2016 ACVIM Forum Research Abstract Program

Dogs were prospectively recruited following implantation of a St. Jude dual-chamber pacemaker system for 3AVB; dogs with evidence of sinus node dysfunction or clinically important arrhythmias other than 3AVB were excluded. All dogs were programmed to VDD at study entry. The average, lowest and highest heart rates during VDD pacing were determined; the average heart rate was programmed as the base rate for VVI and VVIR. The highest heart rate was programmed as the upper tracking rate for VVIR with a threshold of 2.5, slope of 16, and fast reaction and recovery times. The rest function was used for all pacing modalities and was programmed to the lowest heart rate during VDD pacing; if the lowest heart rate was at the lower rate limit, then the rest rate was programmed 20% slower. Dogs were randomly assigned to VVI or VVIR after initial VDD interrogation and echocardiography (2D, Doppler, TDI). Ambulatory ECGs were recorded for 36 hours and the owners were instructed to record the time and duration of 5 specific activities: (1) urination/defecation, (2) eating, (3) sleeping, (4) walking, and (5) play. After three months, echocardiography was repeated, the dog was crossed over to VVI or VVIR pacing, and ambulatory ECG monitoring was repeated. After three additional months, echocardiography was repeated, the pacing modality was programmed to VDD and ambulatory ECG monitoring was repeated. Atrial rate, ventricular rate, and atrialto-ventricular ratio were determined for each of the 5 activities after an initial 12 hours acclimatization period. This is an ongoing study and currently 6 dogs are enrolled where 5 dogs have completed the VVI phase, 4 dogs have completed the VVIR phase, 4 dogs have completed both the VVI and VVIR phases, and 1 dog has completed all VVI, VVIR, and VDD phases. Atrial rates and atrial-to-ventricular ratios for VVI, VVIR, and VDD at each activity are as follows: urination/defecation (156.0 AE 42.9, 2.01 AE 0.39),(134.4 AE 24.0, 0.95 AE 0.14), (105.7, 1.0); eating (116.4 AE 20.8, 1.51 AE 0.23),(126.2 AE 11.7, 0.97 AE 0.22), (95.7, 1.0); sleeping (99.1 AE 38.3, 1.32 AE 0.62),(79.8 AE 15.7, 0.88 AE 0.30), (51.5, 0.76); walking (183.2 AE 24.7, 2.4 AE 0.41), (157.4 AE 38.9, 1.09 AE 0.12), (91.4, 1.0); play (125.4 AE 38.3, 1.66 AE 0.61),(105.8 AE 17.0, 0.83 AE 0.07), (108.9, 1.0). Echocardiographic data is available for all 6 dogs in VDD, 4 dogs in VVIR, and 2 dogs in VVI. The left ventricle appears to be larger in diastole and systole for VVI (LVAd/Ao = 6.85 AE 0.76, EDV/Ao = 26.08 AE 2.80, LVAs/Ao = 2.74 AE 0.19, ESV/Ao = 9.23 AE 0.08) and VVIR (LVAd/Ao = 5.24 AE 0.57, EDV/Ao = 24.78 AE 3.04, LVAs/ Ao = 2.38 AE 0.47, ESV/Ao = 10.65 AE 3.21) than VDD pacing (LVAd/Ao = 5.14 AE 1.38, EDV/Ao = 23.13 AE 7.46, LVAs/Ao = 2.30 AE 0.84, ESV/Ao = 7.43 AE 4.27).