Considerations on the nature of irregularity of the sequence of RR intervals and the function of the atrioventricular node in atrial fibrillation in man based on time series analysis.

Using sinus arrhythmia as a control, we elucidated the random nature of RR intervals during atrial fibrillation in man and determined the function of the atrioventricular (AV) node from the variability of RR intervals. The major difference between the characteristics of sinus arrhythmia and those of atrial fibrillation is the presence of a significant correlation between successive intervals in the former. Since the pattern of distribution of RR intervals in atrial fibrillation is unimodal and skewed to the right and so can be fitted to an Erlang distribution, atrial inputs can be considered to be summated to a certain threshold for ventricular activation in the N region of the AV node, the number of cumulative atrial inputs corresponding to this threshold being the phase of this Erlang distribution. The function of the AV node during atrial fibrillation is to transform an exponentially distributed input into an Erlang-distributed output. Loss of inputs occurs between the atria and the N region and the greater the loss of inputs the slower the ventricular response. However, the greatest loss occurs in the N region for summation of atrial inputs required to elicit ventricular activation.