OBJECTIVE To determine whether the lactate threshold of dogs could be determined by a visual method and to assess the extent of agreement and bias among treadmill velocities for the lactate threshold as determined by visual (LTv) and polynomial (LTp) methods, glucose threshold as determined by visual (GTv) and polynomial (GTp) methods, and heart rate deflection point (HRdp) as a method for estimating the aerobic capacity of dogs. ANIMALS 18 healthy adult Beagles. PROCEDURES Each dog underwent a standardized incremental treadmill exercise test once. The test ended when the dog began to show signs of fatigue. Plasma lactate and glucose concentrations and heart rate (HR) were plotted against exercise intensity (treadmill velocity) for the duration of the test, and the LTv, GTv, and HRdp were determined visually. The LTp and GTp were determined by means of a second-order polynomial function. One-way ANOVA, Pearson correlation, Bland-Altman analyses, and ordinary least products regression were used to assess the extent of agreement and bias among the various threshold velocities. RESULTS Mean velocity did not differ significantly among the thresholds evaluated. There was a strong positive correlation between the LTv velocity and the velocity for GTv (r = 0.91), LTp (r = 0.96), GTp (r = 0.94), and HRdp (r = 0.95). CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that LTv could be determined for dogs undergoing intense exercise on a treadmill, and the treadmill velocity corresponding to the LTv was associated with the velocity for the other hallmarks of endurance. Thus, that method may be useful for prescription and evaluation of conditioning programs for dogs.

Dilated cardiomyopathy (DCM) is characterized by chamber dilation and cardiac dysfunction. Because of the poor prognosis, models are needed for the investigation of and development of new therapeutic approaches, as well as stem cell therapy. Doxorubicin (DOX), used as chemotherapeutic agent, is reported to be cumulative cardiotoxic causing DCM. The aim of the study was to investigate the onset of systolic dysfunction using echocardiography in rabbits receiving two different doses of DOX (1mg/kg twice a week and 2 mg/kg once a week). Twenty rabbits were treated with doxorubicin in two different doses for 6 weeks and compared with a control group treated with NaCl 0.9%. The effect of doxorubicin on the myocardium was investigated with histological analysis and scanning electron microscopy of left ventricle (LV), as well as in the interventricular septum (IVS) and right ventricle (RV). The results showed a high mortality rate for rabbits receiving 2 mg/kg once a week. A significant reduction in systolic function was present in animals treated with DOX after 6 weeks, with decreased ejection fraction and shortening fraction. Histology and electron microscopy revealed vacuolization, intracytoplasmic granulation, necrosis and interstitial fibrosis in LV, as well as in the IVS and RV. Doxorubicin induced changes are present in the LV, RV and IVS, and the administration at the dose of 1 mg/kg twice a week for only 6 weeks is safe and sufficient to induce DCM in rabbits.

The dogs' responses to training exercise are seldom monitored using physiological variables, and cardiac autonomic regulation (CAR) is a relevant determinant of endurance-training adaptation. There are studies in the literature establishing that regular exercise could interfere with CAR in dogs, measured by heart rate and vagal-derived indexes of heart-ratevariability (HRV). However, few studies were found using a prescribed training program based on the lactate threshold (LT) to determine HRV by a 24-h Holter analysis. The purpose of this study was to test whether an endurance-training program (ETP) guided individually by LT raises time-domain measures of HRV in healthy Beagle dogs. Twenty dogs were assigned to two groups: control (C) and trained (T). The dogs from group T underwent an incremental exercise test (IET) to determine their LT. Both LT and velocity corresponding to the LT (VLT) was determined by visual inspection. T group performed an eight-week endurance-training program consisting of treadmill runs set to 70-80% of the VLT. Next, dogs from the group T have submitted to IET again. The maximal velocities (Vmax) at which achieved by the trained dogs in both IETs were determined. The group S did not undergo IETs or ETP. HRV was determined by the 24-hour-Holter at rest, before and on the 2˚, 4˚, 6å nd 8˚training weeks. To examine the HR impact on HRV, standard HRV variables were normalized to prevailing HR. VLT and Vmax rose in group T, indicating an improvement of dogs' aerobic and anaerobic capacity. The normalized standard HRV indexes were relatively attenuated since these variables had a reduction in the degree of correlation concerning an average HR. The ETP resulted in decreased resting heart rate and increased timedomain indices, highlighting the log-transformed square root of the mean sum of the

The aim of the present study was to assess heart rate variability (HRV) in Boxer dogs affected by arrhythmogenic right ventricular cardiomyopathy (ARVC). Fourteen Boxer dogs classified as affected and 28 classified as unaffected were included in a prospective case-control study. Dogs underwent 24-hour ambulatory ECG and were classified as affected (>1,000 VPCs/24 hours) or unaffected (<20 VPCs/24 hours) by ARVC based on the number of ventricular arrhythmias. HRV was assessed using 24-h Holter ECG monitoring; the studied parameters were SDNN, SDANN, SDNNIDX, rMSSD and pNN50. Data were submitted to logarithmic transformation and HRV parameters were compared between groups and correlated according to the disease status, number and severity of ventricular arrhythmias using Student’s t test, linear regression and Spearman’s test. There was no interaction between the HRV parameters and the number and severity of ventricular arrhythmias. SDNNlog (2.35±0.14 vs. 2.46±0.12, P=0.01), SDNNIDXlog (2.18±0.14 vs. 2.24±0.10, P=0.002) and pNN50log (1.47±0.19 vs. 1.64±0.13, P=0.002) were significantly lower in the affected group compared with the unaffected. According to this study, HRV are different in a population of Boxers dogs affected by ARVC compared to a population of unaffected dogs, and these differences are not consequences of low cardiac output caused by ventricular arrhythmias since animals that had higher number and complexity of arrhythmias were not those who had lower values of HRV.

RESUMO:A cardiomiopatia arritmogênica do ventrículo direito (CAVD) é uma doença miocárdica hereditária comumente observada no Boxer adulto, caracterizada pela substituição dos cardiomiócitos do ventrículo direito (VD) por tecido fibroadiposo, gerando áreas propensas à formação de arritmias ventriculares, que podem culminar em morte súbita. Devido aos avanços no mapeamento genético em cães domésticos, pode-se concluir que os Boxers são acometidos pela CAVD de maneira similar ao que ocorre em seres humanos, e, portanto, são considerados um modelo animal natural para o estudo da CAVD na espécie humana. Não há um teste de diagnóstico único e específico para CAVD, portanto, em Medicina Veterinária o diagnóstico baseia-se na presença de uma combinação de achados, que podem incluir presença de taquiarritmia ventricular sem outras causas documentáveis para a arritmia, síncope e histórico familiar de CAVD. O tratamento é direcionado à redução da frequência e complexidade da arritmia ventricular, e sotalol e/ou mexiletine são os antiarrítmicos mais comumente prescritos, bem como o ômega 3 advindo do óleo de peixe. Entretanto, não é sabido se o tratamento em cães assintomáticos está associado à melhores prognósticos. Embora alguns cães acometidos apresentem morte súbita ou desenvolvam insuficiência cardíaca congestiva, muitos deles têm arritmias ventriculares controláveis por antiarrítmicos e vivem uma vida normal. Algumas características dos complexos ventriculares prematuros, tais como polimorfismo e taquicardia ventricular, além da presença de sinais clínicos, e disfunção sistólica ventricular esquerda e direita estão associados à piores prognósticos.Palavras-chave: arritmia; arritmogênese; eletrocardiografia; Holter; prognóstico ABSTRACT: The arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited myocardial disease commonly observed in the adult Boxer, characterized by the replacement of right ventricle (RV) cardiomyocytes by fibrofatty tissue, what generate areas prone to the formation of ventricular arrhythmias, which may culminate in sudden death. Due to advances in genetic mapping in domestic dogs, it could be concluded that Boxers are affected by ARVC in a closed related way to human beings, and therefore are considered a natural animal model for the study of human ARVC. There is not a single and specific diagnostic test for ARVC, thus, in veterinary practice the diagnosis is best based on a combination of findings, which may include the presence of ventricular tachyarrhythmia with no other documented causes for the arrhythmia, as well as syncope, and family history to ARCV. Treatment is directed to decrease the occurrence and the complexity of the ventricular arrhythmias , and sotalol and/or mexiletine are the antiarrhythmics most commonly prescribed, as well as omega 3 from fish oil. However, it is unknown if the treatment on an asymptomatic dog prolongs survival. Although some affected dogs show sudden death or develop congestive heart failure, many of them have ventricular arrhythmias that are ...