Heart Rhythm Disorders: Supraventricular Tachycardia

Basics

Supraventricular tachycardia (SVT) is a rapid heartbeat that begins above the heart’s lower chambers (the ventricles) [Figure 1]. The heart relies on an organized sequence of electrical impulses in order to beat effectively. Any deviation from this normal sequence is known as "arrhythmia." Supraventricular tachycardia is an abnormally fast heart rhythm that begins in one of the upper chambers of the heart (atria), a component of the heart's electrical conduction system called the atrioventricular (AV) node, or both. Although supraventricular tachycardia (SVT) is rarely life-threatening, the symptoms—which include a feeling of a racing heart, fluttering or pounding in the chest or extra heartbeats (palpitations), or dizziness—can be uncomfortable.

Figure 1. The heart

The beating of the heart is controlled by a system of electrical impulses that begin in a group of cells called the sinoatrial (SA) node. The impulses follow a pathway to the atrioventricular (AV) node, where they slow to allow the ventricles to fill with blood. Once this occurs, the electrical impulses are released and travel down special fibers to surround the sides and floor of the ventricles. The ventricles then contract and force blood upward to the major arteries.

Causes

Supraventricular tachycardia happens when the normal electrical impulses that cause the heart to beat are interrupted. The most common cause of SVT is called re-entry, and occurs when a "short circuit" causes electrical impulses to circulate in a merry-go-round-like cycle that takes over the heart's normal rhythm.