From the Guidelines
The normal heart rate of a 7-week-old infant is 100 to 190 beats per minute when awake.
Normal Heart Rate Ranges
- An awake heart rate of 100 to 190 beats per minute is considered normal for a term newborn, which includes a 7-week-old infant 1.
- While sleeping, heart rates as low as 70 beats per minute are also acceptable, as long as there are no signs of circulatory compromise and the infant responds appropriately to activity 1.
Clinical Considerations
It is essential to consider the infant's physiologic state and overall clinical course when evaluating heart rate, as variations in heart rate can be expected based on activity level and other factors 1.
Evaluation of Abnormal Heart Rates
Sustained heart rates near or above the upper end of the normal range may require further evaluation to rule out any underlying conditions that may be contributing to the elevated heart rate 1.
From the Research
Normal Heart Rate in Infants
The normal heart rate (HR) of a 7-week-old infant is not directly provided in the given studies. However, we can look at the HR ranges for newborns and infants in the provided studies:
- A study from 2 found that the 50th percentile of HR in healthy term-born infants was 126 beats per minute (bpm) at age 2 hours and thereafter 120-122 bpm.
- Another study from 3 reported that the median HR at 1 minute after birth was 96 bpm, rising to 139 bpm at 2 minutes and 163 bpm at 5 minutes.
- A study from 4 found that the maximum sinus rate in normal newborns ranged from 150 to 222 bpm (mean, 192 +/- 16) when awake, and the minimum rate ranged from 78 to 140 bpm (mean, 107 +/- 15) when awake.
- A study from 5 assessed HRV in normal newborn infants using 24-hour Holter monitoring, but did not provide specific HR ranges for 7-week-old infants.
- A study from 6 found that the HR in healthy term neonates was around 120 bpm in the first seconds of life, increasing to 149 +/- 33 bpm in the first 40 seconds.
Factors Affecting Heart Rate
Several factors can affect HR in infants, including:
- Age: HR changes over time, with higher rates in the first minutes after birth and decreasing rates as the infant gets older 3, 6.
- Sleep state: HR is higher when awake than when asleep 2, 4.
- Temperature: HR increases with increasing rectal temperature 2.
- Sex: HR is slightly higher in girls than in boys 2.
- Mode of delivery: No significant effect on HR was found 2, 3.
Heart Rate Variability
HRV is an important aspect of cardiac function, and several studies have investigated HRV in newborns:
- A study from 5 found a high degree of correlation among vagal tone-dependent parameters, such as high-frequency power, r-MSSD, and s-NN50.
- The same study reported normative values for HRV in newborns, including frequency-domain parameters, geometric parameters, and time-domain parameters.