Ganglionated Plexi Modulate Extrinsic Cardiac Autonomic Nerve Input Effects On Pulmonary Vein Sleeves And Inducibility Of Atrial Fibrillation In Canis

Objectives:1) This study sought to systematically investigate the interactions between the extrinsic and intrinsic cardiac autonomic nervous system(ANS) in modulating electrophysiological properties and atrial fibrillation(AF) initiation,including sinus node ruction,A-V conduction and the maintanence of AF adjusted by stimulating cervical vagua trunck and ablating SANFP or AVNFP for understanding the mechanism of functional interactions between cervical vagua trunck and ganglionated plexi within the intrinsic cardiac ANS.Systematic ganglionated plexi(GP) ablation to evaluate the extrinsic and intrinsic cardiac ANS relationship has not been detailed.2) To determine if autonomic nerve stimulation within canine atrium and pulmonary vein sleeves initiates arrhythmia formation.3) To explore the possible relationship between the ultrastructural characteristics of pulmonary veins and the pathogenesis of atrial fibrillation originating from pulmonary veins.Methods:1)(1) Eighteen adult mongrel dogs was divided to two groups,both vagosympathetic stimulation was performed by applying high-frequency electrical stimulation(0.5v,1.0v,2.0v,4.0v) to each of the vagosympathetic trunk via a stimulator.The chest was opened via left lateral thoracotomy to record the potentail of LSP,VLIPV.Then closed the left chest,and open the right lateral thoracotomy to recorded he potential of RSPV and RIPV,and further expose the SANFP,AVNFP.With unilateral vagosympathetic trunk stimulation(0.5v,1.0v,2.0v,4.0v,100ms,0.1ms duration),sinus rate(SR),AH interval and the duration of AF were compared before and after sequential ablation of SANFP,SANFP+AVNFP during stimulating cervical vagosympathetic trunks repectively.In another group,with the same stimulation,sinus rate(SR),and AH interval were compared before and after sequential ablation of AVNFP,AVNFP+SANFP during stimulating cervical vagosympathetic trunks.2) Extracellular bipolar and intracellular microelectrode recordings were obtained from isolated superfused canine pulmonary veins(N=24) and right atrium(N=5) during local autonomic nerve stimulation.3)The myocardial sleeves of pulmonary veins from 6 dogs were serially sectioned(2mm) transversely along the vessels.The odd number sections were fixed in 10%phosphate buffered formalin solution and the even number sections were fixed in 3%Glutaral for further electron microscopy observations.The myocardial sleeves of pulmonary veins were embeded in 10%by parrafen and sliced,then lices were tained with hemmatoxylin and eosin.The slices were examined by microscope.Results 1)(1)SANFP ablation significantly attenuated the SR response with right or left vagosympathetic stimulation. After SANFP ablation,AVNFP ablation produced further attenuation of SR slowing induced by right vagosympathetic stimulation.Left vagosympathetic stimulation produced similar but smaller effects on SR slowing compared with right vagosympathetic stimulation,left vagosympathetic stimulation significantly slowed atrial ventricular conductivity the during RAP,SANFP ablation attenuated the maximal effect but there was no the same effect in right vagosympathetic stimulation(0.34±0.13 vs 0.28±0.20). Compaed with SANFP ablation,SANFP+AVNFP ablation further attenuate slowing atrial ventricular conductivity effect(0.93±0.12 vs 034±0.15,0.93±0.12 vs 0.70±0.23). SANFP+AVNFP ablation induced significant changes on eliminating the atrial ventricular conductivity slowing effects.AF duration was shortened after SANFPablation during right vagosympathetic stimulation,after SANFP+AVNFP ablation,stimulation made AF duration became longer than SAN-FP ablation alone during RAP.Left vagosympathetic stimulation can make AF duration longer,but the differences before and after SANFP and SANFP+AVNFP ablation failed to achieve statistical significance at all voltage levels.Right and left vagosympathetic stimulation on ERP:at the level of 1v,left vagosympathetic stimulation shortened the ERP recorded from the right atrium and left atrial appendage(99ms±22 vs 141ms±16),LA(102ms±14 vs 135ms±12),RSPV(105ms±8 vs125ms±8).There is no significant difference between SANFP ablation and SANFP+AVNFP.(2) Compared with AVNFP ablation,AVNFP+SANFP ablation further produced attenuation of SR slowing induced by right vagosympathetic stimulation (99±20.1 vs 51.6±20.4,97.6±20.3 vs 59.2±10.7).There was significant difference in SR slowing between AVNFP ablation alone and AVNFP+SANFP ablation during left vagosympathetic stimulation at the level of 2v,4v(90.2.6±24.8 vs 83.4±23.2,95.6±18.8 vs 85.4±14.8);AVNFP ablation attenuated the maximal effect of slowing the atrial ventricular conductivityn during right or left vagosympathetic stimulation respectively (0.39±0.15 vs 0.74±0.33,0.23±0.13 vs 0.80±0.20).Compaed with SANFP ablation, AVNFP+SANFP ablation did not further attenuate slowing atrial ventricular conductivity effect(0.76±0.28 vs0.74±0.33,0.83±0.21 vs0.80±0.20).AF duration was shortened after SAN-FPablation at the level of 1v,2v,4v(0.75±1.5 vs 35±12,16.8±9.0 vs 60±0,2.5±1.5 vs 60±0),after AVNFP+SANFP ablation,stimulation made AF duration became longer than AVNNFPablation alone during RAP.Left vagosympathetic stimulation can make AF duration longer,but the differences before and after AVNFP and AVNFP+SANFP ablation failed to achieve statistical significance at all voltage levels. Left vagosympathetic stimulation shortened the ERP recorded from the right atrium and left atrial appendage(99ms±22 vs141ms±16),LA(102ms±14 vs135ms±12),RSPV (105ms±8 vs125ms±8).There is no significant difference between AVNFP ablation and AVNFP+SANFP.2) Autonomic nerve stimulation decreased pulmonary vein sleeve action potential duration(APD90=160+/-17 to 92+/-24ms;P＜0.01) and initiated rapid (782+/-158 bpm) firing from early afterdepolarizations in 22 of 28 pulmonary vein preparations.The initial spontaneous beat had a coupling interval of 97+/-26 ms.Failure to induce arrhythmia was associated with a failure to shorten APD90(151+/-18 to 142+/-8ms;P=0.39).Muscarinic receptor blockade(atropine:3.2×10(-8) M) prevented APD90 shortening in 8 of 8 preparations and suppressed firing in 6 of 8 preparations, whereas beta1-adrenergic receptor blockade(atenolol:3.2×10(-8) M) suppressed firing in 8 of 8 preparations.The same stimulus trains produce atropine-suppressed APD90 shortening in superfused right atrial free wall but fail to produce triggered arrhythmia.3) The myocardial sleeves in pulmonary veins can be devided into or three strata,and lasted along pulmnary veins,the direction of myocardial sleeves appeared a change from circular to oblique and longitudinal.At the termials,they were encompassed and separated by connective tissue.3) The muscle fibers in myocardial sleeves were assembled with fasciculation and extened irregularly.The width of myocardial sleeves in RSPV,RIPV,LSPV and LIPV were 0.46±0.14,0.35±0.16,0.37±0.13,0.35±0.11 respectively,and the length were 10.75±3.15,9.46±2.20,9.20±2.88,11.41±2.8 in RSPV, RIPV,LSPV and LIPV.Conclusions:1)The study provides functional evidence that SANFP played an very important role in adjusting sinus node fuction,A-V conduction and the maintainence of atrial fibrillation.While SANFP fad pad was an cooperator, supporting clinical evidence that intercormections within the intrinsic cardiac ANS are critical elements in identifying the targets for atrial fibrillation ablation.Our study also subjected that cervical vagal nervous connected with anatomically and affected fuctionally on ganglionated plexi modulated sinus node,AV nodal function and atrial electrophysiological characteristics together.The GP function as the "integration centers" that modulate the autonomic interactions between the extrinsic and intrinsic cardiac ANS. 2) The data demonstrate triggered firing within canine pulmonary veins with combined parasympathetic and sympathetic nerve stimulation.3) The characteristic distribution of canis myocardial sleeves in pulmonary veins possibly provides modal foundation for the occurance of focal atrial fibriilation.The myocardial fibers are irregularly arranged, which may cause the electric conduction unevenly and nonisotropically.