Impact Of Ablation In Slow Pathway Area On Vagal Modulation To Atria

Part 1Impact of ablation in slow pathway area on vagal modulation to atria vulnerabilityObjective:Atrioventricular node reentrant tachycardia (AVNRT) ablation may modulate the vagal response, which is indicated by the frequently observed sinus tachycardia after ablation. On the other hand, atrial fibrillation (AF), which was found to be associated with vagal function, often coexists with AVNRT. However, little is known about the impact of slow pathway ablation on local vagal innervation to atria.Methods:In 11 dogs, bilateral cervical sympathovagal trunks were decentralized and metoprolol was given to block sympathetic effects. Linear lesion was performed from coronary sinus (CS) ostium to the middle area of Koch triangle by radiofrequency catheter ablation. Atrial effective refractory period (ERP) and vulnerability window (VW) of AF at high right atrium (HRA), inferior right atrium (IRA), distal (CSd) and proximal CS (CSp), and sinus rate (SR) were measured at baseline with and without vagal stimulation before and after ablation. The histological study of ablation and surrounding tissue was also performed.Results:(1)SR shortening during vagal stimulation remained unchang- ed before and after ablation(107±19)bpm vs (108±8)bpm(P>0.05). (2) After ablation, ERP shortening during vagal stimulation remained unchanged at HRA (55±34) ms vs (69±37) ms (P>0.05), and decreased slightly at CSd (55±30) ms vs (42±32) ms (P=0.08). However, at LRA and CSp, ERP was significantly decreased after ablation (66±24) ms vs (19±21) ms (P<0.001); and (46±24) ms vs (7±18)ms (P<0.001), respectively. (3) AF was difficult to be induced at baseline before and after ablation in all sites (VW close to 0). While during vagal stimulation, after ablation VW of AF significantly decreased at LRA (49±36) ms vs (1±3) ms (P<0.005) and CSp (45±34) ms vs (10±12) ms (P<0.05), decreased slightly at CSd after ablation (57±28) ms vs (35±37) ms (P=0.07), and remained unchanged at HRA (63±31) ms vs (63±25) ms (P>0.05). (4) The altered architecture of individual ganglia was histological observed.Conclusions: The decreased ERP shortening to vagal stimulation in CS and IRA induced by ablation at the slow pathway area indicates that ablation in such area may result in the vagal denervation around IRA and CS, thereby attenuating the susceptibility to vagal mediated AF. While unchang- ed SR, ERP shortening and VW to vagal stimulation in sinus node area and HRA indicate that ablation at the slow pathway area could not modify the vagal innervation to these sites.Part 2Vagal modulation to atrioventricular conduction before and after ablation on the slow pathway areaObjective:Vagal modulation to atrioventricular conduction remains unclear. The vagal tone changes after the slow pathway ablation in patients with atrioventricular nodal reentrant tachycardia could be observed. This study aims to investigate the vagal modulation to atrioventricular conduc- tion and the consequence after ablation at slow pathway area.Methods:In 11 dogs, bilateral cervical sympathovagal trunks were decentralized, with Metoprolol administrated. Linear lesion was performed by radiofrenquency catheter ablation from middle area of Koch triangle to the coronary sinus ostium. Before and after ablation, atrioventricular nodal effective refractory period (ERP) and atrioventricular conduction curves were measured at baseline and during vagal stimulation. The histological studies at slow pathway area were also performed.Results:Complete atrioventricular conduction block happened after ablation in 4 dogs. (1) ERP of atrioventricular conduction remained unchanged with or without vagal stimulation (165.7±43.1)ms vs (172.9±55.6)ms(P>0.05), before and after ablation (167.1±53.8)ms vs (171.4±59.8)ms(P>0.05). (2) The atrioventricular conduction time was remarkable prolonged during vagal stimulation before ablation, which means the conduction curve shifted upward and to the right. More important, the curve became discontinuous. (3) The architecture of individual ganglia was significantly altered after ablation at slow pathway area.Conclusions: Certain intensity of vagal stimulation could increase the longitudinal dissociation of the atrioventricular conduction. Ablation could result in the damage of the regional vagal innervation.Part 3Impact of ablation in slow pathway area on atria electrophysiologyObjective:Atrioventricular node reentrant tachycardia (AVNRT) ablation may reduce the atrial fibrillation (AF) inducibility, but the mechanisms remain unknown. We tried to investigate the impact of ablation in slow pathway area on atria refractory period, and to elucidate the underlying mechanism.Methods:Ten patients with AVNRT were enrolled in the study. Atria effective refractory period (ERP) at high right atrium (HRA), inferior right atrium (IRA), distal (CSd) and proximal CS (CSp), as well as sinus rate (SR) and effective refractory period of fast pathway(F-ERP) were measured before and after ablation.Results:(1)After ablation, except HRA,the ERPs at following sites were significantly prolonged:IRA(157.27±6.61)ms,(201.82±14.71)ms, P<0.05;CSd(207.27±10.74)ms,(226.36±14.21)ms,P<0.05;CSp(208.18±12.89)ms,(221.81±16.53) ms,P<0.05,respectively. (2) SCL showed a little decline but without statistic significant before and after ablation(P=0.24).(3) ERP of fast pathway was significantly decreased after ablation:(355.45±29.59)ms,(285.45±26.78)ms,P<0.01.Conclusions:The decrease of ERPs at CS and IRA,as well as F-ERP after ablation may decline atrial fibrillation inducibility and indicated regional vagal denervation to the atrium.