The sinus node is the pacemaker of the heart. It is responsible for generating the electrical impulses that stimulate the heart muscle to contract. Sinus tachycardia refers to a faster than normal heart rate.
The sinus node is very carefully regulated by the brain. During normal activity, the firing rate of the sinus node is maintained according to the metabolic needs of the body. The nervous system stimulates the sinus node to fire faster during times of increased activity, for example during exercise. Likewise, the sinus node fires more slowly (sinus bradycardia) during times of decreased metabolic rate, for example during sleep.
What is Sinus Tachycardia?
Sinus tachycardia refers to a faster than expected heart rate. In an older child or teenager, sinus tachycardia usually means a heart rate over 100 beats per minute. Babies and younger children have faster resting heart rates, so the criteria for sinus tachycardia is different. For a baby, sinus tachycardia is usually means a heart rate over 160-170 beats per minute. In a school age child, sinus tachycardia is usually considered a heart rate over 120 beats per minute.
Sinus Tachycardia Causes
Most of the time sinus tachycardia in children is not a problem, but actually a normal physiologic response of the body. The brain is very good at controlling the heart rate based on the metabolic needs of the body. During exercise, for example, the metabolic requirements of the body and muscles increase dramatically. Therefore the brain signals the heart rate to increase in order to deliver more blood and oxygen to the body. Sinus tachycardia is an expected finding in this setting. Sinus tachycardia is also very common in other stress responses of the body. For example, pain, fever, or emotion cause the body to release adrenaline which increases the heart rate. Again, sinus tachycardia in this setting is expected and normal.
Occasionally a child may be noted to have a faster than expected heart rate, and is subsequently referred to a pediatric cardiologist for evaluation of sinus tachycardia. More commonly a child may be referred because they have the sensation of palpitations. In this setting, the child feels his or her heart beating rapidly. The pediatric cardiologist then works to determine whether these symptoms are due to an expected sinus tachycardia, or something more concerning such as supraventricular tachycardia or Wolff-Parkinson-White syndrome.
Primary pathologic sinus tachycardia in children is rare. Almost always sinus tachycardia is caused by a secondary problem outside the heart. For example fever, infection, hypothyroidism, anemia, or any other problem that increases the metabolic rate can result in sinus tachycardia. Likewise, sinus tachycardia can be seen in any state that produces an increased amount of adrenaline, for example with anxiety or other emotional disorders.
Primary sinus tachycardia caused by a heart related problem is usually due to some type of infectious or inflammatory condition with the heart. Inflammation of the heart muscle (myocarditis) or of the lining of the heart (pericarditis) can produce sinus tachycardia.
Sinus Tachycardia Symptoms
Most children with physiologic sinus tachycardia do not have any symptoms whatsoever. Some children may be aware of their heart beating rapidly and feel it is somewhat unusual because they are not used to the sensation. Other make children may have symptoms primarily related to the adrenaline release causing sinus tachycardia.
Sinus Tachycardia Treatment
Sinus tachycardia in children usually does not require treatment. Most commonly it is a normal physiologic response to the body's messages and needs, and therefore perfectly appropriate.