Issues

Congestive Heart Failure, Right-Sided

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 the 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

 

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

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

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

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.

 

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.

 

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

 

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