Reflex or neurally mediated syncope is the most common form of syncope in any setting and at all ages. It is associated with an autonomic imbalance in which vagal hyperactivity predominates, resulting in vasodilation or bradycardia or both, thereby producing a fall in global cerebral perfusion. It is divided into three types: vasovagal, situational, and carotid sinus syndrome.
Reflex syncope is benign and usually occurs in healthy people; however, very frequent syncope or events without prodromal symptoms can lead to injuries and affect long-term quality of life. Nonpharmacological and medical therapies proven effective in randomized clinical trials are scarce. In certain patients with frequent and burdensome cardioinhibitory reflex syncope, dual-chamber cardiac pacemakers seem to be beneficial. More recently, catheter-based cardiac autonomic modulation, or cardioneuroablation (CNA), has emerged as a novel therapy for reflex syncope, and positive results in small open-label cohort studies, and more recently in the first randomized study, have been reported.
The literature provides sufficient evidence that cardiac pacing should be considered in select patients affected by severe forms of reflex syncope with frequent recurrence and a high risk of injury. Current guidelines suggest that pacemaker therapy should be considered in patients aged more than 40 years with frequent recurrent reflex syncope when asystole has been documented, induced by either carotid sinus massage (CSM) or the head-up tilt test (HUTT), or recorded using an electrocardiogram (ECG) monitoring system (≥3 seconds if syncope, ≥6 seconds if asymptomatic).
Cardiac autonomic system modulation by endocardial ablation targeting atrial ganglionated plexi (GPs), or CNA, has been recently proposed as a novel therapy for reflex syncope.
Cardioneuroablation was introduced by Pachon et al. in 2005. In their initial study, twenty-one symptomatic patients with vasovagal syncope (6 patients), functional high-degree atrio-ventricular block (7 patients), and/or functional sinus node dysfunction (13 patients), were treated with CNA without complications. Follow-up for a mean of 9.2 months demonstrated symptom relief for all patients. After this initial description, several small studies and case series confirmed the efficacy of this approach. In a recent randomized prospective study, Piotrowski et al. documented that not only could CNA significantly reduce recurrences of syncopal episodes in patients with vasovagal syncope, it could also improve quality of life.
The primary strength of this therapeutic approach is that it avoids pacemaker implant, a procedure with a significant complication rate during long-term follow-up in a population composed predominantly of young and otherwise healthy patients.
The excellent results reproduced by many investigators worldwide suggest that CNA should be considered in patients with reflex syncope, especially those who display an important cardioinhibitory component of syncope. However, given that current evidence is limited, and the procedure carries potential risk, a randomized clinical trial to assess the true benefit of CNA and to compare this technique with pacemaker implantation should be performed. Results could guide the physician to the best current choice in this scenario.
