Accessory pathways provide the ‘short-circuit’ required for re-entry circuits and can result in palpitations. The two circuits that can occur are shown. The most common circuit utilises the accessory pathway to conduct from the Ventricle back to the Atrium. This is called “Orthodromic tachycardia” and leads to a narrow complex SVT on the 12 lead ECG. The other circuit uses the accessory pathway to conduct from the Atria to the Ventricles and is called “Antidromic Tachycardia”.
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