A sinus arrhythmia describes variations in heart rhythm that may be either slower or faster than usual. In most cases, this is a sign of a healthy heart.

While an arrhythmia typically refers to an “irregular” heartbeat, this condition isn’t necessarily a cause for concern in newborns. In fact, certain types of sinus arrhythmias are considered typical in children, especially in newborns and infants.

Still, it’s important to know about this type of heart rhythm if a pediatrician connects this with your baby. As always, you should reach out to a doctor immediately if you notice any concerning symptoms in your newborn.

What is a sinus rhythm?

Your sinus rhythm refers to your heart’s usual rhythm that originates in the sinus node within the upper chamber of your heart (atrium). Considered the heart’s “natural pacemaker,” the sinus node controls electrical pulses that control your heart’s rhythm and rate.

The typical heart rate for an adult can range between 60 and 100 beats per minute while at rest. But newborns naturally have higher heart rates of 100 to 205 beats per minute while awake and 90 to 160 beats per minute while asleep.

A sinus arrhythmia means your sinus rhythm is either slower or faster than what is typical.

The causes of sinus arrhythmia in newborns may vary and depend on the type.

The most common type of sinus arrhythmia in newborns is respiratory, which is completely normal. This describes a heart rate that naturally increases and decreases with the breathing cycle.

While less common, other types of sinus arrhythmia could be due to sinus node dysfunction. Problems with the sinus node may arise in other age groups due to medications and surgeries. In newborns, however, sinus node dysfunction is usually due to a congenital heart problem.

Sinus arrhythmia isn’t usually a concern in newborns, but it’s still important to know the different types so you can discuss these further with a doctor.

Respiratory sinus arrhythmia

As the name suggests, a respiratory sinus arrhythmia develops based on your baby’s breathing. In such cases, your baby’s heart rate may fluctuate based on how fast they inhale or exhale.

This type of arrhythmia is a bit of a misnomer, as it’s typical for your heart rate to slow down when you exhale and to increase during inhalation. It’s also the most common type of irregular heart rate seen in children.

Sinus tachycardia

A sinus tachycardia means your heart rate is faster than usual. It’s also common in children.

Like respiratory sinus arrhythmia, this type of heart rhythm isn’t necessarily a cause for concern. Newborns may have sinus tachycardia in times of increased cardiac output when experiencing:

  • stress
  • excitement
  • increased activity
  • fever

Sinus tachycardia isn’t usually a problem unless your baby’s heart rate is higher than usual during rest.

Sinus bradycardia

In newborns, resting heart rate doesn’t typically fall below 80 beats per minute.

The term “bradycardia” means your heart rate is slower than what’s typical for your age. Sinus bradycardia is a slow heart rhythm that may be due to problems with the sinus node.

Unlike other types of sinus arrhythmia, some cases of bradycardia are considered more serious and may require treatment. Sinus bradycardia is most common in premature infants. Possible causes include:

  • breathing issues
  • hypothermia
  • medication exposure before birth

Newborn sinus arrhythmia symptoms may be difficult to detect because your baby cannot tell you what they are experiencing. Some signs you can look out for include:

  • unusual fussiness
  • pale skin
  • lack of energy
  • feeding difficulties

The symptoms may also depend on the type of sinus arrhythmia. For example, respiratory types are natural and coincide with your baby’s usual breath cycles.

Other types of arrhythmias may cause:

To diagnose sinus arrhythmia, doctors perform a physical exam and cardiac testing. While stress tests and wearable heart monitors may be useful in diagnosing older children, helpful methods for babies may include:

  • Electrocardiogram. Also called an EKG, this is often the first-line test used in the diagnosis of an abnormal heart rate and may be used for all ages.
  • Echocardiogram. This test involves ultrasound imaging of the heart and is only typically ordered if a doctor suspects that your baby’s arrhythmia is due to issues with the heart’s structure.

Usually, once sinus arrhythmia is confirmed, no further treatment is required. This is the case for most instances of respiratory sinus arrhythmia and sinus tachycardia.

However, if the arrhythmia is linked to a congenital heart problem, your doctor may refer you to a pediatric cardiologist for further analysis and treatment.

Doctors may use one of the following options to treat abnormal pediatric arrhythmias:

Sinus arrhythmia is relatively typical in children. Possible complications are rare.

In some cases, your baby’s doctor may confirm a suspected sinus arrhythmia as another type of atypical heart rhythm during the diagnostic process. If this occurs, the doctor will advise you regarding next steps.

Most cases of sinus arrhythmia in children are completely normal and no treatment is required. In fact, having a sinus arrhythmia is a sign of good heart health. Its absence could indicate an underlying health problem.

While the term “arrhythmia” may cause concern, sinus arrhythmia is actually a common occurrence that is usually benign. These are especially prevalent in children, with newborns also less likely to experience complications.

As a rule, if you think something isn’t quite right with your newborn, it’s best to err on the side of caution and talk with a doctor. Signs you should see a pediatrician include decreased energy, feeding problems, and excessive irritability.