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 paroxy smal atrial fibrillation in a 67-year-old man. His paroxysmal atrial f ibrillation terminated spontaneously approximately 12 h after the star t of recording. The RR variability of this Holter recording was studie d using Lorenz plots, frequency domain analysis, and time domain analy sis. 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 closel y related to the functional refractory period of the atrioventricular node estimated from the Lorenz plots, and the functional refractory pe riod was significantly correlated with the CV and BF power of RR varia bility. This case suggests that a silent zone on Lorenz plots reflects increased parasympathetic tone. In addition, such a silent zone may b e useful for predicting the course of paroxysmal atrial fibrillation a nd for evaluating the role of the autonomic nervous system in this con dition.