MONOPHASIC ACTION POTENTIAL CHANGES OF RIGHT VENTRICULAR MYOCARDIUM INDUCED BY RADIOFREQUENCY CURRENT IN DOGS

To investigate the monophasic action potential changes of myocardiuminduced by radiofrequency catheter ablation in dogs,the right ventricularepicardium were ablated with radiofrequency(RF)energy(20 w,30 sac)via a 7 Fr.large tip catheter in 8 dogs.Franz catheter was used to record at8 different sites and at 3 different time before and after ablation.Myocsrdial APA,APD90 and Vmax at the ablation site,marginal siteand reference site(20 mm from the ablation site)were measured beforeand after(immediately,30 min)ablation.The interval from stimulationspike(S)(stimulated at right ventricular apex)to the [0] phase of localMAP were also maasured.Results:1.Two to 10 mm from the ablationsite,APA decreased to different degree.There was no change in the APDafter RFCA.2.Vmax of ablation site and marginal zone decreased afterablation(P【0.01);30 min later,Vmax show no change compared with theresult immdietely after ablation(P】0.05).3.S-[0] phase interval increasedfrom ablation site to marginal site after ablation(ablation site 22.50±6.55ms vs 35.63±7.76 ms,P【0.001;marginal site 23.75±7.91 ms vs31.88+9.61 ms,P【0.01).Conclusion:RF energy can destroy or injuremyocardial tissue,and modificate cellular electrophysiology ofperinecrosis myocardium.These findings provide electrophyiologic basisfor sevasal clinincal observations following RFCA. Background:Most AV node reentrant tachycardia are easily induced duringelectrophysiologic studies.However,some could not be induced despite long timestimulation.How to deal with such patients properly is practically important.In thissituation,the radiofrequency ablation may provide a good results,but the experience islimited.The clinical effect need further investigation.Objective:To assess the clinicalefficacy of slow pathway ablation in patients with clinical documented but noninducibleAV node reentrant tachycardia.Methods:The criteria of presumed diagnosis of common-type AV node reentrant tachycardia included tachycardia with pseudo-r’ in lead VI,retrograde p wave on the end of QRS,or without retrograde p wave in all leads duringtachycardia,and/or presence of discontinous curve during the baseline electrophysiologicstudy.The stimuli technique included single,double extrastimuli at 2 basic derive cyclelengths and decremental pacing from atrium,ventricle and coronary sinus.If thetachycardia could not be induced,isoproterenol(1 to 8 ug/min)was used,If thetachycardia could not be initiated with isoproterenol,atropine(1 mg)was given 20 minutesafter termination of isoproterenol infusion.The sites of slow pathway ablation wereseptum or around ostium of coronary sinus with a small fragment A wave and large Vwave.The slow junctional rythms which decreased progressly or dispeared were goodindicator for successful ablation.The endpoints of ablation were elimination of slowpathway and /or significant alternation of Wanckebach point and ERP of AVconduction.The patiants were followed up after procedures.Results:Six patients(4female,2 male)were identified as noninducible AV node reentrant tachycardia.Theaverage age were 53±10 years and the history of tachycardia were 14.8±8.8 years.The heart rates of tachycardia were 180±10 beats/min.Four cases had ECGs oftachycardia,three had retrogrede P wave on the end of QRS wave and pesudo-r’ in VIlead.The remaining one had no retrograde p wave in all leads,The VA retrogradeWenckebach block were seen on 6 cases.Four had jamp of AV conduction(average 86±62 ms).After ablation,the jamp dispeared in three of them,one still had jamp withetrial echo.The ERP and Wenckebach points of AV or VA conduction were changed.During ablation,the junctional rythms were seen in 6 cases,decreased progressly in onecase and dispeared at last in five cases.None of six patients had recurrence of tachycardiaduring follow-up of 18±8.4 months.Conclusion:In patients with documented butnoninducible AV node reentrant tachycardia,the modification of slow pathway canachieve a satisfactory clinical effect.