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The regular rhythm or beat of the heart is maintained by a small electrical circuit that runs through nerves in the walls of the heart. When the circuit is working properly, the heartbeat is quite regular, but when there's a problem in the circuit, an irregular heartbeat, or arrhythmia, can occur. Some children are born with abnormalities in this apparatus, but arrhythmias can be caused by infections or chemical imbalances in the blood.
So-called "premature heartbeats" are another form of irregular rhythm that requires no treatment at all. If these occur in your child, she might say that her heart "skipped a beat" or did a "flip-flop." Your pediatrician may check to see if the irregular beats disappear with exercise; if they do, they are not an indication of heart disease.
If your pediatrician says that your child has a true arrhythmia, it could mean that her heart beats faster than normal (tachycardia), very fast (flutter), fast and with no regularity (fibrillation), slower than normal (bradycardia) or that it has isolated early beats (premature beats). While true arrhythmias are not very common, when they occur they can be serious, causing fainting or even heart failure. Fortunately, they can be treated successfully with medication, so it's important to detect them as early as possible.
Sinus Arrhythmia
Your child's heart rate will normally vary to some degree. Fever, exercise, crying or other vigorous activity makes any heart beat faster. (That's why a person's base heart rate is usually measured when the body is at rest.) And the younger your child, the faster her resting heart rate will be. As she gets older, her rate will naturally slow down. For example, a resting heart rate of 130 beats per minute is normal for a newborn infant, but it's too fast for a 6-year-old child at rest. A resting heart rate of 50 or 60 beats per minute may be normal for an athletic teenager, but it is abnormally slow for a baby.
Even in healthy children there can be other variations in the rhythm of the heartbeat, including changes that occur just as a result of breathing. Such a normal fluctuation is called sinus arrhythmia, and requires no special evaluation or treatment. It is not a sign of heart trouble.
If your child has a true arrhythmia, your pediatrician probably will discover it during a routine visit. If you notice any of the following warning signs between pediatric visits, notify the physician immediately.
· Your infant suddenly becomes pale and listless; her body feels limp.
· Your child complains of her "heart beating fast," even when she's not exercising.
· She tells you she feels uncomfortable, weak or dizzy.
· She blacks out or faints.
Diagnosing Arrhythmia
It's unlikely that your child will ever experience any of the symptoms of arrhythmia, but if she does, your pediatrician will perform additional tests and perhaps consult with a pediatric cardiologist. In the process the doctors may do an electrocardiogram (ECG), to better distinguish a harmless sinus arrhythmia from a true arrhythmia. An ECG is really just a tape recording of the electrical impulses that make the heart beat, and it will allow the doctor to observe any irregularities more closely.
Sometimes your child's unusual heartbeats may occur at unpredictable times, frequently not when the ECG is being taken. In that case, the cardiologist may suggest that your child carry a small portable tape recorder that continuously records her heartbeat over a one- to two-day period. During this time you'll be asked to keep a log of your child's activities and symptoms. Correlating the ECG with your observations will permit a diagnosis to be made. For example, if your child feels her heart "flutter" and becomes dizzy at 2:15 p.m., and the ECG shows her heart suddenly beating faster at the same time, the diagnosis of tachycardia will probably be established.
Occasionally, irregular heartbeats will occur only during exercise. If that's the case with your child, the cardiologist may have your youngster ride a stationary bicycle or run on a treadmill while her heartbeat is being recorded.