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Basics ⬇

Basics

Definition

Failure of the 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 systemic venous circulation.

Pathophysiology

  • High hydrostatic pressure leads to leakage of fluid from venous circulation into the pleural and peritoneal space and potentially into the pericardium and interstitium of peripheral tissue.
  • When fluid leakage exceeds ability of lymphatics to drain the affected areas, pleural effusion, ascites, pericardial effusion, and peripheral edema develop.

Systems Affected

All organ systems can be affected by either poor delivery of blood or the effects of passive congestion from backup of venous blood.

Genetics

  • Some congenital cardiac defects have a genetic basis in certain breeds.
  • Arrhythmogenic right ventricular cardiomyopathy appears to have a genetic basis in boxer dogs.

Incidence/Prevalence

Common

Geographic Distribution

Syndrome seen everywhere, but prevalence of various causes varies with location.

Signalment

Species

Dog and cat

Breed Predilections

Varies with cause

Mean Age and Range

Varies with cause

Predominant Sex

Varies with cause

Signs

General Comments

  • Signs vary with underlying cause and between species.
  • Pleural effusion without ascites and hepatomegaly is rare in dogs with R-CHF.
  • Ascites without pleural effusion is rare in cats with R-CHF.
  • Small volume pericardial effusion without tamponade is relatively common in cats with R-CHF.
  • Interstitial peripheral edema is a rare manifestation of R-CHF in both species.

Historical Findings

  • Weakness
  • Lethargy
  • Exercise intolerance
  • Abdominal distension
  • Dyspnea, tachypnea

Physical Examination Findings

  • Jugular venous distention
  • Hepatojugular reflex
  • Jugular pulse in some animals
  • Hepatomegaly
  • Ascites common in dogs and rare in cats with R-CHF
  • Possible regurgitant murmur in tricuspid valve region or ejection murmur at left heart base (pulmonic stenosis)
  • Muffled heart sounds if animal has pleural or pericardial effusion
  • Weak femoral pulses
  • Rapid, shallow respiration if animal has pleural effusion or severe ascites
  • Peripheral edema (infrequent)

Causes

Pump (Myocardial) Failure of Right Ventricle

  • Idiopathic dilated cardiomyopathy
  • ARVC
  • Hypertrophic cardiomyopathy (cats)
  • Restrictive cardiomyopathy (cats)
  • Trypanosomiasis
  • Doxorubicin cardiotoxicity
  • Chronic hyperthyroidism

Volume Overload of Right Ventricle

  • Chronic AV valve (mitral ± tricuspid) insufficiency caused by endocardiosis
  • Tricuspid valve dysplasia

Pressure Overload of Right Ventricle

  • Heartworm disease
  • Chronic obstructive pulmonary disease with pulmonary hypertension
  • Pulmonary thromboembolism
  • Pulmonic stenosis
  • Tetralogy of Fallot
  • Right ventricular tumors
  • Primary pulmonary hypertension

Impediment to Right Ventricular Filling

  • Pericardial effusion (tamponade)
  • Constrictive/restrictive pericarditis
  • Right atrial or caval masses
  • Tricuspid stenosis
  • Cor triatriatum dexter

Rhythm Disturbances

  • Bradycardia, generally complete atrioventricular block
  • Tachyarrhythmias, generally sustained supraventricular tachycardia

Risk Factors

  • No heartworm prophylaxis
  • Offspring of animal with right-sided congenital cardiac defect
  • Conditions that augment demand for cardiac output (e.g., hyperthyroidism, anemia, pregnancy)

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Must differentiate from other causes of pleural effusion and ascites; generally requires a complete diagnostic work-up that includes CBC, biochemistry profile, heartworm test, thoracentesis or abdominocentesis with fluid analysis and cytologic examination, and, sometimes, thoracic and abdominal ultrasound.
  • Animals with ascites or pleural effusion due to heart failure should have jugular venous distension.

CBC/Biochemistry/Urinalysis

  • CBC usually normal; animals with heartworm disease may have eosinophilia.
  • Mild to moderately high ALT, AST, and ALP because of passive congestion of the liver; bilirubin generally normal.
  • Prerenal azotemia in some animals.

Other Laboratory Tests

Heartworm test may be positive.

Imaging

Thoracic Radiographic Findings

  • Right heart enlargement in some animals
  • Dilated caudal vena cava (diameter greater than the length of the vertebra directly above the heart)
  • Pleural effusion (especially cats)
  • Hepatosplenomegaly and possible ascites (especially dogs)

Echocardiography

  • Findings vary with underlying cause. Especially useful for documenting congenital defect, cardiac mass, and pericardial effusion.
  • Abdominal ultrasound reveals hepatomegaly with hepatic vein dilation, flow reversal in the hepatic veins (Doppler) and, possibly, ascites.

Diagnostic Procedures

Electrocardiographic Findings

  • Small (<1 mV) QRS complexes in all frontal axis leads if animal has pericardial or pleural effusion.
  • Electrical alternans or elevated ST segment in animal with pericardial effusion.
  • Evidence of right heart enlargement (e.g., tall [>0.4 mV] P waves in lead II, deep S waves in leads I, II, aVF, and right axis deviation).
  • Atrial or ventricular arrhythmias.
  • ECG may be normal.

Abdominocentesis

Analysis of ascitic fluid in patients with R-CHF generally reveals modified transudate with a total protein >2.5 mg/dL.

Thoracentesis

  • Cats with pleural effusion associated with R-CHF may have transudate, modified transudate, or chylous effusion.
  • Dogs with pleural effusion and R-CHF may have transudate or modified transudate.

Central Venous Pressure

Central venous pressure is high (>9 cmH2O) or rises dramatically to that level and remains elevated for more than an hour following a fluid bolus (e.g., 5–10 mL/kg IV).

Pathologic Findings

  • Cardiac findings vary with disease.
  • Hepatomegaly in animals with centrolobular necrosis (chronic condition).

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

Most animals treated as outpatients unless dyspneic or collapsed (e.g., significant pleural or pericardial effusion).

Nursing Care

Thoracentesis and abdominocentesis may be required periodically for patients no longer responsive to medical management or for those with severe dyspnea due to pleural effusion or ascites.

Activity

Restrict activity

Diet

Restrict sodium moderately; severe sodium restriction is indicated for animals with advanced disease.

Client Education

  • With few exceptions (e.g., in heartworm disease, arrhythmias, hyperthyroidism, and idiopathic pericardial effusion), R-CHF is not curable.
  • Most patients improve with initial treatment but often have recurrent failure.

Surgical Considerations

  • Surgical intervention or balloon valvuloplasty is indicated to treat certain congenital defects such as pulmonic stenosis or cor triatriatum dexter and Amplatz occluder placement for morphologically appropriate atrial septal defects.
  • Pericardiocentesis or pericardectomy is done if animal has pericardial effusion.
  • Removal of heartworms from the heart via the jugular vein in dogs with caval syndrome.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

Drugs should be administered only after a definitive diagnosis is made.

Diuretics

  • Furosemide (1–2 mg/kg q8–24h) or another loop diuretic is the initial diuretic of choice. Diuretics are indicated to remove excess fluid accumulation.
  • Spironolactone (2 mg/kg PO q12–24h) increases survival in humans with heart failure. Use in combination with furosemide.

Vasodilators

  • ACE inhibitors such as enalapril (0.5 mg/kg q12–24h) or benazepril (0.25–0.5 mg/kg q24h) are helpful in DCM and chronic AV valve insufficiency.
  • Sildenafil (0.5–1 mg/kg PO q12h up to 2–3 mg/kg q8h) may be beneficial in the setting of pulmonary hypertension.

Pimobendan

  • Calcium sensitizer that acts as an inodilator, causing arterial vasodilation and increases myocardial contractility.
  • Especially useful in myocardial failure.
  • Dose-0.25–0.3 mg/kg PO q12h.

Digoxin

  • Digoxin (dogs, 0.22 mg/m2 q12h; cats, 0.01 mg/kg q48 h) is used in animals with myocardial failure (e.g., dilated cardiomyopathy) and atrial fibrillation.
  • Digoxin is also indicated in animals with refractory CHF that have supraventricular arrhythmias (e.g., sinus tachycardia, atrial fibrillation, and atrial or junctional tachycardia).

Contraindications

  • Avoid diuretics in patients with pericardial effusion/tamponade.
  • Avoid vasodilators in patients with pericardial effusion or fixed outflow obstructions.

Precautions

  • ACE inhibitors and arterial dilators must be used with caution in patients with possible outflow obstructions.
  • Pulmonary hypertension, hypothyroidism and hypoxia increase risk for digoxin toxicity; hyperthyroidism diminishes effects of digoxin.
  • ACE inhibitor and digoxin-use cautiously in patients with renal disease.
  • Dobutamine-use cautiously in cats.
  • Spironolactone-may cause facial pruritis in cats.

Possible Interactions

  • Combination of high-dose diuretics and ACE inhibitor may alter renal perfusion and cause azotemia.
  • Combination diuretic therapy promotes risk of dehydration and electrolyte disturbances.

Alternative Drug(s)

  • Patients unresponsive to furosemide, spironolactone, vasodilator, pimobendan and digoxin (if indicated) may benefit from triple diuretic therapy by adding a thiazide diuretic, or substitution of torsemide for furosemide, generally at 0.1–0.2 mg of torsemide for each 1 mg of furosemide previously administered.
  • Potassium and magnesium supplementation if deficiency documented; use potassium supplements cautiously in animals receiving ACE inhibitor or spironolactone.
  • Treat arrhythmias if clinically indicated.
  • Taurine supplementation in cats with DCM and dogs with DCM and taurine deficiency.
  • Carnitine supplementation may help some dogs with DCM (e.g., cocker spaniels and boxers).

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Monitor renal status, electrolytes, hydration, respiratory rate and effort, body weight, and abdominal girth (dogs).
  • If azotemia develops, reduce the diuretic dosage. If azotemia persists and the animal is also on an ACE inhibitor, reduce or discontinue this drug. If azotemia develops, reduce the digoxin dosage to avoid toxicity.
  • Monitor ECG periodically to detect arrhythmias.
  • Monitor digoxin concentrations. Normal values are 0.5–1.5 ng/mL for a serum sample obtained 8–10 hours after a dose is administered.

Possible Complications

  • Pulmonary thromboembolism
  • Arrhythmias
  • Electrolyte imbalances
  • Digoxin toxicity
  • Azotemia and renal failure

Expected Course and Prognosis

Prognosis varies with underlying cause.

Miscellaneous ⬆

Miscellaneous

Age-Related Factors

  • Congenital causes seen in young animals.
  • Degenerative heart conditions and neoplasia generally seen in old animals.

See Also

Abbreviations

  • ACE = angiotensin converting enzyme
  • ALP = alkaline phosphatase
  • ALT = alanine aminotransferase
  • ARVC = arrhythmogenic right ventricular cardiomyopathy
  • AST = aspartate aminotransferase
  • AV = atrioventricular
  • DCM = dilated cardiomyopathy
  • ECG = electrocardiogram
  • L-CHF = left-sided congestive heart failure
  • R-CHF = right-sided congestive heart failure

Suggested Reading

Stickland KN. Pathophysiology and therapy of heart failure. In: Smith FWK, Tilley LP, Oyama MA, Sleeper MM, eds., Manual of Canine and Feline Cardiology, 5th ed.St. Louis, MO: Saunders Elsevier, 2015 (in press).

Authors Francis W.K. Smith, Jr. and Bruce W. Keene

Consulting Editors Larry P. Tilley and Francis W.K. Smith, Jr.

Client Education Handout Available Online