New insights regarding the atrial flutter reentrant circuit - Studies in the canine sterile pericarditis model

Background-We studied atrial activation during induced atrial flutter in th e canine sterile pericarditis model to test the hypothesis that the atrial flutter reentrant circuit includes a septal component. Methods and Results-We studied 10 episodes of induced, sustained (>5 minute s) atrial flutter in 9 dogs. In all episodes, the reentrant circuit include d a septal component. In 6 episodes, there were 2 reentrant circuits, one i n the right atrial free wall and the second involving the atrial septum, Ba chmann's bundle, and the right atrial free wall; both circuits shared a pat hway in the right atrial free wall (figure-of-eight). The direction (superi or or inferior) of the septal wave front of the second circuit correlated w ith the direction (clockwise or counterclockwise, respectively) of the righ t atrial free-wall circuit. A line of functional block in the right atrial free wall was part of both reentrant circuits. In the other 4 atrial flutte r episodes, only 1 reentrant circuit was present, with activation in an inf erior-to-superior direction in the septum and a superior-to-inferior direct ion in the right atrial free wall in 2 episodes and in the opposite directi on in the other 2 episodes. In all atrial flutter episodes, the flutter wav e polarity in ECG lead II was determined by the direction of activation in the left atrium; polarity was positive when the direction was superior to i nferior and negative when the direction was inferior to superior. Conclusions-In this model of atrial flutter, the reentrant circuit (1) alwa ys included a septal component, (2) did not always require a right atrial f ree-wall reentrant circuit, (3) demonstrated figure-of-eight reentry when a reentrant circuit was present in the right atrial free wall, and (4) was a ssociated with a line of functional block in the right atrial free wall.