Esophageal pacing: a diagnostic and therapeutic tool.

The purpose of this study was to develop guidelines for reproducible esophageal pacing of the atria and to determine the incidence of successful initiation and termination of tachycardia using this technique in patients with a history of spontaneous supraventricular tachycardia (SVT). Strength-duration curves were performed in 39 patients using a bipolar esophageal lead with a 2.9-cm interelectrode distance. Unlike strength-duration curves normally obtained -in cardiac tissue, which plateau at pulse durations more than 2.0 msec, the esophageal current threshold decreased progressively as pulse duration was increased to the limit of the stimulator (9.9 msec). At pulse durations of 8.0-9.9 msec, atrial capture was achieved in all patients. At progressively shorter pulse durations, capture was achieved in progressively fewer patients despite use of current up to 30 mA. Stable pacing was achieved in 26 of 39 patients with a pulse duration of 1.0 msec (mean threshold 21 mA), in 33 of 39 patients with a pulse duration of 2.0 msec (mean threshold 18 mA), and in 39 of 39 patients with a pulse duration of 9.9 msec (mean threshold 11 mA). The current requirements did not correlate with the amplitude of the unipolar or bipolar atrial electrogram recorded in the group as a whole, but the lowest thresholds in individual patients occurred at the site where the largest and most rapid atrial deflections were recorded. In 38 patients with documented SVT, overdrive pacing from the esophagus was performed at cycle lengths of 240-400 msec using a pulse duration of 7.0-9.9 msec. Reciprocating tachycardia was induced in 35 of 38 patients and was terminated by overdrive pacing in 33 of 38 patients. Atrial fibrillation was induced incidentally in four patients; sinus rhythm returned spontaneously. Other effects included ventricular pacing in two, unmasking of latent preexcitation in three, induction of ventricular tachycardia by atrial pacing in two patients with a history of ventricular tachycardia, and phrenic pacing in one. We conclude that atrial pacing can be achieved from the esophagus with minimal discomfort in the majority of patients; that lower pacing thresholds can be obtained with the use of wide pulse durations (7.0-9.9 msec) and a bipolar electrode with wide interelectrode distance (2.9 cm); that rapid atrial pacing from the esophagus can be used to induce and terminate SVT for diagnostic or therapeutic purposes; and that esophageal pacing provides a convenient way to assess repeatedly the efficacy of long-term drug therapy and to screen patients for preexcitation syndromes.