Reversal of the cardiac mechanism. An additional note

Since making our previous report on this subject, electrocardiograms have been obtained from the same patient in which occasionally the small downward deflection between R and T fails. The form of the ventricular electrogram in these instances is precisely similar to the others with the sole exception of the absence of the small downward deflection. This we regard as confirmatory evidence of the correctness of the view that the downward deflection is caused by the action of the auricles and that the usual curve is not simply an unusual ventricular complex. In the occasional instances cited conduction seems to have failed.

When this case first came under observation it seemed desirable to attempt to reproduce the condition experimentally. We have performed up to the present time seven experiments with one positive result. Rothberger and Winterberg have published curves showing transient reversal resulting from simultaneous depression of the sinus-region of the right auricle with cold and stimulation of the left ganglion stellatum. The apparent permanence of the condition in our patient leads us to think rather of an anatomical lesion than of nervous influences as the cause of the condition. Our experiments have consisted in depression (with anode) crushing, and excision of the region of the sinus node. In some instances nearly the entire anterior wall of the right auricle including a large part of the walls of the venæ cavæ where they fuse with the auricle, have been excised.

Slowing of the heart beat was the usual result and the auricles and ventricles generally beat nearly or quite simultaneously. In the single positive experiment auricular fibrillation resulted from the application of a clamp to the upper part of the sinus region where the greater bulk of the node is usually found.