The electrical system of the heart (conduction system) is a complex network of cells and fibers in the heart through which electrical impulses travel at lightning speed, triggering a heartbeat. The impulses are first sent out by the sinoatrial node (sinus node or SA node), located in the top of the upper-right chamber of the heart (the right atrium). From there, the impulses spread through the atria, causing them to contract, and then to the atrioventricular node (A-V node), where they are transmitted to the lower chambers of the heart (ventricles) via the bundle branches. Once the impulses reach the ventricles, they cause the chambers to contract and pump out blood in a routine and consistent manner.

If impulses are fired too fast – either from the heart’s normal conduction system or from other parts of the heart – the heart will beat too quickly. In many cases, a temporary rapid heartbeat is not medically significant by itself. For instance, sinus tachycardia is a normal response to increased demands on the heart during exercise. However, persistent severe tachycardia can lead to greater damage and heart malfunction.

Symptoms vary widely among the different types of tachycardias. People are encouraged to read more about a specific tachycardia of interest to learn its symptoms.

Diagnosis is made by 12-lead electrocardiogram (EKG). In cases of intermittent arrhythmias, a Holter monitor or event recorder may be required. Electrophysiology testing may be indicated in some patients to locate areas of ectopic activation, accessory pathways and to determine which patient is vulnerable for fatal arrhythmias.