Sudden cardiac arrest may be caused by almost any known heart condition. Most cardiac arrests occur when the diseased heart’s electrical system malfunctions, producing an abnormal rhythm such as ventricular tachycardia or fibrillation. Some cardiac arrests are caused by extreme slowing of the heart’s rhythm. All these events are called life-threatening arrhythmias.

• Scarring from a prior heart attack or other causes: 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 particularly high-risk period for sudden cardiac arrest in patients with atherosclerotic heart disease.

• A thickened heart muscle (cardiomyopathy) from any cause (typically high blood pressure or valvular heart disease) — especially if you also have heart failure— can make you more prone to sudden cardiac arrest.
  Read more about cardiomyopathy
  Watch an animation of hypertrophic cardiomyopathy

• Heart medications: Under certain conditions, various heart medications can set the stage for arrhythmias that cause sudden cardiac arrest. Paradoxically, antiarrhythmic drugs used to treat arrhythmias can sometimes produce lethal ventricular arrhythmias even at normally prescribed doses. This is called a "proarrhythmic" effect. Regardless of whether there's organic heart disease, 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: Certain electrical abnormalities such as Wolff-Parkinson-White syndrome and long QT syndrome may cause sudden cardiac arrest in children and young people.
  Read more about Wolff-Parkinson-White syndrome
  See an illustration of Wolff-Parkinson-White syndrome
  Read more about long QT syndrome
  See an illustration of long QT syndrome

• Blood vessel abnormalities: Less often, inborn blood vessel abnormalities, particularly in the coronary arteries and aorta, may be present in young sudden death victims. Adrenaline released during intense physical or athletic activity often acts as a trigger for sudden cardiac arrest when these abnormalities are present.

• Recreational drug use: In people without organic heart disease, recreational drug use is an important cause of sudden cardiac arrest.

Know how to recognize the signs of sudden cardiac arrest and what to do.  Immediate emergency treatment is vital to saving lives.

This content is reviewed regularly. Last updated 02/11/09.