A new method for quantifying ventricular regularization during atrial fibrillation

Atrial fibrillation (AF) characteristically results in random variation of the intervals between successive ventricular depolarizations. However, when a patient with AF is treated with excessive amounts of digitalis, regular junctional rhythms may occur. The detection of "regularization" of the ventricular rhythm in patients with AF may signal early digitalis toxicity. In this paper, we describe a new method for quantifying the extent of ventricular regularization by the statistical analysis of the intervals between successive ventricular depolarizations (R-R intervals). This method yields a single index (Z score) which reflects the degree to which a sequence of R-R intervals deviates from a random distribution. Simulation studies demonstrate that our method is sensitive to "regularization" of as little as two to four percent of R-R intervals, even when equal intervals occur in small groups that might easily escape detection by visual electrocardiographic interpretation. Analysis of records from six nondigitalized subjects in AF shows that the sequence of R-R intervals is usually random, or very nearly so. Records obtained from the same patients when digitalized often demonstrate more regularized activity, reflected by an index (Z score) which is higher than expected from chance deviation if a random process is assumed. Preliminary data also suggeest that exercise is associated with substantial regularization of ventricular depolarization.