Distinguishing various types of cardiac arrhythmias is a challenging but important facet of veterinary practice. Rhythm disturbances that are hemodynamically significant or that increase the risk of sudden death require pharmacologic intervention, electrocardioversion, or artificial pacing, depending on the particular diagnosis. A systematic approach to evaluation of the electrocardiogram is key to obtaining an accurate rhythm diagnosis, as this will directly inform patient management.

Tachyarrhythmias are broadly classified as ‘narrow complex’ or ‘wide complex,’ based on the QRS duration. ‘Narrow complex’ tachyarrhythmias are supraventricular in origin, while wide-complex tachycardias most often arise from the ventricles. Anti-arrhythmic therapy is predicated on the electrophysiologic properties of the heart, the trigger the arrhythmia, and the mechanism by which it is perpetuated. Pathologic bradyarrhythmias include atrial standstill, Mobitz type-II 2nd degree atrioventricular block, and 3rd degree atrioventricular block. Ultimately, treatment requires artificial pacing. Ideally, all patients with pathologic arrhythmias should undergo complete cardiovascular screening, and a cardiologist should be consulted to formulate a chronic management strategy.