Characterization of parasympatholytic chronotropic responses following intravenous administration of atropine to clinically normal dogs

Mark Rishniw From the Veterinary Medical Teaching Hospital (Rishniw), and the Departments of Veterinary Medicine and Epidemiology (Kittleson), Population Health and Reproduction (Kass), and Medicine (Jaffe), University of California, Davis, CA 95616-8747.

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 BVSc, MS
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Mark D. Kittleson From the Veterinary Medical Teaching Hospital (Rishniw), and the Departments of Veterinary Medicine and Epidemiology (Kittleson), Population Health and Reproduction (Kass), and Medicine (Jaffe), University of California, Davis, CA 95616-8747.

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 DVM, PhD
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Rory S. Jaffe From the Veterinary Medical Teaching Hospital (Rishniw), and the Departments of Veterinary Medicine and Epidemiology (Kittleson), Population Health and Reproduction (Kass), and Medicine (Jaffe), University of California, Davis, CA 95616-8747.

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 MD
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Philip H. Kass From the Veterinary Medical Teaching Hospital (Rishniw), and the Departments of Veterinary Medicine and Epidemiology (Kittleson), Population Health and Reproduction (Kass), and Medicine (Jaffe), University of California, Davis, CA 95616-8747.

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Abstract

Objective

To determine heart rate (HR) and heart rate variability (HRV) after IV administration of 3 doses of atropine to clinically normal, large-breed adult dogs.

Animals

6 mixed-breed dogs, weighing between 23 and 50 kg.

Procedure

Continuous ECG were recorded prior to and following IV administration of saline (0.9% NaCl) solution and 0.02, 0.04, and 0.06 mg of atropine/kg of body weight. Heart rate and HRV within sympathetic and parasympathetic domains were determined, using customized software, and responses to treatments were compared. Each dog received all treatments with ≥ 2 days between treatments.

Results

HR increased and HRV within the parasympathetic domain decreased after all atropine treatments, compared with pretreatment values. Heart rate was significantly higher after administration of 0.06 mg of atropine/kg than after 0.02 mg/kg but was not different from HR after administration of 0.04 mg/kg. Five of 6 dogs given the 0.04 or 0.06 mg/kg dose attained HR > 135 beats/min, but only 1 of 6 dogs given the 0.02 mg/kg dose attained a HR > 135 beats/min. Heart rate variability within the parasympathetic domain decreased significantly from pretreatment values after all atropine treatments. Atropine doses of 0.04 and 0.06 mg/kg induced significantly lower HRV than did the 0.02 mg/kg dose, but HRV after the higher doses were not different from each other. HRV within the sympathetic domain after any treatment did not change from pretreatment values.

Conclusions and Clinical Relevance

IV administration of 0.04 or 0.06 mg of atropine/kg increased HR and induced complete parasympathetic blockade in clinically normal, large-breed adult dogs. (Am J Vet Res 1999;60:1000-1003)

Abstract

Objective

To determine heart rate (HR) and heart rate variability (HRV) after IV administration of 3 doses of atropine to clinically normal, large-breed adult dogs.

Animals

6 mixed-breed dogs, weighing between 23 and 50 kg.

Procedure

Continuous ECG were recorded prior to and following IV administration of saline (0.9% NaCl) solution and 0.02, 0.04, and 0.06 mg of atropine/kg of body weight. Heart rate and HRV within sympathetic and parasympathetic domains were determined, using customized software, and responses to treatments were compared. Each dog received all treatments with ≥ 2 days between treatments.

Results

HR increased and HRV within the parasympathetic domain decreased after all atropine treatments, compared with pretreatment values. Heart rate was significantly higher after administration of 0.06 mg of atropine/kg than after 0.02 mg/kg but was not different from HR after administration of 0.04 mg/kg. Five of 6 dogs given the 0.04 or 0.06 mg/kg dose attained HR > 135 beats/min, but only 1 of 6 dogs given the 0.02 mg/kg dose attained a HR > 135 beats/min. Heart rate variability within the parasympathetic domain decreased significantly from pretreatment values after all atropine treatments. Atropine doses of 0.04 and 0.06 mg/kg induced significantly lower HRV than did the 0.02 mg/kg dose, but HRV after the higher doses were not different from each other. HRV within the sympathetic domain after any treatment did not change from pretreatment values.

Conclusions and Clinical Relevance

IV administration of 0.04 or 0.06 mg of atropine/kg increased HR and induced complete parasympathetic blockade in clinically normal, large-breed adult dogs. (Am J Vet Res 1999;60:1000-1003)

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