Which dysrhythmia is the most common cause of sudden death in a cardiovascular emergency?

Arrhythmia, also known as abnormal heart rhythm or irregular heartbeat, is the most common cause for sudden cardiac arrest. Our specialist from the Department of Cardiology at National Heart Centre Singapore (NHCS) explains.

How arrhythmia (irregular heartbeat) can cause sudden death

When something goes wrong with the ‘electric circuitry’ of the heart, it can cause the heartbeat to be irregular, fast or slow.

Ventricular fibrillation, an arrhythmia (irregular heartbeat) which causes the lower chambers of the heart to beat too fast, is the most common cause of sudden cardiac arrest.

During ventricular fibrillation, the heart rate can be as fast as 400-500 beats per minute, compared to the normal 60-100 beats. The heart’s lower chambers, which pump blood and oxygen to the body, do not effectively pump blood out of the heart. As a result, insufficient blood is delivered to the brain and the person loses consciousness.

A ventricular fibrillation is a medical emergency and the victim is likely to die within minutes without treatment. Even if the victim survives, there is a high chance of brain damage leading to poor quality of life.

“An extremely slow heart rate can cause sudden cardiac death but it is usually not drastic and sudden, and presents with prior symptoms of giddiness or fainting,” explains Clinical Associate Professor Ching Chi Keong, Senior Consultant, Department of Cardiology and Director, Electrophysiology and Pacing, National Heart Centre Singapore (NHCS), a member of the SingHealth group.

Other heart conditions caused by arrhythmia (irregular heartbeat)

Often, a life-threatening arrhythmia is linked to a heart condition such as:

• Coronary artery disease: The Singapore study found that 81 per cent of all sudden cardiac deaths were caused by coronary artery disease (hardening and narrowing of the arteries supplying the heart).

• Heart attack: Almost 75 per cent of all sudden cardiac arrest patients show signs of a previous heart attack (myocardial infarction).

• Hypertrophic cardiomyopathy: An abnormal thickening of the heart muscle can cause ventricular fibrillation, especially during exertion.

• Electrical disorders of the heart: One of these disorders is Wolff-Parkinson-White (WPW) syndrome, characterised by an extra nerve connecting the heart chambers. This can cause an ‘electrical short-circuit’ in the heart, resulting in a rapid heartbeat. Brugada syndrome and long QT syndrome are also examples of electrical disorders.

See page 1 to learn the difference between a sudden cardiac arrest and heart attack, and what puts you at risk of sudden cardiac arrest.

Ref: R14

Check out other articles on heart health:

Sudden Cardiac Arrest: Early Symptoms, Treatment and Tips

How to Survive a Heart Attack When Alone

Tips for a Healthy Heart

Sudden Chest Pains You Shouldn't Ignore

Heart Palpitations: When Are They Serious?

How a Viral Infection Can Affect the Heart

How Plaque Buildup Can Lead to a Heart Attack

Cardiac arrest may be caused by almost any known heart condition.

Most cardiac arrests occur when a diseased heart’s electrical system malfunctions. This malfunction causes an abnormal heart rhythm such as ventricular tachycardia or ventricular fibrillation. Some cardiac arrests are also caused by extreme slowing of the heart’s rhythm (bradycardia).

Irregular heartbeats such as these are life threatening.

Other causes of cardiac arrest include:

• Scarring of the heart tissue – It may be the result of a prior heart attack or another cause. A heart that’s scarred or enlarged from any cause is prone to develop life-threatening ventricular arrhythmias. The first six months after a heart attack is a high-risk period for sudden cardiac arrest in patients with atherosclerotic heart disease.
• Thickened heart muscle (cardiomyopathy) – Damage to the heart muscle can be the result of high blood pressure, heart valve disease or other causes. A diseased heart muscle can make you more prone to sudden cardiac arrest, especially if you also have heart failure. Learn more about cardiomyopathy. 
• Heart medications – Under certain conditions, some heart medications can set the stage for arrhythmias that cause sudden cardiac arrest. (Oddly, antiarrhythmic drugs that treat arrhythmias can sometimes produce ventricular arrhythmias even at normal doses. This is called a “proarrhythmic” effect.) Significant changes in blood levels of potassium and magnesium (from using diuretics, for example) also can cause life-threatening arrhythmias and cardiac arrest.
• Electrical abnormalities – These, including Wolff-Parkinson-White syndrome and Long QT syndrome, may cause sudden cardiac arrest in children and young people.
• Blood vessel abnormalities – These rare cases occur particularly in the coronary arteries and aorta. Adrenaline released during intense physical activity can trigger sudden cardiac arrest when these abnormalities are present.
• Recreational drug use – This can occur in otherwise healthy people.

Written by American Heart Association editorial staff and reviewed by science and medicine advisers. See our editorial policies and staff.

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