Cardioneuroablation for Reflex Syncope

Introduction.

Reflex syncope due to vasovagal reaction is the most frequent cause of transient loss of consciousness (TLOC) in general population. [1-4] It markedly decreases quality of life and may lead to injury. [5, 6] The mechanism of vasovagal syncope (VVS) is complex. One of the most important mechanisms is enhanced parasympathetic activity triggered by abnormal mechanoreceptor reflex and other mechanisms. This leads to prolonged asystole and/or vasodilatation, resulting in syncope. [7] Treatment of VVS remains a challenge. Non-pharmacological treatment such as fluid and salt intake, avoiding situations triggering syncope or tilt training is not effective in a significant proportion of subjects with syncope. Pharmacotherapy is even less effective. Syncope recurs in 25-65% of patients. Alternative therapy, especially in patients with prolonged asystole, is pacemaker implantation, recommended by the guidelines in patients aged > 40 years with documented spontaneous cardioinhibitory VVS and severe symptoms. However, permanent pacing occurs ineffective in at least 25% of patients. In addition, VVS occurs predominantly in young persons in whom permanent pacing should be avoided as much as possible. [8-13] Thus, the need for new treatment options in VVS is clear.

Ablation for atrial fibrillation (AF) has been successfully performed for almost two decades. Apart from pulmonary vein isolation which is a corner stone of AF ablation, autonomic control of the heart is modified by ablation of ganglionated plexi (GP). It has been well documented that in some patients GP ablation increases the success rate of ablation, especially in patients with vagally-mediated AF. Thus, the technique of GP ablation, mainly using the radio-frequency energy, is well established and safe.

Based on data coming from GP ablation during AF procedures, this method has been recently proposed for patients with VVS. The postulated beneficial mechanisms of GP ablation in VVS are attenuation of parasympathetic activity, leading to elimination or reduction reflex asystole and bradycardia. To date, a few case series consisting of up to 70 patients demonstrated very promising results. [15-18]. However, this experience is limited to a few centers. Also, the optimal methodology of the procedure, called cardioneuroablation (CNA) or cardioneuromodulation, is not known. There is no consensus yet as to how many GP's, in both atria or only in the right atrium, in which order and to what extent should be ablated. Moreover, mechanisms responsible for beneficial effects of CNA as well as methods assessing it's efficacy are not clear.

Aim. To assess the effects of CNA on cardiac autonomic regulation and syncope recurrences in patients with VVS, and to compare this novel approach with standard non-pharmacological treatment.

Hypothesis. CNA using GP ablation causes significant changes in autonomic control of the heart, predominantly parasympathetic withdrawal, which is associated with long-term efficacy of the procedure, and is significantly more effective than standard non-pharmacological therapy.

Methods. This is an open-label, randomized, controlled, prospective study.

Study group. Forty consecutive patients with recurrent cardioinhibitory or mixed VVS will be included between August 2018 and July 2021.

The patients will be randomized into 2 groups:

1. Treatment arm (n=20): CNA

2. Control arm (n=20): standard non-pharmacological treatment The patients from the control arm will be allowed to cross over to the CNA group if syncopal episode occurs despite adherence to the non-pharmacological recommendations.

The number of 40 patients will be enough to demonstrate superiority of CNA over standard approach, assuming that the effectiveness of CNA will be over 90%, and the effectiveness of the standard non-pharmacological treatment will be 50%.

Inclusion criteria:

1. At least one documented spontaneous VVS during preceding 12 months or one syncope in history leading to injury and minimum 2 presyncopal events during preceding 12 months, refractory to all recommended types of standard treatment.

2. In case of lack of ECG documentation during spontaneous syncope and history suggesting reflex syncope, at least 3 seconds of asystole due to sinus arrest or atrio-ventricular block with syncope or bradycardia <40 beats per minute with syncope or presyncope during baseline tilt test

3. Sinus rhythm during ECG and tilt test

4. Significantly decreased quality of life due to syncope

5. Positive response to atropine test

6. Obtained written informed consent.

Exclusion criteria:

1. Other possible and treatable causes of syncope such as significant cardiac disease, cardiac arrhythmia or abnormalities of vertebro-basiliar arteries

2. History of stroke or TIA

3. History of cardiac surgery

4. Contraindications to ablation in the right or left atrium

Cardioneuroablation The procedure is performed under mild sedation (midazolam and fentanyl) using a 3.5 mm irrigated tip catheter (Navistar ThermoCool SmartTouch; Biosense Webster, Diamond Bar, California, USA) with contact force module and electroanatomical system Carto 3 (Biosense Webster, Diamond Bar, California, USA). After gaining transseptal access, an electroanatomical map of the right (RA) and left (LA) atrium is created and anatomically-based ablation of GP is performed. Ablation in the RA is started from the supero-posterior area (superior right atrial GP), to the middle-posterior area (posterior right atrial GP). In the LA, ablation is started at the site of the anterior right GP and is continued downwards along the anterior part of a common vestibulum of the right pulmonary veins (PV), opposite to the right-sided ablation lesions. Finally, area of right inferior GP, close to the RIPV is ablated under intracardiac echocardiography control. Using this technique, GP's located close to the left PV are not ablated. We use a pure anatomic approach without identification of GP by high-frequency stimulation or other imaging techniques.

Measurements.

1. Before CNA:

1. Detailed history taking and assessment of eligibility

2. Baseline 12-lead ECG for heart rate assessment, morphology and duration of the P wave and PR interval

3. 24-hour Holter ECG for heart rhythm (mean, minimal, maximal, pauses) and heart rate variability (HRV) assessment

4. Passive tilt test (70 degrees, 45 minutes) to fulfill inclusion criterion and to assess baseline autonomic parameters such as HRV and baroreflex sensitivity (BRS) using sequential method. These parameters will be calculated from 5 min recordings before and after orthostatic stress (tilt).

5. Atropine test - positive response to intravenous atropine in a dose of 2 mg defined as at least 30% increase in sinus rate compared with baseline value

6. Assessment of quality of life using the SF-36 questionnaire

7. Implantable Loop Recorder (ILR) implantation 2-3 days before CNA

2. During CNA:

1. Heart rate before and immediately after CNA

2. Episodes of bradycardia (sinus arrest or atrio-ventrocular block) during application of RF to GP.

3. Standard electrophysiological parameters (sinus node recovery time, corrected sinus recovery time, refractory atrio-ventricular node, atrio-ventricular conduction - Wenckebach point, A-H and H-V intervals) will be assessed before an immediately after CNA

4. Atropine test (2 mg) will be repeated immediately after CNA.

3. After CNA:

1. 1-2 days after CNA standard ECG

2. Follow-up: 3, 12 and 24 months after CNA assessment of symptoms, 12 lead standard ECG, control ILR, 24-hour Holter ECG, tilt test and atropine test will be performed. Additionally, quality of life will be assessed using SF-36 questionnaire

Definitions used for CNA efficacy assessment:

- Complete efficacy - no syncope or presyncope during two years of follow-up

- Partial efficacy - reduction of the number of syncopal (or presyncopal) episodes or change from syncopal to presyncopal episodes

Primary endpoint

- Time to first syncope recurrence

Secondary endpoints

- Syncope burden (number of syncopal episodes during two years)

- Presyncope burden (number of presyncopal episodes during two years)

- ILR: assessed heart rate and atrio-ventricular conduction if syncope occurs

- CNA-induced changes in autonomic parameters

- Prognostic value of autonomic parameters.

- Safety of CNA: tamponade, stroke, phrenic nerve injury, permanent sinus arrest, local bleeding or vascular complications related to vascular access (hematoma / arteriovenous fistula)

Statistical analysis Results will be presented as mean ± SD or numbers and percentages. Also CNA-induced changes(∆) in analysed parameters will be calculated. The ECG, electrophysiological and autonomic parameters obtained before and after CNA will be compared using student t-test or Mann-Whitney test where appropriate. The values of analysed parameters in predicting CNA efficacy will be assessed by computing sensitivity, specificity, positive and negative predictive value. The ROC curves will be drawn in order to establish optimal cut-off points of analysed parameters in predicting CNA efficacy.

Anticipated results.

1. CNA performed with technique used in the present study is effective in > 90% of patients.

2. CNA-induced changes in analysed ECG and autonomic parameters predict CNA efficacy