Median Nerve Modulation And Ventricular Arrhythmias

Backgrounds:Cardiac autonomic nervous system played an important role in the occurrence of ventricular arrhythmias. Sympathetic hyperactivity or hyperinnervation and/or decreased parasympathetic activity tend to dispose to ventricular arrhythmias. Somatic nerve stimulation could modulate the activity of cardiac autonomic nervous system and influence the occurrence of ventricular arrhythmias. The aims of this research included:1) to test the effect of median nerve stimulation on isoproterenol induced ventricular arrhythmias;2) to test the hypothesis that the inhibition of neurally-mediated ventricular arrhythmias by median nerve stimulation was associated with the reduction of cardiac neurotransmitter norepinephrine;3) to investigate the inhibitory effect of median nerve or vagus nerve stimulation on ventricular arrhythmias and cardiac interstitial norepinephrine levels and if there was difference about their inhibitory effect on ventricular arrhythmias and cardiac interstitial norepinephrine concentration.Methods and results:The occurrences of ventricular arrhythmias in this study were induced by isoproterenol infusion and hypothalamus stimulation in order to test the underlined mechanism about the inhibitory effect of median nerve stimulation on ventricular arrhythmias and to test if there is difference about the inhibitory effect on ventricular arrhythmias between median nerve stimulation and vagus nerve stimulation. Combined with in vivo heart microdialysis technique, this research aimed to study the activity of cardiac sympathetic nerve system during hypothalamus stimulation induced ventricular arrhythmias with or without median nerve stimulation, and to testify the interaction between neuromodulation, ventricular arrhythmias and cardiac sympathetic nervous system.The first part experimental study showed that median nerve stimulation prolonged ventricular effective refractory period, reduced the incidence of ventricular arrhythmias induced by isoproterenol infusion in dogs and postponed the occurrence time of first ventricular arrhythmic beat. Concurrent median nerve stimulation made the changing of heart rate tend to smoothing, and the occurrence time of maximum heart rate was postponed after isoproterenol infusion. The inhibitory effect of median nerve stimulation on ventricular arrhythmias was not affected after bilateral vagotomy.The second part experimental study showed that repeated hypothalamus stimulation without nerve stimulation intervention induced reliable occurrence of ventricular arrhythmias. Metoprolol infusion significantly reduced the incidence of hypothalamus stimulation induced ventricular arrhythmias. The concurrent median nerve stimulation during the third and fourth hypothalamus stimulation episode significantly reduced the incidence of ventricular arrhythmias compared to the episodes without median nerve stimulation and postponed the time of the occurrence of the first ventricular arrhythmic beat during hypothalamus stimulation. However, after pretreatment with naloxone, the number of arrhythmic beats induced by hypothalamus stimulation didn’t showed a significant decrease during the concurrent median nerve stimulation and the retard effect of median nerve stimulation on first ventricular arrhythmic beat disappeared. The change in the interstitial norepinephrine concentration was significantly associated with the number of hypothalamus stimulation induced ventricular arrhythmias.The third part experimental study demonstrated that the concurrent median nerve stimulation during the second and third hypothalamus stimulation significantly reduced ventricular arrhythmic incidence and interstitial norepinephrine concentration compared to the episodes without median nerve stimulation. In the vagus nerve stimulation group, the concurrent vagus nerve stimulation during the second and third hypothalamus stimulation significantly reduced ventricular arrhythmic incidence and interstitial norepinephrine concentration compared to the episodes without vagus nerve stimulation. There was no significant difference about the inhibitory effect on hypothalamus stimulation induced ventricular arrhythmias and hypothalamus stimulation induced elevation of interstitial norepinephrine concentration between median nerve stimulation and vagus nerve stimulation group. Median nerve stimulation showed less effect on heart rate than vagus nerve stimulation.Conclusions:1) median nerve stimulation prolonged ventricular effective refractory period and decreased the incidence of isoproterenol induced ventricular arrhythmias in normal dogs, and this inhibitory effect on ventricular arrhythmias was not affected by the vagal nerves;2) median nerve stimulation reduced the incidence of hypothalamus stimulation induced ventricular arrhythmias via the mechanism of modulating cardiac sympathetic neural activity in rabbits;3) both median nerve stimulation and vagus nerve stimulation decreased the incidence of ventricular arrhythmias and the increase of cardiac interstitial norepinephrine induced by hypothalamus stimulation, and there was no significant difference about the inhibitory effect of median nerve stimulation and vagus nerve stimulation on ventricular arrhythmias and cardiac interstitial norepinephrine levels. But median nerve stimulation showed less effect on heart rate than vagus nerve stimulation.