There are different forms of supraventricular tachycardia (SVT), an abnormal fast heart rhythm. At times, thyroid disease, caffeine, medications with stimulants, or stress can cause an episode of SVT. However, often no trigger is identified.
Remember that your heart has a system of electrical impulses that helps control the rhythm and number of times your heart beats per minute. The electrical signals travel along "pathways." Some types of SVT involve a faulty electrical pathway. Examples include:
Atrioventricular Nodal Reentrant Tachycardia (AVNRT): With AVNRT, the most common form of supraventricular tachycardia, there is a slow pathway in the middle of the heart. An extra beat timed just right sets off a circuit by going down the slow pathway and then going up a fast pathway. This loops around many times and creates a fast heart rate.
Wolff-Parkinson-White syndrome (WPW): With WPW, there is an extra pathway between the upper and bottom chambers of the heart. A circuit can be created with an extra beat going down the normal path and then up this extra pathway. It can go backward as well. Either way, this loops around many times creating a fast heart rate.
Atrial Tachycardia (AT): With atrial tachycardia, a cluster of cells in the upper chamber of the heart fires away, creating a rapid heartbeat.
With SVT, your heart beats very fast for reasons other than stress or exercise. Often, you will notice a sudden increase in your heart rate ( > 100 beats per minute and even rates of > 200 beats per minute). Then, it suddenly returns to normal (about 60-100 beats per minute).
Depending on how fast the heart is beating, the symptoms can include: