Normal Sinus Rhythm
A normal heart rhythm is called normal sinus rhythm (NSR for short). An NSR will have a heart rate (this is the same as the pulse) between 50 and 100 beats per minute and a normal impulse formation from the SA node ( P wave). In the absence of any abnormalities, a completely normal rhythm will also have a normal PR interval (interval from the beginning of the P wave to the beginning of the QRS of .12-.20 seconds), a normal QRS width (time it takes for the ventricles to contract of .04-.10 seconds), a normal QT interval (interval from the beginning of the QRS to the beginning of the T wave of .30-.46 seconds). Also, all the waveforms must be of a normal shape with no ST changes.
In children, normal heart rate ranges are much higher. Infants to 1 year have a normal range to 180 beats per minute, 1-3 years to 150 beats per minute, 4-10 years to 130 beats per minute and 110 beats per minute to age 16.
In the above example, the rate varies slightly from 72-75 beats per minute, the PR interval is .16 seconds, the QRS is .08 seconds and the QT interval is .34 seconds. Also, all the wave forms are normal.
Each individual’s normal resting heart rate will vary, and can range from 40 to 120, higher in young children. A certain amount of variation in heart rate throughout the day is normal as activity levels vary. Even though an individual’s regular rhythm may not exactly fit into the category of normal sinus rhythm, it does not necessarily suggest that a problem exists. In addition, even if an individual’s rhythm is normal, it does not preclude underlying heart disease.