title: Comparison of arrhythmogenic doses of epinephrine in heartworm-infected and noninfected dogs.
abstract: The arrhythmogenic dose of epinephrine (ADE) was determined in heartworm-infected and noninfected (control) dogs during thiamylal-induced and halothane-maintained anesthesia to assess the myocardial sensitization. The ADE in heartworm-infected dogs (2.42 +/- 0.26 micrograms/kg of body weight) was significantly lower than that for the controls (3.36 +/- 0.29 micrograms/kg). After 2 weeks, ADE was determined again in these dogs after atropine treatment. Atropine treatment lowered the ADE to 1.76 +/- 0.33 micrograms/kg and 1.77 +/- 0.19 micrograms/kg in heartworm-positive and -negative dogs, respectively. After 2 weeks more, the ADE was determined after administration of prazosin, an alpha 1-antagonist. Only 2 of 6 controls and 3 of 6 heartworm-positive dogs had arrhythmias after a threefold increase of ADE. The mean ADE in the dogs that responded to treatment were 7.4 micrograms/kg and 7.2 micrograms/kg for heartworm-positive and -negative dogs, respectively. The finding of this study indicated that ADE in heartworm-infected dogs were lower than those in the control dogs, which makes the heartworm-infected dogs more vulnerable to arrhythmia during anesthesia. Atropine did not protect the dogs of either group. However, prazosin protected the dogs of both groups by significantly increasing the threshold of the ADE. On the basis of our findings, to reduce the risk of arrhythmia, we suggest that routine screening of dogs for heartworm infection be done before anesthetics are used.
authors.affiliation: Department of Veterinary Physiology, Pharmacology and Toxicology, School of Veterinary Medicine, Louisiana State University, Baton Rouge 70803.
authors.forename: C S
authors.initials: CS
authors.lastname: Venugopalan
authors.forename: E
authors.initials: E
authors.lastname: Holmes
authors.forename: N A
authors.initials: NA
authors.lastname: O'Malley
mesh_terms: D000769:Anesthesia, Inhalation / Q000662:veterinary*; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000139:chemically induced / Q000517:prevention & control / Q000662:veterinary*; D001285:Atropine / Q000627:therapeutic use; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000097:blood; D004184:Dirofilariasis / Q000503:physiopathology / Q000662:veterinary*; D004283:Dog Diseases / Q000503:physiopathology*; D004285:Dogs; D004837:Epinephrine / Q000009:adverse effects*; D006221:Halothane; D006339:Heart Rate / Q000187:drug effects; D010100:Oxygen / Q000097:blood; D011224:Prazosin / Q000627:therapeutic use; D011292:Premedication / Q000662:veterinary; D013840:Thiamylal
chemical_list: D013840:Thiamylal; D002245:Carbon Dioxide; D001285:Atropine; D010100:Oxygen; D006221:Halothane; D011224:Prazosin; D004837:Epinephrine