Overview
Supraventricular tachycardia (SVT), also called paroxysmal supraventricular tachycardia, is defined as an abnormally fast heartbeat. It's a broad term that includes many forms of heart rhythm problems (heart arrhythmias) that originate above the ventricles (supraventricular) in the atria or AV node.
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). This occurs when the electrical impulses that coordinate your heartbeats don't work properly. It may feel like a fluttering or racing heart.
Most people with rare episodes of supraventricular tachycardia live healthy lives without restrictions or interventions. For others, treatment and lifestyle changes can often control or eliminate rapid heartbeats.
Types
Atrial tachycardia
Atrioventricular nodal reentry tachycardia (AVNRT)
Symptoms
Supraventricular tachycardia may come and go suddenly, with stretches of normal heart rates in between. Symptoms may last anywhere from a few minutes to a few days, and some people have no symptoms at all.
Supraventricular tachycardia becomes a problem when it occurs frequently and is ongoing, particularly if you have heart damage or other coexisting medical problems.
Signs and symptoms of supraventricular tachycardia may include:
A fluttering in your chest
Rapid heartbeat (palpitations)
Shortness of breath
Lightheadedness or dizziness
Sweating
A pounding sensation in the neck
Fainting (syncope) or near fainting
In infants and very young children, signs and symptoms may be difficult to identify. Sweating, poor feeding, pale skin and infants with a pulse rate greater than 200 beats per minute may have supraventricular tachycardia.
The heart is a 4-chambered muscle that functions as a blood pump; the 2 upper chambers are called the atria and the 2 lower chambers are the ventricles. The rhythm of the heart is normally controlled by a natural pacemaker (the sinoatrial node) in the right upper chamber that beats about 60 times per minute at rest and can increase with exercise. Electrical impulses travel from the natural pacemaker through the atria, then pass through a filter called the atrioventricular node (AV) between the atria and ventricles before running down specialized fibers that activate the ventricles.
Figure 1. Diagram of the heart and the electrical conduction
system of the heart. Electrical impulses start in the sino-atrial node and
travel via the atria to the AV node. From there, the electrical impulse travels
through the His fibers and the Purkinje fibers to the left and right
ventricles.
Causes
For some people, a supraventricular tachycardia episode is related to an obvious trigger, such as psychological stress, lack of sleep or physical activity. For others, there may be no noticeable trigger. Things that may lead to, or cause, an episode include:
Heart failure
Thyroid disease
Heart disease
Chronic lung disease
Smoking
Drinking too much alcohol
Consuming too much caffeine
Drug use, such as cocaine and methamphetamines
Certain medications, including asthma medications and over-the-counter cold and allergy drugs
Surgery
Pregnancy
Certain health conditions, such as Wolff-Parkinson-White syndrome
What's a normal heartbeat?
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) located in the right atrium. The sinus node produces electrical impulses that normally start each heartbeat.
From the sinus node, electrical impulses travel across the atria, causing the atria muscles to contract and pump blood into the ventricles.
The electrical impulses then arrive at a cluster of cells called the atrioventricular node (AV node) — usually the only pathway for signals to travel from the atria to the ventricles.
The AV node slows down the electrical signal before sending it to the ventricles. This slight delay allows the ventricles to fill with blood. When electrical impulses reach the muscles of the ventricles, they contract, causing them to pump blood either to the lungs or to the rest of the body.
In a healthy heart, this process usually goes smoothly, resulting in a normal resting heart rate of 60 to 100 beats a minute.
Supraventricular tachycardia occurs when faulty electrical connections in the heart or abnormal areas of electrical activity trigger and sustain an abnormal rhythm. When this happens, the heart rate accelerates too quickly and doesn't allow enough time for the heart to fill before it contracts again. These ineffective contractions of the heart may cause you to feel light-headed or dizzy because the brain isn't receiving enough blood and oxygen.
Types of supraventricular tachycardia
There are three major types of supraventricular tachycardia:
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 supraventricular tachycardia is more commonly diagnosed in people with coexisting heart disease. Unlike AVNRT and AVRT, which always involve the AV node as part of the faulty connection, atrial tachycardia doesn't involve the AV node.
Other types of supraventricular tachycardia include:
Sinus tachycardia
Inappropriate sinus tachycardia (IST)
Multifocal atrial tachycardia (MAT)
Junctional ectopic tachycardia (JET)
Nonparoxysmal junctional tachycardia (NPJT)
How Is Supraventricular Tachycardia Diagnosed?
The electrocardiogram (ECG or EKG) provides a picture of the heart rhythm and is recorded by placing adhesive or gel pads on the chest and limbs. If the patient is experiencing SVT during the ECG, a clear diagnosis can be made. Various other types of electrocardiographic monitors may be used to record the patient’s heart rhythm to help make a diagnosis of SVT. A 24-hour ambulatory Holter monitor may be used to record the heart rhythm continuously for 24 hours. This type of monitor is particularly helpful in documenting asymptomatic or very frequent rhythm abnormalities. For those patients whose arrhythmias occur relatively infrequently, event or loop monitors may be worn. An event monitor is attached to the patient’s wrist or chest whenever symptoms suggesting SVT occur. Activating a button on the monitor will start a recording of the heart’s rhythm. The patient is given instructions about how to download this information to a computer that stores results for later analysis via a special device placed over a telephone mouthpiece. For patients who experience very brief arrhythmias or those accompanied by severe lightheadedness, an event monitor is impractical. In such cases, patients may wear a loop monitor continuously for days to weeks. The loop monitor continuously records the heart’s rhythm so that the patient need only press a button to save a record of the rhythm during the preceding and subsequent 1 to 2 minutes. This permits recording even very transient arrhythmias. The loop monitor record is downloaded using a telephone in the same way that event monitor data are transmitted.
How Is Supraventricular Tachycardia Classified?
An SVT is classified medically on the basis of the path that the electrical signal takes from the atria. One type of SVT (AV nodal reentrant tachycardia or AVNRT) occurs because the electrical impulse travels in a circle using extra fibers in and around the AV node (Figure 2). Another type of SVT occurs because of electrical conduction via extra fibers between the atria and ventricles; this means of conduction is called a bypass tract or accessory pathway. The electrical impulse travels down the AV node to the ventricle and back to the atrium via these extra fibers, producing the SVT called AV reentrant tachycardia, or AVRT (Figure 3). Some patients are told that they have Wolff-Parkinson-White Syndrome (WPW), in which there is evidence of conduction via an accessory pathway from the atrium to the ventricle that may be detected on the ECG even if they are not experiencing SVT. Atrial tachycardias occur when localized regions in the atria develop the ability to fire rapidly on their own.
Figure 2. Diagram of AV nodal reentrant tachycardia (AVNRT).
The electrical impulse travels in a circle using extra fibers in and around the
AV node.
Figure 3. A diagram of AV reentrant tachycardia (AVRT). The
electrical impulse travels down the AV node to the ventricles and back to the
atrium via extra fibers that connect the atria and ventricles
Risk factors
Supraventricular tachycardia is the most common type of arrhythmia in infants and children. It also tends to occur twice as often in women, particularly pregnant women, though it may occur in either sex.
Other factors that may increase your risk of supraventricular tachycardia include:
Age. Some types of supraventricular tachycardia 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 supraventricular tachycardia.
Congenital heart disease. Being born with a heart abnormality 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 contribute to an episode of supraventricular tachycardia.
Anxiety or emotional stress
Physical fatigue
Diabetes. Your risk of developing coronary artery 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 profoundly affect the heart and trigger an episode of supraventricular tachycardia.
How Is Supraventricular Tachycardia Treated?
Medications may be used to treat many patients with SVT. The most commonly used classes of medications are:
β-blockers: These are commonly used to treat high blood pressure and other heart problems such as angina. In SVT, they are used specifically to decrease conduction through the AV node (Figure 1) to stop conduction during the tachycardia.
Calcium channel blockers: These are also used to treat high blood pressure and heart problems. Like β-blockers, they may be used to decrease conduction through the AV node. Examples of calcium channel blockers include verapamil or diltiazem.
Antiarrhythmic agents: These agents are used to treat various arrhythmias and directly affect the atrial or ventricular heart tissue. They are most useful in SVTs that use an accessory pathway or bypass tract or in atrial tachycardias.
You will want to discuss with your physician the medical therapy that is right for you.
A special procedure called radiofrequency ablation (RFA) has been developed as an alternative to medication to treat many patients with SVT. During this procedure, special plastic tubes called catheters are inserted into a vein into the upper leg/groin area and are advanced to the heart using a fluoroscope. The catheters are used to record electrical signals from inside the heart. They can locate precisely the site from which the SVT originates. Radio waves (called radiofrequency energy) are delivered at the tip of this catheter to the precise location of the SVT, creating a small coagulation of the tissue approximately 2 mm in diameter. The procedure has a 90% to 95% chance of successfully treating the SVT, so that it does not recur or require medication. There is approximately a 5% chance that the SVT will recur, usually within the first 1 to 2 months.
RFA can carry the risks described below:
Less than 1% risk of serious or life-threatening complications
Less than 1% risk of damage to the normal conduction system
Bleeding, bruising, or infection at catheter insertion site
Damage to the heart, lungs, blood vessels, or nerves
Blood clots to the lungs
Need for electrical shock to the chest
Rashes
Allergic reactions
Adverse effects of sedatives or anesthetic agents, such as respiratory depression requiring insertion of a breathing tube
Your cardiologist will discuss the complications and benefits of RFA with you and let you know if it is an appropriate treatment for your medical condition.
What Can I Do When I Develop Supraventricular Tachycardia?
You may want to discuss with your physician the steps that you may take when you develop SVT. For instance, your physician may instruct you to perform the Valsalva maneuver to try to stop the SVT yourself if you do not have lightheadedness, shortness of breath, chest pain, or other severe symptoms. To do this maneuver, first lie down, take a deep breath and hold it, and then bear down as if you are having a bowel movement.
If you become quite lightheaded, you should lie down and call for assistance and for immediate transport to a local hospital. If transportation is not immediately available, or if you have chest pain or feel like you might lose consciousness, call 911 right away. You may be brought to the emergency department of a local hospital. There, an ECG will be performed and an intravenous line will be started. You may be given a small amount of a medication called adenosine that is quite effective in stopping the SVT. Adenosine may cause flushing, a hot sensation, and a sudden feeling of breathlessness for 30 seconds or less. It should be used with caution in patients with asthma. Other medications such as verapamil, β-blockers, or diltiazem may also be given intravenously.
Complications
Over time, untreated and frequent episodes of supraventricular tachycardia may weaken the heart and lead to heart failure, particularly if you have other coexisting medical conditions.
In extreme cases, an episode of supraventricular tachycardia may cause unconsciousness or cardiac arrest.
Prevention
To prevent an episode of supraventricular tachycardia, it's important to know what triggers the episodes to occur and try to avoid them. 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 stimulant drugs such as cocaine and methamphetamines
For most people with supraventricular tachycardia, moderate amounts of caffeine do not trigger an episode. 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.
References
NHS and BHF : Supraventricular Tachycardia
Cleveland Cinic: SVT
Circulation. 2002;106:e206–e208
European Society of Cardiology : SVT
