What is supraventricular tachycardia?
Supraventricular tachycardia (SVT) is the most common arrhythmia (abnormal heart rhythm) diagnosed in children. It is said to occur in up to 1 in 2500 children. While the problem is often congenital, meaning it is present at birth, the onset and severity of symptoms varies. Most of the time, the problem occurs in children with otherwise normal hearts but it can occur along with other congenital heart problems. An arrhythmia is an abnormal heart rhythm caused by a problem in the heart's electrical system, also called the cardiac conduction system. When a child has SVT, the heart suddenly starts to beat very fast, at rates of 180 to 280 beats a minute and up to 300 beats a minute in infants. Supraventricular tachycardia means fast heart rate coming from the above the ventricles, in the heart's upper chambers (supra = above, ventricular = the lower heart chambers, tachy = fast, cardia = heart). Below is and example of an electrocardiogram (ECG) that was taken in an infant who had a heart rate of 280-300 beats per minute.Sometimes other names are used for SVT such as paroxysmal (starts and stops without warning) atrial tachycardia (PAT) and paroxysmal supraventricular tachycardia (PSVT). All these terms describe SVT. Wolff-Parkinson-White syndrome (WPW) is one subset of SVT and is the most common type of SVT in young children. The information in this section applies to children with WPW but there are a few differences discussed in that section. When a child has SVT, there is usually an extra pathway (see the diagram below) in the heart's electrical system that connects the top chambers and lower chambers of the heart. Usually the only electrical connection is the AV-node, so the extra connection provides a potential "short circuit" in the heart. Most of the time, the extra pathway does not effect the heart rhythm. However, if there is an early heart beat (called a premature atrial contraction — PAC, or premature ventricular contraction — PVC), the impulse may travel down to the lower chambers using the normal pathway, the AV node, causing the heart to beat, and travel back up the extra pathway to the atria. The impulse then continues going around this circuit, somewhat like "a dog chasing its own tail" driving the heart at a very fast rate. When the electrical loop is blocked anywhere along its route, normal heart rhythm can resume. Another form of SVT in children is called atrioventricular reentrant tachycardia (AVNRT). This is the most common form of SVT in adults. In about 10% of children, SVT results from an extra focus or "pacemaker" in the atria (upper chambers) (see in diagram above - "APB.") that beats faster than the normal pacemaker, the SA node. The diagnosis, outlook and treatment are similar in all of these forms of SVT.
What are the effects of this problem on my child's health?
SVT is almost never life-threatening and treatment outcomes are excellent. It causes intermittent symptoms of heart racing and may cause chest pain, shortness of breath, lightheadedness, and/or fainting. The episodes may or may not be related to exercise. Although the set-up for SVT is often present at birth, the symptoms can start at any time. The episodes seem to occur more during infancy, then again at around 7 to 8 years of age, and then during the teen-age years. The episodes can vary both in frequency and duration over time and may or may not be related to exercise. If present during infancy, it usually resolves by 12 to 18 months of age. There is then a 50% chance that the SVT will recur as an older child. If the SVT starts after the first year of life, it is likely to persist. Most children with SVT are diagnosed because of intermittent symptoms of rapid heartbeat, sometimes called "palpitations". Children may say that "my heart is racing", "my heart is fluttering", "my heart is beeping", or " my heart is beating out of my chest". Other symptoms include dizziness or lightheadedness, chest pain, pressure in the neck, shortness of breath, and/or fainting. If someone tries to count the heart rate during an episode, it is often described as "too fast to count". SVT in babies may diagnosed due to symptoms of congestive heart failure. Babies are able to tolerate a very fast heart rate for many hours without showing symptoms. If the episode lasts many hours (more than 24-36 hours), the heart muscle slowly tires, and pumps with less and less strength. Symptoms at this time include poor feeding, unusual sleepiness, irritability, vomiting, rapid breathing, and/or pale skin color. At first, the symptoms are subtle but they progress unless the fast rhythm stops on its own or the problem is treated. In general, SVT is almost never a life-threatening problem and the episodes do not need to be treated as a medical emergency. If an episode occurs, vagal maneuvers (these are explained in the section below on treatment) should be tried. If the episode lasts longer than 45 minutes the child should be taken (by car without undue haste) to a local emergency room for treatment.
How is this problem diagnosed?
Clinical features: As described above, infants may be diagnosed because of symptoms of congestive heart failure including poor feeding, unusual sleepiness, irritability, vomiting, rapid breathing, and/or pale skin color. In children, the problem is found because of symptoms of "heart racing" that may be associated with dizziness, lightheadedness, chest pain, shortness of breath, and/or fainting. Physical findings: Most of the time the physical exam is normal when the child is not having an episode. Rarely, the problem is associated with a heart defect. In this case, the child has the physical findings associated with that defect. Medical tests: One of the first tests usually done is an electrocardiogram (ECG). However, unless the child has WPW or is having an episode at the time, the ECG at rest is usually normal. In this case, a device called a transtelephonic ECG recorder is used to record an ECG at the time of symptoms. Other tests that may be done include a Holter monitor, echocardiogram, and/or exercise test. If further information is needed a special type of heart catheterization called an electrophysiologic study may be done.
How is the problem treated?
As stated above, the fast heart rate occurs intermittently and is rarely life-threatening. The episodes are started by extra, early heartbeats. Although these extra beats occur in all children and adults, they can be increased in frequency by caffeine and other stimulants such as decongestants found in cold and allergy medications or inhalers used to treat asthma. For this reason, people with SVT are often counseled to avoid caffeine in their diet and to avoid certain medicines. Episodes of SVT can often be stopped by "vagal maneuvers". Vagal maneuvers increase the "slow down" messages sent to the heart by the brain along a nerve called the vagus nerve. These maneuvers include: 1) blowing on the thumb as if it were a trumpet (without letting any air out while blowing); 2) "bearing down" as if passing a bowel movement; 3) placing the face ice water or placing ice to the face while holding the breath, and 4) doing a headstand. Older children can be taught to use these maneuvers on their own. If vagal maneuvers do not work and an episode lasts longer than 45 minutes, the child should be taken to the local emergency room for treatment. Usually an IV medicine called adenosine is used to convert the heart rhythm back to normal. If the episode does not respond to IV medication, in the presence of severe symptoms, electrical cardioversion (shock) may be needed. Treatment of SVT includes 1) watchful waiting with use of vagal maneuvers, 2) medication, or 3) radiofrequency ablation. Treatment decisions are made based on 1) age/size of the patient, 2) in the case of Wolff-Parkinson-White syndrome, whether the extra pathway is able to conduct an electrical signal rapidly from the upper chambers to the lower chambers of the heart, 3) the frequency and severity of symptoms, 4) treatment effectiveness for a particular patient, 5) whether the child wants to play competitive sports, and 6) child/family preference.
Care and services for patients with this problem are provided in the Arrhythmia Clinics and Congenital Heart Clinics at the University of Michigan Medical Center in Ann Arbor.
What are the long-term health issues for these children?
The outlook for children with SVT is excellent. The problem is usually not life- threatening and there are safe and effective treatments available. Exercise guidelines: Exercise guidelines are best made by a patient's doctor so that all relevant factors can be included. Usually no activity restrictions are necessary for children with SVT and the child may participate in all physical activities including competitive athletics. If an episode occurs during competition, the child should remove himself from participation until the arrhythmia is converted. Also, activities that involve climbing or heights should be avoided since an episode may cause dizziness leading to a fall. See the section on Wolff-Parkinson-White syndrome for exercise information specific to this sub-type.
Dick M., O'Connor B, Serwer G, LeRoy S, Armstrong B. Use of radiofrequency energy to ablate accessory connections in children. Circulation 1991; 84:2318-24. LeRoy S. & Dick M. Supraventricular tachycardia. In Zeigler VL & Gillette P, eds. Practical management of pediatric cardiac arrhythmias. Armonk, NY: Futura Publishing Co. 2001: 53-109. Weindling SN, Saul JP & Walsh EP. Efficacy and risks of medical therapy for supraventricular tachycadia in neonates and infants. Am Heart J 1996 131:66.Written by: S. LeRoy RN, MSN, CPNP. Reviewed by: M. Dick, MD, Peter Fischbach Reviewed September, 2012