Introduction

• Cause:retrograde migration of adult heartworms from the pulmonary artery into the right ventricle, right atrium and vena cava.
• Signs:acute onset weakness, lethargy, inappetence, respiratory distress and commonly hemoglobinuria.
• Diagnosis:echocardiography, thoracic radiographs, electrocardiography.
• Treatment:surgical removal of the obstructive mass of heartworms.
• Prognosis:guarded to poor, even with surgical removal reported mortality ranges from 14% to 42%.

Pathogenesis

Etiology

• Dirofilaria immitis Dirofilaria immitis.

Pathophysiology

• Adult heartworms move in a retrograde fashion from the pulmonary artery into the right ventricle, right atrium and vena cava.
• The obstructive worm mass results in an acute onset of tricuspid insufficiency. This, in combination with concurrent pulmonary hypertension Cor pulmonale from chronic heartworm disease, results in signs of low cardiac output and right sided congestive heart failure Heart: congestive heart failure.
• RBC hemolysis ensues as the cells pass through the enmeshed heartworms. Low grade disseminated intravascular coagulation (DIC) Disseminated intravascular coagulation may contribute to schistocytosis.
• Hepatotoxicity Liver: acute disease and nephrotoxicity Nephrotoxicosis may result from a combination of low cardiac output and passive congestion.

Timecourse

• Experimentally, inoculation of 16 dogs with 200 infective L3 larvae yielded caval syndrome in a total of 9 dogs after a mean of 12.3 months post-infection (range 7-17 months).

Diagnosis

Treatment

Outcomes