Most horses that undergo surgery under general anaesthesia have an abnormal heart rhythm afterwards, new research from the University of Liverpool shows.
Sixty seven horses undergoing colic surgery and 37 requiring orthopaedic surgery, with no evidence of gastrointestinal disease, were recruited to the study between September 2009 and January 2011.
A heart monitor (telemetric electrocardiogram )(ECG) was fitted to each horse following recovery from anaesthesia and left in place for 24 hours. Selected electrolytes were measured before, during and after surgery.
The study, funded by the Horse Trust, found that the abnormal rhythms (arrhythmias) occurred in more than 80% of horses and that there was no significant difference in results between the two groups. It seems that the presence or absence of gastrointestinal disease is not as important as the act of general anaesthesia and surgery in the development of arrhythmias. This was unexpected, as factors such as endotoxaemia, and electrolyte disturbance associated with severe gastrointestinal disease might have been expected to be more likely to cause arrhythmias.
Supra-ventricular and bradyarrhythmias, such as sinus arrhythmia, AV block and sinus block predominated in both groups.
The project was led by Ruth Morgan, currently working as The Horse Trust's senior clinical scholar in Equine Internal Medicine at the University of Liverpool.
She said: "We had thought that horses undergoing emergency colic surgery would be more at risk of developing arrhythmias as they are very unwell before the surgery. However, we found that almost all the horses had arrhythmias after surgery, so maybe it is the anaesthesia or surgery itself causing the arrhythmia.
"This research has given us a better understanding of what is going on with the horse's heart following surgery." She suggests that arrhythmias occurring in horses during the post-anaesthetic period require further investigation.
The work has been published in Acta Veterinaria Scandinavica, and the full free access report is available online.
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