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There are many different kinds of abnormal heart rhythms that may occur in children and adults. Learn about the types of arrhythmias that may occur and how they might manifest in children. If an abnormal rhythm occurs, it's important to find out what kind it is. Treatment recommendations depend on its type. Arrhythmias can cause the heart rate to be irregular, fast or slow (View an animation of arrhythmia). Fast rhythms are called tachycardia. Slow ones are called bradycardia.
Abnormal Heart Rhythms
Long Q-T Syndrome is a disorder of the heart’s electrical system, like other arrhythmias. Since the hearts electrical activity is controlled by the flow of ions (that is electrically charged particles such as calcium, sodium, potassium and chloride), these ions move in and out of the cells of the heart. This flow is controlled by very small ion channels. When the heart contracts, it emits an electrical signal. This signal can be recorded on an electrocardiogram (ECG) and produces a characteristic waveform. The different parts of this waveform are designated by letters — P, Q, R, S and T. The Q-T interval represents the time for electrical activation and inactivation of the ventricles, the lower chambers of the heart. A doctor can measure the time it takes for the Q-T interval to occur (in fractions of a second) and can tell if it occurs in a normal amount of time. If it takes longer than normal, it's called a prolonged Q-T interval.
What are the symptoms of LQTS?
eople with LQTS may not have any symptoms. People who do have symptoms often exhibit fainting (syncope) and abnormal rate and/or rhythm of the heartbeat (arrhythmia), a fluttering feeling in the chest. People with this syndrome may show prolongation of the Q-T interval during physical exercise, intense emotion (such as fright, anger or pain) or when startled by a noise. Some arrhythmias are potentially fatal, causing sudden death. In one type of inherited LQTS, the person may also be deaf.
People with LQTS don't necessarily have a prolonged Q-T interval all the time. At the time that they have an electrocardiogram (such as during a routine physical examination), the Q-T interval may actually be normal. Alternatively, some healthy young people may not have a routine ECG, and LQTS may be suspected because of their family history or because of unexplained fainting episodes. In any family where repeated episodes of fainting or a history of sudden death exists, an investigation of the cause, including LQTS, should be undertaken.
How is LQTS treated?
There are treatments for LQTS, including medications such as beta blockers. Sometimes a surgical procedure is performed, and some people may benefit from an implantable defibrillator. Avoid drugs and electrolyte imbalance known to prolong the Q-T interval.
Premature beats or extra beats most often cause irregular heart rhythms. Those that start in the upper chambers (atria) are called premature atrial contractions or PACs. Premature ventricular contractions or PVCs start in the ventricles. If you've ever had the feeling that your heart "skipped a beat," it was probably from this type of arrhythmia. The heart really doesn't skip a beat. Instead, an extra beat comes sooner than normal. Then there's usually a pause that causes the next beat to be more forceful. You felt this more-forceful beat.
Premature beats are very common in normal children and teenagers — most people have them at some time. Usually no cause can be found and no special treatment is needed. The premature beats may disappear later. Even if they continue, your child will stay well and won't need any restrictions. Occasionally premature beats may be caused by disease or injury to the heart. Your child's doctor may recommend more tests to make sure your child's heart is OK.
A fast heart rate is called tachycardia. The definition of "too fast" usually depends on the person's age and physical activity. A newborn has tachycardia if the resting rate is more than 160 beats per minute. A teenager is considered to have tachycardia if the resting heart rate is more than 90 beats per minute. A teenager may have a normal heart rate of up to 200 beats per minute during exercise.
Sinus tachycardia is a normal increase in the heart rate. It occurs with fever, excitement and exercise. No treatment is needed. Rarely, disease, such as anemia (low blood counts) or increased thyroid activity can cause this fast heart rate. In these cases, when the disease is treated, the tachycardia goes away.
The most common abnormal tachycardia in children is supraventricular tachycardia (SVT). It's also called paroxysmal atrial tachycardia (PAT) or paroxysmal supraventricular tachycardia (PSVT). The fast heart rate involves both the heart's upper and lower chambers. This isn't a life-threatening problem for most children and adolescents. Treatment is only considered if episodes are prolonged or frequent. For many infants, SVT is a time-limited problem. Symptoms often stop, with treatment, after six to 12 months.
SVT may occur in very young infants with otherwise-normal hearts. The heart rate is usually more than 220 beats a minute. Infants with an SVT episode may breathe faster than normal and seem fussy or sleepier than usual. This situation must be diagnosed and treated to return the heart rate to normal. Once the rhythm is normal, medication usually can prevent future episodes.
Sometimes SVT can be detected while a baby is still in the womb. Then the mother may take medications to slow her baby's heart rate. If an older infant or child has SVT, the child may be aware of the rapid heart rate. This may be associated with palpitations, dizziness, lightheadedness, chest discomfort, upset stomach or weakness. Some children can learn ways to slow down their heart rate. Straining — such as closing the nose and mouth and trying to breathe out — may be successful. This is called a Valsalva maneuver.
Older children are more likely to have more episodes of tachycardia. They're more likely to need prolonged treatment. They also may need more diagnostic tests. It's unusual for episodes of SVT to keep a child from enjoying normal activities. Most children who have episodes of tachycardia stay well even though they may need to keep taking medicine. Your child will probably need periodic check-ups but will be able to enjoy unrestricted normal activities.
Treating SVT usually has two parts. The first is stopping a current episode; the second is preventing recurrences. The approach to preventing recurrences depends on the child's age. In some cases — especially those of infants — the child may need to enter the hospital for treatment and special studies.
Sometimes simple procedures can stop a fast heart rhythm. Your child's doctor can explain this to you in more detail. At other times intravenous medications may be needed to control or stop the tachycardia. Another way to stop SVT is to place a small catheter (a thin, flexible tube) through the nostril into the esophagus. A small amount of electricity is sent through this catheter to stop the SVT. On rare occasions doctors stop SVT by giving a small electrical shock to the chest wall. This is called electrical countershock or cardioversion. A sedative or anesthetic is given before this procedure.
Ventricular tachycardia (VT) is a fast heart rate that starts in the lower chambers (ventricles). This uncommon but potentially serious condition can threaten a child's life. VT may result from serious heart disease; it usually requires prompt treatment. VT occasionally occurs in children with otherwise normal hearts. Often specialized tests, including an intracardiac electrophysiologic procedure, may be needed to evaluate the tachycardia and the effect of drug treatment. Some forms of VT may not need treatment.
If treatment is required, it includes medicines and addressing the cause, if possible. The type and length of treatment depends on what's causing the problem. In some people radiofrequency ablation or surgery may be needed to control the tachycardia.
A heart rate that's too slow is called bradycardia. What's "too slow" depends on a person's age and activity. A newborn usually won't have a heart rate of less than 80 beats a minute. An athletically trained teenager may have a normal resting heart rate of 50 beats a minute.
Sometimes the sinus node doesn't work properly. Some children who've had open-heart surgery have this problem. When the sinus node's work is seriously disturbed, it's called sick sinus syndrome. A child with this syndrome may not have any symptoms or may be tired, dizzy or faint. Children with sick sinus syndrome have episodes of tachycardia and bradycardia. Fortunately, sick sinus syndrome is unusual in children. If it does occur, an artificial pacemaker, medications or both may be needed.
Heart block means that the heart's electrical signal can't pass normally from the upper to the lower chambers. The electrical signal within the heart is blocked, not the blood flow. When this occurs, another "natural" pacemaker in the lower chambers takes over, but at a slower rate.
Heart block may be present at — or even before — birth. (This is congenital heart block.) Disease or an injury to the electrical conduction system during heart surgery can also cause it. When the natural pacemaker in the lower chambers isn't fast enough or reliable enough, an artificial pacemaker is put in.