Arrhythmias
Supraventricular tachycardia
What is supraventricular tachycardia?
Supraventricular tachycardia (SVT) is a type of arrhythmia, or heart rhythm disturbance, that arises in the atria (which are above the ventricles, or “supraventricular”) and causes the heart to beat too quickly (tachycardia).
Heart contractions: SVT (AVNRT) vs normal heart
The most common form of SVT is a disorder called atrioventricular nodal re-entrant tachycardia (which is, thankfully, abbreviated to AVNRT).
Approximately 95% of all cases of supraventricular tachycardia are caused by AVNRT, and so that’s the specific kind of SVT we’ll discuss in this section.
In SVT the two upper chambers of the heart (the atria) sometimes beat very rapidly, usually 140 – 240 beats per minute. The ventricles beat more slowly, but the result is a heart rate of 100 beats per minute or more.
A normal heart rate is 60 – 100 beats per minute.
Episodes of SVT may be brief, and may begin and end quite suddenly.
SVT is more common in women than men and it often occurs in quite young adults.
If you’d like to learn about a normal heartbeat and how your heart functions, take a look at Your heart: The basics.
What causes SVT?
Your heartbeat is regulated by complex electrical signals. The signals are controlled by the heart’s sinoatrial (SA) node, which is in the right atrium.
With each heartbeat, the SA node fires an electrical pulse that spreads down through the heart to the atrioventricular (AV) node and the ventricles, and causes it to contract in an organized way.
In the AVNRT form of SVT the electrical signal that initiates an atrial contraction is sent prematurely, and it travels around a small extra circuit called a re-entrant or re-entry circuit. This circuit is something you’re born with. The signal sometimes then runs around and around the circuit and causes sudden very rapid heartbeats (tachycardia).
If you have an AV nodal re-entrant circuit, you may have episodes of SVT when something triggers an attack. Common triggers include alcohol, and stimulants such as caffeine, decongestants, and drugs like cocaine and methamphetamine.
To learn more about how your heart’s electrical pulses work, take a look at Your heart’s electrical system.
Electrical signals: SVT (AVNRT) vs normal heart
What are the symptoms of SVT?
Some people with SVT may not know that anything is wrong because episodes may be brief and so the symptoms come and go.
Symptoms of SVT can vary from person to person, but here’s a list of common ones:
- A suddenly racing heartbeat
- Shortness of breath
- Dizziness
- Chest discomfort
- Tiredness
How is SVT treated?
Many people with SVT don’t really require treatment. But if your doctor recommends it, here are some standard options. The first, vagal maneuvers, you can do yourself:
- Vagal maneuvers such as coughing, or holding your breath and straining
- Medications to control your heart’s rate and rhythm
- Cardioversion (a small shock to the chest that resets the heart’s rhythm)
- A catheter-based procedure called cardiac ablation (if medications and cardioversion don’t help)
- Avoiding stimulants like caffeine and decongestants
What are the aims of treatment?
The immediate aims of treatment are to reset the rhythm of your heart and slow your heart rate.
Most people with SVT experience no long-term ill effects, but your doctor may suggest treatment if there is reason to worry about serious but rare complications like cardiac arrest.