Abstract
In reciprocal rhythm an impulse originating in the atrioventricular junctional tissue passes to the ventricle, and in addition by retrograde conduction stimulates the atrium. If the retrograde conduction has been rapid, the cycle terminates; however, if conduction has been slowed, the impulse may find the junctional tissue responsive, and after traversing part of the auricle again stimulate the A-V node and ventricle, producing a reciprocal beat, or “Umkehr-Extr asystole.” Clinical examples of such a mechanism were first described by White, 1 who based his concept of the physiological processes present on the circus mechanism observed earlier by Mines. 2 Reciprocal rhythm has been reported by others, and has been discussed most recently by Scherf. 3
We have recently studied a patient who manifested this type of disturbance, and have taken the opportunity to study the effect of several drugs on the properties of the junctional tissue, presumably in the neighborhood of the A-V node. The clinical features of the case will be described elsewhere, together with certain electrocardiographic findings that may be of theoretical importance. The possibility suggested by Luten and Jensen 4 that some of the reported cases represent a parasystole rather than a reciprocal rhythm, has in this instance been definitely excluded.
By measuring the RP intervals of a large number of complexes, we have determined the retrograde conduction time below which reciprocal stimulation of the ventricle did not occur, but above which reciprocal beats were seen. This value we have taken to represent the refractory period of the junctional tissue.
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