Tachycardia is defined as a heart rate that is too fast for a person’s age and condition. Understanding this concept in children is complex because a child’s normal resting heart rate is significantly higher than an adult’s and decreases progressively as they mature. What is normal for a newborn would be a dangerous heart rhythm for a teenager. Therefore, determining if a child’s heart is beating too quickly requires an age-specific and situational assessment. This article clarifies the numerical definitions and discusses the underlying causes of a rapid heart rate in pediatric patients.
Defining Tachycardia by Age
The heart rate that qualifies as tachycardia is not a single number but a dynamic threshold that shifts across the pediatric lifespan. Medical guidelines, such as those used for Pediatric Advanced Life Support (PALS), establish the specific beats per minute (BPM) considered the upper limit of the normal range for a calm, resting child. When the heart rate exceeds these defined limits, it is categorized as tachycardia.
For newborns up to one month old, a heart rate above 160 BPM is generally considered fast. Infants between one month and one year typically have an upper limit of approximately 150 BPM at rest, meaning a rate exceeding 190 BPM is often viewed as tachycardia. As the child enters the toddler years (one to two years old), the upper limit of the normal resting rate drops further to around 140 BPM.
The threshold continues to decline through childhood. For a preschooler (three to five years), the heart rate limit for the normal range is typically around 120 BPM. School-age children (six to twelve years) are considered to have tachycardia if their heart rate is consistently above 110 to 118 BPM while resting. By adolescence (12 to 15 years), the heart rate range closely mirrors that of an adult, with a resting rate exceeding 100 BPM potentially signaling tachycardia. These thresholds are a starting point for medical evaluation, as a rate slightly above the limit due to crying is less concerning than a persistent elevation.
Common Reasons for Temporary Heart Rate Increases
The most frequent type of rapid heart rate in children is sinus tachycardia, which is the heart’s appropriate and temporary response to systemic demand. This physiological reaction means the heart is working harder to meet the body’s need for increased blood flow and oxygen delivery. The electrical signal originates normally in the heart’s natural pacemaker, the sinus node, and the rhythm remains regular, though fast.
Fever is a common trigger, as the body increases its metabolic rate to fight infection, requiring the heart to circulate blood more quickly. Dehydration from illness or insufficient fluid intake causes a reduction in blood volume, forcing the heart to beat faster to maintain adequate blood pressure.
Intense physical activity, pain, fear, or anxiety are also common causes, as the sympathetic nervous system releases adrenaline, which accelerates the heart rate.
Sinus tachycardia is identifiable because the heart rate usually remains below a certain point—typically under 220 BPM in infants and less than 180 BPM in older children. A key characteristic is the gradual onset and resolution of the rapid rate, which slows down as the underlying cause is addressed. The presence of normal electrical activity, including visible P waves on an electrocardiogram, helps distinguish this temporary response from more serious cardiac rhythm problems.
Recognizing Serious Cardiac Causes
While most pediatric tachycardia is a normal response to illness, pathological tachycardia arises from an electrical or structural abnormality within the heart itself. The most common form of this abnormal rapid rhythm is Supraventricular Tachycardia (SVT), where the electrical impulse bypasses the normal pathway. SVT is characterized by an abrupt, sudden onset and equally sudden cessation, which differs noticeably from the gradual nature of sinus tachycardia.
In infants, an SVT rate is often exceptionally high, typically reaching or exceeding 220 BPM, and in older children, it is frequently over 180 BPM. Unlike sinus tachycardia, the electrical tracing in SVT may show abnormal or absent P waves, indicating a problem with the impulse origin. This rapid rate occurs independently of external stressors and is driven by a short-circuit in the heart’s electrical system.
Other serious causes include Ventricular Tachycardia (VT), where the electrical impulse originates in the lower chambers of the heart, or underlying conditions like myocarditis or heart failure. VT is a dangerous rhythm that can severely compromise the heart’s pumping ability and is often associated with wider electrical complexes on an electrocardiogram. Pathological tachycardias are concerning because the heart beats so quickly that it does not have enough time to fill with blood between beats, leading to reduced overall blood output.
Necessary Steps When Tachycardia is Detected
When a child exhibits a fast heart rate, the first priority is to assess for signs of instability, which indicate the rapid rate is severely compromising circulation. Immediate emergency medical assistance is necessary if the child shows signs of shock, such as pale or mottled skin, difficulty breathing, or a significant change in mental state like lethargy or fainting. These symptoms suggest the child is not compensating well and requires immediate stabilization.
If the child is generally alert, breathing comfortably, and their skin color is normal, they are considered stable, and a non-emergency medical evaluation can be sought. Parents or caregivers should gather specific information for the healthcare provider, including the estimated rate, the exact time the rapid heart rate began, and whether the onset was sudden or gradual. Noting any associated symptoms, such as chest pain or palpitations, and whether the child was ill, active, or anxious helps determine the underlying cause.