STUDIES IN INTRACARDIAC ELECTROGRAPHY IN MAN. III. DISPLACEMENT OF THE CARDIAC PACEMAKER

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Abstract
With a recording electrode near the tip of an intra-atrial catheter, and taking advantage of the fact that the intracardiac electrode records a downward auricular deflection when the impulse recedes from the tip of the catheter and an upward deflection when the impulse approaches the catheter, and of the fact, proved by Wilson, that the cardiac pacemaker can be displaced by vagal stimulation during the period between the hypodermic injn. of atropine and the appearance of its max. physiological effect, more precise information was sought regarding displacement of the auricular pacemaker. Pseudo-displacement was avoided by stimulating on the side opposite that catheterized and by obtaining "spot films" and electrograms while the patient held a maximal inspiration. Ecgs. (usually a VL lead) were recorded simultaneously with the auricular electrogram. Of 16 subjects tested true displacement was produced by carotid sinus or ocular stimulation in 9, pseudo-displacement in 2, and no displacement in 4 individuals, in spite of well-marked slowing. A study of intra-atrial potentials in relation to roentgen-ray examination seemed to place the new site of impulse formation halfway down the right atrium. In only one subject was nodal rhythm produced. Coincident with displacement there was very little or no shortening of auriculo-ventricular conduction time. It is possible that in man the auricular repolarization process may also be altered by vagal stimulation.

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