| Atrial fibrillation(AF) is the most common of all sustained cardiac arrhythmias. Recent studies indicate that interaction between wave fronts in the right and left atrium may be important for the initiation and maintenance of AF. The AF wavelets critical to the maintenance of AF often generate in the left atrial appendage (LAA) and the ectopic beats initiating AF often originate from the pulmonary veins (PV) in some types of AF, but little is know about the activation patterns of the atrial septum and preferential routes of transseptal conduction of the impulse from these sites.Five mongrel dogs were included in the study. Two multielectrode catheters were introduced percutaneously through the femoral veins, one placed in the high anterior septum, the presumed insertion of Bachmann' s bundle (BB), the other in the Fossa ovalis(FO).A decapolar catheter was inserted into the coronary sinus (CS) via the internal jugularvein. Simultaneous bipolar recordings were obtained from BB, FO and the proximal CS (CSp). SjSi pacing with a cycle length shorter than sinus cycle length by 50~100ms was performed from the distal CS (CSd), LAA, the right superior pulmonary vein(RSPV), the right inferior pulmonary vein(RIPV), the left superior pulmonary vein(LSPV)and the left inferior pulmonary vein(LIPV). The activation sequences were analyzed during pacing. The activation times from the pacing sites to BB, FO and CSp were measured. The total septal activation time which was defined as the time from the earliest septal activation to the latest activation was measured.During CSd pacing, the earliest atrial septal activation was near CSp. The mean activation time from stimulus to CSp was shorter than that to FO and BB (17 +10ms versus 37 +15ms and 43 + 16ms, P<0.05). During LAA pacing, the earliest activation was near BB. The mean activation time from stimulus to BB was 15 + 5ms compared with 27 + 8ms to FO(P<0. 05)and 42 + 8ms to CSp(P<0. 05). During LSPV pacing, the earliest activation was near BB and FO. The mean activation times from stimulus to BB and FO were not significantly different from that to CSp, but that had a tendency of decrease (29 + 7ms versus 40?2ms, P>0. 05;29 + 15ms versus 40 + 12ms, P>0. 05). During LIPV pacing, CSp, FO and BB were almost activated simultaneously. The mean activation times from stimulus to these three sites were not significantlydifferent (29 ?12ms, 28 ?8ms and 33 ?10ms). During RSPV pacing, BB and FO were the earliest activation sites. The mean activation times from stimulus to BB and FO were shorter than that to CSp(26?ms versus 40?0ms,P<0. 05;24眑lms versus 40 ?10ms, P<0. 05). During RIPV pacing, BB, FO and CSp were almost activated simultaneously. The mean activation times from stimulus to these three sites were not significantly different(28+15ms, 26 +5ms and 29+14ms).The total septal activation time during LIPV pacing was shorter than that during CSd and LAA pacing(9 +10ms versus 28+llms, P<0. 05; 9 + 10ms versus 27 + 4ms, P<0. 05). The total septal activation time was not significantly different during the inferior pulmonary veins pacing compared with the superior pulmonary veins pacingdl+ 9ms and 21 +10ms), but it demonstrated a tendency of decrease.There are three pathways for electrical conduction between the right and left atria. CSd pacing demonstrated that the preferential site of transseptal conduction is near CSp, LAA pacing near BB and superior pulmonary veins pacing near BB and FO. Inferior pulmonary veins pacing showed that BB, FO and CSp are almost activated simultaneously and the total septal activation time is relatively short. The results of this electrophysidogical study are in accord with the anatomical features of interatrial pathways and may lay a foundation for a better understanding the role ofinteratrial connections in the initiation and maintenance of AF.
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