Establishment of echocardiographic reference values a s a function of breed and body size and the importance of their clinical application and of atrial natriuretic peptide (ANP) plasma concentration measurement for determination of the severity of valvular insufficiencies and associated heart failure in equids

摘要

Compared to other species, cardiac diseases are rather uncommon in the horse. However, in high level sport horses, very small cardiac dysfunctions can result in significantly reduced performance. Furthermore, cardiac pathologies represent the third cause of exercise intolerance in the horse, and among them, valvular insufficiencies are of great concern. Nevertheless, due namely to the large size of these patients, diagnostic methods in equine cardiology are lacking and examination is more difficult resulting in a shortcoming in information indispensable for the diagnosis and prognosis. The aim of our work was to establish and improve diagnostic and prognostic techniques of valvular insufficiencies in the horse using Doppler echocardiography and the measurement of cardiac biomarkers.Reference values of echocardiographic measurements were established in the equine species taking into account the effect of various physiological variables. Indeed, these reference values are indispensable for evaluating horses with cardiac diseases, especially valvular insufficiency.First of all, in order to obtain more accurate and reliable echocardiographic measurements and cardiac functional indices, the repeatability of the measurements obtained from 2D, M-mode and pulsed Doppler in short and long axis echocardiographic views was tested and demonstrated in 10 horses of various breeds and sizes. The comparison of the obtained mean values and repeatability allowed establishing a standardised echocardiographic examination protocol in this species.Then, the effect of various anthopometric parameters on 2D and M-mode echocardiographic measurements was tested and the relationship between those measurements and parameters was studied in 150 horses of various breeds, age and size. Results obtained in this study suggested that the reference values of morphologic echocardiographic measurements should be adapted to the body size and that power equation was the most appropriate model to fit echocardiographic measurements as function of thoracic circumference, body weight or body surface area.Beside the body size, the effect of several other physiological variables such as breed, sex, age, growth, obesity, pregnancy and training on echocardiographic measurements was proved in human and/or domestic animals. Therefore, the effect of such variables on echocardiographic measurements was tested in 212 horses and ponies of various breeds, sex, ages and body sizes. Using a statistic model adjusting the data to the weight of the investigated animal, results obtained in this study suggested a significant effect of breed on most echocardiographic measurements. However, no significant effect was detected for age or sex. Based upon obtained results in the precedent studies and in 239 horses of various breed, echocardiographic measurements reference values corrected for the body size using thorax circumference or body weight were established in each studied breed.These reference values should allow establishing an accurate diagnostic and prognostic in horses with cardiac diseases especially valvular insufficiency.On the other hand, in order to support the diagnostic and prognostic of cardiac diseases with additional tools, the reliability of using the atrial natriuretic peptide (ANP) as an indicator of valvuar insufficiency in the equine cardiology was tested. It had been demonstrated by several authors that plasma concentration of ANP in various species was correlated to the degree of increase in atrial pressure and volume associated to several cardiac diseases. In the equine species, two studies have evaluated the plasmatic ANP concentration in horses suffering from various cardiac pathologies, whom valvular insufficiencies especially. However, those studies were conducted on a small number of horses and results were contradictory between them.Thence, we decided to measure plasma ANP concentration on 91 horses that were suffering or not from valvular insufficiencies of different severity level.Plasma ANP concentration was significantly higher in horses suffering from mild and severe valvular insufficiencies than those presenting no or light valvular insufficiencies. Furthermore, plasma ANP concentrations were higher in horses suffering from mitral or tricuspid insufficiencies compared to horses with aortic insufficiency, and a strong correlation existed between plasma ANP concentrations and the left atrial internal diameter or the dilatation percentage of this left atrium, which suggests that this biomarker seems mostly interesting to detect atrial dilatation or dysfunction as reported in other species.Plasma ANP concentration correlated to the severity of valvular insufficiencies and could be a good indicator of volume overloud in equine cardiology.Conclusions and Perspectives:In conclusion, the results obtained in this thesis allowed establishing a protocol for an echocardiographic examination which permits obtaining repeatable echocardiographic measurements in the equine species. These measurements are significantly influenced by body size parameters especially thoracic circumference, body weight and body surface area, but also by breed. On the other hand, it had been found that power equation is the optimal model to fit echocardiographic measurement in this species, which allowed the establishment of accurate reference values of echocardiographic measurements.In a second time, we found that plasma ANP concentration was significantly correlated to the severity of valvular insufficiency and that it could be a good indicator of volume overloud and a helpful diagnostic and prognostic factor in equine cardiology.