Concealed left anterior accessory pathways: two approaches for successful ablation.

Left anterior accessory pathways are considered to occur rarely because the junction between the aortic and mitral valve areas represents a fibrous continuity. Of 207 patients with concealed left accessory pathways in whom catheter ablation was performed at our institution over the past 8 years, two patients had concealed left anterior accessory pathways. The polarity of the retrograde P waves was positive in the inferior leads and negative in leads I and aVL during orthodromic reciprocating tachycardia. Complete elimination of accessory pathway conduction was achieved using a transseptal approach or with radiofrequency energy application from the left sinus of Valsalva.