The Mechanism of Canine Atrial Flutter

Abstract

In anesthetized dogs, electrograms were recorded simultaneously from six atrial epicardial sites and a limb or esophageal lead in order to study the mechanism of atrial flutter induced electrically after an intercaval crush in comparison with atrial tachysystole induced by aeonitine. In the former, with limb lead records resembling classical human flutter in form and regularity, activation occupied most of the atrial cycle and progressed in sequence caudally in the right atrium and cranially in the left (counterclockwise flutter); flutter was usually terminated by another crush extending from the initial one to the right atrioventricular junction. The most prominent wave in limb and esophageal leads coincided with left atrial activity. Sometimes activation proceeded clockwise. The two atrial appendages may be activated simultaneously during counterclockwise flutter. These findings support the circus movement hypothesis as the mechanism of pure atrial flutter. In contrast, with aeonitine tachysystole, activation proceeded over both atria at once and was so brief that it left most of the slightly irregular atrial cycle electrically silent. Although limb leads after aeonitine sometimes resembled those of flutter, the contrast in direction and duration of excitation demonstrates profound physiological differences between the two arrhythmias.

New Insights Regarding the Atrial Flutter Reentrant Circuit

“…In fact, as previously summarized, 14 all reliable models of atrial flutter have had to alter the underlying atrial substrate, either by administering exogenous substrates 15,16 or by creating selected lesions. [17][18][19][20][21] Nevertheless, Lewis et al 13 mapped a few selected sites during induced atrial flutter in 4 canine atria and showed that the reentrant circuit traveled either up (inferior to superior) or down (superior to inferior) the right atrial free wall. The remainder of the reentrant circuit was assumed to include left atrial activation and activation around one or both of the great veins (superior and inferior vena cavae).…”

“…Five subsequent limited mapping studies 15,18 -21 in which either a crush lesion or an incisional lesion was made between the cavae also permitted reliable induction of atrial flutter, again suggesting the importance of a line of block between the cavae to achieve stable atrial flutter. Of note, in one of these studies, 18 incomplete intercaval block in 1 dog resulted in failure of atrial flutter induction.…”

Participation of atrial specialized conduction pathways in atrial flutter.

“…29 "T he internodal pathways form closed loops between the sinoatrial (SA) and atrioventricular (AV) nodes; as preferential pathways, they could play a role in the genesis and maintenance of atrial flutter.' 9 To test this hypothesis, we have examined the possibility of producing circus movement flutter by applying rapidly repetitive stimuli to the left atrium, on the assumption that the junction of Bachmann's bundle with the anterior internodal pathway would provide an asymmetric input into the right atrial internodal complex. We have also studied the effects of increasing the plasma potassium concentration on established flutter.…”

Circus movement in the canine atrium around the tricuspid ring during experimental atrial flutter and during reentry in vitro.

“…The second step extended the incision caudally to the tricuspid valve and completely transected the ring of atrial tissue around the tricuspid orifice. The reentrant impulse stopped abruptly when it reached the incision, as shown in figure 5. The tachycardia stopped and could not be reinduced after this incision was made.…”