I purpose, in this communication, to emphasize the distinction that should be made between the terms "reversed mechanism" and "reversed rhythm" of the heart.
The term "reversed mechanism" should be confined to express a reversal of the mechanism of impulse formation and conduction. Normally, the impulse originates in the sinus and traverses the auricles to be conducted through the auriculoventricular junctional tissues into both ventricles. In reversal of the mechanism, the impulse first originates in the auriculoventricular node, or the junctional tissues, or at a lower level in the heart and travels backward into the auricular musculature. Thus the term "reversed mechanism" implies a direction of stimulus conduction opposite to the normal.
Illustrative of such cases may be mentioned instances of auriculoventricular rhythm. In these cases, a ventriculo-auricular (R-P) interval may be exhibited with inversion or distortion of the auricular (P) wave. Williams and James,1 Heard and Strauss,2 White,3 and