• short PR interval, less than 3 small squares (120 ms)
• slurred upstroke to the QRS indicating pre-excitation (delta wave)
• broad QRS
• secondary ST and T wave changes

Localising the accessory pathway

An accessory pathway, bundle of Kent, exists between atria and ventricles and causes early depolarisation of the ventricle. The location of the pathway may be deduced as follows:-

  LOCATION                   V1   V2   QRS axis
left posteroseptal (type A)  +ve  +ve  left
right lateral      (type B)  -ve  -ve  left
left lateral       (type C)  +ve  +ve  inferior (90 degrees)
right posteroseptal          -ve  -ve  left
anteroseptal                 -ve  -ve  normal