Stanford Cardiac Arrhythmia Service

Sudden Cardiac Death

Definition
Sudden cardiac arrest  (SCA) is death resulting from an abrupt loss of heart function, most commonly occurring from a life-threatening heart rhythm problem . Cardiac arrest may occur within minutes after symptoms appear or without any warning symptoms at all. The most common underlying condition in individuals with cardiac arrest is an abnormality of heart function or coronary heart disease due to atherosclerosis. Less commonly, SCA may also result from other conditions of the heart (see below) or medical conditions affecting organs other than the heart.

SCA is a major public health problem in the United States and worldwide. In the United States, about 300,000 people die of SCA in the United States each year, resulting in more deaths than stroke, lung cancer, and breast cancer combined. (source: American Heart Association).

Causes
Most cardiac arrests are due to life-threatening heart rhythm problems.  These rhythm problems occur when the electrical impulses in the lower chambers of the heart (ventricles) become very rapid (ventricular tachycardia) or chaotic (ventricular fibrillation). These abnormal heart rhythms (arrhythmias) are so rapid that they prevent the heart from effectively beating or pumping blood to the entire body. This results in loss of blood flow to the vital organs including the brain, leading to loss of consciousness. 

Ventricular tachycardia is a rapid heart rhythm occurring from the ventricles, the main pumping function.  The rates are most commonly 150 to 250 beats per minute but ventricular tachycardia may occur at  relatively slow rates such as 110 to 150 beats per minute, sometimes due to medications that slow the ventricular tachycardia or advanced degrees of heart impairment. 

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