# Translational Echocardiography: The Dog as a Clinical Research Model of Cardiac Dysfunction
## 6 Dilated Cardiomyopathy (DCM), a Human and Canine Common Disease  
Cardiomyopathies are cardiac muscle disorders that could lead to mechanical and electrical heart malfunctions [96,97]. Cardiovascular disease is the fourth most common cause of death in dogs [98] and one of the most prevalent causes of death in humans [99]. Dilated cardiomyopathy (DCM) is the second most prevalent form of heart disease in domestic canines, accounting for 10% of heart disease in this species [97]. It is estimated to be the third most common hereditary heart disease in humans, affecting 35 patients in every 100,000, according to data that are considered underestimated [96].  
Due to the similarities of DCM in humans and dogs regarding phenotypic characteristics and pathology progression, studies have suggested that canine MCD may act as a model for this pathology in humans. The above may apply to other fields, such as comparative clinical imaging research [100]. The scientific observation of the clinical course of this disease in the dog can guide improvements in clinical care and echocardiographic techniques in both canine and human patients.  
Animal models of dilated cardiomyopathy are a useful research area because they can provide relevant information on the disease's cellular, structural, and hemodynamic progression, which is essential in improving treatment regimens [101], interventional procedures, and diagnostic imaging techniques. While there are many animal models in which dilated cardiomyopathy is induced, naturally occurring cases in dogs are particularly valuable concerning the disease's natural progression, especially when the underlying mechanisms are similar in dogs and people [96]. In addition to providing a potential natural model for human DCM in canines, it is potentially useful for studying new strategies and technologies for echocardiographic diagnosis in humans.  
A significant association exists between dilated cardiomyopathy and congestive heart failure in dogs characterized by enlargement and impaired left ventricle contraction [96,102]. It is possible to classify dilated cardiomyopathy into three major stages [96]. At stage one, the heart appears normal, with no clinical evidence of cardiac disease, and often includes  
Figure 12: Altered E/e ratio in a canine patient with congestive heart failure.  
dogs genetically predisposed to this pathology [96]. Stage two, classified as the preclinical or occult phase, involves morphologic and electrical changes in the heart, but with no overt clinical symptoms. Finally, stage three includes clinical signs of congestive heart failure [96].  
The ideal standard approach for diagnosing DCM is based on 24 h echocardiographic and electrocardiographic (ECG) evaluations and monitoring the clinical presentation and patient progress [103]. In addition to a color Doppler echocardiographic evaluation, an electrocardiogram should also be performed simultaneously. The basic protocol includes all measurements performed in triplicate for volume and, ideally, five sequential cardiac cycles for M-mode testing [96]. Congenital or acquired heart disease other than DCM may also cause volume overload, systolic dysfunction, or both, and must be distinguished as a differential diagnosis in the dog. Volume overload in dogs can be caused by pathologies such as patent ductus arterious, ventricular septal defect, mitral valve dysplasia, and the myxomatous degeneration of the mitral valve [102].