Vagal denervation in atrial fibrillation ablation: A comprehensive review

Effects on heart rate from direct current block of the stimulated rat vagus nerve

Objective.Although electrical vagus nerve stimulation has been shown to augment parasympathetic control of the heart, the effects of electrical conduction block have been less rigorously characterized. Previous experiments have demonstrated that direct current (DC) nerve block can be applied safely and effectively in the autonomic system, but additional information about the system dynamics need to be characterized to successfully deploy DC nerve block to clinical practice.Approach.The dynamics of the heart rate (HR) from DC nerve block of the vagus nerve were measured by stimulating the vagus nerve to lower the HR, and then applying DC block to restore normal rate. DC block achieved rapid, complete block, as well as partial block at lower amplitudes.Main Results. Complete block was also achieved using lower amplitudes, but with a slower induction time. The time for DC to induce complete block was significantly predicted by the amplitude; specifically, the amplitude expressed as a percentage of the current required for a rapid, 60 s induction time. Recovery times after the cessation of DC block could occur both instantly, and after a significant delay. Both blocking duration and injected charge were significant in predicting the delay in recovery to normal conduction.Significance. While these data show that broad features such as induction and recovery can be described well by the DC parameters, more precise features of the HR, such as the exact path of the induction and recoveries, are still undefined. These findings show promise for control of the cardiac autonomic nervous system, with potential to expand to the sympathetic inputs as well.

Comparison of Fragmented Electrogram Based Strategy and High Frequency Stimulation for Detection of Ganglionated Plexi

Ganglionated plexus (GP) ablation is an emerging technique in patients with cardioinhibitory vasovagal syncope and vagally mediated atrial fibrillation. Localization of GPs can be impacted by the technique used. A reproducible methodology for GP detection is needed to account for individual variations during electrophysiologic study. In this article, we aim to compare and contrast high-frequency stimulation vs. a fragmented electrogram guided strategy for GP localization.

Evaluation of atrial fibrillation risk in patients with vasovagal syncope

BACKGROUND

This study aimed to determine whether autonomic dysfunction in patients with vasovagal syncope with a positive tilt test may cause an alteration in atrial electromechanical properties and pose a risk for subsequent atrial arrhythmias, especially atrial fibrillation.

METHODS

The data of 27 patients with vasovagal syncope and a matched control group comprising 28 healthy individuals were compared. All patients underwent a tilt table test. Atrial electromechanical intervals (PA) were measured from the mitral lateral annulus, mitral septal annulus, and tricuspid annulus with tissue Doppler imaging. Left atrium volumes were measured with the disc method in apical four-chamber imaging.

RESULTS

Although atrial electromechanical intervals such as lateral PA, septal PA, and tricuspid PA durations were significantly longer (p = 0.009, p = 0.002, p = 0.011, respectively), interatrial, right intra-atrial, and left intra-atrial durations were similar in the vasovagal syncope group and the control group (p = 0.298, p = 0.388, p = 0.069, respectively). Left atrial volumes (maximum, minimum, and presystolic) were significantly increased in the vasovagal syncope group when compared with the control group (p = 0.001, p = 0.001, p = 0.007, respectively). There was no difference between vasovagal syncope types in terms of atrial electromechanical intervals.

CONCLUSION

Interatrial and intra-atrial intervals were similar in the vasovagal syncope group and the control group. However, an increase in atrial volumes and a prolongation of certain atrial electromechanical intervals were observed in patients with vasovagal syncope. These findings suggest an alteration in atrial electromechanics caused by autonomic dysfunction that can lead to subsequent atrial arrhythmias, especially atrial fibrillation.

Medium-term results of cardioneuroablation for clinical bradyarrhythmias and vasovagal syncope: effects on QT interval and heart rate

PURPOSE

Although parasympathetic effects of cardioneuroablation (CNA) in vagally mediated bradyarrhythmias (VMB) were studied, sympathetic effects have not been elucidated, yet. We aimed to investigate the acute and medium-term outcomes of CNA as well as the impact of CNA on ventricular repolarization by using corrected QT interval (QTc) measurements.

METHODS

Sixty-five patients (58.5% men; age 39.4 ± 14 years) undergoing CNA were included in the study. Patients who underwent CNA due to VMB were divided into two groups: (1) bi-atrial CNA and (2) right-sided CNA. QTc was calculated at 3 time points: before the procedure (time point 1); 24 h post-ablation (time point 2); and at the last follow-up visit (time point 3).

RESULTS

The mean follow-up time was 20.0 ± 20 months. Acute success was achieved in 64 (98.4%) of cases. In the whole cohort, from time point 1 to 2, a significant shortening in QTcFredericia, QTcFramingham, and QTcHodges was observed which remained lower than baseline in time point 3. Although the difference between measurements in time point 1 and 2 was not statistically significant for QTcBazett, a significant shortening was detected between time point 1 and 3. There was significant difference between groups for shortening in QTcFredericia and QTcFramingham (p = 0.01). Event-free survival was detected in 90.7% (59/65) of cases.

CONCLUSIONS

Our results demonstrate a significant shortening of QTc in addition to high acute and medium-term success rates after CNA. The most likely mechanism is the effect of CNA on the sympathetic system as well as on the parasympathetic system. Bi-atrial ablation was found related to higher QTc shortening effect.

Can We Predict Vagal Response to Cryoballoon Application Using Intracardiac Recordings?

The effects of cryoballoon (CB) ablation in non-pulmonary vein sites have not clearly elucidated. Herein we present a new definition method which helps to predict autonomic modification effect of CB application using atrial electrogram (EGM) characteristics and vagal responses (VRs). A 54-year-old man underwent pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation. Both atria were mapped with the aid of electroanatomical mapping system prior to ablation procedure. The atrial EGMs were divided into 3 groups according to duration, amplitude, and number of deflections. The sites demonstrating fractionated pattern on 2.5 centimeters outside of pulmonary vein ostia were tagged on the mapping to predict the relationship between VR and EGM characteristics during CB application. CB application in the PV demonstrating intensive fractionated EGMs caused a significant VR. We concluded that our case may be starting point to understand mechanism of PVI induced VR during CB application.

Clinical Effects of "Selective Drug" Regulating Vagus Nerve Signal Pathway in Vagally-Mediated Atrial Fibrillation

Background

The cardiac autonomic nervous system plays a crucial role in genesis and development of atrial fibrillation (AF) through the G protein signal transduction pathway. Therefore, intervening in the G protein signal transduction pathway may be a new “selective drug” method to regulate autonomic nerve activity to prevent vagally-mediated AF.

Material/Methods

Seventeen adult beagles were randomized into 3 groups: shame-operation control group (group A, n=5), empty vector gene control group (group B, n=6), and Gα_i2ctp gene experimental group (group C, n=6). Group A was injected with normal saline into the anterior atrial wall, and group B and group C animals were injected with recombinant adenovirus with empty vector or Gα_i2ctp vector in the same region. AF was induced by the method of rapid atrial pacing in groups B and C. To determine the clinical effect of vagal modulation, the effective refractory periods (ERP) and field action potential duration (FAPD) were evaluated by electrophysiological study. The expression levels of tyrosine hydroxylase (TH) and choline acetyl transferase (CHAT) in different parts were determined with immunohistochemistry.

Results

After successful Gα_i2ctp gene transfer, in group B, the ERP and FAPD significantly decreased (P<0.05), and TH and CHAT expression observably increased (P<0.05), while those differences were absent between groups A and C (P>0.05).

Conclusions

Recombinant adenovirus-mediated overexpression of Gα_i2ctp in canine myocardial cells can interfere with the activity of the vagus nerve, reverse the development and progression of electrical remodeling, and reduce the incidence of AF.