Treatment of lidocaine-refractory ventricular tachycardia using procainamide in an anesthetized horse

To highlight the use of procainamide as a potential alternative treatment modality in cases of ventricular tachycardia that are refractory to lidocaine and magnesium sulfate.

1 adult horse weighing 380 kg.

A 25-year-old Arabian gelding presented with severe colic signs. Due to persistent pain, it was elected to carry out an exploratory laparotomy. During the procedure a diagnosis of severe, unstable ventricular tachycardia was made based on the ECG findings, with an initial heart rate of 195 beats per minute and severe hypotension.

Initial treatment consisted of discontinuing dobutamine and the administration of a 2 mg/kg IV lidocaine bolus followed by a continuous rate infusion at 50 μg/kg/min. Twenty grams magnesium sulfate (5 mg/kg) was administered IV in 1 L of lactated Ringer solution as a slow bolus over 30 minutes. Ventricular tachycardia persisted with poor peripheral pulses, a severely dampened arterial waveform, and a MAP of 30 to 45 mm Hg. Two milligrams/kg IV procainamide was administered over 3 minutes, 3 separate times, at 5-minute intervals. Immediately following the third dose sinus rhythm was detected on the ECG, the arterial waveform improved, and MAP increased to 85 mm Hg.

Ventricular tachycardia is a rare but potentially life-threatening complication in horses undergoing general anesthesia. The potential of this arrhythmia to progress to ventricular fibrillation is of grave concern, as the option to attempt to externally defibrillate horses back to normal sinus rhythm does not exist. This case highlights procainamide as a potential option for cases of ventricular tachycardia that are refractory to more standard treatment modalities.