Mechanism of the Wenckebach-Luciani Cycles

The development of Wenckebach-Luciani cycles was studied in dogs anesthetized with pentobarbital, with the heart denervated, the S.A. node crushed, and the adrenals ligated. When the auricle is stimulated with increasing frequency there is at first a 1:1 correspondence between the A and the V impulses. At a critical frequency the correspondence becomes n A:( n – 1)V, where n > 2. At higher frequencies, n = 2, i.e., the ventricle alternates. The hypothesis that the cycles ( n > 2) are due to cumulative impairment of the propagating system is deficient. The cycles are due to the modulation of two frequencies, that of the stimuli and that determined by the longest functional refractory period of the conducting elements. The laws of the cycles are formulated mathematically. V-A cycles also develop when the ventricle is stimulated. They are often obscured by the appearance of impulses that return from the auricle to the ventricle. The mechanism of these cycles is similar to that of the A-V cycles.