Orthodromic incessant atrioventricular reciprocating tachycardia in a dog

A diagnosis of orthodromic atrioventricular reciprocating tachycardia (OAVRT) was made in a 6-year-old male Boxer based on electrocardiographic and Holter-ECG findings. The surface electrocardiogram showed a narrow-complex tachycardia, with a regular ventricular rhythm ranging from 280 to 300 bpm, QRS alternans, and retrograde P waves present in the late part of ST segment, with a RP'/P'R ratio < 1. The dog was successfully treated short-term with intravenous verapamil, and long-term with procainamide and diltiazem. This report shows the utility of the surface electrocardiogram in the diagnosis of OAVRT with a concealed accessory pathway in the dog, as it was previously reported in human literature.