Heartworms in a Young Dog

Patient Information:

Species/Breed: Canine/Chihuahua

Age: Estimated just under 1 year old

Gender: Male

Weight: 6.6 lbs

History:

The patient was adopted about 3 months prior to presentation with no prior history. The patient was presented for lethargy, disorientation (walking into walls), inappetence, coughing, and syncopal episodes. An echocardiogram was recommended to rule out a cardiac cause for syncope.

Pertinent Echocardiogram Findings:

The tricuspid valve appears normal with mild tricuspid regurgitation. The TR velocity is increased, suggesting severe pulmonary arterial hypertension, and the right ventricle appears subjectively dilated.

Multiple parallel lines are seen in the right atrium and ventricle crossing the tricuspid valve, consistent with adult heartworms.

Image 1: Heartworms within the right heart (near field) seen in the right parasternal long axis 4 chamber view

Image 2: Heartworms within the right heart (left screen) seen in the left apical 4 chamber view

Image 3: Heartworms seen falling from the right atrium into the right ventricle in the left parasternal cranial right atrial view.

Diagnosis:

In view of the clinical signs and echocardiogram findings, caval syndrome is suspected with the adult heartworms migrating from the pulmonary arteries into the right heart, causing obstruction and cell lysis. Hemoglobinuria is likely.

There is severe pulmonary hypertension present, which is concerning for the long term.

Recommendations:

Pimobendan (0.2 - 0.3 mg/kg every 12 hours) and sildenafil (1 - 3 mg/kg every 8 hours) should be started. In some cases, this can cause the worms to move back into the pulmonary arteries.

Urgent referral to a specialist center for heartworm extraction is strongly recommended.

Longer-term treatment should include doxycycline and prednisolone as per the American Heartworm Association recommendations:

• Exercise restriction
• Heartworm prevention
• Doxycycline at 10 mg/kg BID for 4 weeks
• Prednisolone 0.5 mg/kg BID, tapering every 7 days
• Melarsomine on days 60, 90, and 91, with repeated tapering of prednisolone after injection
• Testing on days 120 and 365

Recommend a recheck echocardiogram in 3 months to assess any resolution of the pulmonary hypertension.

Follow-Up:

The owner declined referral for heartworm extraction. The patient has been treated medically and is currently doing well.

Sonographer: Cary Sparkman, DVM

Special thanks to Crater Road Veterinary Hospital and Simon Swift, MA, VetMB, CertSAC, DipECVIM-CA (Cardiology), MRCVS with DVMSTAT