Accessory pathways (AP)

• Some people are born with an extra piece of heart muscle tissue [1]
• That connects directly between the atria and the ventricles, bypassing the AV node altogether[1]
• This abnormal piece of muscle is referred to as a bypass tract or an accessory pathway [1]

1. Kent - WPW [ delta wave, PQ<0.12 ] [LA-RA or RA-RV]
2. James - LGL [ no delta wave, PQ<0.12 ] [ LA-Hiss ]
3. Mahaim - [ small delta wave ] [ Hiss - V ]

• Accessory pathways (AP) typical, atypical, non-evident. [3]
• Typical
• Left sided (Left atrium - left ventricle)
• ECG changes (PR < 0.12 and pre-excitated wide QRS) [3]
• delta wave - manifest
• Atypical 
• Right sided(right atrium - right ventricle)
• ECG changes (PR > 0.12 and normal or pre-excitated wide QRS) [3]
• Non-evident - ECG normal [3]
• interatrial conduction delays (enlarged or diseased atria) [3]
• accessory pathway conduction delay (Ebstein anomaly, atriofasicular track etc.) [3]
• anterograd directed conduction. ECG changes (normal PR and normal QRS) [3]
• no delta wave - concealed
• if there is delta wave then it called manifes, else concealed.
• WPW Type A
• 
• WPW Type B
• 

• 

References

1. Wolff-Parkinson-White Syndrome and Accessory Pathways James Kulig, Bruce A. Koplan. Circulation 2010
2. Basic of Pre-excitation syndrome, Leonardo Paskah. Slideshare
3. The Esc Textbook of cardiovascular medicine, 2nd edition. page 1061.