Diagnosing heart failure (Proceedings)

The clinical signs of canine and feline heart failure are limited, but they must be distinguished from pulmonary dysfunction and also systemic problems. Heart disease often results in secondary respiratory signs (e.g., coughing or dyspnea); conversely, disease of the lung or its vasculature can result in secondary right heart disease (e.g., corpulmonale). It is rare to find in any individual instance all the signs and other abnormalities that may characterize a specific disease. More commonly, an animal will manifest only some of these signs, usually in a way that the clinical elements of the disease emerge over time rather than being grouped at the outset.

The definition of congestive heart failure is the failure of the left and/or right side of the heart to advance blood at a sufficient rate to meet the metabolic needs of the patient or to prevent blood from pooling within the pulmonary venous circulation.

Asymptomatic Heart Disease

At this level, a cardiac murmur or an ultrasound diagnosis of heart disease has occurred, but clinical signs are absent. Re-evaluation is the standard, and medication is not required.

Mild to Moderate Heart Failure

Clinical signs of heart failure are evident at rest or with mild exercise and adversely affect the quality of life. Typical signs of heart failure include exercise intolerance, cough, an increased respiratory rate, dyspnea, and mild to moderate ascites. Home treatment is often indicated at this stage.

Advanced Heart Failure

Clinical signs of advanced congestive heart failure are immediately obvious. These clinical signs could include respiratory distress (dyspnea), marked ascites, profound exercise intolerance, or hypoperfusion at rest. In most cases, hospitalization is mandatory.

Cardiomyopathy

Cardiomyopathy is a disorder of the heart in which the abnormality lies within the muscle tissue (myocardium). A secondary cardiomyopathy is a disease that affects the myocardium secondary to infectious, toxic, metabolic, or other disease processes. The majorities of cardiomyopathies diagnosed today are of unknown etiology (primary or idiopathic) and are currently classified in the literature as representing the hypertrophic or intermediate forms.

Primary cardiomyopathies are classified according to their morphologic appearance:

• Hypertrophic cardiomyopathy (HCM)

• Idiopathic dilated cardiomyopathy (DCM)

• Restrictive cardiomyopathy (RCM)

• Unclassified cardiomyopathies

Secondary causes of cardiomyopathy include:

• Nutritional (taurine deficiency)

• Metabolic (hyperthyroidism, acromegaly)

• Infiltrative (neoplasia, amyloidosis)

• Inflammatory (toxins, immune reactions, infectious agents)

• Genetic (hypertrophic cardiomyopathy is suspected)

• Toxic (doxorubicin)

• Hypertrophic cardiomyopathy (HCM)

Hypertrophic cardiomyopathy (Feline)

Electrocardiography: Left atrial enlargement (p-mitrale – widened P-waves) and left ventricular enlargement (increased R-wave amplitude and/or increased QRS duration) are present. Arrhythmias are frequent. Most cats with hypertrophic cardiomyopathy will have a sinus tachycardia. Atrial and ventricular arrhythmias may be present. Interventricular conduction deficits, such as left anterior fascicular block, are occasionally present.

Radiography: Variable enlargement of the cardiac silhouette is seen. Left atrial enlargement is often most prominent. The cardiac silhouette may be normal. Cats with congestive heart failure may demonstrate enlargement of the pulmonary veins, variable pulmonary edema, and pleural effusion.

Echocardiography: Left ventricular hypertrophy involving the left ventricular free wall and, usually to a greater degree, the interventricular septum is present.

References

Tilley, L.P., and Smith, F.W.K. (Eds): The Five Minute Veterinary Consult-Canine & Feline Medicine 4th Edition. Ames, Iowa, Wiley Blackwell Publishing, 2008.

Tilley, L.P., Smith, F.W.K., Oyama, M., and Sleeper, M.: Manual of Canine & Feline Cardiology, 4th Edition.Elsevier, St. Louis, 2008.

Kittleson, M.D., Kienle, R.D.: Small Animal Cardiovascular Medicine. Philadelphia, Mosby, 1998.