Role Of Pulmonary Veins And Left Atrium In Sustained Vagotonic Atrial Fibrillation In Canines

Background The aim of this study was to investigate the role of pulmonary veins (PVs) and left atrium(LA) in sustained vagotonic atrial fibrillation in canines.Methods Seven dogs were studied. The cervical vagal trunks were isolated and decentralized, and stimulated with electrical stimulation (frequency 20 Hz, voltage 0-1.44 v). All canines were instrumented with epicardial electrode pathes on free walls of both right atrium (RA) and LA via bilateral thoractomy. Sustained atial fibrillation (AF) was induced by a home-made stimulator with frequency of 50 Hz and 1 second duration. Isolation of the PVs, "C" shape isolation and complete isolation of the LA were performed, respectively. Atrial effective refractory period (AERP), inducibility and duration of AF were measured before and after each procedure during cervical vagal nerve stimulation (VNS).Results (1) Before VNS, the AERP of left atrium (AERP_LA) and right atrium (AERPra) were 120.8±14.6 ms and 143.2±14.7 ms, respectively. Sustained AF could not be induced. (2) During VNS, both AERP_LA and AERP_ra shortened dramatically (92.0±21.9ms vs. pre-stimulation at the LA, P<0.05;105.6±19.2 ms vs. pre-stimulation at the RA , P<0.05). Sustained AF could be induced and maintained as long as VNS continued. Atrial fibrillation cycle length (AFCL) of LA and RA were 75.4±17.6 ms and 112.0 + 8.4 ms, respectively. (3) PVs isolation increased the AERP_la to 114.6±14.7 ms ( p=0.001) and AERPra to 123.6±13.7 ms (P=0.002) . AFCL of left atrium(AFCL_LA) and right atrium(AFCLRA) were 83.1±15.8ms (P=0.007, vs. pre-isolation) and 127.3±9.5 ms (p=0.002, vs. pre-isolation) , respectively. (4) After "C" shape isolation of the LA, the AERP_la and AERP_ra were 120.0±13.3 ms and 120.0±11.0 ms, respectively. Sustained AF could be induced, and AFCL_LA and AFCLra were 135.3±12.2 ms and135.0±14.5 ms. (5) After complete isolation of the LA, the AERPla andAERPra were 121.2±14.7 ms and 121.2±10.3 ms, respectively. AF couldterminate simultaneously in 30 seconds. (6) The AERP difference between RAand LA before VNS, VNS, after PVs isolation, after "C" shape isolation of the LAand complete isolation of the LA were 11.7 + 7.3 ms, 15.4 + 7.6 ms, 11.1 ±10.3ms, 3.7 + 3.5 ms(p<0.05, vs. pre-isolation) and 2.0 + 4.6 ms (p<0.05, vs.pre-isolation).Conclusion In the perpetuation of vagotonic AF, the LA may play a criticalrole.