In an adult, a heart rate faster than 100 beats/minute is considered tachycardia. This number varies with age, as the heartbeat of a younger person is naturally faster than that of an older person’s. During exercise the sinus node increases its rate of electrical activity to accelerate the heart rate. Such normal fast rate that develops is called sinus tachycardia. In contrast, arrhythmias that are due to fast, abnormal electrical activity can cause tachycardias that are dangerous. If the ventricles of the heart experience one of these tachycardias for a long period of time, there can be deleterious effects. Individuals may sense a tachycardia as a pounding sensation of the heart, known as palpitations. If a tachycardia lowers blood pressure it may cause lightheadedness or dizziness, or even fainting (syncope). If the tachycardia is too fast, the pump function of the heart is impeded, and rarely may lead to sudden death.

SADS, or sudden arrhythmia death syndrome, is a term used to describe sudden death due to cardiac arrest brought on by an arrhythmia. The most common cause of sudden death in the US is coronary artery disease. Approximately 300,000 people die suddenly of this cause every year in the US.

Sudden arrhythmia death syndrome (SADS) can also occur from other causes. Also, there are many inherited conditions and heart diseases that can affect young people that can cause sudden death. Many of these victims have no symptoms before dying suddenly.

Causes of SADS in young people are long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, hypertrophic cardiomyopathy, and arrhythmogenic right ventricular dysplasia (“arrythmia”-causing, “right ventricle”-involving, pre-cancerous malformation).