Standard deviation
The standard deviation is calculated by the standard formula for the entire series of pulse intervals. The standard deviation is one of the indicators of heart rate variability. According to the standard deviation, together with the coefficient of variation, variational range, and the number of sharply different pulse intervals, the following conclusions are made about background arrhythmias: rigid rhythm, normal rhythm variability, moderate arrhythmia, severe arrhythmia. The standard deviation characterizes the state of regulatory mechanisms and indicates the state of automatism of the sinus node. The normal value of the standard deviation is from 0.03 to 0.06 s. The value of the standard deviation in the range of 0.07-0.09 s indicates the presence of arrhythmia, and more than 0.1 s indicates a pronounced arrhythmia or a violation of automatism. A decrease in the standard deviation of less than 0.02 s is observed at a stable (rigid) rhythm.
