Study population
Between February 2017 and October 2019, we prospectively enrolled 13 patients in three hospital centers, with documented episodes of severe functional bradyarrhythmias suggestive of vagal etiology (sinus bradycardia and / or arrest, brady-tachy syndrome, transient AV block and cardioinhibitory syncope). Functional bradyarrhythmias were acknowledged after exclusion of reversible causes, such as negative chronotropic drugs, ionic disorders, thyroid dysfunction, cardiac ischemia, obstructive sleep apnea, intrinsic sinus or AV node disease and in patients engaged in competitive sports, after deconditioning. Intrinsic sinus and AV node disease were excluded after assessment of a positive chronotropic response on 24-hour Holter monitoring and on exercise treadmill test, with absence of exercise induced AV block and when bradyarrhythmias were suggestive to occur in a vagal setting as during sleep, post meals or prolonged standing. Patients with suspected vagal syncope underwent tilt testing that exhibited syncope with predominant cardioinhibitory response. An ECG was performed in all patients and the HR and PQ interval was measured. Patients with abnormal ECG apart from sinus bradycardia, first-degree or second-degree Mobitz type I AV block or with abnormal transthoracic echocardiogram were excluded.
Included patients were either symptomatic (syncope / pre-syncope related to bradycardia) or had severe bradycardia with an indication for pacing regardless of symptoms as outlined in the current European Society of Cardiology Guidelines for the management of bradyarrhythmias(10).