Variation of d-dimer values as assessment of pulmonary thromboembolism during adulticide treatment of heartworm disease in dogs

Dirofilaria immitis adult worms lodged in the pulmonary arteries are the causative agent of heartworm disease, characterized by endarteritis and obstruction of the blood flow. Dying worms form embolic fragments which trigger thrombosis. Thus, pulmonary thromboembolism is an inevitable consequence of successful adulticide therapy. Clinical signs of pulmonary thromboembolisms are highly variable and non-specific, and its diagnosis is often difficult to obtain. The d-dimer assay is considered the marker of choice for dogs with a suspicion of pulmonary thromboembolism. The aim of the present study was to evaluate the variation of d-dimer and platelets in 15 heartworm-infected dogs during the adulticide treatment with ivermectin, doxycycline and melarsomine. Nine dogs were considered to have a low parasite burden and 6 had a high burden. Measurements were carried out on days 0, 60, and afterwards weekly on days 67, 75, 82, 91, 98, 106, 113, 120, and finally on day 271 after treatment. 40% of dogs showed pathological concentrations of d-dimer and 40% showed slight or mild thrombocytopenia on day 0. The levels of d-dimer decreased by day 60, probably due to the joint action of the ivermectin, doxycycline and exercise restriction. All dogs with high parasite burden showed elevated values of d-dimer on several occasions during the treatment, reaching the highest values the first and second week after the injections of melarsomine. Only 33.3% of the dogs with low parasite burden showed elevated d-dimer levels at some point during the treatment, and all of them showed undetectable levels from the third week after the first injection of melarsomine. On day 271, all dogs showed undetectable levels of d-dimer. There was no correlation between thrombocytopenia and levels of d-dimer during the treatment. The evaluation of serum d-dimer appears to be a supportive test in the assessment and monitoring of pulmonary thromboembolism in dogs with heartworm disease during the adulticide treatment.