The Effects Of Transcutaneous Electrical Stimulation Of Auricular Branch Of Vagus Nerve On The Autonomic Nerve System To Improve Treatment In Heart Failure

Myocardial infarction(MI),is an acute and serious heart disease,the symptoms are different degrees of chest pain discomfort,may also be associated with weakness,sweating,dizziness,vomiting,dyspnea,palpitations,heartbeat instability,and sometimes Loss of consciousness.The cause is part of the myocardial blood circulation suddenly all interrupted,the heart can not get enough oxygen due to damage.Typically,coronary blood vessels that supply blood to the heart are blocked by vulnerable plaques caused by white blood cells or lipids.Myocardial infarction is generally a life-threatening medical emergency,and it requires immediate first aid.Myocardial infarction is one of the leading causes of death in developing countries.Ventricular remodeling in pathological factors under the action of cardiac hypertrophy,increased extracellular matrix,collagen network fracture,deformation,ventricular hypertrophy and expansion of some pathological process.In recent years,the study found that changes in autonomic nervous activity and ventricular remodeling,especially after myocardial infarction is closely related to the occurrence of ventricular remodeling,autonomic dysfunction,especially sympathetic activity increased,can significantly increase the pathological process of ventricular remodeling.Therefore,the intervention of autonomic nerve activity of the method can effectively inhibit the occurrence of ventricular remodeling.Vagal stimulation in the ear can regulate the balance of autonomic nervous system and enhance the activity of vagus nerve.It has a good curative effect in the treatment of atrial fibrillation in animal experiment and clinical experiment.This study was designed to investigate the effects of otogenic vagal stimulation on ventricular remodeling after myocardial infarction.Part 1 Chronic intermittent low-level transcutaneous electrical stimulation of the auricular branch of the vagus nerve improves left ventricular remodeling in conscious dogs with healed myocardial infarctionObjectives:Vagus nerve stimulation(VNS)attenuates left ventricular(LV)remodeling after myocardial infarction(MI).Our previous study found a noninvasive approach to deliver VNS by transcutaneous electrical stimulation of the auricular branch of the vagus nerve.So we hypothesize chronic intermittent low-level tragus stimulation(LL-TS)could attenuate LV remodeling in conscious dogs with healed MI.Methods:Thirty adult male beagle dogs(body weight,10 to 15 kg)which were anesthetized with Na-pentobarbital,40 mg/kg,and ventilated with room air by a positive pressure respirator were randomly divided into three groups,MI group(left anterior descending artery and major diagonal branches ligation to introduce MI,n=10),LL-TS group(MI plus chronic intermittent LL-TS,n=10)and Control group(sham surgery without stimulation,n=10).Tragus stimulation was delivered to bilateral tragus by ear-clips connected to a custom-made stimulator.The voltage slowing sinus rate was used as the threshold for setting LL-TS at 80%below that.LL-TS group was given four hours’ stimulation at 7-9AM and 4-6PM on conscious dogs.Doppler echocardiography(Vivid E9,GE healthcare,USA)was carried out under continuous ECG monitoring with a 3.5 MHz electronic probe on conscious dogs lying in lateral recumbency at the day before the surgery,30 days and 90 days after surgery.The infarct size was assessed with 0.5%Evans Blue and 1.0%triphenyltetrazolium chloride(TTC)staining in 5 dogs of LL-TS group and 5 dogs of MI group.At the end of protocol,the hearts(5 dogs in LL-TS group,5 dogs in MI group)were removed from the chest for sectioning from apex to base into three transverse rings of 5mm in thickness for histomorphometric measure.The volume fraction of replacement fibrosis(VFRF),as calculated from trichrome-stained sections as the percent total surface area occupied by fibrosis.The volume fraction of interstitial fibrosis(VFIF)was calculated as the percent total surface area occupied by interstitial space minus the percent total area occupied by capillaries.The hearts of 10 dogs from control group and the hearts sectioned in histomorphometric measurements were used for western blotting.Plasma C-reactive protein(CRP)level,Plasma NE concentrations and plasma NT-proBNP contents were determined using a validated radioimmunoassay method.Results:At the end of 90-day follow-up,the baseline of echocardiographic measurement was comparable in three groups.The LV end-diastolic volume,end-systolic volume were significant higher and LV ejection fraction,E/A were significant lower in MI group than control group at both 30 and 90 day.But LL-TS group significantly reduced LV dilatation,improve left ventricular contractile and diastolic function compared with MI group at the 30-day follow-up.Interestingly,the treatment of LL-TS better improved cardiac function at the end of 90-day(all P<0.01).Myocardial infarct size expressed as AAR was a little larger in MI group than LL-TS group.(M:49.8±10.7%vs.S:40.4±6.5%,P=0.13).However,LL-TS treatment significantly reduced mean infarct area by about 50%compared with MI group(M:40.9±9.1%vs.S:20.2±5.6%).Treatments with LL-TS significantly decreased the VFRF and VFIF in the tissue of infarction border area compared with dogs in MI group(All P<0.01).The protein level of TGF-β1,MMP-9,collagen Ⅰ and collagen Ⅲ was remarkably increased in MI and LL-TS group than control group(All P<0.01).However,LL-TS group significantly reduced TGF-β1,MMP-9,collagen Ⅰ and collagen Ⅲ protein level in left ventricular free wall compared with MI group at the end of follow-up(All P<0.05).Plasma levels of hs-CRP increased significantly after induction of myocardial infarction,LL-TS therapy markedly attenuated the increase in plasma hs-CRP levels at both 30th and 90th day.(Figure 6,upper panel,both P<0.05)Plasma NE levels also increased from the 1st day after surgery.However,the levels were significantly lower in LL-TS group than MI group from the 1st day to 90th day.(Figure 6,middle panel,all P<0.05)Plasma NT-proBNP levels were obviously increased from the 1st day after surgery.LL-TS group significantly reduced plasma NT-proBNP levels from the 1st day to 90th day compared with MI group.(Figure 6,bottom panel,all P<0.05)Conclusion:Chronic intermittent low-level transcutaneous electrical stimulation of the auricular branch of the vagus nerve can attenuate LV remodeling in conscious dogs with healed MI.Part 2 Low-level Transcutaneous Electrical Stimulation of the Auricular Branch of Vagus Nerve Ameliorates Left Ventricular Remodeling and Dysfunction By Down-regulation of Matrix Metalloproteinase 9 and Transforming Growth Factor β1Introduction:Vagus nerve stimulation(VNS)improves left ventricular remodeling by down-regulation of matrix metalloproteinase 9(MMP-9)and transforming growth factor β1(TGF-β 1).Our previous study found low-level transcutaneous electrical stimulation of the auricular branch of the vagus nerve(LL-TS)could be substituted for VNS to reverse cardiac remodeling.So we hypothesize that LL-TS could ameliorate left ventricular remodeling by regulation of MMP-9 and TGF-β1 after myocardial infarction(MI).Methods:Twenty-two adult male beagle dogs(body weight,10 to 15 kg)were randomly divided into three groups.A control group(MI was induced by permanent left anterior descending artery[LAD]ligation,n=8),a LL-TS group(MI plus LL-TS,n=8)and a normal group(sham ligation without stimulation,n=6).Two hours of LL-TS was first started at 3 hours after induction of MI,then four hours of stimulation at 7-9AM and 4-6PM were performed everyday for 6 weeks.None received other background therapy.A Harris two-stage occlusion was performed on the left anterior descending artery with 3-0 silk above the first diagonal branch to produce a MI.The vessel was partially occluded for 20 minutes and then completely tied off.The voltage necessary to slow the sinus rate was used as the threshold and the LL-TS was delivered at 80%below that.Transthoracic doppler echocardiography was performed at baseline and 6 weeks after MI on conscious dogs,which were lying in lateral recumbency.Paraffin-embedded cross-sections of the heart were stained for collagen(sirius red/picric acid).WB was used for MMP-9,Collagen I and III,TGF-β1 protein.Plasma MMP-9 level,plasma TGF-β1,plasma aldosterone and plasma noepiphrine level was determined by a validated radioimmunoassay method.Results:At the end of 6 weeks follow-up,MI induced a significant LV dilation reflected by the increased ESD and EDD(P<0.01).The systolic function was impaired as evidenced by a decrease in LV ejection fraction(P<0.01).MI also deteriorated the LV diastolic function,leading to an increase in the ratio of early(E)to late(A)ventricular filling velocities(E/A ratio;P<0.01).Chronic treatment with LL-TS reduced the ESD from 29 ± 3mm in the control group to 21 ± 2mm in the LL-TS group and the EDD from 38 ± 5mm to 32 ± 4mm(both P<0.01).Also LL-TS significantly improved the systolic and diastolic function,raising the ejection fraction(64 ± 5%vs.48 ± 4%,P<0.01)and the E/A ratio(1.27 ± 0.07 vs.1.48± 0.06 P<0.01)in comparison with the control group.Less collagen accumulation was found in the LV myocardial tissue after LL-TS treatment.Interstitial fibrosis markedly increased in the noninfarcted heart tissues in the control group compared with the normal group(5.7 ± 0.4%vs.2.8 ± 0.5%;P<0.01);treatment with LL-TS completely prevented this effect(3.4 ± 0.4%vs.5.7 ± 0.4%;P<0.01).Also the protein level of collagen I and collagen III was significantly increased in the control group compared with the normal group(Both P<0.01).However,the LL-TS significantly reduced both the collagen protein level(Both P<0.01).MMP9 protein level was upregulated post-MI(5.8-fold;P<0.01),but LL-TS treatment significantly attenuated the augmentation.In the control group,the TGF-β 1 protein expression was significantly upregulated,but the regulation was completely abolished by the LL-TS.the plasma concentration of MMP-9 and TGF-β 1 tended to be elevated 6 weeks post-MI,the LL-TS treatment normalized their plasma level(both P<0.01).And the plasma NE and aldosterone levels also significantly increased 6 weeks post-MI in the LL-TS and control group.However,the augmentation was significantly attenuated in the LL-TS group compared with the control group.(P<0.01).Conclusions:LL-TS treatment could impart cardioprotection against acute ischemia-reperfusion injury through prevention of mitochondrial dysfunction.