# Translational Echocardiography: The Dog as a Clinical Research Model of Cardiac Dysfunction
## 5 (MDMV) Comparative Pathology and Pathophysiology
### Mitral Regurgitation Quantification in the Canine Model  
The Proximal Isovelocity Surface Area (PISA) method is a widely accepted gold standard for quantifying the extent of mitral regurgitation jet in humans [60; 61]. While a clinical study has shown that this method is repeatable and reproducible in awake dogs [62], it is less practical and requires several precautions to obtain optimal flow convergence images in dogs with mitral disease [63; 64]. Therefore, in veterinary practice, the use of PISA should be employed with caution, taking into account the potential limitations and technical challenges associated with its application. The severity of mitral regurgitation in dogs can be determined by the regurgitation fraction (RF) obtained through the proximal isovelocity surface area (PISA) method. Several studies have demonstrated that RF is closely associated with the severity of degenerative valve disease and other important echocardiographic indicators, such as the ratio of the left atrium to the aorta (LA/Ao) and pulmonary artery systolic pressure [62; 65]. A different clinical study found that PISA quantification of mitral regurgitation showed a wide range of RF, which is why it is not routinely performed in cardiologic evaluation in dogs [62]. The severity of mitral regurgitation can be semi-quantified using color-flow Doppler to measure the mitral regurgitan maximum jet area (MRA) ratio in relation to the left atrial area (LAA). This method has been validated in dogs and demonstrates a strong correlation with Doppler-derived regurgitant volume and effective regurgitan orifice area, making it a reliable tool for assessing mitral regurgitation severity [66; 67]. In human medicine, mitral regurgitation has been widely studied, and there are several stratification scales and widely disseminated echocardiographic evaluation guidelines [61; 68; 69]. In the same way, as in TTE studies of canine patients, the characteristics and changes in mitral structure and morphology and signs of valvular remodeling are evaluated. Doppler technology is also useful for assessing mitral regurgitation qualitatively, semi-qualitatively, and quantitatively. Most of the echocardiographic variables used in the human patient have been studied in domestic canine medicine; in the same way, these methods require extensive training to obtain repeatable results in the measurements and avoid measurement variability in the generation of erroneous results [70]. Color flow imaging of the mitral regurgitation jet area is the most commonly used technique for assessing the severity of mitral regurgitation in dogs. The former method is not used in humans, as it is not considered reliable for determining the severity of mitral insufficiency [68; 69]. This method has become widespread in the -domestic canine patient because it is easy to perform; however, some studies have indicated that the correlation of the jet area with the severity of mitral regurgitation is poor, as well as its reproducibility [67]. One of the most commonly used semiquantitative techniques in veterinary TTE is the measurement of the effective regurgitant orifice or the width of the vena contracta. This method, compared with other qualitative methods, is equally useful for evaluating eccentric and central jets. However, it is unreliable in multiple jets as it depends on the geometry of the regurgitant orifice [69]. A study in dogs with Mitral Myxomatous Degeneration reported that vena contracta and E-vel correlated strongly with mitral regurgitant fraction reported in cardiac MRI studies. However, E-vel had superior repeatability, being more reliable in dogs [71]. Among quantitative methods, proximal isovelocity surface area assessment is one of the most widely used methods to evaluate the effective regurgitant orifice area and regurgitant volume. However, its reliability in eccentric jets has been questioned [69; 72].