Arrhythmias with Bystander Accessory Pathways.

An accessory pathway (AP) could manifest its presence exclusively during an orthodromic supraventricular tachycardia or with preexcitation during sinus rhythm (SR). The manifestations of the presence of an AP depend on its ability to conduct antegradely from atrium (A) to ventricle (V), retrogradely (V to A), or both. AP retrograde conduction is necessary to establish an atrioventricular reentrant tachycardia circuit. If an AP can only conduct antegradely, it will function as a bystander AV connection during independent arrhythmias. The correct diagnosis of this condition is very important, as it will determine the immediate and long-term management.