Origin of the atrial electrogram recorded from the esophagus.

The purpose of this study was to ascertain the origin of the atrial electrogram recorded on the esophageal lead. The atria and esophagus were mapped during reciprocating tachycardia in 11 patients with the Wolff-Parkinson-White syndrome and one patient with atrioventricular nodal reentry, and during right ventricular pacing in four additional patients. The esophagus was mapped by recording atrial electrograms at 1-cm intervals throughout the esophagus beginning at the most distal area where atrial depolarization was seen. The retrograde atrial activation time recorded on the esophageal lead in its distal position occurred at the same time as atrial septal depolarization in all patients. In 14 of 16 patients, the distal esophageal ventriculoatrial (VA) conduction time was also the shortest esophageal VA conduction time recorded. In two of five patients with left lateral accessory pathways, the shortest esophageal VA conduction time was noted during pullback of the lead from the esophagus instead of at the most distal area. The most likely explanation for this was an unusual anatomic relationship between the esophagus and left atrium in these two patients. We conclude that 1) the most distal esophageal atrial electrogram probably records posterior paraseptal atrial depolarization; 2) it is unusual to record clearly identifiable left atrial activation in the esophagus; and 3) the esophageal lead is not useful in locating left-sided accessory pathways.