2016 ACVIM Forum Research Abstract Program

tigation. Decreased heart rate variability (HRV) has been found in dogs in congestive heart failure (CHF) and previous studies have acknowledged the use of HRV indices as prognostic indicators in patients with mitral valve disease (MVD). The vasovagal tonus index (VVTI) is an unconventional time domain indicator of HRV, which is mainly influenced by cardiac parasympathetic tone. In this cross-sectional observational study, we sought to investigate the VVTI in dogs with MVD. Electrocardiographic recordings of 30 dogs (7-16 years, 3.5-15.5 kg) previously classified into ACVIM stages A (controls), B, or C (10 dogs each group) were used to calculate the VVTI. For this, 20 consecutive R-R intervals were measured from each ECG recording (R-R1 to R-R20), and the index was obtained from the formula VVTI = LN [VAR (R-R1 -R-R20)], where LN: natural logarithm and VAR: variance. Bad quality ECG tracings and recordings from dogs with non-sinus rhythms or animals undergoing anti-arrhythmic treatment were not included in this investigation. Also, we recorded the BW-indexed LV in diastole and systole, wall stress index in diastole and systole, fractional shortening, left atrium-to-aorta ratio, mitral E wave, mitral E/A, isovolumetric relaxation time, and the E-to-IVRT ratio. All data underwent the Shapiro-Wilk test to check for normal distribution, while ANOVA, followed by Tukey's test, were used to compare the VVTI between groups. Pearson's test was used to search for linear correlations between the VVTI and the echocardiographic data. The mean values (with lower and upper 95% CI of mean) of VVTI for dogs in stages A, B, and C were, respectively: 8.45 (7.36 -9.54), 6.09 (4.47 -7.71) and 6.34 (5.01 -7.68). A significant difference was found between groups (P = 0.0189), with the mean VVTI being significantly higher in control animals as compared to dogs with stage B MVD (P < 0.05). When it comes to the relationship between VVTI and cardiac rhythms, a significant difference existed between animals in sinus rhythm (SR), sinus arrhythmia (SA), and sinus tachycardia (ST) (P = 0.0083). The lowest VVTI was documented for dogs in ST (5.82; 95% CI 4.14 -7.49), while the higher was found for animals presenting SR (8.27; 95% CI 7.40 -9.15). Significant negative correlations were found between VVTI and LA/Ao (R = À0.3699; P = 0.0443), as well as between VVTI and heart rate (R = À0.4864; P = 0.0064). Although no correlation existed between body weight and the VVTI, age and VVTI attained a significant negative correlation (R = -0.3827; P = 0.0369). The negative correlation between VVTI and heart rate is likely ascribed to the role played by the parasympathetic tone in VVTI, therefore producing higher values when slower rates and irregular rhythms are present. Even though uncontrolled conditions during ECG recording, including stress and agitation, may increase HR, the lower VVTI found in animals exhibiting sinus tachycardia may suggest a sustained sympathetic activation. Although further investigation is warranted, the confidence intervals of this study point to the VVTI <5 being a potential prognostic indicator for CHF, whereas a VVTI >7.7 is likely suggestive of reduced risk for congestion. This is supported by the correlation between VVTI and LA/Ao, as well as the difference between the means of control dogs (stage A) and stage B MVD animals. (6%), Poodle (6%) and Dachshund (6%), besides a mongrel dog (6%). There was a predominance of female dogs (71%). The most