CONGESTIVE HEART FAILURE IN DOGS

Heart failure is a condition caused by the inability of the heart to maintain adequate cardiac output to meet the tissue's perfusion needs. The failing heart is unable to pump normal quantities of blood to the tissues of the body. Often heart failure leads to fluid retention in the lung and the body cavities, leading to congestive heart failure. Most cases of heart failure are associated with pulmonary edema, pleural effusion or ascites. This fluid accumulation can lead to shortness of breath and other problems such as coughing and difficult breathing. Congestive heart failure leads to inadequate blood flow to the tissues of the body, resulting in depression and fatigue. Accumulation of fluid often impairs breathing. When pulmonary edema or pleural effusion occurs, the condition can become life threatening.

DIAGNOSIS OF CONGESTIVE HEART FAILURE

ETIOLOGY AND RISK FACTORS

• Causes - Many causes exist for heart failure, including congenital defects of the heart, degeneration of the heart valves, cardiomyopathy, heartworm disease, diseases of the pericardium and arrhythmias.
• Risk factors
• Age - Older dogs tend to develop heart failure from abnormal function of the heart valves as the valve tissue degenerates.
• Breed/genetics - Giant breed dogs are predisposed to developing cardiomyopathy-related heart failure. Small breed dogs tend to develop heart failure associated with valve degeneration.
• Sex - No known risk
• Geographic/environmental - Since heartworm infection can lead to heart failure, those geographical areas endemic for heartworms may have an increased incidence of heart failure.
• Other medical disorders - Any underlying heart disease, hypertension, valvular disease and some endocrine disorders can predispose to heart failure.
• Prevention - In general, heart failure cannot be prevented. Once diagnosed, excessive physical activity or excitement, high heat/humidity and high salt foods or treats should be avoided.

HISTORY AND CLINICAL SIGNS

• Species affected - Dogs and cats (See in-depth Congestive Heart Failure in Cats)
• Presenting signs and historical problems - The signs of heart failure are related to increased activity of the nervous system and to increased concentrations of circulating hormones. Common signs include coughing, shortness of breath, dyspnea, weight loss and fatigue.

PHYSICAL EXAMINATION FINDINGS

• General
• Attitude - Mental status varies from mild lethargy to profound weakness. Some pets may be anxious and frantic if unable to breathe.
• Body condition - The body condition varies. Some pets are overweight. Some pets with chronic heart disease are thin due to muscle atrophy
• Vital signs - The temperature may be normal. The heart rate may be elevated and cardiac arrhythmias may be ausculted. Tachypnea is often present
• Mucous membranes - The gum color is often pale and cyanotic.
• Hydration status - Dehydration is possible due to renal insufficiency and a lack of water intake.
• Head and neck - The jugular veins may be distended and a jugular pulse may be present.
• Eyes - Often unremarkable except the conjunctiva may be pale.
• Oral cavity - Gum color is often pale and cyanotic. The remainder of the oral cavity is unremarkable
• Thorax (cardio-pulmonary) - The primary signs of CHF are associated with the cardiopulmonary system. Cardiac arrhythmias may be present. The dog is often dyspneic, and lung crackles and wheezes are often ausculted. A cough may be easily elicited on tracheal palpation. If pleural effusion is present, the lung sounds may be dull.
• Abdomen (gastrointestinal/urinary) - Hepatomegaly, and sometimes splenomegaly, may be palpable. If ascites is present, the abdomen may be distended.
• Reproductive system - Unremarkable
• Lymph nodes - Unremarkable
• Integumentary system - Unremarkable
• Neurologic examination - Mental status varies from anxiety to profound lethargy. Syncope may also occur. Many dogs with CHF tire easily.
• Musculoskeletal examination - Dogs with chronic heart disease may develop muscle atrophy.

DIAGNOSTIC STUDIES

• Special examination techniques - Arterial blood pressure should be determined. Hypertension and hypotension can occur in cats with congestive heart failure. Thoracocentesis or abdominal paracentesis may be necessary to provide relief from excessive fluid accumulation. In cases of dilated cardiomyopathy, a blood taurine level is recommended.
• Clinical laboratory tests
• CBC - The CBC is an important test used to rule out anemia as a complicating factor in heart failure.
• Serum biochemical tests - The biochemical profile is recommended to evaluate organ function, particularly renal function, and electrolyte levels. Azotemia is common in CHF.
• Urinalysis - Urinalysis is recommended to determine overall health of the pet. Oliguria is common.
• Serology/immunologic tests - Thyroid tests (T4, free T4, TSH) should be performed to exclude hypothyroidism as a complicating factor. A heartworm test is recommended in patients in endemic areas that are not on heartworm prevention. Animals on prevention that have not had a recent heartworm antigen test should also be tested.
• Microbiology - Blood cultures are recommended in suspected infection of the heart valves.
• Diagnostic imaging
• Radiographs (thoracic/abdominal) - A thoracic radiograph is usually needed to identify heart enlargement and fluid accumulation in the lung and to exclude some of the previously mentioned conditions that can mimic heart failure.
• Ultrasound (thoracic/ECHO) - Echocardiogram may be needed for a definitive diagnosis. The echocardiogram is usually the test of choice to establish the final diagnosis of the cause of congestive heart failure, but this examination may require referral to a specialist. Doppler studies more accurately diagnose blood flow disturbances.
• Electrodiagnostics
• ECG - An electrocardiogram (EKG) is often obtained to identify cardiomegaly and to determine the cardiac electrical activity.

DIAGNOSIS AND PROGNOSIS

• Differential diagnosis - The conditions most often confused with heart failure are diseases of the airways, the lung and the pleural space including:
• Tracheal collapse
• Chronic bronchitis
• Pneumonia
• Pulmonary fibrosis
• Heartworm disease
• Pulmonary neoplasia
• Pleural effusion
• Recommended tests - Thoracic radiographs and echocardiogram
• Summary of diagnostic criteria - The results of the recommended tests are described above.
• Prognosis - The prognosis varies depending on the cause and severity of the heart failure. Survival over one year after initial heart failure is common if properly treated. If severe heart failure occurs, the life expectancy averages 3 to 9 months.

TREATMENT OF CONGESTIVE HEART FAILURE

TREATMENT PRINCIPLES

The principles of therapy for congestive heart failure include improving heart function, preventing fluid accumulation, preventing further deterioration of the heart muscle and antagonizing chemicals and hormones produced in excessive quantities in heart failure. Rarely is it possible to treat the heart disease. The most important causes of heart failure in dogs are valve degeneration and cardiomyopathy. Heart failure caused by pericardial effusion is not treated by drugs but instead requires drainage of the fluid or removal of a portion of the pericardial membrane. Congenital heart defects should be referred to a specialist for management.

INITIAL/HOSPITAL THERAPY

• Initial treatment for heart failure may require hospitalization with a diuretic, oxygen and other hospital-administered treatments. Vasodilator drugs, such as nitroglycerine (1/2 to 1 1/2 inches of paste on skin s.i.d. to b.i.d.), may be administered. In some forms of heart failure, the use of dobutamine or other potent stimulators of the heart muscle may be necessary. Pleural effusion may require thoracocentesis.
• Treatment usually includes a diuretic such as furosemide. The dose will vary depending on the severity of the pulmonary edema. In severe dyspnea, an initial dose of 4 to 6 mg/kg is given IM or IV. Then the dose can be reduced to 1 to 2 mg/kg IV or IM b.i.d. to q.i.d. Diuretics are usually prescribed for home care to prevent fluid retention, dosed at 1 to 4 mg/kg s.i.d. to t.i.d. The dose must be sufficient to prevent fluid retention but, at the same time, it cannot be so high as to cause kidney failure or excessive loss of potassium.
• Other diuretics may be prescribed in selected patients. For example, spironolactone (2 to 4 mg/kg s.i.d. to b.i.d.) prevents fluid retention and may protect the heart muscle from further damage in dilated cardiomyopathy.
• A potassium supplement may be recommended in some patients.
• Most patients with chronic heart failure are treated with an angiotensin-converting enzyme inhibitor such as enalapril or benazepril. Enalapril (0.25 to 0.5 mg/kg s.i.d. to b.i.d.), benazepril (0.5 mg/kg s.i.d. to b.i.d.) and related drugs block some of the harmful hormones that circulate in heart failure to prolong life and reduce clinical symptoms in canine heart failure. Dosing is critical as these drugs can lower blood pressure excessively or lead to kidney failure.
• The diet may be modified to limit sodium intake and prevent fluid retention. Specialized diets are available for this purpose though some senior diets are also relatively low in sodium.
• Digoxin is prescribed in some patients. The dose of this drug must be critically determined to prevent side effects such as loss of appetite and vomiting. The daily dose of digoxin is 0.01 to 0.015 mg/kg divided twice daily.
• Dietary supplements are used in some forms of cardiomyopathy. The amino acid taurine is sometimes prescribed for cardiomyopathy in spaniel breeds. L-carnitine is sometimes recommended for treatment of dilated cardiomyopathy. Other nutritional supplements, such as vitamin E and coenzyme Q10, are recommended by some, but there is no evidence of their benefit in heart failure in dogs.
• Special treatments are needed for some causes of heart failure. Anti-arrhythmic drugs are used to control the heart rhythm. Beta-blockers, such as metoprolol, propranolol or atenolol, may be prescribed to control heart rate, to control arrhythmias and protect the heart muscle. Calcium channel blockers, such as the drug diltiazem or amlodipine, are used in some circumstances. Direct vasodilator drugs are sometimes prescribed for dogs with advanced heart failure. These treatments are recommended in special circumstances, and the use of some of these drugs is best guided by a specialist.

LONG-TERM/HOME THERAPY

Medications are continued as described above. The pet should be monitored for appetite, exercise capacity and interest in family activities. Any breathing difficulty should prompt an examination.

FOLLOW-UP CARE

Periodic measurement of arterial blood pressure is recommended. Blood work should be performed to monitor renal function and electrolytes. Patients on digoxin should have digoxin levels monitored. Thoracic radiographs should be repeated to evaluate for pulmonary edema or pleural effusion. An electrocardiogram is recommended if there is a heart arrhythmia.