Hemodynamic Alterations in Dogs with Shock Induced by Intravenous Injection of Heartworm Extract.

Abstract

ABSTRACT. To elucidate one way of the shock mechanisms, the hemodynamic alterations were examined in 7 dogs with heartworm (HW) extract-induced shock. The first alteration observed after injection of HW extract was a decrease in right ventricular end-diastolic pressure (RVEDP). After that, left ventricular (LV) end-diastolic pressure, LV systolic pressure, and LV dp/dt fell significantly, followed by a decrease in the cardiac output of all dogs to below the detectable level (1.00 l/min). Since RVEDP depends on blood flow into the right ventricle, the decrease in RVEDP means a reduction in venous return. Therefore, this study showed that the first trigger of a decrease in blood pressure in HW extract-induced shock is the reduction in venous return.KEY WORDS: heartworm, hemodynamics, shock.J. Vet. Med. Sci. 63(2): 179-182, 2001 It is well known that the administration of prophylactics for Dirofilaria immitis (heartworm, HW), such as diethylcarbamazine (DEC) [1,14], milbemycin D [15], and ivermectin [5], induces shock in dogs with microfilaremic HW infection (mf-induced shock). In human beings, treatment of onchocerciasis and lymphatic filariasis with DEC and ivermectin also induces shock, which leads to the failure of many control programs [3,12]. On the other hand, shock resulting from HW adult worms occurs clinically when such worms are injured during surgical treatment of the host [6,7]. However, to the authors' knowledge, the mechanisms of these shocks in both veterinary medicine and human medicine have not yet been clarified. Thus, there is a need to elucidate the mechanisms of such shocks in order to improve prophylaxis and treatment of filariasis, not only in veterinary but also in human medicine. We have previously reported that intravenous injection of HW extract induces shock in dogs irrespective of HW infection [8][9][10]. The clinicopathologic and pathologic findings of HW extractinduced shock were fundamentally similar to those associated with mf-induced shock [8][9][10]. Therefore, investigation of the mechanisms of HW extract-induced shock would be useful in elucidating the mechanisms of shock due to injured adult worms and mf-induced shock.The main clinical findings of HW extract-induced shock were hyperemia of the mucous membranes, palpitation, and tachypnea observed immediately after intravenous injection of HW extract, followed by collapse due to a sudden decrease in blood pressure 5 to 30 min after injection [9]. During collapse, clinical signs indicating circulatory failure such as paleness of the mucous membranes, weak heart sounds, dyspnea, and cold skin were observed. In the shock-related pathologic findings, centralobular congestion in the liver, and congestion and hemorrhage in mucous membranes of the gastrointestinal tract were observed during collapse [8]. These pathologic findings and the collapse disappeared simultaneously. The cardiac muscle and vessels in dogs with shock were normal in the morphologic findings. Moreover, hemorrhage and edema, which suggested a decrease in circula...

Physiological and haematological findings and clinical observations in a model of acute systemic anaphylaxis inDirofilaria immitis‐sensitised cats

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