Silent zone on Lorenz plots of the ventricular response before termination of paroxysmal atrial fibrillation--report of a case.
An ambulatory 24 h Holter electrocardiogram was recorded during paroxysmal atrial fibrillation in a 67-year-old man. His paroxysmal atrial fibrillation terminated spontaneously approximately 12 h after the start of recording. The RR variability of this Holter recording was studied using Lorenz plots, frequency domain analysis, and time domain analysis. A silent zone appeared on the Lorenz plots beginning a few hours before the termination of his attack. The coefficient of variance (CV) and the power of the high-frequency component of RR variability (HF) gradually increased toward the termination. The silent zone was closely related to the functional refractory period of the atrioventricular node estimated from the Lorenz plots, and the functional refractory period was significantly correlated with the CV and HF power of RR variability. This case suggests that a silent zone on Lorenz plots reflects increased parasympathetic tone. In addition, such a silent zone may be useful for predicting the course of paroxysmal atrial fibrillation and for evaluating the role of the autonomic nervous system in this condition.