Neural effects on sinus rate and atrioventricular conduction produced by electrical stimulation from a transvenous electrode catheter in the canine right pulmonary artery

Ganglionated Plexi Ablation Suppresses Chronic Obstructive Sleep Apnea-Related Atrial Fibrillation by Inhibiting Cardiac Autonomic Hyperactivation

Background: Previous studies have reported that right pulmonary artery ganglionated plexi (GP) ablation could suppress the onset of atrial fibrillation (AF) associated with obstructive sleep apnea (OSA) within 1 h. Objective: This study aimed to investigate the effect of superior left GP (SLGP) ablation on AF in a chronic OSA canine model. Methods and Results: Fifteen beagles were randomly divided into three groups: control group (CTRL), OSA group (OSA), and OSA + GP ablation group (OSA + GP). All animals were intubated under general anesthesia, and ventilation-apnea events were subsequently repeated 4 h/day and 6 days/week for 12 weeks to establish a chronic OSA model. SLGP were ablated at the end of 8 weeks. SLGP ablation could attenuate the atrial effective refractory period (ERP) reduction and decrease ERP dispersion, the window of vulnerability, and AF inducibility. In addition, chronic OSA leads to left atrial (LA) enlargement, decreased left ventricular (LV) ejection fraction, glycogen deposition, increased necrosis, and myocardial fibrosis. SLGP ablation reduced the LA size and ameliorated LV dysfunction, while myocardial fibrosis could not be reversed. Additionally, SLGP ablation mainly reduced sympathovagal hyperactivity and post-apnea blood pressure and heart rate increases and decreased the expression of neural growth factor (NGF), tyrosine hydroxylase (TH), and choline acetyltransferase (CHAT) in the LA and SLGP. After SLGP ablation, the nucleotide-binding oligomerization domain (NOD)-like receptor signaling pathway, cholesterol metabolism pathway, and ferroptosis pathway were notably downregulated compared with OSA. Conclusions: SLGP ablation suppressed AF in a chronic OSA model by sympathovagal hyperactivity inhibition. However, there were no significant changes in myocardial fibrosis.

Interactive atrial neural network: Determining the connections between ganglionated plexi

BACKGROUND

The electrophysiologic functions of the intrinsic cardiac autonomic nervous system (ANS) are not well understood.

OBJECTIVES

The purpose of this study was to investigate the functional interactions between ganglionated plexi within the intrinsic cardiac ANS.

METHODS

The hearts of 21 dogs were exposed via right and/or left thoracotomy to expose the (1) anterior right ganglionated plexi near the caudal end of the sinoatrial node, (2) inferior right ganglionated plexi at the junction of inferior vena cava and atria, and (3) superior left ganglionated plexi near the junction of left superior pulmonary vein and left pulmonary artery. Ganglionated plexi were stimulated at 0.6 to 8.0 V (square waves, 20 Hz, 0.1-ms duration). Sinus rate, AH interval during atrial pacing, and ventricular rate during atrial fibrillation were compared before and after ganglionated plexi stimulation and after their ablation.

RESULTS

Anterior right ganglionated plexi stimulation induced significant AH prolongation and slowing of ventricular rate and sinus rate. When inferior right ganglionated plexi was ablated, slowing of sinus rate by anterior right ganglionated plexi stimulation was unaltered, but inhibition of AV conduction was eliminated. Superior left ganglionated plexi stimulation induced similar effects on sinus and AV nodal function, and sinus rate slowing was markedly attenuated by anterior right ganglionated plexi ablation. Ablation of both anterior right ganglionated plexi and inferior right ganglionated plexi eliminated AV conduction inhibition but not sinus rate slowing by superior left ganglionated plexi stimulation.

CONCLUSION

This study provides functional evidence for the interconnections between ganglionated plexi to modulate sinus and AV nodal function, supporting clinical evidence that interconnections within the intrinsic cardiac ANS are critical elements in identifying the targets for atrial fibrillation ablation.

Electrophysiological control of ventricular rate during atrial fibrillation

Thirteen anesthetized canine subjects (17-29 kg) were used to demonstrate that mild cervical left vagal stimulation could control ventricular rate effectively during atrial fibrillation (AF). Two studies are presented. The first study used six subjects to demonstrate the inverse relationship between (manually applied) left vagal stimulation and ventricular excitation (R wave) rate during AF. As left vagal stimulation frequency was increased, ventricular excitation rate decreased. In these studies, a left vagal stimulus frequency of 0-10 per second reduced the ventricular excitation rate from > 200/min to < 50/min. The decreasing ventricular excitation rate with increasing left vagal stimulation frequency was universal, occurring in all 26 trials with the six subjects. This fundamental principle was used to construct an automatic controller for use in the second study, in which seven subjects were used to demonstrate that ventricular rate can be brought to and maintained within a targeted range with the use of an automatic (closed-loop) controller. A 45-minute record of automatic ventricular rate control is presented. Similar records were obtained in all seven subjects.

New technique for vagal nerve stimulation

INTRODUCTION

The vagus nerve travels in a neurovascular bundle with the carotid artery and internal jugular vein. The present study was designed to assess whether transvascular stimulation through the carotid artery of the dog can be used to directly stimulate the vagus nerve and increase parasympathetic tone.

METHODS

In five anesthetized dogs, a steerable electrode catheter was positioned under fluoroscopic guidance in the right carotid artery in the mid neck via the femoral artery. Multipolar catheters were positioned transvenously through the femoral vein in the right atrium, across the tricuspid valve to record a His-bundle electrogram, and in the right ventricle.

RESULTS

In all five animals, vagal nerve stimulation was successfully achieved with outputs ranging between 10 and 30 mA. Sinus cycle length increased from 473 +/- 113 ms at baseline to 894 +/- 315 ms (P < 0.025) during stimulation from the right carotid artery. There was an increase in the AH interval from 55 +/- 14 to 77 +/- 23 ms (P < 0.03), a shortening of the atrial effective refractory period from 136 +/- 8 to 126 +/- 6 ms (P < 0.01), and a fall in the systolic blood pressure from 135 +/- 20 to 117 +/- 20 mmHg (P < 0.005) with stimulation from the right carotid artery. A prolongation of the AV and VA block cycle lengths and the AV nodal effective refractory period was also noted with stimulation from the right carotid artery. Atrial fibrillation was not induced at baseline in any animal. During stimulation from the right carotid artery, atrial fibrillation was induced in three of five animals and persisted for the duration of stimulation from the right carotid artery.

CONCLUSION

Cardiac parasympathetic stimulation can be achieved by positioning a catheter in the neurovascular bundle in the neck adjacent to the vagus nerve with resultant effects on cardiac electrophysiology.

Absence of significant changes in heart rate variability after slow pathway ablation of AV nodal reentrant tachycardia by using serial Holter recordings

BACKGROUND

Persistent inappropriate sinus tachycardia may evolve as a complication after radiofrequency (RF) fast pathway ablation of atrioventricular nodal reentrant tachycardia (AVNRT). Parasympathetic denervation may serve as one of the possible mechanisms. We performed a study to show the prevalence of this phenomenon in RF ablation of the slow pathway.

METHODS AND RESULTS

Thirty-three patients (25 women, 8 men) aged 53 +/- 16 years were investigated. A median of 3 pulses was used to selectively modify or ablate the slow pathway and render AVNRT noninducible. Heart rate (HR) and different indexes in the time and frequency domain of heart rate variability were evaluated in serial 24-hour Holter recordings. Data were obtained 1 day, 1 month, and 3 months after the procedure and compared with preablation values. Despite a trend of increasing HR and decreasing heart rate variability within the first month after RF ablation, no significant changes were detected.

CONCLUSIONS

RF ablation of the slow pathway in AVNRT does not change parameters of HR and heart rate variability significantly by means of serial 24-hour Holter recordings.

Alterations of heart rate and of heart rate variability after radiofrequency catheter ablation of supraventricular tachycardia. Delineation of parasympathetic pathways in the human heart

BACKGROUND

Persistent inappropriate sinus tachycardia has been reported as a complication after radiofrequency (RF) ablation of the fast atrioventricular (AV) nodal pathway. The purpose of this study was to evaluate the prevalence of this complication and its mechanism using heart rate variability analysis.

METHODS AND RESULTS

Time and frequency domain analysis of heart rate was performed in the electrophysiology laboratory immediately before and immediately after RF ablation in 64 patients with supraventricular tachycardia. Ablation targets in these 64 patients included the fast AV nodal pathway (n = 3), the slow AV nodal pathway (n = 14), a posteroseptal accessory pathway (n = 23), and a left lateral accessory pathway (n = 24). A control group of 21 patients undergoing diagnostic study but not ablation underwent identical analysis immediately before and at the conclusion of their procedure. Patients undergoing ablation also had time and frequency domain analysis performed on ambulatory 24-hour Holter tapes recorded before ablation and at 1 day, 1 month, and 6 months after ablation. Compared with preablation values, time domain analysis immediately after ablation revealed a significant increase in mean heart rate and significant reductions in heart rate variability expressed as SD, MSSD, and PNN50 in patients undergoing AV nodal modification or posteroseptal accessory pathway ablation. Frequency domain analysis revealed marked attenuation of high frequency (0.15 to 0.40 Hz) components, indicating parasympathetic denervation. These acute changes were not seen after ablation of left lateral accessory pathways or after diagnostic study without ablation. Time and frequency domain analysis of 24-hour ambulatory Holter monitors performed serially after ablation revealed resolution of abnormalities of heart rate and of heart rate variability 1 to 6 months after ablation, with reappearance of the high frequency parasympathetic component suggestive of reinnervation.

CONCLUSIONS

RF ablation in the anterior, mid, and posterior regions of the low interatrial septum may disrupt preganglionic or postganglionic parasympathetic fibers located in these regions that are destined to innervate the sinus node. Such fibers become more scarce along the left AV groove with increasing distance from the posteroseptal space. Parasympathetic denervation may be one mechanism for persistent inappropriate sinus tachycardia after RF ablation.

Local epicardial chemical ablation of vagal input to sino-trial and atrioventricular regions of the canine heart

In open-chest, pentobarbitalized dogs, right and left cervical vagi were electrically stimulated (20 Hz, 5.0 ms, 4-6 volts) before and after carefully painting phenol (90%) over each of 6-8 narrow strips (2-3 mm width) and over restricted portions of the superior and inferior right atrium. Successive phenol strips were applied until the sino-atrial nodal (SAN) region had been completely surrounded, and also applied over a triangular fat pad at the junction of the inferior vena cava (IVC) and inferior left atrium (ILA). Electrical excitation of the autonomic trunks following each sequential epicardial phenol blockade resulted in successive deletion of cardio-inhibitory responses, a majority of sympathetic excitatory responses remaining intact. We conclude that most vagal fibers reach the SAN region via the superior-posterior right atrium (SVC and superior pulmonary veins) and these can be ablated leaving most vagal fibers to the atrioventricular nodal AVN region unimpaired. Phenol painting at the junction of IVC and ILA abolished vagal inhibition of conduction across the A-V junction. These studies illustrate distinct vagal distributions to the SAN and AVN regions of the canine heart. After all responses to vagal stimulation have been abolished, sympathetic alterations in heart rate and A-V conduction remain, thus revealing important differentiation in sympathetic fiber distribution to these key regions of automaticity and conduction.