Cardiovascular responses to transvenous electrical cardioversion of atrial fibrillation in anaesthetized horses.
OBJECTIVE
To examine the influence of direct current shock application in anaesthetized horses with atrial fibrillation (AF) and to study the effects of cardioversion to sinus rhythm (SR).


METHODS
Prospective clinical study.


METHODS
Eight horses successfully treated for AF (transvenous electrical cardioversion after amiodarone pre-treatment).


METHODS
Cardioversion catheters and a pacing catheter were placed under sedation [detomidine 10 microg kg(-1) intravenously (IV)]. After additional sedation (5-10 microg kg(-1) detomidine, 0.1 mg kg(-1) methadone IV), anaesthesia was induced with ketamine, 2.2 mg kg(-1) and midazolam, 0.06 mg kg(-1) (IV) in a sling and maintained with isoflurane in oxygen. Flunixin meglumine, 1.1 mg kg(-1), was administered IV. Shocks were delivered as biphasic truncated exponential waves, synchronized with the R-wave of the electrocardiogram. Monitoring included pulse oximetry, electrocardiography, capnography, inhalational anaesthetic agent concentration, arterial blood pressure, LiDCO and PulseCO cardiac index (CI) and arterial blood gases. Values before and after the first unsuccessful shock and before and after cardioversion to SR were compared.


RESULTS
Values before the first shock were comparable to reported values in healthy, isoflurane anaesthetized horses. Reliable CI measurements could not be obtained using the PulseCO technique. Intermittent positive pressure ventilation was required in most horses (bradypnea and/or PaCO(2) >8 kPa, 60 mmHg), while dobutamine was administered in two horses (0.3-0.5 microg kg(-1) minute(-1)). After the 1st unsuccessful shock application, systolic arterial pressure (SAP) was decreased (p = 0.025), other recorded values were not influenced (CI measurements not available for this analysis). SR was associated with increases in CI (p = 0.039) and stroke index (p = 0.002) and a decrease in SAP (p = 0.030).


CONCLUSIONS
Despite the presence of AF, cardiovascular function was well maintained during anaesthesia and was not affected by shock application. Cardiac index and stroke index increased and SAP decreased after cardioversion.
Schauvliege
Stijn
S
Faculty of Veterinary Medicine, Department of Surgery and Anaesthesia of Domestic Animals, Ghent University, Salisburylaan, Merelbeke, Belgium. stijn.schauvliege@ugent.be
van Loon
Gunther
G
De Clercq
Dominique
D
Devisscher
Lindsey
L
Deprez
Piet
P
Gasthuys
Frank
F
D000638:Amiodarone / Q000627:therapeutic use; D000768:Anesthesia, General / Q000662:veterinary*; D018681:Anesthetics, General / Q000494:pharmacology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000627:therapeutic use; D001281:Atrial Fibrillation / Q000628:therapy*; D001794:Blood Pressure / Q000187:drug effects; D004554:Electric Countershock / Q000379:methods*; D006339:Heart Rate / Q000187:drug effects; D006734:Horse Diseases / Q000628:therapy*; D006736:Horses
D018681:Anesthetics, General; D000889:Anti-Arrhythmia Agents; D000638:Amiodarone