCA is ventricular fibrillation. Here, the ventricle stops pumping in a coordinated manner, and instead wriggles weakly. Ventricular fibrillation is caused by an abnormality in the way that the electrical impulses spread across the heart and is almost immediately fatal.

Risk factors for SCA

While death due to cardiac arrest may occur in any group or age, there are some well-defined risk factors, such as:

  • Age
  • Male gender
  • Heart disease
  • Inherited heart problems
  • Heart failure
  • Drug abuse


The diagnosis of SCA always occurs following the event, and depends on ruling out other causes of the patient’s collapse. However, if an individual is at high risk for the condition, a cardiologist may help to reduce the risk. To assess the patient's risk, they may be advised to undergo tests like:

  • Electrocardiography (ECG)
  • Echocardiography (ECHO)
  • Multigated acquisition scan (MUGA) or Cardiac magnetic resonance imaging (MRI)
  • Cardiac catheterization
  • Electrophysiology tests
  • Blood tests to rule out electrolyte imbalances


The only immediate treatment for SCA is to prevent death by getting the heart to beat normally again, which is typically achieved using defibrillation. An automated external defibrillator is a portable device that is used to deliver an electric shock to the heart, causing it to resume its normal electrical and muscular rhythm. For the shock to be delivered, the device must sense that the heart’s normal electrical activity is dangerously abnormal. This prevents defibrillation from being attempted with a normally beating heart.

Survivors of an SCA are tested to identify the cause and further treated in the hospital. Management will include various steps to prevent a recurrence. For example, in some cases, a device that automatically shocks the heart into action, known as an implantable cardioverter-defibrillator (ICD), is implanted under the skin to help abort any future dangerous arrhythmias.

Other ways to prevent SCA include:

  • Surgical treatment of coronary heart disease to restore normal blood flow through the blocked coronary vessels.
  • Medical treatment to stabilize the heart rhythm.
  • The use of a pacemaker device to initiate cardiac electrical activity if the natural pacemaker is damaged.


Further Reading

Last Updated: Feb 16, 2023

Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.


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