Atrial pacing thresholds measured in anesthetized patients with the use of an esophageal stethoscope modified for pacing

Abstract

Transesophageal atrial pacing (TAP) with the use of standard, thermistor-equipped, esophageal stethoscopes, modified for pacing by incorporation of a 4-French, bipolar TAP probe (pacing esophageal stethoscope [PES]), was evaluated in 100 adult patients under general anesthesia. A commercially available TAP pulse generator supplied 10-ms pulses with current variable between 0 and 40 mA. Pacing distances (in centimeters) were measured from the infraal-veolar ridge to midway between PES electrodes (1.5-cm interelectrode distance). Pacing thresholds (milliamperes) were measured at the point of a maximum-amplitude P-wave (PMAX) in the bipolar esophageal electrogram and points 1 cm proximal or 1, 2, or 3 cm distal to PMAX TAP (70–100 beats per min) was used for sinus bradycardia ≤ 60 beats per min (36 patients) or atrioventricular (AV) junctional rhythm (2 patients) and blood pressure changes with TAP documented. In male patients (n = 49), PMAX was 32.7 ± 0.3 cm (mean ± SE) and minimum pacing threshold 5.1 ± 0.4 mA (range, 1–13 mA) at 33.6 ± 0.3 cm (range, 30–37 cm). In female patients (n = 51), PMAX was 30.4 ± 0.4 cm and minimum pacing threshold 4.4 ± 0.4 mA (range, 2–14 mA) at 31.1 ± 0.4 cm (range, 26–40 cm). TAP produced an average 13–16 mmHg increase in systolic, diastolic, or mean-arterial pressure in patients with sinus bradycardia or AV junctional rhythm. There were no subjective patient complaints (epigastric discomfort, dysphagia) that could be attributed to TAP; objective evaluation (esophagoscopy) was not performed. It is concluded that TAP is widely applicable to anesthetized adults; low TAP thresholds can be obtained by first determining PMAX and positioning the PES electrode 1 cm or less distal to PMAX; and TAP can be used to increase blood pressure in patients with sinus bradycardia or AV junctional rhythm.