Vasovagal Tonus Index Research Articles

Evaluating heart rate variability by a novel stethoscopic approach to minimise stress in cats.

Stress associated with manipulation during electrocardiography (ECG) recording in cats potentially limits the assessment of autonomic function through heart rate variability (HRV) in the feline population. This study proposed an alternative, cat friendly, stethoscopic approach to evaluate HRV with an easily acquired vasovagal tonus index (VVTI). The aim of this prospective study was to evaluate whether VVTI derived from heart sound signals could distinguish between relaxed and stimulated states. A total of 29 cats with 56 recordings of heart sound and ECG on 31 occasions were included. In 25 cats in their home environment, a stethoscope connected to a digital recording device was used to record 2 mins of heart sounds twice - with the cats in a relaxed state and immediately after stimulation. The VVTI was calculated from 20, 60 and 120 consecutive beat-to-beat intervals on the heart sound spectrogram (stethoscopic-VVTI 20, 60 and 120), using the natural logarithm of the variance of the intervals based on previous literature. A 2-min ECG recording was obtained at home with the intention of avoiding strict restraint. To demonstrate the feasibility of the stethoscopic approach in a hospital setting, six cats (two of which were also recorded at home) underwent heart sound and ECG recordings during planned veterinary visits. Stethoscopic-VVTI 20 (5.43 to 4.79, P = 0.001), 60 (6.20 to 5.18, P <0.001) and 120 (6.24 to 5.60, P = 0.02) all significantly decreased after stimulation, indicating a reduced vasovagal tone as expected. Calculations of stethoscopic-VVTI from different sections of the recording yielded statistically similar results. Stethoscopic-VVTI showed a negative correlation with the corresponding heart rate. Bland-Altman analysis revealed a mean bias for the differences between stethoscopic-VVTI and ECG-VVTI of 0.50 and 1.07 at home and in the hospital, respectively. VVTI can be successfully detected through a stethoscopic approach, serving as a less stressful tool for HRV evaluation in cats during routine auscultation.

Evaluation of vasovagal tonus index and electrocardiographic parameters in horses using a new modified base apex lead method.

Vasovagal tonus index (VVTI) serves as a straightforward assessment tool for autonomic function during both physiological and pathological conditions, including pregnancy, in horses. Obtaining VVTI through a modified base apex lead system could be a practical and comfortable solution. In this study, we assessed VVTI in horses with respect to training status and electrocardiographic measurements utilizing a novel modified base apex lead technique. A total of 12 Thai native crossbred horses and 12 Arabian horses, all free of cardiac abnormalities, were enrolled in the study. Animals underwent electrocardiogram (ECG) and VVTI using both the base-apex lead method and its modified version. 25 mm/s and 10 mm/mV ECG recordings provided standard bipolar limb leads. The amplitudes and durations of P waves, QRS complexes, PR interval, QT interval, and T duration were assessed. The T wave's shape was examined. Each recording's R-R interval was utilized to assess heart rate. Twenty consecutive beats were used to compute the variability of heart rate (VVTI). The P wave amplitude was the only significant difference (p < 0.05) between the base apex lead method and the modified base apex lead method, with no variations in heart rate, P duration, PR interval, T duration, and QRS duration and amplitude. Both methods showed mainly biphasic T wave patterns. The VVTI values of all horses did not differ significantly between the base apex and modified base apex methods. There was no significant difference in VVTI between Thai crossbred horses and Arabian horses in either method. This study provided the first evidence that VVTI can be evaluated using the modified base apex lead system and may be useful for cardiovascular function monitoring in horses.

Effects of pregnancy on electrocardiographic, vasovagal tonus index, and echocardiographic variables in horses.

Pregnancy affects maternal hemodynamics. The changes in autonomic nervous system activity for hemodynamics adaptation in pregnant horses are still unclear. Thus, this study aimed to examine the effect of pregnancy on electrocardiographic, vasovagal tonus index, and echocardiographic variables in horses. A total of 23 Thai native crossbred mares without any cardiac abnormalities were included in this study. The animals were assigned into two groups, a non-pregnant mare group (n =12) and a pregnant mare group (n = 11). Electrocardiogram recordings (paper speed = 25 mm/s and calibration = 10 mm/mV) were performed to obtain six limb leads (leads I, II, III, aVR, aVL, and aVF). The vasovagal tonus index (VVTI) was calculated to assess variability in heart rate over short periods using just 20 consecutive beats. Cardiac structure and function were evaluated by echocardiography. Heart rate, P wave duration, PR interval, QRS duration, QT interval, and T wave duration were significantly different between non-pregnant and pregnant horses (p < 0.05). Pregnant horses had significantly lower VVTI than non-pregnant (p < 0.05). There were no significant differences in cardiac structures including % interventricular septum (IVS), % left ventricular posterior wall (LVPW), IVS in diastole, left ventricular internal diameter at end-diastole, LVPW thickness at end-diastole, IVS in systole, left ventricular internal diameter at end-systole, LVPW thickness at end-systole, and left atrium/aortic roots ratio between the two groups. However, the pregnant horses had a significantly higher cardiac output and % ejection fraction than non-pregnant horses (p < 0.05). This study provided the first evidence that hemodynamic adaptations during pregnancy modified cardiac conduction, vasovagal tonus index, and echocardiographic variables in horses.

The effect of eye stimulation using graded external weights on the oculocardiac reflex in beagle dogs

The objective of this study was to determine to what extent the oculocardiac reflex (OCR) progressively rises with increasing external pressures over the superior eyelid. Controlled external weights were applied to the left eyelid of ten conscious healthy adult beagle dogs, using an electronic von Frey aesthesiometer with a modified probe. Four different weights (200 g, 300 g, 400 g and 800 g) were applied on four different non-consecutive days (with one-week intervals). Pressure was applied by pushing the device against the superior eyelid. The baseline heart rate was primarily recorded using an electrocardiograph (ECG). Then, indices of heart rate variability such as R-R intervals and vasovagal tonus index (VVTI) were calculated from the ECG tracings using twenty consecutive QRS complexes from each dog, before and after a selected set of graded weights were applied to the eye. Median R-R interval significantly increased when an external weight of 200 g was applied and peaked at 300 g. VVTI values peaked at 400 g. With higher pressures, the proportional increase was smaller in both R-R intervals and VVTI. We concluded that external eye pressure using a weight of 200 g or more is sufficient to elicit an OCR response in conscious dogs. Pressures above 400 g started to activate compensatory mechanisms that counteracted with the OCR, probably linked to an adrenergic response induced by the animal’s discomfort. Changes in R-R intervals might be used as an early OCR marker, while VVTI apparently was less influenced by potential sympathetic responses.

Comparison between intravenous lidocaine and fentanyl on cough reflex and sympathetic response during endotracheal intubation in dogs

ObjectiveTo compare the effects of intravenous (IV) lidocaine and fentanyl on the cough reflex and autonomic response during endotracheal intubation in dogs. Study designRandomized, blinded, superiority clinical trial. AnimalsA total of 46 client-owned dogs undergoing magnetic resonance imaging. MethodsAfter intramuscular methadone (0.2 mg kg–1), dogs were randomized to be administered either IV lidocaine (2 mg kg–1; group L) or fentanyl (7 μg kg–1; group F). After 5 minutes, alfaxalone was administered until endotracheal intubation was possible (1 mg kg–1 IV over 40 seconds followed by 0.4 mg kg–1 increments to effect). Total dose of alfaxalone was recorded and cough reflex at endotracheal intubation was scored. Heart rate (HR) was continuously recorded, Doppler systolic arterial blood pressure (SAP) was measured every 20 seconds. Vasovagal tonus index (VVTI) and changes (Δ) in HR, SAP and VVTI between pre-intubation and intubation were calculated. Groups were compared using univariate and multivariate analysis. Statistical significance was set as p < 0.05. ResultsGroup F included 22 dogs and group L 24 dogs. The mean (± standard deviation) alfaxalone dose was 1.1 (± 0.2) and 1.35 (± 0.3) mg kg–1 in groups F and L, respectively (p = 0.0008). At intubation, cough was more likely in group L (odds ratio = 11.3; 95% confidence intervals, 2.1 – 94.2; p = 0.01) and HR increased in 87.5% and 54.5% of groups L and F, respectively (p = 0.02). The median (range) ΔHR between pre-intubation and intubation was higher (13.1%; – 4.3 to + 55.1) in group L (p = 0.0021). Between groups, SAP and VVTI were similar. Conclusion and clinical relevanceAt the stated doses, whilst reducing the alfaxalone dose, fentanyl is superior to lidocaine in suppressing the cough reflex and blunting the increase in HR at endotracheal intubation in dogs premedicated with methadone.

Establishing reference standards for the vasovagal tonus index in a cohort of healthy French Bulldogs.

The vasovagal tonus index (VVTI), a time-domain indicator of heart rate variability, has been suggested as a diagnostic and prognostic tool in dogs with cardiac disease and heart failure. Brachycephalic breeds tend to have a higher VVTI than non-brachycephalic breeds.11 The objective of this study was to obtain standard VVTI reference values from a representative cohort of healthy French Bulldogs based on a single ECG recording. A second aim of this study was to evaluate the practicability of a VVTI screening in the clinical routine by evaluating repeatability of the VVTI across five successive measurements. In order to determine baseline factors potentially influencing the VVTI, the impact of stress, activity and character as well as sex and neutering status were evaluated. Out of 73 French Bulldogs screened, 60 dogs were considered healthy based on their medical history, physical examination, blood pressure and ECG, and no evidence of congenital or acquired heart disease on echocardiographic examination. The VVTI was calculated based on the variance of 20 R-R intervals and the corresponding HR extrapolated to one minute from the same 20 R-R intervals. In addition, a maximum of five consecutive VVTI values were calculated based on 100 successive R-R intervals recorded from each dog. VVTI values ranged from 5.66 to 11.3 with a mean (standard deviation [SD]) of 8.82 (1.43); the corresponding HR ranged from 78 to 173 bpm with a mean (SD) of 120 (23) bpm. Importantly, VVTI and HR values were negatively correlated (R = 0.689; adjusted R² = 0.466), which must be considered for clinical interpretation of the VVTI. The repeatability across five successive sets of 20 heartbeats was shown (mean intra-individual variability of 6.1%). Stress significantly influenced the VVTI and HR (p < 0.001). The VVTI range established in this study may be used as reference to assess the HRV of presumably healthy brachycephalic dogs at routine health checks. Deviations from the reference may permit the clinician to adapt the schedule and focus of subsequent follow-up investigations.

Electrocardiographic, endocrine and biochemical stress indices of electroejaculated Egyptian Baladi goat bucks

This study aimed to evaluate the stress response to electroejaculation (EE) through electrocardiogram (ECG) indices alongside hormonal and biochemical indices. Lead II base-apex ECG was recorded at rest (control, T0) and immediately after EE (T1), repeated in four consecutive weeks. The collected ejaculates were evaluated for standard semen characteristics (ejaculate volume, mass motility, individual motility, sperm cell concentration and total sperm count per ejaculate). Blood samples were collected at rest (T0), 10 (T2) and 120 min (T3) after EE for determination of biochemical and hormonal stress indices. EE induced sinus tachycardia with simultaneous marked increase in P waves amplitude and decrease in all waves and intervals durations (except for QRS complex and PR interval). Similarly, significant variation between the first and the last EE sessions were observed in heart rate (HR) indices (mean RR, mean, maximum and minimum HR), some wave amplitudes and segment durations. While the stress index significantly increased in the 3rd week only. This was associated with significant short term increases in serum level of cortisol and progesterone (P4) with significant decrease of glucose and globulins at T2. Furthermore, at T3 there was significant increase in cardiac troponin I (CTnI) concentration, while free triiodothyronine (FT3), potassium (K+), calcium (Ca2+) and glucose levels decreased significantly. There were significant increases between the first and the last EE sessions in cortisol, FT3 and significant decrease in Lactate dehydrogenase (LDH) concentrations. On contrary, there were no significant changes in time related to EE and weekly repetitions in the corrected QT interval (QTc), root mean square of sum of squares of normal to normal difference (RMSSD), standard deviation of the normal to normal (SDNN) vasovagal tonus index (VVTI) and semen characteristics. In conclusion, although repeated EE causes acute stress response which increases with repetition, the response appeared transient and not deleterious to the cardiac activity and semen characteristics evidenced by non-persistent significant increases in CTnI and absence of significant changes in the standard semen characteristics of the bucks. Additionally, ECG might be beneficial in assessing the welfare of electroejaculated bucks. Further assessment of heart rate variability (HRV) indices of bucks after EE using frequency and non-linear indices in a larger animal population is recommended.

Sedative and electrocardiographic effects of low dose dexmedetomidine in healthy cats

ABSTRACT: In feline veterinary practice sedation is often needed to perform diagnostic or minimally invasive procedures, minimize stress, and facilitate handling. The mortality rate of cats undergoing sedation is significantly higher than dogs, so it is fundamental that the sedatives provide good cardiovascular stability. Dexmedetomidine (DEX) is an α2-adrenergic receptor agonist utilized in cats to provide sedation and analgesia, although studies have been utilized high doses, and markedly hemodynamic impairments were reported. The aim of this study was to prospectively investigate how the sedative and electrocardiographic effects of a low dose of DEX performing in cats. Eleven healthy cats were recruited; baseline sedative score, systolic arterial pressure, electrocardiography, and vasovagal tonus index (VVTI) were assessed, and repeated after ten minutes of DEX 5μg/kg intramuscularly (IM). A smooth sedation was noticed, and emesis and sialorrhea were common adverse effects, observed on average seven minutes after IM injection. Furthermore, electrocardiographic effects of a low dose of DEX mainly include decreases on heart rate, and increases on T-wave amplitude. The augmentation on VVTI and appearance of respiratory sinus arrhythmia, as well as sinus bradycardia in some cats, suggesting that DEX enhances parasympathetic tonus in healthy cats, and therefore will be best avoid in patients at risk for bradycardia.

Vasovagal tonus index in dog with myxomatous mitral valve disease

ABSTRACT: The vasovagal tonus index (VVTI) is a useful and assessable index, obtained from standard ECG recordings, that is used to estimate heart rate variability (HRV), and may provide valuable information regarding the likelihood of progression into congestive heart failure (CHF). In this paperwork, we investigated how the vasovagal tonus index (VVTI) behaves in dogs with naturally-occurring myxomatous mitral valve disease (MMVD) Electrocardiographic (ECG) recordings and echocardiographic data of 120 patients diagnosed with MMVD were reviewed. The VVTI was calculated from twenty consecutive RR intervals for each dog enrolled in the study. Lower VVTI values were found in MMVD patients in American College of Veterinary Internal Medicine (ACVIM) stage C compared with stages B1 and B2. Values were also lower in patients with severe cardiac remodeling. When a cut-off value of 6.66 is used, VVTI was able to discriminate MMVD patients in stage C from B1 and B2 dogs with a sensitivity of 70 per cent and a specificity of 77 per cent. MMVD dogs in which VVTI is lower than 6.66 are 30% more likely to develop congestive heart failure (CHF).

Vasovagal tonus index (VVTI) as an indirect assessment of remission status in canine multicentric lymphoma undergoing multi-drug chemotherapy

Vasovagal tonus index (VVTI) is an indirect measure of heart rate variability and may serve as a marker of disease severity. Higher heart rate variability has predicted lower tumour burden and improved survival in humans with various tumour types. The purpose of this pilot study was to evaluate VVTI as a biomarker of remission status in canine lymphoma. The primary hypothesis was that VVTI would be increased in dogs in remission compared to dogs out of remission. Twenty-seven dogs were prospectively enrolled if they had a diagnosis of intermediate to high-grade lymphoma and underwent multidrug chemotherapy. Serial electrocardiogram data were collected under standard conditions and relationships between VVTI, remission status and other clinical variables were evaluated. VVTI from dogs in remission (partial or complete) did not differ from dogs with fulminant lymphoma (naive or at time of relapse). Dogs in partial remission had higher VVTI than dogs in complete remission (p = 0.021). Higher baseline VVTI was associated with higher subsequent scores (p < 0.001). VVTI also correlated with anxiety level (p = 0.03). Based on this pilot study, VVTI did not hold any obvious promise as a useful clinical biomarker of remission status. Further investigation may better elucidate the clinical and prognostic utility of VVTI in dogs with lymphoma.

Heart rate variability in Mangalarga Marchador horses after physical exercise

The aim of this study was to evaluate the influence of physical exercise (marcha gait) on heart rate variability indices in Mangalarga Marchador horses. Twenty-five animals, fourteen females and eleven males, aged 6.4 ± 2.7 years and with a mean weight of 428.3 ± 24.7 kg, were used. Electrocardiograms were recorded at two different time points: rest and immediately after exercise (40 min of aerobic exercise, marcha gait). Time domain analyses of heart rate variability were made using vasovagal tonus index (VVTI) and standard deviation of normal intervals (SDNN). Variables were analysed for normality using the Shapiro-Wilk test and comparisons were made between T0 and T1 using the paired t-test (VVTI) or Mann-Whitney (SDNN), considering P &amp;lt; 0.05. The Pearson coefficient was calculated to evaluate the correlation between heart rate and VVTI and the Spearman coefficient was calculated for heart rate and SDNN. There was an increase in heart rate after exercise (P &amp;lt; 0.0001), from 45.7 ± 12.7 to 77.3 ± 13.5 beats/min, and a reduced VVTI (P &amp;lt; 0.0001), from 8.66 ± 1.45 to 4.65 ± 1.25 and a reduced SDNN (P &amp;lt; 0.0001), from 80.09 to 11.67 ms. No correlation was observed between heart rate and VVTI or SDNN. It was possible to conclude that the physical activity carried out by Mangalarga Marchador horses influenced the autonomic response and consequently heart rate variability indexes, suggesting the possible use of these indices for the evaluation of Mangalarga Marchador performance.

Evaluation of environment and a feline facial pheromone analogue on physiologic and behavioral measures in cats.

Objectives This study assessed behavioral and physiologic stress parameters in cats placed in two environments: home and the veterinary hospital. With a widely used scale, several parameters were assessed, including respiratory rate (RR), heart rate (HR), systolic blood pressure (SBP), vagosympathetic responses using calculated intervals (heart rate variability [HRV]10, HRV20 and vasovagal tonus index [VVTI]) and 'stress attitude', such as struggling, vocalization and agitation during handling. In addition, we evaluated whether a feline facial pheromone analogue (FFPA) had an effect on any of these measures in either environment. Methods Using a placebo and a pheromone substance, we evaluated 30 adult and healthy cats at home and in veterinary hospitals. Statistical analyses were performed using the Shapiro-Wilk, Kruskal-Wallis, and Dunn or ANOVA and Tukey tests, as well as Spearman's correlation ( P <0.05). Results We found that exposure to FFPA did not reduce the effects of stress. Some parameters presented differences with regard to environment: the RR was 45 and 70 breaths/min and stress attitude score was 1.3 and 0.0 for cats evaluated at home and at the hospital, respectively. The HR and two vagosympathetic responses were also different between the two environments, with a HR of 160 and 187 beats/min, HRV10 of 14.24 and 14.00, and HRV20 of 14.89 and 14.65 in cats at home and the hospital, respectively. There was no variation in SBP and VVTI parameters between the environments. Conclusions and relevance Exposure to FFPA does not reduce the physiologic and behavioral changes measured in this study. Furthermore, environmental change, physical restraint and manipulation during the physical examination alter RR, HR, HRV and behavior but not SBP and VVTI. This study is relevant because physiologic and behavioral stress can affect the quality and interpretation of physical examination results. This study presents detailed data that show the effects of environment and manipulation on such parameters. Furthermore, this study shows a lack of effect of FFPA on any of these parameters.

Longitudinal Electrocardiographic Evaluation of Dogs with Degenerative Mitral Valve Disease

BackgroundIncreased heart rate (HR) and decreased heart rate variability (HRV) are evident in some dogs with degenerative mitral valve disease (DMVD).ObjectivesEvaluation of the factors influencing HR and HRV (assessed by the vasovagal tonus index; VVTI) and their change over time in dogs with DMVD.AnimalsClient‐owned dogs (n = 257) with DMVD recruited from first opinion practice.MethodsProspective longitudinal follow‐up at six‐monthly intervals of dogs with DMVD. Dogs followed up for at least 18 months (n = 102) were grouped according to their outcome as dogs dying/euthanized because of cardiac disease (n = 28; Group 1), noncardiac disease (n = 40; Group 2) and dogs alive (n = 34; Group 3). HR and VVTI were measured on 1‐minute ECG recordings. Repeated measures linear models were constructed to investigate the factors that influence HR and VVTI and their changes over time.ResultsHeart rate and VVTI were affected by disease severity and were different in Cavaliers compared to other breeds. Group 1 and Group 2 dogs underwent an increase in HR and decrease in VVTI, evident at least 18 months before death. Group 1 had a further decrease in VVTI followed by an increase in HR approximately 1 year and 6 months before death, respectively.Conclusions and Clinical ImportanceDogs with DMVD have an increase in HR and decrease in HRV over a year before death, with greater changes in those dogs dying/euthanized because of cardiac disease. Both HR and VVTI can potentially be regarded as biomarkers for all‐cause mortality.

Effects of Behavior Responses on the Vasovagal Tonus Index in Healthy Dogs

Effects of Behavior Responses on the Vasovagal Tonus Index in Healthy Dogs

Time and frequency domain analysis of heart rate variability in cattle affected by bovine spongiform encephalopathy

BackgroundHeart rate variability (HRV) analysis is a method to assess the function of the autonomic nervous system. Brainstem nuclei that influence HRV are affected by vacuolar changes and accumulation of disease-associated prion protein (PrPd) in bovine spongiform encephalopathy (BSE) resulting in clinical signs suggestive of an increased parasympathetic tone. It was hypothesised that BSE in cattle causes changes in the autonomic nervous system; this was tested by comparing HRV indices derived from 1048 electrocardiograms, which were recorded from 51 naturally or experimentally infected cattle with BSE confirmed by postmortem tests, 321 clinical suspect cases or cattle inoculated with potentially infectious tissue without disease confirmation and 78 BSE-free control cattle.FindingsStatistically significant differences were found for low or high frequency power, their normalised values and ratio when the last recording prior to cull or repeated recordings were compared but only between male and female cattle of the three groups and not between groups of the same gender, even though BSE cases of each gender appeared to be more nervous during the recording. The same findings were made for heart rate, deviation from the mean RR interval and vasovagal tonus index when repeated recordings were compared. BSE cases with severe vacuolar changes in the parasympathetic nucleus of the vagus nerve had a significantly lower low:high frequency power ratio but not a lower heart rate than BSE cases with mild vacuolation, whereas severity of vacuolar changes in the solitary tract nucleus or intensity of PrPd accumulation in both nuclei did not appear to have any affect on either index. Abnormalities in the electrocardiogram were detected in 3% of the recordings irrespective of the BSE status; sinus arrhythmia was present in 93% of the remaining recordings.ConclusionsHRV analysis was not useful to distinguish BSE-positive from BSE-negative cattle grouped by gender, and HRV indices appeared to be mainly influenced by gender. There is agreement with earlier studies that vacuolar changes in the brainstem may be associated with an increased parasympathetic tone in BSE and that abnormalities in an electrocardiogram can be detected in cattle without evidence of heart disease.

The vasovagal tonus index as a prognostic indicator in dogs with dilated cardiomyopathy

To investigate the prognostic and diagnostic value of heart rate variability (HRV) using the vasovagal tonus index (VVTI) in dogs suffering from idiopathic dilated cardiomyopathy (DCM). Electrocardiographic (ECG) recordings of 369 patients presented to a referral centre between 1993 and 2006 were reviewed. VVTI values were calculated from 132 dogs. Lower VVTI values were found in patients in International Small Animal Cardiac Health Council (ISACHC) heart failure (HF) class 2 and 3 compared with class 1. VVTI was found to be positively correlated with survival time (ST) in class 2 and 3 patients. When a cut-off value of 7.59 for VVTI was used, the test could differentiate patients in ISACHC HF class 1 versus 2 and 3 with a sensitivity of 89 per cent and a specificity of 62.5 per cent. The ST for patients with VVTI values less than 7.59 was significantly lower. The VVTI is a useful index, obtained from a standard ECG recording that estimates HRV in dogs and does not require any specific equipment for its calculation. It can be useful as a diagnostic tool to assess the severity of HF and is a useful prognostic tool in dogs with DCM.

The effect of heart disease, heart failure and diuresis on selected laboratory and electrocardiographic parameters in dogs

Objectives To evaluate the influence of heart disease and heart failure on 9 parameters: the serum sodium, potassium, chloride, creatinine and urea concentrations, heart rate, vaso-vagal tonus index (VVTI), red cell number and hematocrit. Background Previous studies have demonstrated that heart disease, heart failure and their treatment are associated with changes in laboratory and electrocardiographic parameters. Animals, materials and methods Data were retrieved from 92 client-owned dogs with naturally occurring heart disease. Dogs were classified according to the severity of their heart disease and or the presence of heart failure. The effects of heart disease, the progression into heart failure, the initiation of successful therapy and the administration of diuretics on these parameters were determined. Results Worse heart failure was characterized by the following changes: a significant fall in serum sodium and chloride concentrations and VVTI, and a significant increase in the serum urea concentration and heart rate. The onset of heart failure was characterized by a fall in VVTI and chloride concentration. The successful treatment of heart failure was characterized by a fall in heart rate, an increase in creatinine and sodium concentrations. Dogs receiving diuretics had higher heart rates, lower VVTI, higher urea concentrations, lower potassium, sodium and chloride concentrations. Conclusions Numerous complex alterations in some of the studied parameters are associated with heart disease, heart failure and their treatment. Further consideration of these changes may improve our skills in diagnosis, prognostication and treatment.

Differences between breeds of dog in a measure of heart rate variability

The vasovagal tonus index (VVTI), a time-domain indicator of heart rate variability, was measured in 92 dogs of six breeds (German shepherd dogs, labrador retrievers, cocker spaniels, boxers, bulldogs and...