A statistical study of the ventricular irregularity of atrial fibrillation

Abstract

EKG records consisting of 2000 successive R- R intervals were obtained from 24 patients with atrial fibrillation. These records were subjected to automatic data processing routines which calculated the R- R interval histogram and related parameters and examined the relationship between neighboring intervals using the joint distribution function and other techniques. The unimodal and occasionally bimodal histograms obtained in this manner uniformly had minimum interval lengths between 300 and 500 msec and exponential right-hand tails. In half the records adjacent intervals tended to be equal in length, but adjacent intervals in the remaining records were nearly statistically independent. On the basic of the results of this study, it is suggested that the mechanism of action of the A-V node in blocking atrial impulses may be threefold: (1) a fully refractory phase after ventricular activation; (2) the ability to depolarize partially without discharging the ventricle (the phenomenon of concealed conduction): and (3) the blocking of incoming impulses by decremental conduction at the atrionodal junction.