Crawford TM; Dick M 2d; Bank E; Jenkins JM Med Instrum (United States), Jan-Feb 1986, 20(1) p40-4. To determine the thresholds for transesophageal atrial capture, as well as factors that might influence the thresholds, the authors measured the minimal current and pulse duration required to pace the atrium through transesophageal bipolar lead systems in 32 patients during 42 trials. Mathematical modeling suggested that the current density at the posterior atrial wall was dependent upon the current delivered, the electrode distance, and, most importantly, the esophageal-atrial geometry, expressed as the distance from the esophagus to the excitable tissue. To examine this esophageal-atrial distance, 17 different patients, aged 11 months to 44 years, were studied concurrently with either computerized tomography or magnetic resonance imaging of the chest. The thresholds needed to capture the atrium from the esophagus were 13.2 +/- 3.7 mA at a pulse duration of 5.8 +/- 3.1 msec. Further, the data demonstrated that the threshold for transesophageal atrial pacing was poorly related to the patient's age or size. The fit between these data and the mathematical model suggested that the distance between the left atrial posterior wall and the esophagus was approximately 5-6 mm. Likewise, the minimal esophageal-atrial distance as measured by the two imaging techniques was equal to or less than 3.3 mm. These observations suggest that the distance (anterior-posterior dimension) between left atrial posterior wall and the esophagus is small and remains constant despite obvious changes in somatic and linear growth.