How sildenafil and pimobendan help move heartworms in dogs

Abstract

Four dogs, referred for management of heartworm (HW) disease, were found to have HWs entangled in their tricuspid valve apparatus. None of the dogs were actively hemolyzing or showed signs of acute cardiovascular collapse that would have necessitated emergency transvenous HW extraction, and surgery was not performed at time of presentation. The dogs received pimobendan and sildenafil within 24 h of identifying HW in the tricuspid valve apparatus, and the HW moved to the pulmonary arteries within 2 days in most cases (median 2 days, range 1-14 days). All dogs survived to discharge from the original hospital admission and were subsequently treated with adulticide (melarsomine) without complication. All dogs were HW antigen negative 6 months after their last melarsomine injection. Four dogs appeared to respond positively to medical management aimed at decreasing pulmonary arterial pressure and improving the right ventricular function, but movement of HW out of the heart for other reasons cannot be excluded. This therapeutic option is not advised when dogs with HW disease are presented for acute collapse, ongoing hemolysis, and hypotension as surgical extraction is still considered the best option in these cases. It remains unknown if medical management is a safe option for all dogs with intracardiac HW without clinical signs of caval syndrome. Controlled prospective studies are required to determine the efficacy and safety of this treatment regimen in comparison with surgical extraction.