An appraisal of "supernormal" A-V conduction.

Certain temporal patterns of A-V and V-A transmission in experimental preparations resemble phenomena attributed to "supernormal" conduction in the clinic. Detailed study of the properties of the A-V transmission system in such experiments reveals alternative explanations in which supernormality is clearly eliminated. By application of similar principles, supernormality can be eliminated as a factor in most if not all of the published examples. Three major categories can be discerned: (1) occult 2:1 A-V block, in which an idioventricular beat "retracts" an otherwise refractory barrier within the A-V node; (2) alternation between dissociated intranodal transmission pathways; and (3) "ventriculophasic" (vagal) depression of nodal conductivity.