Coakley et al., in various animal species and in three human hearts, found that some of the muscle fibers related to the CS and the oblique vein, resemble fibers of the sinus and A-V nodes
. The presence of Purkinje-like cells coupled with the finding of node-like P cells lead the authors to postulate the presence of a CS node having perhaps all of the known properties of automaticity seen in A-V nodal or sinus nodal tissue.
In contrast, conduction back to the atria via a slow nodal pathway might well leave a path of refractorness in the A-V node
and transitional tissue that would prevent return of the impulse to the ventricles.
The refractory period of A-V bypass tracts often is long, which is the basis of the initiation of orthodromic A-V reciprocating tachycardia when an atrial premature complex blocks in the bypass tract and is conducted down the A-V node
. In this patient, the absence of manifest conduction in the bypass tract of the second or third P waves of each Wenckebach period suggests that the refractory period of the bypass tract is unusually long.