What’s the Protocol?

bsoManaging Dogs with Severe Heartworm Disease

Marisa Ames,DVM, DACVIM (cardiology)
Associate Professor
Colorado State University,
College Of Veterinary Medicine

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Managing Dogs with Severe Heartworm Disease

Fortunately, most infected dogs have no clinical signs or only mild signs of heartworm disease (HWD) and tend to undergo adulticide therapy with few major complications. The likelihood of complications associated with HWD increases with the chronicity of infection. Prognosis is dependent on stabilization, the ability to administer subsequent adulticide therapy and the ability of the family to commit to treatment of chronic conditions. Following is a brief overview of these complications, including clinical signs, diagnosis and treatment. For information on drug dosages, please visit www.heartwormsociety/treating-severe-HWdisease.

What it is: Inflammation in the pulmonary parenchyma due to HWD
Cause: Death of microfilaria and/or the presence of adult worms
Common clinical signs: Cough, tachypnea
How to diagnose: Radiographs typically show unstructured interstitial infiltrate
Treatment: Steroid therapy, rest and oxygen as needed

What it is: Thrombus formation from dead and dying worms; thrombi and
worm fragments may stay in place or embolize
Cause: Worm death, which may occur 3-21 days after adulticide administration
or spontaneously
Common clinical signs: Lethargy, shortness of breath, cyanosis and/or syncope
How to diagnose: Echocardiographic assessment for PH, which is usually present (see above);
rarely may see thrombus in pulmonary trunk or branches
Treatment: Sildenafil, rest, corticosteroids and oxygen if needed; anticoagulant therapy when
there is high suspicion of HW-PTE (e.g. cyanosis and collapse 3-21 days after adulticide or
visualization of thrombus) and no contraindications

What it is: PH puts chronic pressure load on the right heart, leading to
right ventricular failure
Common clinical signs: Lethargy, abdominal distension, shortness of
breath, jugular venous distension and/or pulsation, syncope
How to diagnose: Echocardiography shows right-sided heart remodeling;
presence of transudate or modified transudate cavitary effusions
Treatment: Mechanical removal of effusions, diuretic, pimobendan, and sildenafil (to treat
underlying PH); also consider spironolactone and/or angiotensin-converting-enzyme inhibitor

What it is: PH and decreased right ventricular function allow worms to relocate
to the right heart and cavae
Cause: Worms cause disruption of the tricuspid valve and/or cavae, decreasing
venous return to the right heart, reducing stroke volume and cardiac output;
worm mass can also lead to microangiopathic anemia and pigmenturia
Common clinical signs: Lethargy, right-sided systolic murmur, syncope,
collapse, pallor and pigmenturia
How to diagnose: Clinical signs of above in dogs known to be heartworm+
Treatment: Stabilization (IV fluids, vasopressors, blood products), worm extraction, and
management of specific related issues (e.g. pneumonitis, PH or R-HF)