The "hidden" concealed left sided accessory pathway: An uncommon cause of SVT in young people.

BackgroundConcealed left-sided accessory pathways (CLAP) are a cause of supraventricular tachycardia (SVT) in the young. Most are mapped with right ventricular (RV) apical/outflow pacing. Rarely, alternative means of mapping are required. We review our experience from three pediatric electrophysiology (EP) centers with a rare form of hidden CLAP. MethodsAll patients<21 years undergoing EP study from 2008 to 2014 with a hidden CLAP (defined as an accessory pathway [AP] for which RV pacing at cycle lengths [CL] stable for mapping did not demonstrate eccentric retrograde conduction) were included. Exclusion criteria: preexcitation. Demographic, procedural, and follow-up data were collected. ResultsA total of 23 patients met the criteria (median age, 14.3 years [range 7-21], weight, 51kg [31-99]). 21 (96%) had SVT and one AFIB (4%). APs were adenosine sensitive in 7/20 patients (35%) and VA conduction was decremental in six (26%). CLAP conduction was demonstrable with orthodromic reentrant tachycardia in all patients, with RV extrastimulus testing in seven (30%) and with rapid RV pacing (更多