Induced atrial flutter in a normal canine heart. The arrows illustrate the putative re-entrant pathway. I.V.C. = inferior vena cava; P.V. = pulmonary vein; S = site stimulated; S.V.C. = superior vena cava. Reprinted, with permission, from Lewis (14).

Activation maps of the atrial epicardium (left) and atrial septum (right) during sustained atrial flutter in the canine sterile pericarditis model due to a single re-entrant circuit (top panel) and figure-of-8 re-entry (bottom panel). Blue and orange arrows indicate the re-entrant circuit, gray arrows indicate daughter wave fronts generated by the re-entrant circuit, isochrones are at 10-ms intervals, dashed black line indicates line of functional block, and blue asterisks indicate epicardial breakthrough of septal activation and site of entry from epicardium to atrial septum. Numbers equal activation time in milliseconds. Letters A to H are sites from which selected bipolar atrial electrograms were exhibited in the originally published figure. LAA, left atrial appendage; RAA, right atrial appendage; other abbreviations as in Figure 1. Modified, with permission, from Uno et al. (15).

Location and direction of re-entry in 6 examples of atrial flutter (AFL) induced in a canine acetylcholine infusion model of AFL. The AFL cycle lengths ranged from 65 to 145 ms (average: 109 ms). Reprinted, with permission, from Allessie MA, Lammers WJEP, Bonke FIM, et al. Intraatrial re-entry as a mechanism for atrial flutter induced by acetylcholine in rapid pacing in the dog. Circulation 1984;70:123–35.

(Left panel) Activation map during induced atrial flutter (AFL) (cycle length, 134 ms). The thick black line indicates the line of fixed (lesion) block. The hatched areas indicate functional extension of the fixed line of block (LoB). The AFL re-entrant circuit travels up the right atrial free wall (arrow) and down the interatrial septum (dashed arrow). White asterisk indicates epicardial breakthrough; black asterisk indicates septal entry; a to d are recording sites from which electrograms are shown in the right panel. (Right panel) Electrograms recorded from the sites a to d. The double potentials in electrograms b and c indicate that a LoB exists between sites a and d during AFL. Abbreviations as in Figures 1 and 2. Reprinted, with permission, from Tomita et al. (17).

The 2 tracings in each panel are continuous and show electrocardiography (ECG) lead II recorded simultaneously with a bipolar right atrial (RA) electrogram (A_EG). (Top panel) The * denotes a premature atrial beat, which induces atrial fibrillation (AF). (Middle panel) The AF continues until, at the *, atrial flutter develops. (Bottom panel) The stable AFL continues. Time lines are at 1-s intervals. II = lead II. Reprinted, with permission, from Waldo and Cooper (6).

(Top panel) The ECG lead II recorded simultaneously with bipolar A_EGs from the sulcus terminalis and Bachmann’s bundle. The * indicates a premature atrial beat that induces type II AFL (rate of 390 beats/min), which in turn causes AF (see ECG) due, we suggest, to fibrillatory conduction. (Bottom panel) The tracings are continuous with the top panel. Type II AFL persists in the A_EGs, as does AF in the ECG, until AFL abruptly develops (*). We suggest that during the period of AF generated by the type II AFL, the functional components of the typical AFL re-entrant circuit evolved. Time lines at 1-s intervals. BB_EG = electrogram from the Bachmann’s bundle; ST_EG = electrogram from the sulcus terminalis; other abbreviations as in Figure 5. Reprinted, with permission, from Waldo and Cooper (6).