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


METHODS
All 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.


RESULTS
A total of 23 patients met the criteria (median age, 14.3 years [range 7-21], weight, 51 kg [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 (<CL 300) in three (13%). Left ventricular (LV) pacing demonstrated CLAP conduction in 17/17 (100%) patients in whom it was used. All 23 CLAPs were successfully ablated (100%) via transseptal approach with radiofrequency energy. Specific ablation techniques included: 16 (70%) during LV paced rhythm, four (17%) during orthodromic reciprocating tachycardia (ORT; 3/4 ventricular entrained), and three (13%) with brief rapid RV pacing. There were no complications. At 18 months (range 3-96), there was one recurrence (4%).


CONCLUSIONS
Some CLAPs are only demonstrable with LV pacing, entrained ORT, or rapid RV pacing. LV pacing facilitated preferential AP conduction, allowing for mapping while maintaining stable hemodynamics.
['Pass|Robert H|RH|0000-0001-8030-3367', 'Liberman|Leonardo|L|', 'Silver|Eric S|ES|', 'Janson|Christopher M|CM|', 'Blaufox|Andrew D|AD|', 'Nappo|Lynn|L|', 'Ceresnak|Scott R|SR|']
D058606:Accessory Atrioventricular Bundle D000293:Adolescent D002304:Cardiac Pacing, Artificial D002648:Child D056149:Epicardial Mapping D005260:Female D006801:Humans D008297:Male D000078703:Radiofrequency Ablation D012189:Retrospective Studies D013617:Tachycardia, Supraventricular D016896:Treatment Outcome D055815:Young Adult
accessory pathway supraventricular tachycardia pediatrics orthodromic reciprocating tachycardia