Myxomatous mitral valve degeneration (MMVD) is the most common canine cardiac disease.

In the studies presented in this dissertation, we used advanced echocardiographic techniques to elucidate several aspects of MMVD in dogs. Our hypothesis was that the mitral valve (MV) morphology could have a role in the development of MMVD. First, we tested whether we could use real time three-dimensional transthoracic echocardiography (RT-3DTTE), and an offline software for MV analysis to evaluate canine MV. We described that the technique was feasible and repeatable, we evaluated the morphology of the MV in healthy dogs, and we provided reference values for MV morphologic variables in this species. Then, we used the same technique to compare healthy dogs to dogs affected by MMVD. We found that dogs affected by MMVD have more circular and flatter valve. We then analyzed the MV of healthy Cavalier King Charles Spaniels (CKCSs), given the high predisposition of this breed for MMVD. Our findings indicate that compared to healthy dogs of other breeds, the MV of healthy CKCSs is flatter and has less leaflet tenting, corroborating our hypothesis that an altered MV morphology could represent a predisposing factor for disease development. We also used RT–3DTTE to characterize the area of the regurgitant MV orifice of dogs affected with MMVD, finding that the technique requires further standardization in order to become clinically useful.

The elevation of pulmonary venous pressure caused by MMVD can, in some dogs, cause pulmonary arterial hypertension (PH), which is a risk factor associated with worse outcome in dogs with MMVD. Diagnosis of PH in dogs with MMVD is usually made by estimating pulmonary pressure using Doppler echocardiography. We are currently evaluating the accuracy of this technique, compared to invasive measurement of pulmonary pressure. Only preliminary data are presented regarding this study, as the disclosure of the blinding would have infringed the power of the study. Our preliminary results demonstrate that there is only moderate agreement between the two techniques, indicating that caution should be used when deriving the non-invasive estimation of systolic pulmonary pressure in order to make clinical decisions.