# Translational Echocardiography: The Dog as a Clinical Research Model of Cardiac Dysfunction
## 6 Dilated Cardiomyopathy (DCM), a Human and Canine Common Disease
### Echocardiographic Measurements on DCM  
Experience and clinical evidence point to TTE as a sensitive and specific medical resource in diagnosing dilated cardiomyopathy in dogs with congestive heart failure due to heart failure with reduced ejection fraction [104]. .1.1 Measurement of Left Ventricular Volume by Simpson's Method of Disks and Left Ventricular M-Mode  
M-mode echocardiography is widely used in canine cardiology. Its one-dimensional nature limits the spatial information it provides, and the technique is based on geometric assumptions, which may vary according to the heart disease conditions, as shown in Figure 13[102; 103]. The American Society of Echocardiography recommends against using linear measurements to calculate left ventricular volume in the human patient and suggests that the biplanar Simpson's disk method (SMOD) is more suitable for this purpose [100]. Similarly, in a clinical study in dogs, the SMOD method was more sensitive than M-mode for detecting the presence of early echocardiographic changes, as shown in Figure 14a,b[96], and these results recommend that SMOD reference values should be used as a priority in the detection of early changes [103]. LV volume using the SMOD method is calculated in the right parasternal four-chamber long-axis view and in the left apical four-chamber view (in this technique, the aorta should not be visualized in either of these views), and it is important to trace the endocardial border in each image used. The image frame used to measure end-diastolic volume is selected by referencing the frames related to the onset of the QRS complex signaled by the synchronous electrocardiographic trace when the mitral valve is closed and the volume is at its peak. When measuring end-systolic volume in the heart, cardiologists choose the final frame just prior to the opening of the mitral valve. This is often the frame that follows the end of the T wave on an ECG and corresponds to a point in the cardiac cycle where volume is at its minimum. By selecting this specific frame, clinicians can obtain an accurate assessment of the heart's function. The right parasternal and left apical views should be measured, and larger volumes should be used, reducing the possibility of volume underestimation. It is important to note that the natural tendency for apical shortening in the heart can result in an underestimation of end-systolic and end-diastolic volumes. This phenomenon can complicate the interpretation of echocardiographic data [96]. The SMOD formula is a commonly used method to estimate left ventricular volume. This formula is based on tracing the endocardial border through the mitral valve annulus and measuring the longitudinal axis of the left ventricle. The left ventricular cavity is then divided into 20 disks of equal height to calculate the volume of the left ventricle. The cross-sectional area of each disk is determined by measuring the diameters of the left ventricle from two orthogonal views, which allows for a more accurate calculation of left ventricular volumes, and the end-diastolic (EDV) and end-systolic (ESV) volumes should be calculated by the sum of the stacked disks, which is determined by the software of the current echocardiography equipment. The quantified volumes can be normalized concerning body surface area to obtain volume indices (EDV-I and ESV-I). Current guidelines indicate that an ESV-I greater than 80 mL/m\({}^{2}\) indicates systolic dysfunction [96; 102]. Ejection fraction (EF) is calculated similarly to fractional shortening, but volume measurements are determined using the formula presented below:  
\[\text{EF}=(\text{EDV}-\text{ESV})/\text{EDVEF}=\text{EDV}-\text{ESV}/\text{EDV}\]  
Ejection fraction (EF) considers radial and longitudinal cardiac variations, and dogs with ejection fraction less than 40% are considered to have reduced contractile capacity [102].