The mechanism of the silent zone on Lorenz plots in atrial fibrillation.

Lorenz plot is an acknowledged method of the evaluation of sequences of ventricular beats in cardiac arrhythmias, particularly in atrial fibrillation. Lorenz plots are scatterplots that show the R-R intervals as a function of the preceding R-R intervals. The authors of this paper conducted studies of 83 cases of atrial fibrillation; histograms of 500 consecutive R-R intervals were made, determining the mean R-R interval, the functional refraction period (FRP) of AV node and Lorenz plots. In 22 cases (26.5%) the presence of the silent zone on a Lorenz plot was observed, similarly to the study of Nakatsu and al. The silent zone appeared only in cases when the statistical distribution of R-R intervals was reflected by a bimodal histogram (less frequently by a trimodal histogram). The silent zone was never observed in cases of monomodal distribution of R-R intervals. The authors discuss Nakatsu's findings and argue that the silent zone in a Lorenz plot is a morphological expression of bimodal distribution of R-R intervals in atrial fibrillation. The silent zone may be caused by pharmacotherapy (e.g. digoxin), increased parasympathetic tension or other factors prolonging FRP. The presence of the silent zone is not a predictor of a spontaneous termination of atrial fibrillation.