In rare cases of pre-excited AVRT, the return conduction occurs via a second accessory AV pathway. AF can occur in patients with accessory pathways, which may result in extremely rapid conduction to the ventricle over a manifest pathway, which increases the risk of inducing ventricular fibrillation and SCD. Other SVTs, such as AVNRT, AT, and atrial flutter, can also conduct rapidly over a manifest accessory pathway; in these instances, the pathway is con- sidered a bystander because it is not part of the tachy- cardia circuit. Most accessory pathways have conduction properties similar to the myocardium and do not demon- strate decremental conduction. A unique form of AVRT involves a concealed accessory pathway, usually located in the posteroseptal region, with retrograde decremental conduction properties resulting in a form of orthodromic reentrant tachycardia termed PJRT. This tachycardia has deeply inverted retrograde P waves in leads II, III, and aVF, with a long RP interval due to the location and decremental conduction properties of the accessory pathway (Figure 6). The incessant nature of PJRT may result in tachycardia- induced cardiomyopathy that usually resolves after suc- cessful treatment. Another unusual accessory pathway is the atriofascicular fiber (also called a Mahaim fiber) that connects the right atrium to a fascicle of the distal right bundle branch and has decremental anterograde conduction while not allowing conduction in the retrograde direction; this pathway can allow reentrant tachycardia with a cir- cuit that involves anterograde conduction over the acces- sory pathway with characteristic left bundle-branch block morphology and retrograde conduction through the AV node/His Purkinje system. Other rare accessory pathway connections that may participate in reentrant tachycardia are nodofascicular pathways (connecting the AV node to a fascicle) and nodoventricular pathways (connecting the AV node to the ventricular myocardium). 