Results of 24-hour ambulatory electrocardiography in dogs undergoing ovariohysterectomy following premedication with medetomidine or acepromazine.
OBJECTIVE
To investigate heart rate characteristics in dogs undergoing ovariohysterectomy following premedication with medetomidine or acepromazine.


METHODS
Clinical trial.


METHODS
43 client-owned dogs.


METHODS
24-hour ambulatory electrocardiography was performed beginning approximately 1 hour prior to administration of premedications. Dogs were premedicated with medetomidine and butorphanol (n = 21) or acepromazine and butorphanol (22) and, approximately 85 minutes later, were anesthetized with propofol and isoflurane. Electrocardiographic recordings were examined to determine heart rate, cardiac conduction disturbances (ventricular premature complexes and atrioventricular block), and indices of heart rate variability (HRV).


RESULTS
Minimum heart rate during the 24-hour recording period was significantly lower among dogs given medetomidine than among dogs given acepromazine, but during the postoperative period, heart rate increased in all dogs as they became physically active. Intraoperative time domain HRV indices were lower and the low frequency-to-high frequency ratio was higher among dogs given acepromazine than among dogs given medetomidine; however, significant differences between groups were no longer seen by 6 hours after surgery. There was no significant difference between groups with regard to the number of ventricular premature complexes or to values of scaling exponent alpha2 (a nonlinear measure of HRV).


CONCLUSIONS
Results suggest that there are greater enhancements in vagally related heart rate indices in medetomidine-treated dogs that may persist until 6 hours after surgery. Despite the low heart rates, dogs given medetomidine showed expected responses to surgery and positional stimuli, and the 2 preanesthetic protocols may not result in different prevalences of ventricular premature complexes.
Väisänen
Misse A M
MA
Department of Veterinary Clinical Sciences, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland.
Vainio
Outi M
OM
Raekallio
Marja R
MR
Hietanen
Heikki
H
Huikuri
Heikki V
HV
D000075:Acepromazine / Q000494:pharmacology*; D000818:Animals; D002077:Butorphanol / Q000494:pharmacology; D004285:Dogs / Q000502:physiology* / Q000601:surgery; D018492:Dopamine Antagonists / Q000494:pharmacology*; D015716:Electrocardiography, Ambulatory / Q000379:methods / Q000662:veterinary*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D007044:Hysterectomy / Q000662:veterinary; D007530:Isoflurane / Q000494:pharmacology; D020926:Medetomidine / Q000494:pharmacology*; D010052:Ovariectomy / Q000662:veterinary; D011184:Postoperative Period; D011229:Preanesthetic Medication / Q000379:methods / Q000662:veterinary*; D015742:Propofol / Q000494:pharmacology; D011897:Random Allocation; D013997:Time Factors
D018492:Dopamine Antagonists; D006993:Hypnotics and Sedatives; D000075:Acepromazine; D007530:Isoflurane; D020926:Medetomidine; D002077:Butorphanol; D015742:Propofol