Experimental Bidirectional Ventricular Tachycardia in the Dog.

Bidirectional ventricular tachycardia is an uncommon cardiac arrhythmia and reports of only 50 cases have hitherto been published. Levy and Lewis (1911) were the first to notice this arrhythmia during their experimental work on cats, while Schwensen (1922) reported the first case of bidirectional ventricular tachycardia in man. Since then there has been general agreement that this arrhythmia has a serious prognosis. There is also a concensus of opinion on the manner in which the arrhythmia appears. Bidirectional ventricular tachycardia is characterized by two ventricular complexes of prolonged duration and cardiopathic aberrant shape, which alternate rhythmically in opposite directions. However, this alternation in the direction of complexes is not invariable. According to the classification of Scherf and Kisch (1939) this arrhythmia is of three types. (1) With diastolic intervals equal to those of regular rhythm but with the QRS complexes always alternating in direction. (2) With alternation of longer and shorter diastolic intervals as well as that of QRS configurations. In this variety the interval between the complexes that resemble each other is usually equal, and between those that do not resemble each other it is unequal. (3) With the length of the diastole as well as the shape of the ventricular complexes varying irregularly. Its genesis is a subject of considerable uncertainty, as many as seven theories having been postulated to explain its mechanism. No experimental work on this matter, or on the manner of production of the arrhythmia has been found in earlier publications on this subject.