BIDIRECTIONAL TACHYCARDIA

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Abstract
Two cases of bidirectional tachycardia are reported. The upward and downward complexes were regular in both cases, the distance between them being 0.34 second in one and 0.26 second in the other. Pressure over the carotid slowed the rate in the 2d of these 2 patients; in the 1st one the paroxysmal tachycardia was preceded by nodal rhythm and nodal extrasystoles with conduction defect. Conversion of unidirectional to bidirectional tachycardia by gradual change from incomplete bundle-branch block in alternate beats, the presence of all types of conduction disturbance, e. g., nodal rhythm, nodal tachycardia with right or with left bundle-branch block, nodal extrasystoles with conduction though right or left bundle, and blocked nodal extrasystoles, are all in support of this tachycardia being nodal in origin. The effect of K and Mg on the tachycardia and the necropsy findings of one case with the results of histopathological study of the heart are described, and the possible mechanisms of production of this type of tachycardia are discussed.