Vectorcardiographic finding of varying degrees of left anterior hemiblock. A case report

A 16-year-old high school boy showed various types of aberrant QRS complexes during supraventricular premature beats. The aberrant beats showed right bundle branch block pattern associated with varying degrees of left axis deviation. Rosenbaum et al explained it by slowing in conduction through the anterior fascicle in a bifascicular nature of human left bundle system. The alternative explanation might be possible if we consider a fan-like left bundle as proposed by Massing et al: namely incomplete or slight left axis deviation results from block of a small group of anterior parts of the fan-like left bundle, whereas marked left axis deviation results from block of a large number of fibers. The initial QRS force also changed to various degrees according to changes of the QRS axis. This case suggested the existence of an incomplete type of left anterior hemiblock, which produced not only an incomplete QRS axis change but also an incomplete change of the initial QRS forces.