Heart failure is not a specific disease or diagnosis. It is a syndrome in which severe dysfunction results in failure of the cardiovascular system to maintain adequate blood circulation. There are limited and specific mechanisms by which heart disease can bring on failure of the cardiovascular system. Therefore, there are limited and specific signs that can develop as a result of heart failure.

Types of Heart Failure

Heart failure can be divided into 4 functional classifications: systolic myocardial failure, impedance to cardiac inflow, pressure overload, and volume overload (see Heart and Blood Vessel Disorders of Dogs: Mitral stenosis and regurgitation.)

Systolic myocardial failure is a general reduction in the ability of the heart muscle to contract. This can be identified with echocardiography (ultrasonography). There is reduced wall motion during contraction of the ventricles. If the reduction is significant, normal blood flow cannot be maintained. It may be caused by trauma, infection, drugs or poisons, electric shock, heat stroke, or tumors. Some cases have no known cause.

Heart failure resulting from the impedance (obstruction) to cardiac inflow may result in a decrease in blood flow. This may be caused by external compression of the heart (for example, fluid in the sac surrounding the heart), diastolic dysfunction resulting in a stiff ventricle and reduced ventricular filling, or abnormalities of physical structures of the heart.

Heart failure caused by pressure overload occurs as a result of longterm increases in stress to the heart wall during contraction. This may result from the obstruction of blood flow from the heart or increased blood pressure throughout the body or in the arteries of the lungs.

Volume overload heart failure occurs as a result of any disease that increases volume of blood in the ventricle (s), thus increasing blood flow. Eventually, this can bring on signs of congestive heart failure. Diseases that result in volume overload myocardial failure include valve disease (for example, degenerative valve disease of the atrioventricular valves), left-to-right shunts (for example, patent ductus arteriosus, ventricular septal defect), or high-output states (such as those caused by hyperthyroidism or anemia).

Compensatory Mechanisms

The cardiovascular system maintains normal blood pressure and blood flow. In heart disease, the body uses specific mechanisms to attempt to normalize these functions and offset negative effects the disease is having on the body. Unfortunately, longterm activation of these compensatory mechanisms can damage the heart muscle and other organs, leading to further heart failure (see Heart and Blood Vessel Disorders of Dogs: Compensatory Mechanisms).

Signs of Heart Failure

Signs associated with heart failure depend on the causes of the heart failure and the heart chamber that is affected. With left-sided congestive heart failure, signs are associated with a backup of pressure in the vessels delivering blood to the left ventricle. Fluid in the lungs and congestion (coughing and difficulty breathing) are the most common signs, although cats with heart failure are far less likely to cough than dogs with the disease. Increased breathing rate, loss of appetite, or exercise intolerance may also be noted.

Right-sided congestive heart failure results in increased pressure in the body's veins and capillaries. This can result in an accumulation of fluid in the abdomen, chest cavity, or limbs.

Biventricular failure can arise when both the right and left ventricles are not working, such as in cats with heart failure resulting from dilated cardiomyopathy or toxin (poison) exposure. Signs attributable to both forms of congestive heart failure can be noted, although commonly signs of one type of congestive heart failure will outweigh the other.

Treatment

It is important to treat heart failure in order to improve heart muscle performance, control arrhythmias and blood pressure, improve blood flow, and reduce the amount of blood filling the heart before contraction. All of these can further damage the heart and blood vessels if not controlled. It is also necessary to reduce the amount of fluid in the lungs, abdomen, or chest cavity.

There are many types of drugs available for treating heart failure. The specific drugs, dosage, and frequency used will vary depending on the causes and severity of the heart failure and other factors. Your veterinarian is best able to decide on the appropriate medications for your cat. All drugs prescribed by your veterinarian must be given as directed. Otherwise, they may not be effective and may even cause serious complications and harm.

Diuretics are usually prescribed to reduce fluid overload. Digitalis and digoxin, part of a group of drugs known as positive inotropes, may be used to help the heart muscle contract. ACE inhibitors (ACE stands for angiotensin-converting enzyme) and vasodilators can widen blood vessels and thus lower blood pressure. Beta-adrenergic blocking drugs (also called beta-blockers) and calcium channel blockers are also helpful in some cases of congestive heart failure.

In addition to drugs, other types of treatment are sometimes recommended. These may include a low-sodium diet (prescription or commercial diets are available), oxygen therapy to raise the level of oxygen in the blood, or surgical procedures to remove excess fluid buildup from the chest cavity or abdomen.

Last full review/revision July 2011 by Davin Borde, DVM, DACVIM; Jorge Guerrero, DVM, PhD, DEVPC (Ret); Michelle Wall, DVM, DACVIM; Clay A. Calvert, DVM, DACVIM; Benjamin J. Darien, DVM, MS, DACVIM