Supraventricular tachycardia, or "SVT," refers to a rapid heart beat that originates from cardiac tissues above the ventricles of the heart ("supra" means "above"). The term SVT is a very generic one, as it refers to at least a dozen different kinds of arrhythmias (including sinus tachycardia as well as atrial fibrillation / atrial flutter). When doctors say "SVT" they most often are referring to a sub-classification of arrhythmias known as Paroxysmal Supraventricular Tachycardia or PSVT (the old term for these arrhythmias was Paroxysmal Atrial Tachycardia or "PAT"). Paroxysmal simply means that the tachycardia starts suddenly and stops suddenly (a paroxysm is another term for an "episode" or temporary disturbance in the heart rhythm). The paroxysm can last anywhere from seconds to days, is usually recurrent, and generally feels like a rapid regular racing of the heartbeat. PSVT includes a large number of complicated arrhythmias that may be due different electrical abnormalities in the heart. Most commonly, there is a "short circuit" somewhere in the electrical system of the heart. This causes the electrical signal to continuously travel around in a circle, forcing the heart to beat rapidly, a situation known as Reentry (a Disorder of Impulse Conduction remember?). One example of PSVT occurs when the signal travels around the atrium, and so that arrhythmia is referred to as Intra-atrial Reentry Tachycardia. Another PSVT is due to the signal traveling around the AV nodal tissues, and is called AV Nodal Reentry Tachycardia. Some patients have an extra electrical connection between the atria and the ventricles (in addition to the AV node). This abnormal connection is called an Accessory AV Pathway or "Bypass Tract." Bypass tracts are frequent causes of one particular tachycardia known as AV Reentry Tachycardia. If the bypass tract also happens to cause the QRS complex to appear abnormal on the electrocardiogram, then a condition known as Wolff-Parkinson-White (WPW) Syndrome is present. Sometimes bypass tracts do not show themselves on the ECG. These hidden short circuits are referred to as "concealed accessory pathways." PSVT can cause severe symptoms of palpitations, lightheadedness, shortness of breath, sweating, and even chest pain. Some people may even pass out at the onset of a rapid PSVT. When PSVT occurs, it usually makes a person want to stop what they are doing and lay down until it stops. When symptoms such as these occur frequently, medication can be effective in reducing the frequency and severity of PSVT. Usually, PSVT is not a life-threatening condition, although the WPW Syndrome has rarely been associated with sudden death in young people. A relatively new treatment known as Radiofrequency Catheter Ablation can be used to permanently eliminate PSVT in most cases. This procedure involves locating the abnormal electrical pathway in the heart and cauterizing (i.e. burning) it using a wire through a vein. It is done while the patient is awake but sedated and has a very high success rate with an acceptably low risk of complications. PSVT is one of the few cardiac disorders that can now be "cured."
Rarely, PSVT can be caused by a Disorder of Impulse Generation in the atrium or the AV node. "Automatic Atrial Tachycardia" is the name for one of these arrhythmias. This can also cause a rapid heart beat, but not because of a short circuit. Rather, an area in the atrium is sending out rapid signals that are faster than the sinus node and so "take over" as the primary pacemaker in the heart. Often, the arrhythmia occurs in short bursts (known as "salvos") but sustained tachycardia can also occur. Different medications are used to treat these arrhythmias, since those used to treat reentry PSVT are often ineffective. Catheter ablation can also be used to eliminate the abnormal area and cure the problem.