Paroxysmal AV block in children with normal cardiac anatomy as a cause of syncope

Background: Syncope due to episodes of paroxysmal atrioventricular (AV) block, defined as transient advanced second or third-degree block, is rarely reported in pediatric patients without congenital heart disease. Methods: We reviewed our institutional arrhythmia database from January 1988 to January 2007 to identify all patients less than 18 years of age with normal cardiac anatomy and episodes of syncope associated with paroxysmal AV block. Demographic and clinical information was collected. Results: Six patients were identified (Table I). Five of the six patients were female, with an average age of 9.3 ± 4.4 years. Patients had episodes of syncope for an average of 5.6 ± 3.3 years prior to diagnosis. All patients had normal physical examinations, electrocardiograms, and echocardiograms. None were on medications known to interfere with AV nodal function, and laboratory evaluation including Lyme titers were negative. Five of the six patients' episodes were atypical for vasovagal syncope (except patient 6). All patients had documented paroxysmal AV block on either inpatient cardiac monitor, Holter monitor, or event recorder at the time of syncope. There was maintenance or acceleration of the sinus rate during episodes of syncope in all patients (mean atrial rate 107 ± 37 bpm). All six patients had permanent transvenous pacemakers implanted with resolution of symptoms over a mean follow-up of 5.2 ± 6.3 years. Conclusion: Paroxysmal AV nodal block is a rare finding in pediatric patients, but should be considered as a possible etiology in patients presenting with episodes atypical for vasovagal syncope. Pacemaker therapy prevented future episodes in all six of our patients.