What is Sudden Cardiac Death?

By Dr Liji Thomas, MD

Sudden cardiac death is defined as death due to the sudden and unexpected stoppage 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 apparently normal healthy people.

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


Sudden cardiac death may be due to severe bodily fatigue, which pushes up the adrenaline levels to dangerous levels. Electrolyte imbalances are another cause. Lack of oxygen can also cause SCA in some cases. 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.

The important fact to remember is that SCA is often the first, and only, symptom or sign of heart disease. It accounts for more than half 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 which 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 which 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 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

Diagnosis and treatment

Diagnosis of SCA is always following the event, and depends on ruling out other causes of the patient’s collapse. However, if you are at high risk for the condition, a cardiologist may help you reduce your risk. To assess your risk, you may be advised to undergo tests like:

  • Electrocardiography
  • Echocardiography
  • MUGA or Cardiac 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. This is done using defibrillation. An automated external defibrillator is a portable device which 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 hospital. Management will include steps to prevent a recurrence.

Sometimes, a device which automatically shocks the heart into action, called an implantable cardioverter defibrillator, or 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 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: Nov 15, 2015

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