Supraventricular tachycardia (SVT) is as an abnormally fast or erratic heartbeat that affects the heart's upper chambers. An abnormal heartbeat is called an arrhythmia. SVT is also called paroxysmal supraventricular tachycardia.

A normal heart rate is 60 to 100 beats per minute. A heart rate of more than 100 beats per minute is called a tachycardia (tak-ih-KAHR-dee-uh). During an episode of SVT, your heart beats about 150 to 220 times per minute, but it can occasionally beat faster or slower.

Most people with supraventricular tachycardia live healthy lives without restrictions or treatment. For others, lifestyle changes, medication and heart procedures may be needed to control or eliminate the rapid heartbeats and related symptoms.

The main symptom of supraventricular tachycardia (SVT) is a very fast heartbeat (100 beats a minute or more) that may last for a few minutes to a few days. The fast heartbeat may come and go suddenly, with stretches of normal heart rates in between.

Some people with SVT have no signs or symptoms at all.

Signs and symptoms of supraventricular tachycardia may include:

• Very fast (rapid) heartbeat
• A fluttering or pounding in your chest (palpitations)
• A pounding sensation in the neck
• Weakness or feeling very tired (fatigue)
• Chest pain
• Shortness of breath
• Lightheadedness or dizziness
• Sweating
• Fainting (syncope) or near fainting

In infants and very young children, signs and symptoms may be difficult to identify. They include sweating, poor feeding, pale skin and a rapid pulse. If your infant or young child has any of these symptoms, ask your child's doctor about SVT screening.

When to see a doctor

Supraventricular tachycardia is generally not life-threatening unless you have heart damage or other heart problems. However, in extreme cases, an episode of SVT may cause unconsciousness or cardiac arrest.

Call your doctor if you have an episode of a very fast heartbeat for the first time, and if the abnormal heartbeat lasts longer than a few seconds.

Some signs and symptoms may be related to a serious health condition. Call 911 or your local emergency number if you have an episode of SVT that lasts for more than a few minutes, or if you have an episode with any of the following symptoms:

• Chest pain
• Shortness of breath
• Weakness
• Dizziness

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)

Supraventricular tachycardia is the most common type of arrhythmia in infants and children. It also tends to occur more often in women, particularly pregnant women, though it may occur in anyone.

Other things that may increase your risk of supraventricular tachycardia are:

• Age. Some types of SVT are more common in people who are middle-aged or older.
• Coronary artery disease, other heart problems and previous heart surgery. Narrowed heart arteries, a heart attack, abnormal heart valves, prior heart surgery, heart failure, cardiomyopathy and other heart damage increase your risk of developing SVT.
• Congenital heart disease. Being born with a heart defect or heart disease may affect your heart's rhythm.
• Thyroid problems. Having an overactive or underactive thyroid gland can increase your risk of supraventricular tachycardia.
• Drugs and supplements. Certain over-the-counter cough and cold medicines and certain prescription drugs may trigger an episode of supraventricular tachycardia.
• Anxiety or emotional stress
• Physical fatigue
• Diabetes. Your risk of developing heart disease and high blood pressure greatly increases with uncontrolled diabetes.
• Obstructive sleep apnea. This disorder, in which your breathing is interrupted during sleep, can increase your risk of supraventricular tachycardia.
• Nicotine and illegal drug use. Nicotine and illegal drugs, such as amphetamines and cocaine, may trigger an episode of supraventricular tachycardia.

Over time, untreated and frequent episodes of supraventricular tachycardia may weaken the heart and lead to heart failure, particularly if there are other coexisting medical conditions.

In extreme cases, an episode of supraventricular tachycardia may cause unconsciousness or cardiac arrest.

To prevent an episode of supraventricular tachycardia, it's important to know what triggers the episodes to occur and try to avoid them. Healthy lifestyle changes can help protect your heart. You might want to try:

• Eating a heart-healthy diet
• Increasing your physical activity
• Avoiding smoking
• Keeping a healthy weight
• Limiting or avoiding alcohol
• Reducing stress
• Getting plenty of rest
• Using over-the-counter medications with caution, as some cold and cough medications contain stimulants that may trigger a rapid heartbeat
• Avoiding illegal drug use, such as cocaine, ecstasy or methamphetamines

For most people with supraventricular tachycardia, moderate amounts of caffeine do not trigger an episode of SVT. Large amounts of caffeine should be avoided, however.

Consider keeping a diary to help identify your triggers. Track your heart rate, symptoms and activity at the time of an SVT episode.

To diagnose supraventricular tachycardia, your doctor will ask questions about your symptoms and your medical history and perform a physical exam. Blood tests are usually done to check for other health conditions that could cause your symptoms, such as thyroid disease.

Your doctor may also order several tests to check your heart health. Tests to diagnosis SVT include:

• Electrocardiogram (ECG). During an ECG, sensors (electrodes) that can detect the electrical activity of your heart are attached to your chest and sometimes to your limbs. An ECG measures the timing and duration of each electrical phase in your heartbeat.
• Holter monitor. This portable ECG device can be worn for a day or more to record your heart's activity as you go about your routine.
• Event monitor or mobile telemetry device. For sporadic episodes of SVT, you may be asked to wear an ECG device for a longer period of time (up to 30 days or until you have an SVT episode or arrhythmia or typical symptoms).
• Echocardiogram. In this noninvasive test, a hand-held device (transducer) placed on your chest uses sound waves to produce images of your heart's size, structure and motion.
• Implantable loop recorder. This device detects abnormal heart rhythms and is implanted under the skin in the chest area.

If your doctor doesn't find a heart rhythm problem during those tests, you may need other tests, such as:

• Stress test. For some people, supraventricular tachycardia is triggered or worsened by stress or exercise. During a stress test, you'll be asked to exercise on a treadmill or stationary bicycle while your heart activity is monitored. If you can't exercise and your doctor thinks heart disease may be causing your arrhythmia, you may receive a drug to stimulate your heart in a way that's similar to exercise.
• Tilt table test. Your doctor may recommend this test if you've had fainting spells. Your heart rate and blood pressure are monitored as you lie flat on a table. The table is then tilted as if you were standing up. Your doctor observes how your heart and the nervous system that controls it respond to the change in angle.

• Electrophysiological testing and mapping. In this test, doctors thread thin tubes (catheters) tipped with electrodes through your blood vessels to several areas within your heart. Once in place, the electrodes can map the spread of electrical signals through your heart.

  In addition, your cardiologist can use the electrodes to stimulate your heart to beat at rates that may trigger — or stop — the arrhythmia. This test allows your doctor to see the location of the arrhythmia and what may be causing it.

Most people with supraventricular tachycardia do not require medical treatment. However, if you have long or frequent episodes, your doctor may recommend the following:

• Carotid sinus massage. A doctor applies gentle pressure on the neck where the carotid artery splits into two branches. During this type of massage, the body releases chemicals that slow the heart rate. Don't attempt to do this on your own.
• Vagal maneuvers. You may be able to stop an episode of SVT by using particular movements such as holding your breath and straining as you would during a bowel movement, dunking your face in ice water, or coughing. These maneuvers affect the nervous system that controls your heartbeat (vagus nerves), often causing your heart rate to slow.

• Cardioversion. If you're unable to stop an episode of SVT on your own using vagal maneuvers, your doctor may use cardioversion. Cardioversion may be done using medications or during a heart procedure.

  In the procedure, a shock is delivered to your heart through paddles or patches on your chest. The current affects the electrical signals in your heart and can restore a normal rhythm.

• Medications. If you have frequent episodes of SVT, your doctor may prescribe medication to control your heart rate or restore a normal heart rhythm. It's very important to take the medication exactly as directed by your doctor in order to reduce complications.
• Catheter ablation. In this procedure, the doctor inserts thin, flexible tubes called catheters through the veins or arteries, usually in the groin. Sensors on the tip of the catheter use heat or cold energy to create tiny scars in your heart to block abnormal electrical signals and restore a normal heartbeat.
• Pacemaker. Rarely, a small, implantable device called a pacemaker is used to stimulate your heart to beat at a normal rate. The pacemaker is placed under the skin near the collarbone in a minor surgical procedure. A wire connects the device to your heart.

Your doctor may suggest that you make lifestyle changes to keep your heart as healthy as possible.

Heart-healthy lifestyle changes include:

• Eat heart-healthy foods. Eat a healthy diet rich in fruits, vegetables and whole grains. Limit salt and saturated fats.
• Exercise regularly. Exercise daily and increase your physical activity.
• Quit smoking. If you smoke and can't quit on your own, talk to your doctor about strategies or programs to help you break a smoking habit.
• Maintain a healthy weight. Being overweight increases your risk of developing heart disease.
• Keep blood pressure and cholesterol levels under control. Make lifestyle changes and take medications as prescribed to correct high blood pressure (hypertension) or high cholesterol.
• Limit alcohol. If you choose to drink alcohol, do so in moderation. For healthy adults, that means up to one drink a day for women of all ages and men older than age 65, and up to two drinks a day for men age 65 and younger.
• Maintain follow-up care. Take your medications as prescribed and have regular follow-up appointments with your doctor. Tell your doctor if your symptoms worsen.

Some types of complementary and alternative therapies may help reduce stress, which can trigger SVT in some people. Stress-relieving techniques include:

• Yoga
• Meditation
• Relaxation techniques

If you think you may have supraventricular tachycardia, make an appointment with your family doctor. If it's found early, your treatment may be easier and more effective. You may be referred to a doctor trained in heart conditions (cardiologist).

Appointments can be brief. Because there's often a lot to discuss, it's a good idea to be prepared for your appointment. Here's some information to help you get ready for your appointment, and what to expect from your doctor.

What you can do

• Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance, such as restrict your diet. You may need to do this if your doctor orders any blood tests.
• Write down any symptoms you're having, including any that may seem unrelated to heart arrhythmia.
• Write down key personal information, including a family history of heart disease, stroke, high blood pressure or diabetes, and any major stresses or recent life changes.
• Make a list of all medications, vitamins or supplements that you're taking. Include those bought without a prescription.
• Take a family member or friend along, if possible. Sometimes it can be difficult to remember all the information provided to you during an appointment. Someone who accompanies you may remember something that you missed or forgot.
• Write down questions to ask your doctor.

For supraventricular tachycardia, some basic questions to ask your doctor include:

• What's the most likely cause of my symptoms?
• Are there other possible causes for my symptoms?
• What kinds of tests will I need? Do I need to do anything to prepare for these tests?
• What's the most appropriate treatment?
• Are there any foods or drinks that you recommend I avoid? Is there anything you suggest that I add to my diet?
• What's an appropriate level of physical activity?
• How often should I be screened for heart disease or other complications of supraventricular tachycardia?
• I have other health conditions. How can I best manage these conditions together?
• Is there a generic alternative to the medicine you're prescribing?
• Are there any brochures or other printed material that I can take home with me? What websites do you recommend visiting?

What to expect from your doctor

Your doctor is likely to ask you many questions. Being ready to answer them may save time to go over anything you want to spend more time on. Your doctor may ask:

• When did you first begin having symptoms?
• Do you always have symptoms, or do they come and go?
• How severe are your symptoms?
• Does anything seem to improve your symptoms?
• What, if anything, appears to worsen your symptoms?
• Do you have a family history of abnormal heart rhythms?