Prevalence of Post-Anesthesia Cardiac Arrhythmias in Horses

A team of British researchers recently completed a study examining the prevalence of post-general anesthesia cardiac arrhythmias and found that irregularities are common in horses' hearts during the post-surgical recovery period.

"Texts report that horses undergoing emergency exploratory laparotomy (colic surgery) commonly have arrhythmias in the post-operative period, yet there is very limited literature in this area," explained lead author Ruth A. Morgan, MA, VetMB, MRCVS, Horse Trust senior clinical training scholar in equine internal medicine in the University of Liverpool's Department of Veterinary Clinical Sciences. "If the prevalence and nature of arrhythmias in the post-anesthetic period is determined, then clinicians will be better able to identify, understand, and manage those horses developing post-operative arrhythmias."

Armed with that information, Morgan and her colleagues set out to determine the prevalence of arrhythmias in post-surgical patients; compare the incidence in horses with and without gastrointestinal (GI) disease; and evaluate identifiable risk factors for arrhythmia development post-anesthesia.

In the prospective study the team evaluated 104 horses of varying age, breed, and sex presented for surgery at the Univeristy of Liverpool's Philip Leverhulme Equine Hospital between September 2009 and January 2011; 67 horses with GI disease and 37 without GI disease were included. Each horse's electrolyte levels were measured before, during, and after surgery, and each horse's cardiac activity was monitored with an electrocardiogram (ECG) for 24 hours after surgery.

Upon reviewing the results of the study, the team found that post-anesthesia cardiac arrhythmias were very common in horses with and without GI disease. Supraventricular arrhythmias (those arising mainly from the atria [the two upper chambers of the heart]) and bradyarrhythmias (those that occur at a normal or low heart rate, the most common form of arrhythmia found in normal horses at rest) were the most common abnormalities found in both groups of horses, the team noted. They also found that "post-operative tachycardia (rapid heartbeat) and sodium derangements were associated with the development of any type of arrhythmia."

Morgan noted that in the majority of cases, horses recover from arrhythmias without treatment and without incident.

"The findings of this study indicate that rather than a primary disease predisposing horses to post-operative arrhythmias, it may be general anesthesia, surgery, and recovery," Morgan relayed.

All horses in the current study survived for at least 24 hours following surgery, Morgan noted, but added that additional work on arrhythmias is needed on horses that do not survive.

"It is possible that the prevalence of arrhythmias in those horses that do not survive may be different and potentially more clinically significant, because these may represent the most critically ill group," she relayed. "Further work is required to ascertain the prevalence and nature of arrhythmias in those horses that fail to survive the immediate post-operative period."

The study, "The prevalence and nature of cardiac arrhythmias in horses following general anaesthesia and surgery," was published in November 2011 in the open-access journal Acta Veterinaria Scandinavica and can be viewed online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.