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tvpjournal.com | November/December 2015 | ToDay's VeTeriNary PracTice aHs HearTWorM HoTLiNe Peer reviewed 67 lead to cardiac insuffciency, HWD alone can notably diminish cardiac function through several mechanisms (Table 3). Obstruction & Insuffciency Combined Unlike obstructive disease in which blood fow is impacted solely by increased vascular resistance, cardiac insuffciency causes reduced fow due to diminished ejection of blood volume. in either case, because HWD can cause both obstructive disease and cardiac insuffciency simultaneously, a reduction in pulmonary arterial fow can become signifcant enough to allow heartworms to relocate to the right heart and/or vena cava. IN SUMMARY Understanding the pathophysiology of cs is an essential frst step to diagnosing and treating this serious and complex condition. While cs is not common, practitioners who see HWD should be prepared to identify patients with cs. cs = caval syndrome; HWD = heartworm disease; HWi = heartworm infection References 1. atkins ce. caval syndrome in the dog. Semin Vet Med Surg (Small Anim) 1987; 2(1):64-71. 2. atkins ce. Heartworm caval syndrome. in Kirk rW, Bonagura JD (eds): Current Veterinary Therapy XI Small Animal Practice. Philadelphia: WB saunders, 1992 pp 721-725. 3. strickland KN. canine and feline caval syndrome. Clin Tech Small Anim Pract 1998; 13(2):88-95. 4. atkins ce, Keene BW, McGuirk sM. investigation of caval syndrome in dogs experimentally infected with Diroflaria immitis. J Vet Intern Med 1988; 2(1):36-40. 5. Kuwahara y, Kitagawa H, sasaki y, ishihara K. cardiopulmonary values in dogs with artifcial model of caval syndrome in heartworm disease. J Vet Med Sci 1991; 53(1):59- 64. 6. Mccall JW, Genchi c, Kramer LH, et al. Heartworm disease in animals and humans. Adv Parasitol 2008; 66:193-285. 7. Kitagawa H, Kubota a, yasuda K, et al. cardiopulmonary function in dogs with serious chronic heartworm disease. J Vet Med Sci 1992; 54(4):751-756. 8. Kitagawa H, sasaki y, ishihara K, Kawakami M. Heartworm migration toward right atrium following artifcial pulmonary arterial embolism or injection of heartworm body fuid. Jpn J Vet Science 1990; 52(3):591-595. 9. Kitagawa H, sasaki y, ishihara K. canine diroflarial hemoglobinuria induced by milbemycin D administration. Jpn J Vet Sci 1986; 48:517-522. 10. Kitagawa H, sasaki y, ishihara K. canine diroflarial hemoglobinuria: changes in right heart hemodynamics and heartworm migration from pulmonary artery towards right atrium following B1-blocker administration. Jpn J Vet Sci 1987; 49:1081-1086. 11. Kitagawa H, sasaki y, ishihara K. canine diroflarial hemoglobinuria: changes in right heart hemodynamics inducing heartworm migration from pulmonary artery. Jpn J Vet Science 1987; 49:485-489. 12. Kitagawa H, sasaki y, ishihara K. clinical studies on canine diroflarial hemoglobinuria: relationship between the presence of heartworm mass at the tricuspid valve orifce and plasma hemoglobin concentration. Jpn J Vet Science 1986; 48(1):99- 103. 13. sasaki y, Kitagawa H, Hirano y. relationship between the pulmonary arterial pressure and lesions in the pulmonary arteries and parenchyma, and cardiac valves in canine diroflariasis. J Vet Med Sci 1992; 54(4):739-744. 14. Ninomiya H, Wakao y. scanning electron microscopy of vascular corrosion casts and histologic examination of pulmonary microvasculature in dogs with diroflariosis. Am J Vet Res 2002; 63(11):1538-1544. 15. rawlings ca. The pulmonary arterial response to adult Diroflaria immitis. in Heartworm Disease in Dogs and Cats. Philadelphia: WB saunders, 1986, pp 1-39. 16. ishihara K, Kitagawa H, sasaki y, yokoi H. changes in cardiopulmonary values after heartworm removal from pulmonary artery using fexible alligator forceps. Jpn J Vet Sci 1988; 50(3):731-738. 17. Kitagawa H, sasaki y, Hirano y. contribution of live heartworms harboring in pulmonary arteries to pulmonary hypertension in dogs with diroflariasis. Jpn J Vet Sci 1990; 52(6):1211-1217. stePHen l. Jones Stephen L. Jones, DVM, is the President of the American Heartworm Society and a general practitioner/practice partner at Lakeside Animal Hospital, Moncks Corner, South Carolina. He received his DVM from University of Georgia. Read more about Dr. Jones at lahmc.com/ veterinarians.php. FIGURE 9. View from the right ventricle showing a dead heartworm intertwined in the chordae tendineae of the tricuspid valve. TAblE 3. mechanisms of diminished Cardiac function in Heartworm disease • Reduced cardiac output against high pulmonary artery pressure • Tricuspid insuffciency secondary to increased pulmonary artery pressure • Tricuspid interference by worm entanglement ( figure 9) • Tricuspid regurgitation due to worm intrusion through the valve orifce • Vasoactive substance release associated with worm death and subsequent systemic cardiovascular compromise