Wolff-Parkinson-White syndrome with gradual transition from type A to type B

This report documents a case which showed type A, type B and intermediate patterns of pre-excitation on different days. A vagotonic maneuver and digitalis induced a type A pattern, while exercise, atropine and isoproterenol caused a type B pattern of activity. A gradual transition from type A to B was demonstrated with vectorcardiograms. Despite the variations in the QRS morphology, the direction of the initial vector was not altered and was directed straight anteriorly. In this case, an accessory pathway may be located in the posterior paraseptal region or the lateral free wall of the left ventricle, and a variable size of pre-excited area may have caused type A and type B patterns of pre-excitation.