Changes in conduction within the diffuse sinoatrial node of the chicken following premature atrial stimulation

Premature atrial stimulation was used to estimate sinoatrial conduction within the diffuse sinoatrial node of the bird (chicken), and compare its conduction with that reported for mammals. While sinoatrial conduction could not be determined in the chicken because reset did not occur, the premature wavefront did have an effect on the sinoatrial node because the recovery interval following the premature stimulus became less than compensatory with shortening of the premature stimulus interval. This less than compensatory non-reset recovery interval is interpreted as a conduction dependent response in which the intrinsic wavefront leading to the first recovery atrial activation conducts out of the node faster than normal. This conduction dependent recovery interval is seen infrequently in mammals (rabbit, dog and man). The absence of reset and the presence of a less than compensatory non-reset response in the chicken suggests that while the general organization of the sinoatrial node of the chicken is similar to that in mammals, a larger transitional cell network in the chicken prevents a premature wavefront from reaching the pacemaker cells and resetting them.