Prenylamine toxicity can manifest as torsade de pointes and QRS axis variation in sinus rhythm due to partial ventricular refractoriness.
A case of torsade de pointes attributed to prenylamine is described. In addition, the authors show QRS axis variation of a similar nature in sinus rhythm. It is postulated that these changes of QRS axis direction, seen in ventricular tachycardia and sinus rhythm, are both manifestations of partial refractoriness, within the ventricle, producing gross changes in the mean QRS vector.
Meanock et al. (1981) studied this question.