The Experimental And Clinic Research Of The Effects Of Ventriculoatrial Conduction On Sinus Node Function And Electrophysiological Characteristics Of Cardiac Atrium

Cardiac pacing is important therapy for bradycardia induced by sinus node dysfunction. Recently, contrasting study on modes of both pure cardioventricular pacing and AV synchrony pacing in clinic, which revealed long-term harmful effects that pure cardioventricular pacing can induce atrial arrhythmia besides hemodynamics abnormity. But mechanisms atrial arrhythmia induced by pure cardioventricular pacing is still unclear. Because ventriculoatrial conduction is common in pure cardioventricular pacing, whether ventriculoatrial conduction can produce harmful effects on sinus node function and electrophysiological characteristics of cardiac atrium which induces the atrial arrhythmia or not, Further research for ventriculoatrial conduction is necessary.The rabbit model of sinus node dysfunction is object in the trial, which was established in rabbits with radiofrequence ablation method (ablated the sinus node region of the rabbits), to plan exclusion of cardiac atrium itself pathological changes which can interfere electrophysiological characteristics of cardiac atrium. The pure cardioventricular pacing was done in the rabbit model of pure sinus node dysfunction to study the effect induce by ventriculoatrial conduction on sinus node function and electrophysiological characteristics of cardiac atrium, to approach for electro -physiological mechanism of supraventricular arrhythmia induced by ventriculoatrial conduction. And the pure atrial pacing was also done in the rabbit model of pure sinus node dysfunction to study the effect induced by the pure atrial pacing on sinus node function and electrophysiological characteristics of cardiac atrium. The trial aims are to supply evidence in theory for choice the optimal pacing mode to prevent supraventricular arrhythmia induced by the pure cardioventricular pacing. Part1.Electrophysiologic characteristics of the atrium in rabbits with sinus node dysfunctionObjectives: The aim of the study is to establish a rabbit sinus node dysfunction(SND) model for the study of electrophysiologic characteristics of the atrium and to investigate the electrophysiologic mechanisms of rabbites with SND to develop atrial fibrillation(Af) and atrial tachycarsia(AT). Methods: The model of SND was established in 30 rabbits with radiofrequence ablation method(ablated the sinus node region of the rabbits).At a drive cycl length of 200 ms,atrail effective refractory(ERP),the duration of atrial activation (A1 and A2) and atrial latency (S1-A1 and S2-A2) were measured. Wavelength index(WLI) was calculated(WLI=ERP/A2).Results: We did not find significant statistical differences regarding S1-A1 and S2-A2 before and after SND. In contrast, A1,A2 Width were notable lenthening and WLI and ERP was significantly shortening in 2h,4h,6h,7d after SND.Conclusion: In rabbits with SND, atrial ERP and WLI shortening , A1,A2 Width lengthening ,at least in part, the tendency of rabbits with SND to develop Af,AT as a part of its natural history. Atrial electrophysiologic disturbances was an important mechanisms of rabbits with SND to develop Af and AT during natural course. Part2.Effects of Ventricular atrial Conduction on Functions of Sinoatrial Node and Atrial Electrical ActivitiesObjective: The aim of the study was to investigate the influences of ventricular atrial conduction(VAC) on functions of sinoatrial node and atrial electrical activities in rabbit sinus node dysfunction model.Methods: Sinus node dysfunction models were made in 32 health rabbits. The rabbits were divided into 1:1 VAC group and non 1:1 VAC group by pacing right ventricle at 200 beat percent minute(bpm). The changes of right atrial pressure, atrial effective refractory period,atrial activity time,wave length index and corrected sinus node recovery time were examined at 1, 2, 4 hours and 7 days after pacing.Results: (1)1:1 VAC auto-randomized controlled group: At one hour of pacing right atrial pressure was increased significantly (p<0.01),however there were no significant differences in atrial effective refractory period, atrial activity time, wave length index and corrected sinus node recovery time (P>0.05). At 2 hours of pacing right atrial pressure continued to step-up(p<0.01), atrial effective refractory period and wave length index decreased (p<0.01) while corrected sinus node recovery time and atrial activity time increased respectively (p<0.01).The changes of right atrial pressure, atrial effective refractory period, atrial activity time, wave length index and corrected sinus node recovery time become more significant at 4 hours of pacing(P<0.01).At 7 days of pacing , right atrial pressure reduced to the basedline (p>0.05) and the changes of atrial effective refractory period, atrial activity time, wave length index and corrected sinus node recovery time become even significant(p<0.001). (2)non 1:1 VAC auto-randomized controlled group: At 1 hour of pacing right atrial pressure increased significantly(p<0.01), however there were no significant differences in atrial effective refractory period, atrial activity time, wave length index and corrected sinus node recovery time (p>0.05).At 2 and 4 hours of pacing, right atrial pressure continued to increase and there were no significant differences in atrial effective refractory period, atrial activity time, wave length index and corrected sinus node recovery time (p>0.05). At 7 days of pacing 1:1 VAC can reduced atrial effective refractory period and elongate atrial activity time significantly(p<0.05), but there were no significant differences in corrected sinus node recovery time and wave length index (P>0.05). (3) 1:1 VAC group and non 1:1 VAC controlled group: at 1 hour of pacing ,there were no significant differences in right atrial pressure , atrial effective refractory period, and corrected sinus node recovery time (p>0.05),but atrial activity time elongated and wave length index decreased in 1:1 VAC group. Atrial activity time and corrected sinus node recovery time elongated and wave length index decreased respectively (p<0.01) in 1:1 VAC group at 2 hours of pacing.The changes of atrial effective refractory period, atrial activity time, wave length index and corrected sinus node recovery time become more significant while there was no significant difference in right atrial pressure (P>0.05) at 7 days of pacing in 1:1VAC group(p<0.001).Conclusions: VAC can influence the functions of sinoatrial node and atrial electrical activities in rabbit sinus node dysfunction models. VAC should be avoided in patients with sick sinus syndrome. The patients with sick sinus syndrome should be installed with physical pacemaker. Part3. Experimental study of atrial ventricular conduction and ventricular atrial conduction on the atrial electrophysiological characteristics in rabbit sinus node dysfuction modelObjective: To study the influences of atrial ventricular conduction and ventricularatrial conduction on the atrial electrophysiological characteristics in rabbit sinus node dysfuction model.Methods: 50 out of 60 selected health rabbits were copied to sinus node dysfunction models successfully by RFCA the boundary between right-atrial and superior vena cava under opening chest and 50 rabbits with sinus node dysfunction were divided into three group: 1:1 atrial ventricular conduction group ,1:1 ventricular atrial conduction group and non 1:1 ventricular atrial conduction group randomly. The changes of atrial effective refractory period, atrail activity time and atrial wave length index were observed under blocking autonomic nerve in three groups after 1 hour,2 hours ,4 hours and 7 days of pacing.Results: In 1:1 VAC auto-randomized controlled group atrial effective refractory period decreased significantly,atrial activity time increased and wave length index decreased obviously. In non1:1 VAC group, atrial effective refractory period elongated and atrial wave length index increased, there was no significant changes in A2. And comparing 1:1 VAC group with non 1:1 VAC group: pacing in the same time, there was significant difference in the amount of AERP,A2 and WLI between two groups. Otherwise, 1:1 atrial ventricular conduction could elongate atrial effective refractory period, improve atrial wave length index and decrease atrail activity time.Conclusions: Atrail ventricular conduction can anti-atrail disorder in sinus node dysfunction animal model, However ventricular atrail conduction can auxo-atrial disorder in sinus node dysfunction animal model. Part4.Influences of ventricular-atrial conduction on the atrial electrophysiological characteristics and sinus node function in normal peopleObjective: To study the influences of ventricular-atrial conduction on the atrial electrophysiological characteristics and sinus node function in normal people. Methods: 32 health people by RFCA the kent branch successfully were selected. They were divided into two groups: 1:1 ventricular-atrial conduction(VAC) group and non1:1 ventricular-atrial conduction group randomly by ventricular pacing. The changes of atrial effective refractory period, atrail activity time and atrial wave length index were observed under blocking autonomic nerve in two groups after 1 hour ventricular pacing and 1 hour atrial pacing.Results: 1)1:1 VAC made atrial effective refractory period decrease significantly,atrial activity time increase and wave length index decrease obviously. And AERP, A2 and WLI can regain by 1 hour atrial pacing. In non 1:1 VAC group, there was no significant changes in atrial effective refractory period, atrial wave length index and A2. And comparing 1:1 VAC group with non 1:1 VAC group: after 1 hour ventricular pacing, there was significant difference in AERP and A2 . But WLI decreased significantly in 1:1 VAC group. 2)Atrial pacing and ventricular pacing with 1:1 VAC all can inhibit sinus node function.Conclusions: Ventricular-atrail conduction can cause auxo-atrial disorder and inhibit sinus node function in health people, which can induce atrial arrhythmias.