[Characteristics of atrial activation sequence of atrial fibrillation and flutter in a canine model]

In order to induce either atrial fibrillation (af) or atrial flutter (AF) in 22 dogs under pentobarbital anesthesia, a right atriotomy parallel to the sulcus terminalis was performed, but closed with running sutures. Effective refractory periods (ERP) were measured in the sites of the appendages and the bodies in both atria. Further, we developed a computerised mapping system which enabled us to reveal sequential activation of various parts of the heart. As a result, we could assess the circuit of excitation which gave rise to AF. AF occurred in 7 of the 22 dogs, and af in the remaining 15 dogs. It was revealed that during AF there was a counterclockwise (5 dogs) or clockwise (2 dogs) reentrant pathway involving the right atrial free wall and superior vena caval orifice with consequent left atrial activation. Although standard limb lead electrocardiogram showed af, all dogs with sustained af had a regular activation sequence in the left atrium [at a cycle length (period) of 140.1 +/- 16.9 msec, arising either in the left atrial appendage (8 dogs) or adjacent to the left pulmonary vein (7 dogs)]. However, 12 of the 15 dogs had a chaotic activation sequence whereas the other 3 dogs showed a regular activation sequence in the right atrium. Statistically, during AF there was no significant difference between RA ERP (153.2 +/- 12.6 msec), LA ERP (146.4 +/- 14.4 msec) and LA cycle length (period) (140.1 +/- 16.9 msec). During af, there was no significant difference between LA ERP (131.7 +/- 15.2 msec) and LA cycle length (period) (125.7 +/- 9.1 msec), but RA ERP (165.4 +/- 15.5 msec) was significantly longer than the LA cycle length (period) (p < 0.0001). Although in the present experiment regular left atrial activation and complex right atrial activation were observed predominantly, the activation sequence of af was different in each dog. These results clearly indicate that to employ a mapping system like ours is necessary to determine relevant surgical procedures to stop af and AF.