Resolution of sustained ventricular tachycardia in a horse presenting with colic with magnesium sulfate

Summary Case reports demonstrating a return to sinus rhythm from sustained ventricular tachycardia (VT) are limited. VT is uncommon in horses but can be life threatening and has been reported in horses with primary gastrointestinal disease. Treatment is recommended if there is poor perfusion, if heart rate exceeds 100 beats/min, if multiform/polymorphic complexes or torsades des pointes is present. Lidocaine or magnesium sulfate is the first‐line medication. In this case, a 19‐year‐old Warmblood gelding with a history of exploratory laparotomy presented with an irregularly irregular cardiac rhythm and heart rate of 80 beats/min. ECG demonstrated VT with a heart rate of 75 beats/min. As the horse was already receiving a lidocaine bolus, the VT was treated with multiple boluses of intravenous magnesium sulfate over a period of several hours. This converted the VT to normal sinus rhythm (NSR) with heart rate of 44 beats/min and the horse remained in NSR until discharge 8 days later.