Causes

SVT occurs when the electrical signals that coordinate your heartbeats don't work properly.

For some people, a supraventricular tachycardia episode is related to an obvious trigger, such as exercise, stress or lack of sleep. Some people may not have a noticeable trigger.

Things that may cause an SVT episode include:

• Heart disease
• Heart failure
• Other heart problems, such as Wolff-Parkinson-White syndrome
• Chronic lung disease
• Consuming too much caffeine
• Drinking too much alcohol
• Drug use, particularly stimulants such as cocaine and methamphetamines
• Pregnancy
• Smoking
• Thyroid disease
• Certain medications, including asthma medications and over-the-counter cold and allergy drugs

What's a normal heartbeat?

SVT starts above the heart's ventricles (supraventricular) in the two upper chambers or a cluster of cells called the atrioventricular (AV) node. To understand how this occurs, it can be helpful to understand how the heart beats.

Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles).

The rhythm of your heart is normally controlled by a natural pacemaker (the sinus node) in the right upper chamber (atrium). The sinus node sends out electrical signals that normally start each heartbeat. These electrical signals move across the atria, causing the heart muscles to squeeze and pump blood into the ventricles.

Next, the signals arrive at the AV node. The AV node slows down the electrical signals. This slight delay allows the lower heart chambers to fill with blood. When the electrical signals finally get to the muscles of the ventricles, the lower heart chambers squeeze (contract), which pumps blood to the lungs or to the rest of the body.

In a healthy heart, this heart signaling process usually goes smoothly, resulting in a normal resting heart rate of 60 to 100 beats a minute.

SVT occurs when faulty electrical connections in the heart set off a series of early beats in the atria. When this happens, the heart rate becomes so fast so quickly, the heart doesn't have enough time to fill with blood before the chambers contract. As a result, you may feel light-headed or dizzy because your brain isn't getting enough blood and oxygen.

Supraventricular tachycardia falls into three main groups:

• Atrioventricular nodal reentrant tachycardia (AVNRT). This is the most common type of supraventricular tachycardia in both males and females of any age, although it tends to occur more often in young women.
• Atrioventricular reciprocating tachycardia (AVRT). AVRT is the second most-common type of supraventricular tachycardia. It's most commonly diagnosed in younger people.
• Atrial tachycardia. This type of SVT is more commonly diagnosed in people who have heart disease. Atrial tachycardia doesn't involve the AV node.

Other types of supraventricular tachycardia include:

• Sinus tachycardia
• Sinus nodal reentrant tachycardia (SNRT)
• Inappropriate sinus tachycardia (IST)
• Multifocal atrial tachycardia (MAT)
• Junctional ectopic tachycardia (JET)
• Nonparoxysmal junctional tachycardia (NPJT)