Definition of Heart Failure

Heart failure is the pathophysiologic state where abnormal cardiac structure or function prevents the heart from pumping blood at a rate necessary for metabolic tissue requirements, or does so at elevated filling pressures. Many diseases may be causative. Systematic examination is required to: 1) establish a specific anatomic diagnosis, 2) determine the extent of functional cardiac impairment, and 3) develop therapeutic strategies. Despite advances in imaging technologies and an increasing array of diagnostic tests, the cornerstone of diagnosis is careful clinic evaluation coupled with radiography and ECG.

Signalment

Useful information can sometimes be obtained from the age, breed, and gender. Young animals with murmurs for example, are highly suspect for having congenital anomalies. In contrast, acquired lesions (e.g., thyrotoxicosis, myxomatous valvular degeneration) are most commonly encountered in middle aged to older pets. Breed predispositions for certain types of congenital heart disease are well established given the inherited nature of many congenital abnormalities. Some reported breed predilections include: patent ductus arteriosus-toy and miniature poodle, German shepherd, Shetland sheep dog, collies, English Springer spaniel, Maltese, Pomeranian; aortic stenosis-Newfoundland, golden retriever, Rottweiler, Boxer, German shepherd; pulmonic stenosis-English bulldog, beagles, Samoyed, miniature schnauzer, terriers; ventricular septal defects-English bulldogs. Gender predisposition occurs for certain diseases such as PDA, sick sinus syndrome (females), and cardiomyopathy and chronic acquired valvular disease (males).

The History

A detailed general medical history should be followed by specific questions related to the owners complaint and suspected disease. The history is essential to help determine onset and severity of clinical signs, rate and degree of disease progression or regression, assessing client compliance in following a treatment plan, determine the degree of therapeutic success, and discover contributing or additional medical disorders. A history of congenital heart disease, heart failure, or heart murmur in the pets lineage should be obtained in young animals and is helpful in establishing a diagnosis of congenital anomalies. Concern should focus on nutrition and diets; coughing and dyspnea (date of onset, progression, response to exertion); exercise tolerance; the effect of activity on clinical signs; episodic weakness or syncope; weight gain, weight loss, abdominal distension; underlying systemic or metabolic diseases; and past or current medications, including dosages, frequency of administration, and clinical responses if any.

Clinical Signs of Heart Disease

Observation of the pet at rest and during exertion can provide useful diagnostic information and help support or refute the client's stated clinical complaints. Cardinal signs of congestive heart failure include dyspnea and tachypnea, exercise related fatigue, cyanosis, syncope and episodic weakness. The clinician must keep in mind that these signs may represent the expression of many systemic and metabolic diseases as well as cardiopulmonary disorders. For example, sudden dyspnea could suggest pulmonary edema, pneumothorax, pneumonia, pulmonary embolism, or airway obstruction, as well as severe pleural effusion, anxiety, severe acidosis, or pain. In heart failure, dyspnea is an expression of pulmonary venous and capillary hypertension and may occur with exercise during early disease stages, or at rest in advanced cases. Syncope or episodic weakness may accompany excitement or exertion with aortic stenosis, hypertrophic cardiomyopathy, and pericardial tamponade for example. In small breed dogs with advanced mitral regurgitation, syncope is also often precipitated during coughing and excitement. Brady or tachyarrhythmias may contribute or be causative in and of themselves. Cyanosis is seen as a bluish coloration of skin and mucous membranes occurring when there is increased quantities of reduced hemoglobin. It may result from decreased arterial oxygen saturation caused by right-to-left shunting of blood from congenital heart disease, or impaired pulmonary function. Coughing is one of the most common signs in cardiorespiratory disease. Causes include a variety of infectious, inflammatory, neoplastic and allergic conditions of the respiratory system. Cardiovascular dysfunction resulting in coughing includes disorders which cause pulmonary venous and capillary hypertension, interstitial and alveolar pulmonary edema, pulmonary infarction, or tracheobronchial compression. Most coughs sound alike and many animals have concurrent cardiac and respiratory diseases. Other signs may be present and related to heart failure or multi-organ involvement (e.g., weight loss associated with cardiac cachexia with long standing mitral regurgitation and DCM in dogs; ascites and peripheral edema may result in weight gain).

The Physical Examination

A thorough and detailed general examination is a prerequisite for evaluation of the heart. Cardiac manifestations of systemic disease must be identified in order to appropriately treat precipitating underlying conditions. Examination of the cardiovascular system involves 1) external patient inspection at rest and during activity (when indicated) to assess respiratory effort and respiratory passages; 2) assessment of the larynx and neck for laryngeal obstruction, and palpation of the neck for tracheal conformity and masses; 3) examination of the oral cavity; 4) observation of the external jugular veins for abnormal distension or pulsations; 5) palpation of the femoral arterial pulse for strength, regularity and contour (normal, hypokinetic, hyperkinetic, etc.); 6) palpation of the precordium for the cardiac apex beat (location, strength of pulsation, point of maximal impulse) and thrills (vibratory sensations which are palpable manifestations of loud, harsh, low frequency murmurs); 7) auscultation of the heart and lungs; 8) thoracic percussion.

MANAGEMENT OF HEART FAILURE

An integrated approach is directed to provide individualized therapy for each patient based upon the history, physical examination, clinical pathology, ECG, radiography and echocardiography. Goals of therapy prolong survival, enhance quality of life, and reduce morbidity (hospitalizations, repeat heart failure).

Remove or Stabilize the Underlying Cause of Heart Failure

Search for reversible causes of heart failure. Examples include taurine deficiency dilated cardiomyopathy (now rare in cats and dogs); American cocker spaniel dogs in heart failure may be also be taurine deficient. Some boxers and Doberman pinschers have had documented carnitine deficiency. Feline hyperthyroidism is a common cause of reversible cardiac dysfunction. Anemia may precipitate CHF in marginally compensated animals. So will severe brady or tachyarrhythmias. Heartworm disease is often a treatable cause of right-sided CHF. Volume overload secondary to patent ductus arteriosus is usually readily correctable by surgical or coil occlusion techniques. A number of systemic and metabolic disorders may cause or contribute to heart failure including endocarditis, myocarditis, pheochromocytoma, diabetes, and growth hormone excess.

Control the Congestive Heart Failure State

Pharmacologic therapies are directed to:

1.  Reduce Cardiac Workload

a.  Cage rest/exercise reduction

2.  Reduce Cardiac Preload (Excess Water Retention)

a.  Diuretics (loop agents)

b.  2% nitroglycerin ointment

c.  ACE inhibitors

d.  Sodium nitroprusside

e.  Low sodium diets

3.  Reduce Cardiac Afterload (Resistance to Ventricular Outflow)

a.  ACE Inhibitors

b.  Hydralazine

c.  Sodium nitroprusside

d.  Calcium channel blockers (Amlodipine)

4.  Arrhythmia Management

a.  Antiarrhythmics: Class I Agents (procainamide, quinidine, lidocaine, mexiletine, tocainide); Class II Agents (beta blockers); Class III Agents (amiodarone; sotalol); Class IV Agents (calcium channel blockers)

b.  Digitalis glycosides

c.  Pacemaker therapy

5.  Improve Cardiac Contractility (Ventricular Pumping Performance)

a.  Sympathomimetics (dobutamine, dopamine)

b.  Digitalis glycosides

c.  Phosphodiesterase III inhibitors; (amrinone, milrinone)

d.  Nutraceuticals (Taurine; L-Carnitine; others)

6.  Acutely Reduce Excessive Fluid Retention (Mechanical Fluid Removal)

7.  Close Clinical Monitoring to Reduce Morbidity

a.  Physical Examinations (include body weight) ;

b.  Electrocardiography

c.  Thoracic Radiography

d.  Clinical Pathology (biochemical profile; Serum T4)

e.  Echocardiography

f.  Arterial blood pressure

Drugs Used To Manage Heart Failure (Adapted from Keene, BW*)

Cardiac Drug Actio Dog/C Route General Dosage Target [Plasma] (Trademark) n at Recommendation

Action Codes: 1) Positive Inotrope (increases contractility); 2) Negative Inotrope (decreases contractility); 3) Positive Chronotrope (increases heart rate and enhances AV conduction); 4) Negative Chronotrope (decreases heart rate and slows AV conduction)/Supraventricular antiarrhythmic; 6) Beta adrenergic receptor blocker; 7) Calcium channel blocker; 8) Preload Reducer; 9) Afterload Reducer; 10) Angiotensin Converting Enzyme Inhibitor; 11) Narcotic Analgetic; 12) Ventricular Antiarrhythmic; 13) Bronchodilator