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Today's VeTerinary PracTice | July/august 2015 | tvpjournal.com HearT Failure in dogs: 6 PracTical TiPs From cardiologisTs Peer reviewed 24 Heart failure is a complex condition. Despite multiple underlying causes and clinical manifestations, successful management is possible. This article describes canine heart failure, provides in-depth information about the most common diseases that lead to heart failure, and offers practical tips for diagnosis and management. DEFINITION Heart failure is a complex condition that can develop from congenital or acquired heart disease in dogs. Depending on the specifc disease process, it can affect the left and right sides of the heart, manifesting in respiratory signs and weakness due to: • Fluid retention: Congestion; sometimes called backward failure • Pump failure: Low cardiac output; sometimes called forward failure. While the underlying heart disease can vary depending on age and breed, chronic heart failure management for degenerative mitral valve disease (DMVD) and dilated cardiomyopathy (DCM) initially relies on a combination of a diuretic, angiotensin- converting enzyme (ACE) inhibitor, and pimobendan, with additional medications added as necessary. DEGENERATIVE MITRAL VALVE DISEASE DMVD is the most common acquired heart disease in dogs. Common clinical signs and pathophysiology include: • Heart murmur due to mitral valve (and, sometimes, tricuspid valve) regurgitation, leading to left atrial and left ventricular dilatation • Progressive dilatation of the left ventricle, ultimately leading to systolic dysfunction • Significant left atrial enlargement, leading to atrial (supraventricular) arrhythmias • Development of pulmonary hypertension, which can contribute to clinical signs, such as respiratory distress and syncope. Not all dogs with DMVD will develop heart failure, characterized by pulmonary edema (see Progression to Congestive Heart Failure). In general, dogs with heart enlargement are at greater risk for heart failure, but only 30% of dogs with asymptomatic DMVD develop clinical signs and require heart failure therapy. DILATED CARDIOMYOPATHY DCM is a primary disease of the heart muscle, characterized by a relatively long asymptomatic stage (1–2 years) followed by sudden death (due to arrhythmias) or heart failure. Changes associated with DCM, starting with the earliest, include: • Reduced systolic function of predominantly the left ventricle • Dilatation of the left ventricle and, to a lesser degree, the left atrium due to systolic dysfunction and high preload • In some dogs, mitral regurgitation, once the heart is sufficiently dilated, because the mitral annulus is stretched to a degree that prevents the mitral valves from closing effectively. Arrhythmias are common in this disease, both in the asymptomatic and symptomatic stages, and often require treatment. The most common 6 Practical tiPs from cardiologists Heart Failure in Dogs Ashley B. Saunders, DVM, Diplomate ACVIM (Cardiology), and Sonya G. Gordon, DVM, DVSc, Diplomate ACVIM (Cardiology) Texas A&M; University As heart function deteriorates, fuid volume within the heart and vasculature increases as a consequence of activation and upregulation of neurohormonal systems, such as the renin-angiotensin-aldosterone system. This complex pathophysiology leads to increased: ` Preload ` Stretch of heart chambers ` Hydrostatic pressure in vessels that supply the left (pulmonary veins) and right (vena cavae) atria. The result is either: ` Congestion and pulmonary edema (left-sided heart failure) ` Ascites with or without pleural effusion (right-sided heart failure). Progression to Congestive Heart Failure