The Effects Of Radiofrequency Catheter Ablation Of Posterior Wall Of Left Atrium On Electrophysiological Characteristics In Canine

Objective: To study the changes of refractory period and conduction velocity of atrium in canine by abolishing left atrial posterior wall with radiofrequency energy.Method: 10 healthy mongrel canines (weight 15 to 20 kg) were anesthetized with sodium pentobarbital, endotracheal intubation. Multielectrode catheters were positioned in the high right atrium and coronary sinus guided by X ray. The ablation catheter was placed in left atrium by transeptal access. S1S2 stimulates were delivered at high right atrium, coronary sinus, left atrial appendage and posterior wall of left atrium respectively,measuring atrial refractory period, conduction times. Radiofrequency catheter ablation (RFCA) was given at 4 sites of posterior wall of left atrium randomly with 50oC, 15W and 120 second in every site. Electrophysiology studies were repeated after RFCA. Result: ① The atrial effective refractory period(AERP)of the left atrial appendage, the posterior wall of left atrium and the distal coronary sinus increased after RFCA (Before RFCA:104±20ms, 102±19ms, 91±12ms; After RFCA: 114±13ms,113±17ms,113±18ms,P<0.05),however, the AERP of the coronary sinus ostium and the high right atrium decreased.( Before RFCA: 111±23 ms ,102±12 ms; After RFCA: 95±23 ms,95±1 ms P <0.05) .② There was no significant change of the dispersion of atrial effective refractory period (dAERP) of right atrium, left atrium and both atria (Before RFCA:26±18ms,20±11ms,33±14 ms;After RFCA:20±10 ms,20±13 ms,38±13 ms, P>0.05). ③ The Conduction time from the high right atrium to the coronary sinus ostium and from the distal coronary sinus to the left atrial appendage were decreased after RFCA (Before RFCA: 34±14ms, 38±11ms; After RFCA: 40±17ms, 45±7ms, P<0.05), while the Conduction time from the high right atrium to the distal coronary sinus had no marked difference before and after RFCA (38±8 ms VS 39±5 ms, P>0.05). ④The atrial relative refractory period (ARRP) of the high right atrium decreased after RFCA (133±39 ms VS 111±29 ms, P<0.001), however, the ARRP of the left atrial appendage increased (104±14 ms VS 124±18 ms, P<0.05). the ARRP of the posterior wall of left atrium , the distal coronary sinus ,the coronary sinus ostium did not change significantly after RFCA(Before RFCA:124±29 ms,119±27 ms,114±15 ms; After RFCA: 127±17 ms,124±17 ms,111±22 ms, P>0.05). the window between ARRP and AERP of the 5 Sites had no marked changes(the high right atrium: 22±20 ms VS 16±13 ms; the coronary sinus ostium: 13±9 ms VS 15±14 ms; left atrial appendage: 21±16 ms VS 14±7 ms; the posterior wall of left atrium: 18±13 ms VS 11±7 ms; the distal coronary sinus: 14±13 ms VS 11±6 ms,P >0.05) ⑤ Before ablation, atrial arrhythmia was induced 16 times in 5canines by programmed atrial stimulation with a single extra stimulus, and there are 4 times maintained for >30 second among which, whereas after ablation, atrial arrhythmia was induced 3 times in 1 canine by programmed atrial stimulation, and atrial arrhythmia maintained for >30 second was no longer inducible .all atrial arrhythmia that was induced maintained for <2 minutes either before or after RFCA .the AERP , dAERP , did not differ significantly between the canines in which atrial arrhythmia can be induced and the canines in which no atrial arrhythmia was induced. ⑥ Macroscopic postmortem inspection of the ablation sites in the left atrium. The RFCA lesions were found to be located at the posterior wall of left atrium。Conclusion: ①Atrial refractory period and conduction changed both right atrium and left atrium after abolishing posterior wall of left atrium with radiofrequency anergy. This may explained by the effects of autonomic nerve. ②The atrial arrhythmia induced by extra stimulus has a tendency of decrease after ablation may suggests that there is substrate related to arrhythmias in left atrium.