Participation of atrial specialized conduction pathways in atrial flutter.

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Abstract
The circus movement theory of flutter is supported by numerous theoretical, experimental and clinical studies, but there is little consideration of the possible participation of the specialized conduction pathways of the atria. Experimental [dogs] atrial flutter was studied in relation to the behavior of these pathways, in response to elevated K and to surgical interruption. Application of trains of stimuli at frequencies appropriate to induce a self-sustained flutter revealed that 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, flutter can be initiated by appropriate trains of stimuli without the creation of an artificial obstacle and flutter exhibits the same characteristic behavior, with or without artificial obstacles. Doses of K that elevate the plasma concentration to 9.5 mM l cause total inactivation of atrial myocardium without suppressing flutter waves as recorded from the vicinity of the internodal 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 specialized internodal pathways maybe important in the genesis and maintenance of circus movement flutter.