Participation of atrial specialized conduction pathways in atrial flutter.

The circus movement theory of flutter has been supported by numerous theoretical, experimental, and clinical studies, but there has been little consideration of the possible participation of the specialized conduction pathways of the atria. In the present work we have studied experimental atrial flutter in relation to the behavior of these pathways, in response to elevated potassium and to surgical interruption. Application of trains of ttimuli at frequencies appropriate to Induce a self-sustained flutter revealed that (1) flutter can be more easily induced by stimuli applied to the left atrial insertion of Bachmann's bundle than to the body of the right atrium, (2) flutter can be initiated by appropriate trains of stimuli without the creation of an artificial obstacle, and (3) flutter exhibits the same characteristic behavior, with or without artificial obstacles. Doses of potassium that elevate the plasma concentration to 9.5 mM/liter cause total inactivation of atrial myocardium without suppressing flutter waves as recorded from the vicinity of the intemodal pathways. Section of the middle internodal pathway reduces the frequency of experimental flutter, section of both the middle and posterior pathways prevents the establishment of flutter. The results suggest that the specialized intemodal pathways play an important role in the genesis and maintenance of circus movement flutter.