Momentary Atrial Electrical Axes in Paroxysmal Tachycardia.

A recent study 1 of our cases of paroxysmal atrial tachycardia has shown the presence of some grade of A-V block with dropped ventricular beats in a large proportion of the group. The block varied in duration as well as degree, and seemed most likely to appear in patients who had either severe myocardial disease or digitalis over-dosage. This led us to the observation 2 , which has also been reported by Barker and his associates 3 , that this group of patients was prone to develop atrial flutter or fibrillation, or both, in close association with the episodes of paroxysmal tachycardia with block. These facts logically raise the question of a possible resemblance between the fundamental disturbances of atrial mechanism in these 3 types of arrhythmia. Barker et al. 4 have suggested, in fact, that a circus movement is probably present in each instance. Others have made similar proposals, which have been reviewed elsewhere. 2 , 5

Lewis, after preliminary animal experiments, reported studies of 3patients, 6 one who had flutter and 2 who had fibrillation. Using simultaneous chest leads placed in 3 planes, he was able to calculate the direction of movement of the atrial electrical axis for each 1/50 second. His results are compatible with the presence of a circus movement in flutter and fibrillation, though they can scarcely be said to supply conclusive proof. One possible approach to the above problem seemed to be the analysis of similar tracings, taken in patients with paroxysmal atrial tachycardia. It is fortunate that the electrocardiograms of the patients most likely to show flutter or fibrillation, i.e., those with A-V block during the paroxysm, are best suited for this type of analysis; while the block is present, at least half of the P waves will avoid superimposition on the preceding T wave.