VETgirl October 2024 Beat e-Magazine

QUARTERLY BEAT / OCTOBER 2024

anticholinergic may be used to increase heart rate and cardiac output resulting in improved blood pressure. Conversely, when bradycardia is associated with hypertension because of administration of an alpha2 adrenergic agonist, treatment is often not warranted. When tachycardia with hypotension under anesthesia is experienced, identifying the contributing cause of hypotension is prioritized. Rarely does the tachycardia require direct treatment with a beta blocker or calcium channel blocker. Regardless of brady- or tachycardia, electrocardiographic (ECG) evaluation should be performed. Heart rates with accompanying dysrhythmias often have a negative impact on cardiac output, blood pressure, and perfusion. With arrhythmias, priority is given to identification of the arrhythmia, resolving the underlying cause, and returning to normal electrical rhythm and rate. WHAT ABOUT CATS? Unlike dogs, domesticated cats are relatively similar in size and metabolic rate. This minimizes variation in accepted normal ranges. Slight variations in reference manuals exist but the normal heart rate in cats is 100-250 bpm.(1) Bradycardia in cats has been identified as heart rates under 100 bpm. (1) Tachycardias have been identified over 250 bpm.(1) While species variation in response to peri-anesthetic drugs do exist, target blood pressure values for cats are comparable to dogs. Like dogs, evaluating the whole patient prior to the administration of peri-anesthetics is ideal. While not always possible in cats, evaluating heart rate with blood pressure and tissue perfusion in the context of the patient’s physical examination history aides the veterinary professional in identification of heart rate and rhythm disturbances that could result in increased morbidity and mortality.

SUMMARY Heart rate is one of the measurable variables veterinary professionals can use to assess the cardiovascular system. In conjunction with arterial blood pressure and subjective means of evaluating perfusion (i.e., capillary refill time, mucous membrane color), ensuring a normal heart rate and rhythm helps ensure the cardiovascular system is working optimally. Additionally, in anesthetized patients using heart rate, rhythm, and blood pressure to evaluate circulation, along with the use of pulse oximetry to evaluate oxygenation and capnography to assist in the evaluation of ventilation, by a dedicated, trained veterinary professional can optimize patient outcomes.

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REFERENCES

1. Shelby AM, McKune CM. Small Animal Anesthesia Techniques. 2 ed. Hoboken, NJ: John Wiley & Sons, Inc.; 2023. 2. Muir W. Cardiovascular System. In: Tranquilli W, Thurmon J, Grimm K, editors. Lumb & Jones’ Veterinary Anesthesia and Analgesia. Ames, IA: Blackwell Publishing; 2007. p. 61-116. 3. Greene SA, Hartsfield SM, Tyner CL. Cardiovascular effects of butorphanol in halothane-anesthetized dogs. Am J Vet Res 1990;51(8):1276-9. 4. Farver TB, Haskins SC, Patz JD. Cardiopulmonary effects of acepromazine and of the subsequent administration of ketamine in the dog. Am J Vet Res 1986;47(3):631-5. 5. Pagel PS, Hettrick DA, Kersten JR, et al. Dexmedetomidine produces similar alterations in the determinants of left ventricular afterload in conscious dogs before and after the development of pacing-induced cardiomyopathy. Anesthesiology 1998;89(3):741- 8. 6. Henao-Guerrero N, Riccó CH. Comparison of the cardiorespiratory effects of a combination of ketamine and propofol, propofol alone, or a combination of ketamine and diazepam before and after induction of anesthesia in dogs sedated with acepromazine and oxymorphone. Am J Vet Res 2014;75(3):231-9. 7. Muir W, Lerche P, Wiese A, et al. Cardiorespiratory and anesthetic effects of clinical and supraclinical doses of alfaxalone in dogs. Vet Anaesth Analg 2008;35(6):451-62. 8. Muir W, Lerche P, Wiese A, et al. The cardiorespiratory and anesthetic effects of clinical and supraclinical doses of alfaxalone in cats. Veterinary Anaesthesia and Analgesia 2009;36(1):42-54. 9. Rodríguez JM, Muñoz-Rascón P, Navarrete-Calvo R, et al. Comparison of the cardiopulmonary parameters after induction of anaesthesia with alphaxalone or etomidate in dogs. Veterinary Anaesthesia and Analgesia 2012;39(4):357-65.

KEY CONCEPT: NORMAL HEART RATES IN DOGS AND CATS

100-250 BPM

60-160 BPM

Figure courtesy of Amanda M. Shelby, RVT, VTS (Anesthesia & Analgesia)

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