Signal averaged ECGs and quality control

The signal variance used to estimate the noise energy during signal averaging and its square root (the standard deviation) are used to estimate the noise amplitude. This latter value, which is observed as a function of the number of heart beats, can be presented in two ways. The first is an estimate of the noise process which is interfering with the signal of interest. This noise function with the signal of interest. This noise function will approach a constant. The constant is obtained by dividing the noise function by √N (N is the number of cardiac cycles), so that an estimate of the noise in the signal average is obtained. This function approaches zero as more beats are included in the average