Canine Dirofilarial Hemoglobinuria : Changes in Right Heart hemodynamics and Heartworm Migration from Pulmonary Artery towards Right Atrium following β₁-blocker Administration

Abstract

In order to investigate whether heartworm migration was induced or not, metoprolol, an anti-hypertensive agent with a cardioselective β-adrenoceptor blocking action (β₁-blocker), was administered to heartworm-infected dogs under general anesthesia. After about 8mg/kg body weight of metoprolol administration, heart rate and right cardiac output reduced significantly in all 6 dogs. Heartworms migrated from the pulmonary artery to the right atrium in 5 dogs, and hurdled the pulmonary valve transiently in 1 dog on two-dimensional echocardiogram. However, the worms returned to the pulmonary artery in a short time in 4 cases. The pressures at the right ventricle and the pulmonary artery and stroke volume did not show uniform changes after the administration. It was considered that the decrease of heart rate and cardiac output, namely, decreased blood flow volume and velocity at the pulmonary artery by metoprolol administration induced the heartworm migration in the direction opposite blood flow.