My child's heart seems to beat very fast. Does she have an irregular heartbeat?
Your child's heart rate normally will vary to some degree. Fever, crying, exercise, or other vigorous activity makes any heart beat faster. And the younger the child, the faster the normal heart rate will be. As your child gets older, her heart rate will slow down. A resting heart rate of 130 to 150 beats per minute is normal for a newborn infant, but it is too fast for a six-year-old child at rest. In a very athletic teenager, a resting heart rate of 50 to 60 beats per minute may be normal.
The heart’s regular rhythm or beat 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 heart circuitry, but arrhythmias also can be caused by infections or chemical imbalances in the blood. 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 fluctuation is called sinus arrhythmia, and requires no special evaluation or treatment because it is normal.
So-called premature heartbeats are another form of irregular rhythm that requires no treatment. If these occur in your child, she might say that her heart “skipped a beat” or did a “flip-flop.” Usually these symptoms do not indicate the presence of significant 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 do occur they can be serious. On rare occasions they can cause fainting or even heart failure. Fortunately, they can be treated successfully so it’s important to detect arrhythmias as early as possible.
Signs and symptoms
If your child has a true arrhythmia, your pediatrician probably will discover it during a routine visit. But should you notice any of the following warning signs between pediatric visits, notify your doctor immediately.
Your infant suddenly becomes pale and listless; her body feels limp.
Your child complains of her “heart beating fast,” when she’s not exercising.
She tells you she feels uncomfortable, weak, or dizzy.
She blacks out or faints.
Diagnosis
It's unlikely that your child will ever experience any of these symptoms, 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 normal sinus arrhythmia from a true arrhythmia. An ECG is 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, often 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. When your child is old enough to participate in sports, ask your pediatrician if any special tests or restrictions are necessary.
Source - 11/21/2015
Caring for Your Baby and Young Child: Birth to Age 5 (Copyright © 2009 American Academy of Pediatrics)