Equine Internal Medicine Q&A 12

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This ECG was obtained from a horse with acute onset of exercise intolerance. Auscultation revealed an irregular rhythm with a rate of 40–50bpm, but periods of a rapid (about 80bpm) regular rhythm were also heard. There were no murmurs.

Question	Answer		Article
What is the rhythm?	Atrial fibrillation with paroxysmal ventricular tachycardia. Notice that there are no P waves, and that there are QRS-T wave forms of two types. The large QRSs with negative T waves are ventricular in origin.		Link to Article
What other diagnostic procedure(s) should be performed?	An echocardiogram should be done to determine if any structural heart disease, such as a cardiomyopathy/myocarditis, exists. A CBC and chemistry panel were done in this horse to determine if any systemic disorders or electrolyte disturbances were present. Serum cardiac isoenzymes were also evaluated. All these tests were normal.
What would be a logical treatment regimen for this horse assuming the test(s) in the answer to part 2 is/are normal?	The ventricular tachycardia was not considered to be life threatening because of the rate (less than 100bpm), that it was uniform (one foci in ventricle), and because the horse was asymptomatic at rest. Atrial fibrillation may resolve spontaneously within 24 hours, therefore re-evaluation after 24 hours of onset of signs would be appropriate. The drug of choice for treatment of this arrhythmia is quinidine. It is effective in treating both ventricular arrhythmias and atrial fibrillation. After 24 hours, the ventricular tachycardia had resolved, but the atrial fibrillation was still present. The atrial fibrillation was successfully converted to sinus rhythm after several doses of quinidine sulphate had been given by nasogastric tube. Quinidine gluconate administered in intravenous boluses may also be used to treat atrial fibrillation of under two weeks duration in the horse.		Link to Article