Myxomatous mitral valve disease (MMVD) is one of the most common acquired diseases of the cardiovascular system of genetic etiology in small breed dogs. A long asymptomatic course characterizes the disease. Presently, the main diagnostic technique for heart diseases is echocardiography. This study evaluates individual echocardiographic indices of the left atrial and ventricular morphology with the determination of the diagnostic value of each of them in predicting the course of the disease. The study was conducted in a private veterinary hospital “Eurovet” and on the basis of the clinic of the Department of internal animal diseases and clinical diagnostics of Stepan Gzhytskyi National University of Veterinary Medicine and Biotechnology Lviv during 2018–2019. The objects consisted of 46 dogs with a confirmed diagnosis of myxomatous mitral valve disease according to the recommendations of the American College of Veterinary Internal Medicine (ACVIM) and no signs of comorbidities. During the study, three experimental groups of animals were formed according to the clinical and functional status characteristic of each stage of MMVD development – B1, B2, C. According to the results, all experimental dogs showed changes in the mitral apparatus in the form of thickening of the anterior and posterior cusps, mitral valve (MV) prolapse into the left atrial (LA) cavity and regurgitation (MR), the severity of which increased with the stage of the disease (from 20 % to 60 %). In 44.4 % of animals in group B2, thickening of the left ventricular walls was diagnosed in diastole and in 22.2 % in systole. Instead, these values increase to 46.1 % and 53.8 % in group C, respectively. However, the degree of hypertrophy is disproportionate. With the development of the disease, we detect its decrease from 0.64 ± 0.03 (group B1) to 0.50 ± 0.04 (group B2) and 0.51 ± 0.03 (group C) also we observed an increase in LVEDD/2 from 1.30 ± 0.05 cm (group B1) to 1.46 ± 0.12 cm (group B2) and 1.54 ± 0.13 cm (group C). The value of nLVEDD in B1 was 1.36 times (P < 0.001) lower compared to B2 and C. Higher values of this parameter were found in 23.1 % of dogs in group C compared to the maximum value of B2. As MV insufficiency progresses, the LA/Ao index increases slightly (1.08 times) in B2, followed by an increase in C (1.38 times, P < 0.001). At the same time, we diagnose an increase (P < 0.05) in PV/PA by 1.18 times in B2 and 1.46 times (P < 0.001) in C. Thus, an increase in the severity of mitral regurgitation, a rapid increase in nLVEDD, the dynamics of the decrease in the degree of hypertrophy h/R, as well as an increase in LA/AO, PV/PA indices are predictors of unfavorable prognosis of myxomatous degeneration of the mitral valve in dogs.

An important pathogenetic link of the progression of chronic heart failure of various genesis is the development of arrhythmias. They significantly complicate the course of CHF, because they lead to decreased cardiac output and increased hypoxia. The aim of our study was to investigate and evaluate the electrical activity of the heart of dogs with CHF. The research was performed on the basis of the private veterinary center “Vetmed” (Lviv) in 2016–2017. The study included 36 dogs of different breeds, ages, sexes with symptoms of chronic heart failure. A standard six-lead electrocardiogram (ECG) was recorded in all dogs in the right lateral position using an electrocardiograph “Vet ECG Ve – 300” (speed 50mm/s, sensitivity of the device 1mV = 10 mm). The obtained data were compared with reference values, and also took into account the variation of individual indicators depending on body weight. According to the results of our study, it was found that the frequency of arrhythmias in dogs with CHF is 75.0 %, of which 8.3 % – life-threatening, 38.9 % of the examined animals needed treatment, and 27.8 % – annual ECG monitoring. The signs of remodeling processes are found in 63.9 % of sick dogs, signs of ischemia – in 25 % and only in 2.8 % of animals – ECG without changes. The structure of arrhythmia in dogs with CHF is dominated by sinus tachycardia (47.2 %), sinus bradycardia (8.3 %), ventricular arrhythmias (5.6 %), atrial fibrillation (5.6 %), ventricular tachycardia (2.8 %). Among conduction disorders, we register intraatrial blockade (13.9 %) and AV-blockade of the first degree (8.3 %). In 13.9 % of animals ECG signs of fibrosis, ischemia are combined with changes in the size of the heart chambers. The results of our study show that a significant number of dogs with CHF have arrhythmias and conduction disorders. In order to improve diagnosis and treatment, the prospect of further research is to establish an association between ECG and echocardiographic changes in dogs with CHF, which can be both a cause of CH and its consequence and a predictor of an unfavorable prognosis.