2017 ACVIM Forum Research Abstract Program

Twenty-four dogs with SND and 24 age/size matched control dogs were studied. Geometric HRV was assessed using Poincar e plots and tachograms from Holter recordings. Autonomic tone was assessed using time and frequency domain HRV. A computer model was designed to assess beat-to-beat behavior. Inputs included (1) sinusoidal oscillations of vagal tone with a 4-second period (respiration), slowly varying component of sleep-wake cycle, and randomly varying noise; (2) oscillator of sinus node with variation dependent on vagal tone and a random component based on previous exit block; (3) probability of exit block with threshold dependent on vagal tone. SND dogs had higher indices of HRV than control dogs. In contrast to control dogs, recordings from SND dogs showed >2 beat-to-beat clusters that approximated multiples. Depending on input, control and SND dog beat-to-beat patterns could be mimicked by the model. The computer model verified a pattern representing exit block (Frames A,B,C). SND dogs had Poincar e plots that failed to reveal an inherent sinus node rate (90-100 bpm) as did the control dogs. Instead, the shortest intervals were faster (120-170 bpm) with multiple bifurcations as the rate slowed.