Ventricular tachycardia in a thoroughbred racehorse.

Background of Ventricular Tachycardia

• Ventricular tachycardia is an arrhythmia that can result from primary cardiac disease, systemic disease, or drug toxicity.
• If sustained and the ventricular rate exceeds 90 beats per minute, it is critical and potentially deadly. This is due to the potential to lead to hypotension, myocardial ischemia, syncope, seizure, shock, or even sudden death.

Presentation of the Horse

• The subject of the study was a 5-year-old thoroughbred racehorse who began showing signs of illness three days after a disappointing race performance.
• Initial symptoms included lethargy and signs of distress and upon examination, it showed signs of depression, irritation, increased respiratory rate, and irregular pulse.
• The horse’s heart rate was exceeds 100 per minute and irregular. Periods of paroxysmal tachycardia were observed, with sequences of 3 to 4 beats, a pause, followed by 6 to 7 beats, another pause, and then a series of 20 beats or more.

Diagnosis and Prognosis

• An electrocardiogram was recorded which showed long runs of ventricular tachycardia with isolated escape and capture beats.
• The horse’s owner was informed of the severity of the condition and advised to move the horse to a hospital. However, the owner opted for stable rest overnight and by morning, a normal rhythm had returned and the heart rate had dropped to 35 beats per minute.
• The prognosis given was poor, but with a returned normal rhythm, it was considered stable.

Laboratory Findings and Recovery

• Lab results of the blood cell count suggested slight dehydration but everything was within normal range. There were slight indications of a stress response.
• Total serum protein, albumen, globulin, bilirubin, alkaline phosphates, gamma glutamyl transferase, urea, creatinine and electrolytes all fell within normal limits.
• However, Creatinine phosphokinase and lactic dehydrogenase were slightly elevated.
• Rest was continued for one week throughout which the horse’s heart remained normal on auscultation. A follow-up resting electrocardiogram showed occasional sino atrial block consistent with excess vagal tone and one complex consistent with a ventricular premature contraction.