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Understanding Supraventricular Tachycardia

Supraventricular tachycardia (SVT) is a type of abnormal heart rhythm that results in fast heartbeats. The heart normally beats 60 to 100 beats per minute while you are at rest and awake. With SVT, the heart beats more than 100 times a minute. It may even beat over 200 times a minute. This is caused by a problem in the electrical system of the heart. It can lessen the amount of blood pumped through the heart.

How the heart beats

A heartbeat is the rhythm of the heart as it contracts to squeeze blood through the body. It’s caused by electrical signals in the heart. A beat starts when a special group of cells give off an electrical signal. These cells are in the sinoatrial (SA) node. The SA node is in the upper right chamber of your heart (atrium). The signal from the SA node travels down to the 2 lower chambers of your heart (ventricles). On the way, the signal goes through the atrioventricular (AV) node. This is a special group of cells between the atria and ventricles. From there, the signal travels to your left and right ventricles. As it travels, the signal tells nearby parts of your heart to contract. This causes your heart to pump in a coordinated way.

What is SVT?

When you have SVT, the signal to start your heartbeat doesn’t come from the SA node. Instead it comes from another part of the left or right atrium. Or it comes from the AV node. Some area outside the SA node begins to fire quickly, causing a rapid heartbeat of over 100 beats per minute or the electrical signals are caught up in an abnormal looping circuit. This shortens the time your ventricles have to fill. If your heartbeat is fast enough, your heart may be unable to pump enough blood forward to the rest of your body. The abnormal heartbeat may last for a few seconds to a few hours before your heart returns to its normal rhythm. Some SVT rhythms can last for days or weeks, or even become permanent.

Types of SVT

There are several types of SVT. They include:

  • Atrial fibrillation. This is most common type of SVT. The upper chambers of the heart quiver very fast instead of pumping due to disorganized electrical activity in the atria.

  • Atrial flutter. This type of SVT is a milder form of fibrillation. The upper chambers of the heart flutter instead of pumping normally.

  • Atrioventricular nodal reentrant tachycardia. It occurs when you have two channels through the AV node, instead of just one. The signal goes down one channel and up the other.

  • Atrioventricular reciprocating tachycardia. With this condition, there is an extra connection of muscle between the atrium and the ventricle. This is known as an accessory pathway and can conduct electricity upwards and downwards. The signal goes down the AV node and back to the atrium through the accessory pathway. It then goes down the AV node again. In rare cases, this condition leads to an abnormal heart rhythm that causes sudden death. This is a congenital defect, which means you were born with it.

  • Atrial tachycardia. This is another common type of SVT. A small group of cells in the atria begin to fire abnormally and trigger the fast heartbeat.

  • Multifocal atrial tachycardia. Multiple groups of cells in your atria fire abnormally and trigger a fast heartbeat.

What causes SVT?

Some types of SVT run in families. Some people have heart problems from birth that cause SVT. High blood pressure, heart failure, mitral valve disease, sleep apnea, thyroid problems, and heart attacks can cause SVT. Smoking, excess caffeine or alcohol, and some medicines can increase your risk of having SVT.

Symptoms of SVT

When SVT happens, you may feel no symptoms. Or you may have:

  • Fluttering feelings in your chest (palpitations)

  • A tight feeling or pain in your chest

  • A pulsing feeling in your neck

  • Dizziness

  • Shortness of breath

  • Tiredness

  • Fainting

  • Nausea

In very rare cases, SVT can cause sudden death.

Diagnosing SVT

Your primary healthcare provider may diagnose you. Or you may see a heart doctor (cardiologist). The doctor will ask about your health history. He or she will also give you a physical exam. You may also have tests. These help show what kind of SVT you have, and what may cause it. They also help check for other problems. The tests may include:

  • Electrocardiogram (ECG), to analyze the abnormal rhythm

  • Continuous heart monitors such as a holter monitor or an event recorder to watch your heart rhythm over a longer period in an attempt to catch the SVT rhythm

  • Blood tests, to look for various causes such as thyroid problems or electrolyte abnormalities

  • Chest X-ray, to check for lung problems and look at the size of your heart

  • Exercise stress test, to see how well your heart works under stress

  • Echocardiography, to check your heart structure and function

  • Electrophysiologic study (EPS), an invasive procedure using wires in the heart to check the heart's electrical signals and diagnose the SVT

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