The term bradycardia refers to a slow heart rate. Normal electrical conduction in a child's heart involves the generation of electricity in the sinus node in the upper right portion of the heart. Electricity then travels through both atrium to the AV node in the middle of the heart. From here, electricity is spread out through both ventricles. As electricity moves through the ventricles, heart muscle contracts.
A normal heart rate varies quite a bit based on age as well as activity level. In the normal teenager, a resting heart rate is typically between 60 and 100 beats per minute. With activity, the heart rate may get as high as 200 beats per minute. During sleep, the heart rate can occasionally drop as low as 30-40 beats per minute.
Bradycardia refers to a slow heart rate. The most common cause of his bradycardia in children and teenagers is sinus bradycardia. This simply means that the sinus node is firing at a slow rate. Most of the time sinus bradycardia is a normal physiologic response. For example, a healthy, well conditioned athlete may have a slow resting heart rate. In addition, the heart rate normally slows during rest or sleep. Abnormal sinus bradycardia is fairly uncommon in children and seem most commonly following heart surgery. It can also be seen as a secondary problem in infants, especially premature babies.
Other causes of bradycardia include certain forms of AV block. In second degree AV block, transmission of electricity from the top part of the heart to the bottom part of the heart is intermittently blocked. In complete AV block, or complete heart block, transmission of electricity from the atria to the ventricles is completely interrupted. With complete AV block, some other area below the AV node must take over and become responsible for generating electricity for the heart. Usually this happens at a much slower rate than normal, resulting in bradycardia.
Treatment of bradycardia depends on the underlying cause. Physiologic bradycardia in a child requires no treatment whatsoever. Pathologic bradycardia, for example that associated with complete AV block often requires a pacemaker.