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PEER REVIEWED 72 JULY/AUGUST 2018 BOX 1. Indications The American College of Veterinary Internal Medicine (ACVIM) consensus statement describes 4 stages of heart disease and failure. The ACVIM consensus statement for DMVD outlines a staging system for preclinical (stage B) and clinical (stages C and D) disease. 7 Preclinical DCM (Stage B2) This stage is characterized by systolic dysfunction (dilated left ventricle in systole) that is usually associated with left ventricular dilation in diastole, with or without left atrial enlargement, and with or without supraventricular and ventricular arrhythmias. Abnormalities are identified by screening with echocardiography and electrocardiography (ECG). The primary diagnostic criterion for preclinical DCM is significant systolic left ventricular dysfunction. Therefore, echocardiography is required to establish a diagnosis (see CASE 1 ). Research data from studies of Doberman pinschers 8 and Irish wolfhounds 9 with preclinical DCM show that pimobendan use was associated with Reduced left ventricular size in systole and diastole 8 Delayed average time to onset of CHF or sudden death 8,9 Longer overall survival times 8,9 Pimobendan may be considered for use in other breeds with echocardiographic confirmation of preclinical DCM ( TABLE 1 ). Clinical DCM (Stages C and D) Clinical DCM is characterized by left ventricular systolic dysfunction and dilation complicated by CHF. It is manifested by pulmonary edema, with or without ascites, and, more rarely, pleural effusion, with or without significant ventricular arrhythmias or atrial fibrillation. Pimobendan added to heart failure therapy (furosemide and benazepril) improves clinical status, delays onset of refractory signs of heart failure, and increases survival times. 10,11 Preclinical DMVD (Stage B2) DMVD is most common in middle-aged to older small breed dogs and is characterized by a left-sided systolic murmur over the mitral valve (left apex). Dogs with stage B2 heart disease show radiographic and echocardiographic evidence of heart enlargement without clinical signs attributable to heart disease. Stage B2 will progress to CHF in only 30% of dogs; however, all of these dogs are at risk for disease progression characterized by progressive heart enlargement. 12 Pimobendan delays the onset of CHF, in part through reduction in heart size, and increases survival times. 13,14 Pimobendan use is recommended for dogs that have a confirmed diagnosis of preclinical DMVD and radiographic and echocardiographic heart size measurements that meet or exceed the following criteria used in the EPIC study 13 (see CASE 2 ): Radiographic vertebral heart size (VHS) >10.5 Two-dimensional echocardiographic left atrium/aorta ratio (LA/Ao-2D) ≥1.6 Echocardiographic normalized left ventricular internal dimension in diastole indexed to body weight (LVIDdN) ≥1.7 15 If echocardiography is not available but the signalment and murmur characteristics support DMVD and the dog has radiographic evidence of cardiomegaly with a VHS ≥11.5, pimobendan can be considered on the basis of recommendations created by the Cardiac Education Group ( TABLE 1 ). 16 If the VHS is >10.5 but <11.5, echocardiography is strongly recommended to guide recommendations regarding pimobendan use. 16 Clinical DMVD (Stages C and D) Characteristics of these stages are similar to those of stage B2 but include past or present clinical signs consistent with CHF. For dogs with clinical DMVD, pimobendan doubles the time to sudden death, treatment failure, or euthanasia for cardiac reasons. 17 In dogs with at least moderate pulmonary hypertension, it decreases tricuspid regurgitation outflow velocities, indicating reduced pulmonary pressures. Treatment with pimobendan is clearly indicated for dogs with stage B2 (asymptomatic that meet EPIC heart size entry criteria) or stages C and D (symptomatic) DMVD with or without pulmonary hypertension, characterized by elevated left atrial pressures. In dogs with concurrent pulmonary hypertension secondary to DMVD, the positive effects are probably multifactorial. The effects may be secondary to reduced left atrial pressure, increased right heart systolic function associated with increased inotropy, and reduced pulmonary vascular resistance associated with vasodilation. 18 ■ Pulmonary hypertension unrelated to DMVD, resulting in right-sided CHF (ascites) refractory to standard therapy (i.e., cor pulmonale, advanced heartworm disease, pulmonary thromboembolism). For these patients, pimobendan can be added to other therapies; however, we recommend first consulting a cardiologist. CONTRAINDICATION When ascites is the result of pericardial effusion that requires pericardiocentesis, use of pimobendan is not recommended. PRECAUTIONS Pimobendan seems to be safe and well tolerated. Reported adverse effects are relatively rare and are typically limited to gastrointestinal upset associated

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