• Clinical Abstracts

    Clinical Abstracts on Positioning of Esophageal Electrodes for Cardiac Pacing and Recording

    Positioning the pacing esophageal stethoscope for transesophageal atrial pacing without P-wave recording: implications for transesophageal ventricular pacing. Roth JV, Brody JD, Denham EJ (Albert Einstein Med Ctr, Philadelphia) Anesth Analg 1996 Jul;83(1):48-54 This study determined guidelines for positioning a new pacing esophageal stethoscope (PES) used for transesophageal atrial pacing (TEAP) without having to record esophageal P waves. In 44 patients with heights ranging from 142 cm (4'8") to 193 cm (6'4"), the PES was inserted to a depth of insertion (DOI) of 43 cm. As the PES was withdrawn, TEAP thresholds were determined at every DOI in 1-cm intervals between 43 and 25 cm DOI inclusive. TEAP was accomplished in all 44 patients. The minimum TEAP threshold (mean +/- SD 10.8 +/- 4.0 mA) was <= 17 mA in 43 of 44 patients (98%). Except for one patient, TEAP could be accomplished over a 9- to 19-cm (mean +/- SD, 13.7 +/- 2.8 cm) wide range of DOI. Unintentional transesophageal ventricular pacing (TEVP) occurred in 15 of 44 (34%) of patients. TEVP occurred over a 1- to 7-cm (mean +/- SD, 3.7 +/- 1.7 cm) wide range of DOI; the minimum TEVP threshold averaged 30.4 +/- 6.4 mA. TEAP was consistently accomplished at DOIs more proximal than where TEVP could occur and with lower currents than that required for TEVP. An insertion depth, in centimeters, equal to half of the patient's height, in inches, produced successful TEAP in all 44 patients; the minimum TEAP threshold occurred on average at a DOI 2.6 cm more proximal. Asynchronous TEVP can be avoided by using lower currents at shallow DOIs. 

    Atrial pacing thresholds measured in anesthetized patients with the use of an esophageal stethoscope modified for pacing. Pattison CZ; Atlee JL 3d; Mathews EL; Buljubasic N; Entress JJ. Medical College of Wisconsin. Anesthesiology, May 1991, 74(5) p854-9. 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 infraalveolar 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 less than or equal to 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. 

    Transesophageal atrial pacing threshold: role of interelectrode spacing, pulse width and catheter insertion depth. Benson DW Jr, Sanford M, Dunnigan A, Benditt DG. Am J Cardiol 1984 Jan 1;53(1):63-7. This study evaluated the role of interelectrode spacing, pulse widths greater than 10 ms, and depth of esophageal insertion on minimizing transesophageal atrial pacing threshold in 30 patients aged 1 day to 77 years. Interelectrode spacings of 15, 22 and 28 mm were evaluated by establishing strength-duration curves in 2 or more serial studies in 12 patients; electrode spacing had no effect on pacing threshold. In 23 patients studied with 22-mm electrode spacing, pulse widths of 15 and 20 ms had no significant effect on current threshold requirements compared with 10-ms pulse widths. In 20 patients, pacing threshold and esophageal electrograms were obtained at 1.0- to 2.5-cm intervals with a 22-mm lead using a pulse width of 10 ms. Average minimal pacing threshold was 10.2 mA (range 4.5 to 20). The site of minimal pacing threshold was highly correlated with patient height (r = 0.987), and occurred within 1.1 cm (0 to 2.5 cm) of the site of the maximal bipolar atrial electrogram amplitude and 0.95 cm (0 to 3 cm) of the site of the maximal unipolar atrial electrogram. Bipolar electrode spacing of 15, 22 or 28 mm has little effect on transesophageal pacing threshold. In most patients, pulse widths greater than 10 ms do not significantly decrease pacing threshold. Correct catheter insertion depth is critical to minimize pacing threshold and may be predicted by either the site of the maximal atrial electrogram amplitude or patient height.

    Optimal mode of transesophageal atrial pacing. Nishimura M, Katoh T, Hanai S, Watanabe Y. Am J Cardiol 1986;57(10):791-6. The optimal mode of transesophageal atrial pacing was determined by clinical electrophysiologic studies in 15 healthy adult volunteers. The point at which the unipolar atrial electrogram was biphasic and largest in amplitude (35.4 +/- 1.6 cm from the incisors) was considered the best stimulation site for atrial pacing. The stimulation threshold on bipolar pacing (using the proximal pole as cathode and the distal pole as anode) at this site was 27 +/- 7 mA, which was significantly lower (p < 0.001, n = 10) than that on unipolar cathodal stimulation (41 +/- 8 mA). Although the stimulation threshold tended to be higher with a No. 10Fr electrode catheter (30 +/- 5 mA) than with a No. 6Fr catheter (27 +/- 7 mA), the difference was statistically insignificant (n = 9). When the interpolar distance in bipolar stimulation was varied in 5 steps from 12 to 80 mm, the threshold was lowest at the distance of 24 mm. Of the 10 pulse durations tested, ranging from 0.25 to 128 ms, 8 ms appeared most desirable in minimizing the total amount of current and chest discomfort accompanying the pacing. With the optimal site, interpolar distance and pulse duration, transesophageal atrial pacing was successfully performed in all patients, without producing significant complications such as chest pain. Transesophageal atrial pacing is noninvasive, technically simple and efficient, and may be valuable in the diagnosis and treatment of various cardiac arrhythmias.

    Electrocardiographic verification of esophageal temperature probe position. Brengelmann GL, Johnson JM, Hong PA. J Appl Physiol 1979 Sep;47(3):638-42. Esophageal temperature (Tes) varies with depth of insertion. Characteristic features of the esophageal electrocardiogram (ECG) can be used to place probes in the region where the esophagus is between the aorta and the left atrium. This describes a suitable catheter for recording of Tes and ECG and how features of the electrical activity of the atria may be used to place the probe tip. Records of Tes versus depth obtained during heating of four human subjects are included. The technique eliminates the need for radiographic verification of probe position. It could readily be employed in clinical situations with the advantage of having both a central temperature and an electrocardiogram available from a simple, readily inserted, and readily tolerated catheter.

    Electrode-myocardium distance in transesophageal atrial stimulation. Boden H, Paliege R, Klinik fur Innere Medizin, Suhl. Gesamte Inn Med 1990 Nov 1;45(21):643-6  In 9 voluntary test persons with a sound heart, comparative examinations were carried out to discover the optimum depth of insertion by unipolar and bipolar determination of the absolute threshold and transoesophageal derivation as well as the correlation of the optimum depth of insertion with external measurements of the body. The methods mentioned to ascertain the optimum depth of insertion are equivalent concerning the bipolar arrangement of the electrodes in the oesophagus. The average effective depth of insertion can simplified be defined. A correlation of the average effective depth of insertion concerning external measurements of the body could not be found, so that the conscientious discovering of the optimum depth of insertion is a necessity for every patient. The average value found could attain an orientating importance with the primary placing of the probe concerning the average effective depth of insertion of 37 cm.

    Clinical application of modified proportional unit of middle finger to determine the depth for intra-esophageal atrial pacing to stop supraventricular tachycardia. Huang SL, Luo X, Wu YS. First Affiliated Hospital of Jiangxi Medical College, Nanchang. Chung Kuo Chung Hsi I Chieh Ho Tsa Chih 1997 Feb;17(2):68-9. OBJECTIVE: To determine the location for catheter electrode of intra-esophageal atrial pacing. METHODS: The catheter load was placed at a length eleven times that of the modified proportional unit of middle finger for intra-esophageal atrial pacing to stop the supraventricular tachycardia of 21 patients. RESULTS: Ninteen of them showed remarkable effect and 2 were effective. Tachycardia of all the patients was stopped, symptoms and signs such as chest distress, palpitation relieved and the blood pressure normalized. CONCLUSION: This is an accurate localization, rapid, convenient method with remarkable effects, it is a new way in rescuing supraventricular tachycardia patients.

    The optimum site and strength-duration relationship of transesophageal indirect atrial pacing. Chung DC; Townsend GE; Kerr CR. Anesthesiology 1986, 65(4) p428-31. Stimulation threshold for atrial capture was investigated at varying levels of the esophagus and the relationship between pulse strength and duration was evaluated with respect to atrial capture. Study population consisted of  6 anesthetized patients undergoing gynecological or orthopedic surgery and 5 patients undergoing examination for paroxysmal supraventricular tachycardia. A quadratic relationship was found between depth of catheter insertion (cm) and threshold current (mA), with minimum threshold ranging from 4.6 to 9.3 mA. The stimulus strength-duration relationship showed a rapid decline in threshold current amplitude as pulse duration was increased from 1 to 5 msec, with relatively no change in threshold over the range 5 to 9.9 msec. In conclusion, transesophageal atrial pacing is safe and has few complications. Signs of irritation during pacing in conscious patients (e.g. coughing) are observed with proximal insertion of electrodes. An average depth of insertion of 36 cm and pulse width of 10 msec are recommended, allowing for atrial capture with stimulus current below 15 mA in most patients. (CardioCommand abstract).