S. Moise, A. Gladuli, S. A. Hemsley, N. F. Otani, 'Zone of avoidance': RR interval distribution in tachograms, histograms, and Poincare plots in a Boxer dog, Journal of Veterinary Cardiology 12, 191-196 (2010).


The RR intervals of sinus and ventricular beats were determined by analysis of a 24-h ambulatory electrocardiogram in a Boxer before and after treatment with sotalol. These RR intervals were plotted using tachograms, histograms, and Poincare plots. The tachogram demonstrated a ‘band’ wherein a range of RR intervals was infrequent, the histogram did not take the form of a single Gaussian distribution of RR intervals, and the Poincare plot showed nonhomogeneous beat-to-beat variability. This type of patterning was described as a “zone of avoidance” potentially caused by the clustering of beats within specific ranges. Treatment with sotalol enhanced the “zone of avoidance”. Further investigation is needed to understand the mechanism for this observation as well as any clinical implications.