Profound vagal hyperreactivity unmasked after pacemaker implantation: a rare indication for cardioneuroablation-a case report.

BACKGROUND: Asystole caused by vagal activity with prolonged sinus arrest and absent escape rhythm is rare and may overlap with intrinsic conduction system vulnerability. Cardioneuroablation (CNA) is an emerging option for cardioinhibitory syncope, but its role after pacemaker implantation has been rarely reported. CASE SUMMARY: A 43-year-old man presented with recurrent syncope due to abrupt, prolonged sinus arrest of up to 25 s without escape rhythm. Cardiological evaluation, including tilt-table testing, echocardiography, Holter monitoring, and positron emission tomography, revealed no structural or inflammatory substrate. A dual-chamber pacemaker with left bundle branch area pacing was implanted, preventing further syncope. However, after implantation, the patient reported severe sleep fragmentation and debilitating daytime somnolence. Device diagnostics showed 1704 nocturnal rate-drop response activations since pacemaker implantation, despite normal polygraphy. Given the exceptional burden of presumed vagally mediated nocturnal events and marked functional impairment, CNA was performed, resulting in substantial suppression of nocturnal vagal episodes and marked symptomatic improvement. DISCUSSION: This case demonstrates an unusual combination of profound vagally mediated asystole and possible intrinsic conduction vulnerability. Pacemaker therapy eliminated cardioinhibitory vasovagal syncope but unmasked severe nocturnal vagal hyperreactivity, leading to frequent symptomatic rate-drop responses by the pacemaker. CNA successfully restored autonomic balance, reduced pacemaker rate-drop responses and resolved symptoms. This case highlights the utility of CNA in patients with vagal hyperreactivity and cardioinhibitory vasovagal syncope on top of pacemaker implantation.