IntroductionFive-minute heart-rate variability (HRV) measurement is a useful tool for assessing the autonomic nervous system (ANS) balance in humans, but there are no studies on healthy dogs. The aim of the study was, therefore, to provide the reference ranges in small and medium-sized breeds for short-term HRV time and frequency domain (TFD) analyses.Material and MethodsA total of 79 healthy dogs were included in the study between 2015 and 2019. Grouping by age with the breakpoint at six years and subgrouping by reproductive status and sex was imposed. All the dogs were included after physical and cardiological examinations and blood analyses. The TFD of HRV were analysed from a five-minute-long digital ECG recording after removal of non-sinus complexes.ResultsThere were no statistically significant differences in any TFD parameters between age, reproductive status or sex groups. A mild increase in all time domain parameters and the high-frequency (HF) band was observed in older dogs, and the low frequency (LF):HF ratio decreased in these dogs. In males, the time domain parameters and HF band increased slightly.ConclusionThe normal ranges for HRV derived from short-term ECG recording in the usual clinical environment now have proposed reference ranges. Our findings suggest that accommodation time, age, sex, or reproductive status do not influence the results derived from these recordings, indicating that this method is reliable for assessing the ANS function in small and medium-sized dog breeds.

Background: Myxomatous mitral valve disease (MMVD) is the most common cardiac disease in dogs. The association of QRS notching (nQRS) or fragmentation (fQRS) with disease severity is currently unknown.Objective: To assess the prevalence of nQRS and fQRS in dogs with MMVD and its severity according to ACVIM classification and to compare the results with a group of healthy dogs. Methods:This retrospective cross-sectional study included 34 healthy control dogs and 155 dogs with spontaneous MMVD (42% of dogs in class B1, 23% in class B2 and 35% in class C). fQRS was defined as nQRS complexes in two contiguous leads in the frontal plane (leads I and aVL) and (II, III or aVF). A one-way ANOVA with Bonferroni posthoc test was used to assess the differences in continuous data between control and MMVD groups.Results: Of the MMVD group, 58% showed nQRS in at least one lead and 27% presented fQRS. There was no difference between the number of leads with a nQRS and disease severity (p=0.75) nor did the number of leads with a nQRS correlate with left atrial size (r=-0.48; p=0.5). The number of dogs with fQRS did not differ among classes of MMVD (p=0.21). nQRS and fQRS were more prevalent in dogs with MMVD compared to control dogs (p<0.01).Conclusions: This study did not identify any relationship between the number of leads with a nQRS and disease severity. However, dogs with MMVD had a higher prevalence of nQRS and fQRS compared to control group.

Background Evaluation of heart rate variability (HRV) is used for risk assessment in a variety of cardiac diseases including myxomatous mitral valve degeneration (MMVD). Objectives To compare the geometric analysis of HRV using visual patterns of Poincaré plot among different classes of MMVD in dogs and to analyse the differences in beat-to-beat variability using tachograms and sequential Poincaré plots among different shapes. Animals and methods Healthy and MMVD dogs were retrospectively reviewed. Five-minute ECG data was used to create Poincaré plots and shapes were compared among groups. Furthermore, a sub-analysis of 50 consecutive R–R intervals was performed. Pearson Chi-square with adjusted standardized residuals was used to compare the categorical data between groups. Results Fifteen healthy dogs and 157 dogs with MMVD were included in the study. Normal and B1 groups showed a predominance of triangular shape (73% and 60% respectively; p < 0.05). In B2 group the predominant shape was comet (40%; p < 0.05) while comet and torpedo were predominant in Ca group (41% and 36% respectively; p < 0.05). Visual geometric analysis revealed a lower dispersion of the cloud clustering towards the left lower corner of the plot with MMVD progression. Diamond and triangle revealed a lower mean heart rate compared to comet and torpedo shapes ( p < 0.01). Interclass correlation between 3 observers was 0.906 (95% CI of 0.8 − 0.96). Conclusions Poincaré plot shape changes with MMVD progression suggesting that geometrical analysis of HRV in dogs with cardiac conditions could be a useful tool in the risk assessment and further studies are warranted.

A 14 years old, 6 kg, mix-breed male dog with severe azotemia due to urinary bladder herniation was presented to our Veterinary Teaching Hospital (VTH). Electrocardiography revealed normal heart rate of 100 bpm, evidence of sinus respiratory arrhythmia (SRA) and frequent second degree atrio-ventricular block following peak inspiratory phase suggestive of vagally-induced atrio-ventricular conduction delay. Echocardiographic examination showed mild mitral regurgitation without any other cardiac changes, and systolic (SAP) and diastolic (DAP) blood pressure values were 185/90 mmHg (SAP/DAP). Cardiac troponin I (cTnI) was increased to 7.3 ng/mL, suggesting a myocardial injury. A Holter examination revealed evidence of overall decrease in heart rate variability with evidence of sympathetic overdrive on time and frequency domain as well as when the non-linear Poincaré plot was analyzed. Based on the author’s knowledge, this is the first report of a second degree atrio-ventricular block associated with vagal activity in a dog, with evidence of sympathetic overdrive and severe azotemia.