01.CIR.65.2.336

Esophageal Pacing: A Diagnostic and Therapeutic Tool JOHN J. GALLAGHER, M.D., WARREN M. SMITH, M.D., CHARLES R. KERR, M.D., JACK KASELL, LAURA COOK, R.N., MICHAEL REITER, PH.D., M.D., RICHARD STERBA, M.D., AND MARIE HARTE, M.D. Downloaded from http://ahajournals.org by on June 30, 2023 SUMMARY 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 tech- nique 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 inter- electrode 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 dura- tion 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 re- quirements 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 pa- tients 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, un- masking 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. THE PROXIMITY of the esophagus to the atria is diagnostic technique was limited by the need for the basis of using esophageal electrodes to record elec- tachycardia at the time of the esophageal recording. trical activity from the atria. Several investigators The possibility of using the same esophageal lead to have suggested using this route to deliver electrical induce tachycardia by atrial pacing prompted the stimuli to the atria or ventricles for diagnostic and present study, in which we attempted to develop guide- therapeutic purposes,\"'1 but this application has been lines for reproducible pacing of the atria and to assess limited by lack of consistent capture and patient dis- our ability to induce and terminate SVT by es- comfort resulting from high current requirements. ophageal pacing in a series of consecutive patients with documented SVT. We recently reported the value of recording ven- triculoatrial (VA) intervals from the esophagus dur- Materials and Methods ing supraventricular tachycardia (SVT) to help define the mechanism of SVT. An absolute VA interval The study group consisted of 65 patients, 45 males shorter than 70 msec during SVT excluded participa- and 20 females, mean age of 35 years (range 7-70 tion of an accessory Kent bundle pathway.'6 This years). Forty-six patients had SVT associated with a concealed or manifest preexcitation syndrome, five From the Divisions of Cardiology, Departments of Medicine and had SVT due to reentry confined to the atrioventric- Pediatrics, Duke University Medical Center, Durham, North ular (AV) node, five had paroxysmal atrial fibrilla- Carolina. tion, three had postoperative restudy after surgical division of a Kent bundle, four had ventricular tachy- Supported in part by NIH grant HL-15190. cardia, one patient had atrial tachycardia and one pa- This work was done during Dr. Gallagher's tenure as an tient had sick sinus syndrome. Established Investigator of the American Heart Association and during Dr. Kerr's tenure as a Fellow of the Medical Research Coun- Patients were studied in the postabsorptive state. cil of Canada. Antiarrhythmic therapy was discontinued for 48 Presented in part at the 53rd Scientific Sessions of the American hours. An i.v. catheter was always inserted before the Heart Association, November 19, 1980, Miami Beach, Florida. procedure. In 50% of the patients, small i.v. doses of Address for correspondence: John J. Gallagher, M.D., Box 3816, diazepam or meperidine were used for sedation. Duke University Medical Center, Durham, North Carolina 27710. Received March 9, 1981; revision accepted May 12, 1981. A bipolar permanent transvenous pacing electrode Circulation 65, No. 2, 1982. (Medtronic 6992) with electrodes spaced at 29 mm 336

ESOPHAGEAL PACING/Gallagher et al. 337 ..... .... .. .. ..... .. ...... ..... Threshold determinations were made as a function of interelectrode distances of 0-8 cm; the pulse duration Downloaded from http://ahajournals.org by on June 30, 2023 FIGURE 1. Transvenous catheter electrode used for es- was held constant at 9.9 msec. ophageal pacing. A discarded permanent transvenous bi- polar coronary sinus lead with interelectrode distance of 2.9 Induction Termination of Tachycardia cm was used. In 38 consecutive patients with a history of SVT, we was used (fig. 1). In a subgroup of seven patients, a tried to induce and terminate their arrhythmias. The \"sliding\" electrode lead was used to determine the op- majority of these patients subsequently underwent a timal interelectrode distances for bipolar pacing. detailed electrophysiology study. We tried to induce SVT by rapid pacing (cycle length 240-400 msec) Placement of Esophageal Electrode using a wide pulse duration (7.0-9.9 msec) and enough current to maintain atrial capture (mean 15 mA). With the patient in the supine position, the bipolar After induction of SVT and recording of the VA inter- pacing electrode was passed through the nares into the vals, we tried to terminate SVT using the same pacing distal esophagus; unipolar and bipolar electrograms criteria. were monitored during the procedure. The unipolar tracings were filtered at 0.1-1 kHz and bipolar trac- Results ings were filtered at 50-1 kHz. The lead was secured where the unipolar atrial electrograms exhibited the Placement of Esophageal Electrode greatest amplitude and the most rapid deflection. The distance from the nares to the proximal electrode was Satisfactory atrial electrograms were recorded with recorded and the potentials were carefully calibrated. the esophageal electrode in all 65 patients. Maximal The lead was generally positioned so that the proximal bipolar potentials ranged from 0.3-1.8 mV (mean 0.9 electrode showed the greatest amplitude; this elec- + 0.34 mV) (± SD). The maximal unipolar potential trode was then designated as the cathodal (negative) ranged from 0.5-3.6 mV (mean 1.3 ± 0.6 mV). The pacing terminal. All recording and pacing was per- maximal unipolar potential was recorded 27-45 cm formed with the patient supine. from the nares (mean 38.5 + 5 cm). Strength-Duration Curves Strength-Duration Curves Strength-duration curves were performed in 39 pa- Strength-duration curves were performed in 39 pa- tients by means of a constant-current generator tients (fig. 2). In this patient, no capture occurred at capable of delivering 0. 1-9.9-msec square-wave pulses 0.2-msec pulse duration; capture at 0.4-msec pulse with amplitudes of up to 30 mA. Current was duration required 29 mA, but with increasing pulse measured across a 1000-Q resistance. A pacing cycle duration, current requirements decreased. Unlike length of 500 msec was most often selected. Deter- strength-duration curves normally obtained in cardiac minations of current thresholds were made at a pulse tissue, which plateau at pulse durations more than duration of 0.1 msec and then pulse duration was in- 2 msec,'6 the current requirements continually creased in 0.2-msec increments from 0.2-2.0 msec; decreased as pulse duration was increased up to the thereafter, pulse duration was increased in 0.5-msec limit of the stimulator (9.9 msec). steps. At the completion of the strength-duration curve, attempts were made to pace the ventricle using The group results of strength-duration determina- a pulse duration of 9.9 msec and a current of ap- tions in all 39 patients are shown in figure 3. In all pa- proximately 20 mA as the esophageal lead was withdrawn from the stomach to the nasopharynx. 30J Threshold as a Function of Interelectrode Distance 25 - In seven patients, a \"sliding\" electrode lead was 20 used to determine the optimal electrode spacing. 10 5 I L _ _ I__I_..1L I9 __J 1.0 2,0 3.0 4.0 5.0 6.0 70 8.0 9.( 10.0 PULSE DURATION [msecl FIGURE 2. Representative strength-duration curve deter- mined by means of esophageal pacing. The current required for stable atrial pacing is plotted as a function ofpulse dura- tion. No capture occurred at a pulse duration of 0.2 msec despite passage of current up to 30 mA. A trial capture first occurred at a pulse duration of0.4 msec at a threshold of29 mA, but with increasing pulse duration, current thresholds decreased.

338 CIRCULATION VOL 65, No 2, FEBRUARY 1982 ci20 -Nz 1.2 ± 1.6 msec). The current thresholds at this N minimal pulse duration ranged from 15-30 mA (mean 27 ± 3 mA). N~ ~ ~~ One might expect that the larger the amplitude of _ 10 the bipolar or unipolar electrogram recorded, the closer the proximity of the esophageal lead to the 0.2 0.4 0.6 0.8 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 9.9 atria; thus, patients with atrial electrograms of greater amplitude might be expected to manifest lower pac- PUlSE DURATION [ msec ] ing thresholds than patients with atrial electrograms of smaller amplitude. However, analysis of group FIGURE 3. Esophageal strength-duration determinations results for the current threshold determined at a pulse in 39 patients. The current threshold is plotted as afunction duration of 9.9 msec showed a poor correlation with ofpulse duration. The number ofpatients successfully paced the amplitude of either the bipolar atrial electrogram using current up to 30 mA is indicated by N. See text for dis- (r = 0.22) or the unipolar atrial electrogram (r cussion. -0.04). tients,-the current requirements decreased as pulse Ventricular pacing via the esophagus (fig. 4) was observed in only two patients during withdrawal of the duration was increased. Stable atrial pacing was lead from the stomach to the esophagus. In both pa- tients, a large ventricular electrogram without evi- Downloaded from http://ahajournals.org by on June 30, 2023 achieved in 26 of 39 patients using a pulse duration of dence of an atrial electrogram was recorded at the time ventricular pacing was noted. The anatomic posi- 1.0 msec (mean threshold321 5 mA);-in 33 of 39 pa- tion of the ventricles relative to the esophagus in these two patients probably facilitated ventricular pacing. tients using a pulse duration of 2.0 msec (mean Ventricular pacing was not noted when the lead was positioned with a predominant atrial deflection before threshold 18 ±3 5 mA); and in 39 of 39 patients using a institution of pacing. lpulse duration of 9.9 msec (mean threshold 5 Threshold as a Function of Interelectrode Distance mA). In our experience, moderate discomfort accom- In seven patients, threshold determinations were made as a function of interelectrode distances of 0-8 panies delivery of current in excess of 18 mA to the es- cm, with the pulse duration held constant at 9.9 msec. In this subgroup (table 1), the optimal spacing ophagus. Conventional external stimulating devices appeared to be 3 cm, compared with 2.9 cm for per- forming strength-duration curves. are typicatlly limited to pulse durations of 2.0 msec. Induction and Termination of Tachycardia Pacing at a pulse duration2o.f0i msec would therefore Thirty-eight patients were entered into this part of result in a lower success rate, higher current- re- the study, 33 with reentry utilizing VA accesso-ry pathways and five with reentry confined to the AV quirements, and more symptoms in patients in whom node. Supraventricular tachycardia was induced one atrial capture occurred. or more times in 35 of 38 patients (figs. 5 and 6). Tachycardia could not be induced in three patients The minimal pulse duration at which successful who had manifest preexcitation and short antegrade capture occurred ranged from 0.1-8.0 msec (average effective refractory periods of their accessory pathways. SVT could not be induced with catheter Vtriculor Jp bck Afriol IPacinguabc -T-F2ftPcing f ITF - ItX FIGURE 4. Ventricular pacing during es- L_H_4-li_ftlt_tl_lt 4tVIA A M'AtXfNI VI.__V _ i1 7fA ophageal stimulation. In this example, the IF F:4I rl rI IIIFL.fottLL I Z.tlttm I -7 esophageal lead was passed to the level of .... ..I RJI NU B.) a Is the stomach. Pacing was performed using a pulse duration of 9.9 msec and a current of I < 15 mA. The esophageal lead was progres- jlE sively withdrawn to the level of the atrium. Ventricular pacing occurred initially; upon X ai-n- r-:T -U -A4-A---L-;-- withdrawal of the esophageal lead to the level of the atrium, atrial pacing alone was noted. mI =tl- !~IIT4;; 1 ATMi 11 7 A 1,- i \" i1 Fr A Til/I1

ESOPHAGEAL PACING/Gallagher et al. 339 ESOPHAGEAL PACING RT NSR NSR RT 'iiifllFlllt.IlI llllii-m ll lr M.-IM,I\" FIGURE 5. Induction and termination of supraventricular tachycardia in a patient with documented reentry in the atrioventric- ular (A V) node. (left) Sinus tachycardia is initially present because of the prior ad- ministration of 1.0 mg of atropine to facilitate induction of reentry in the A V node. Overdrive atrial pacing by means of the esophageal electrode at a cycle length of 260 msec successfully initiates a supra- ventricular tachycardia. (right) Delivery of stimuli at the same cycle length results in a return to sinus rhythm (NSR) after a single junctional escape beat. RT = reciprocating tachycardia. Downloaded from http://ahajournals.org by on June 30, 2023 technique in these same patients using atrial stimula- ing. In two of the four patients who had sustained tion. Ventricular stimulation was required to induce ventricular tachycardia, overdrive esophageal atrial tachycardia. pacing during tachycardia demonstrated fusion and capture beats. In these cases, atrial pacing was com- SVT was terminated one or more times in 33 of 38 bined with the administration of atropine (0.5 and 1.0 patients. In one patient SVT could not be terminated mg), which enhanced AV nodal conduction and per- and required drug therapy. In the remaining four pa- mitted ventricular overdrive. Phrenic pacing was tients, SVT was converted to atrial fibrillation (fig. 7), observed with high pacing thresholds in only one of 65 which spontaneously reverted to sinus rhythm. The patients. Finally, one patient with incessant SVT same response to overdrive pacing was observed in demonstrated 2: 1 AV block associated with a slower these patients during subsequent electrophysiologic ventricular response during rapid esophageal pacing, study using intracardiac pacing. NSR RT We did not try in this study to induce atrial fibrilla- tion. Such a study is under way and preliminary A results suggest that atrial fibrillation can be induced by this technique to characterize the ventricular IS 4__ ~4z1frq > f response during atrial fibrillation in patients with pre- excitation syndromes. RT I 50 mm/sec Other Effects Observed During Esophageal Pacing A I Esophageal pacing resulted in unmasking of pre- ESO ___: .I. excitation due to a left lateral accessory AV pathway in three patients (fig. 8). Four patients with a history of ventricular tachycardia were studied and rapid atrial pacing resulted in induction of ventricular tachycardia in two. In one of these patients, the ven- tricular tachycardia was nonsustained; in the other, tachycardia was terminated by overdrive atrial pac- TABLE 1. Esophageal Pacing Threshold as a Function of Electrode Spacing (n = 7) Bipolar Mean 100 mm/sec separation (cm) current (mA) FIGURE 6. Esophageal (ESO) recordings obtained during 1 15.2 study of a patient with supraventricular tachycardia due to reentry in the atrioventricular (A V) node (same patient as in 2 13.6 figure 5). Bipolar recordings during sinus rhythm (NSR) and after the induction of supraventricular tachycardia using 3 13.2 overdrive esophageal pacing are shown. During supra- ventricular tachycardia, the atrial electrogram recorded 4 14.3 from the esophagus occurs nearly simultaneously with the QRS complex. R T = reciprocating tachycardia; I = stan- 5 15.2 dard ECG lead I; A = atrial electrogram. 6 15.7 7 17.2 8 17.2 The pulse duration was constant at 9.9 msec.

340 CIRCULATION VOL 65, No 2, FEBRUARY 1982 FIGURE 7. Inadvertent induction of atrial fibrillation during attempts to overdrive supraventricular tachycardia in a patient I with documented Wolff-Parkinson- White syndrome. Supraventricular tachycardia with a normal QRS complex is initially pres- ent with a cycle length of 330 msec. Four stimuli are delivered from the esophageal electrode at a cycle length of 240 msec, resulting in atrialfibrillation with antegrade conduction occurring over an accessory pathway in the left lateral atrioventricular groove. The atrial fibrillation spontane- ously reverts to sinus rhythm. The artifact between the second and third stimuli was caused by movement of the patient. Atrial fibrillation was also elicited by overdrive atrial pacing during subsequent invasive study of this patient. IA FIGURE 8. Unmasking oflatent preexcita- IIIvx mil~~~~X~Ft- H- 4Ff0 tion in a patient with documented Wolff- Downloaded from http://ahajournals.org by on June 30, 2023 -r ! : ' I l --I --I vr -1- - - r r T T~~~~-T- -T- T-T Parkinson- White syndrome. Sinus rhythm is initially present in this patient, who had a history of supraventricular tachycardia and a normal resting ECG. Initiation of atrial pacing from the esophagus at a cycle length of 400 msec results in unmasking ofpreex- citation, which was subsequently shown to be due to an accessory pathway in the left lateral atrioventricular groove. and was stabilized for several hours until a msec or less, which resulted in high current re- transvenous catheter could be implanted before open heart surgery. quirements, patient discomfort, pacing of thoracoab- Patient Tolerance of Esophageal Pacing dominal muscles and inconsistent capture. Ordinarily, All patients experienced discomfort, most fre- strength-duration curves performed in cardiac tissue quently described as a mild burning sensation or chest in close contact with the stimulating electrode show a pain and likened to that of indigestion. Most patients tolerated this discomfort easily. Occasional moderate plateau with little change in threshold achieved by in- discomfort was noted, almost invariably in patients creasing the pulse duration in excess of 2.0 msec.16 In with thresholds in excess of 18 mA. Intravenous this study we demonstrated a progressive decline in diazepam or meperidine was administered to ap- current requirement up to a pulse duration of 9.9 proximately half of the patients. No patient had dis- comfort severe enough to force discontinuation of the msec. This relationship has not been reported, and study. Approximately 15% of the patients underwent suggests a capacitance effect due to the distance and two or more studies for assessment of drug therapy or for termination of tachycardia. nature of the tissues between the esophagus and Discussion atrium. The combined effect of using a long pulse duration and a wide interelectrode distance permitted The use of an esophageal lead to stimulate the heart reliable atrial capture at comparatively low thresholds was first reported by Zoll1 in 1952 as a technique for in our series. pacing the ventricles. Later investigators reported use of unipolar or bipolar esophageal leads to stimulate Esophageal pacing provides a relatively noninvasive the atria or ventricles.2\" In general these applica- method for pacing the atria without fluoroscopy, tions were undertaken with pulse durations of 2.0 sterile precautions or cardiac catheterization, and thus compares favorably with temporary transvenous atrial pacing. Consistent atrial capture, especially at rapid pacing rates, may be difficult by the transvenous route, which requires placing the pacing catheter in the right atrial appendage or the coronary sinus. Esophageal pacing can also be performed ex-

ESOPHAGEAL PACING/Gallagher et al. 341 Downloaded from http://ahajournals.org by on June 30, 2023 peditiously in ambulatory, bedside or emergency Acknowledgment situations and can be repeated chronically. Because The authors thank University Photography and Illustration for atrial pacing is performed from outside the heart, es- the medical artwork and Sue Chiaramonti for typing the ophageal pacing is particularly well suited to the study manuscript. of patients with known or suspected preexcitation. We previously showed'7 that accessory pathways located References on the tricuspid annulus or in the septal area can be partially or completely obtunded temporarily owing to 1. Zoll PM: Resuscitation of the heart in ventricular standstill by catheter trauma. More recently, a left free-wall external electrical stimulation. JAMA 247: 768, 1952 accessory pathway was traumatized in our laboratory during manipulation of a coronary sinus catheter and 2. Whipple GH, Penton GB: Transesophageal ventricular defibril- has not regained function after 1 year. Pacing studies lation. Clin Res Proc 4: 105, 1956 in patients with preexcitation can be accomplished from the esophagus without disrupting the accessory 3. Shafiroff BGP, Linder J: Effects of external electrical pathway. pacemaker stimuli on the human heart. J Thorac Surg 33: 544, 1957 Certain precautions seem reasonable. Pacing of the ventricle occurred in two of 65 patients, and only when 4. McNally EM, Meyer EC, Langendorf R: Elective counter- the esophageal lead was advanced far enough to shock in unanesthetized patients with use of an esophageal elec- record a large ventricular electrogram. Nevertheless, trode. Circulation 33: 124, 1966 pacing should always be instituted at a slow rate to en- sure that the ventricle is not inadvertently paced at 5. Burack B, Furman S: Transesophageal cardiac pacing. Am J rapid rates. Atrial fibrillation may be inadvertently in- Cardiol 23: 469, 1969 duced by rapid atrial pacing and may result in a rapid ventricular response in patients with preexcitation 6. Rowe GG, Terry W, Neblett I: Cardiac pacing with an es- syndromes. For the above reasons, an intravenous ophageal electrode. Am J Cardiol 24: 548, 1969 catheter should be in place before esophageal pacing, and cardioversion equipment should be readily 7. Lubell DL: Cardiac pacing from the esophagus. Am J Cardiol available. All recording and stimulating equipment 27: 641, 1971 should be electrically isolated. 8. Stopczyk MJ, Zochowski RT: P wave triggered permanent In this study, we used esophageal pacing to reliably atrial pacing in a case of transient sinus arrest. Br Heart J 34: induce and terminate reentrant SVT. However, es- 318, 1972 ophageal pacing may be extended to all reported uses of temporary atrial pacing. Possible indications in- 9. Stopczyk MJ, Pieniak M, Sadowski Z, Zochowski RT: clude determination of sinus node recovery times, Transesophageal atrial pacing as a simple diagnostic and stress of AV conduction and screening for latent therapeutic procedure. In The Third International Conference antegrade preexcitation, temporary management of on Medical Physics, Including Medical Engineering, edited by bradyarrhythmias due to sinus node dysfunction, in- Kadefors R, Magnusson RI, Petersen I. Goteborg, Sweden, duction and termination of supraventricular tachy- Third ICMP Executive Committee, 1972, pp 40-45 cardias for diagnostic or therapeutic purposes,'5 in- duction of atrial fibrillation in patients with pre- 10. Montoyo JV, Angel J, Valle V, Gausi C: Cardioversion of excitation for prognostic considerations, conversion of tachycardias by transesophageal atrial pacing. Am J Cardiol flutter to sinus rhythm or atrial fibrillation with a 32: 85, 1973 slower ventricular response, demonstration of capture and fusion in patients with ventricular tachycardia, 11. Mitsui T, Tanaka T, Saigusa M: An esophageal balloon elec- and repeated assessment of the long-term efficacy of trode for cardiac pacing. In Cardiac Pacing, edited by Thalen drug therapy for supraventricular arrhythmias. HJT. The Netherlands, Van Gorcum and Co, 1973, pp 282-287 Addendum 12. Brunetto JF, Sgammini HO, Ledesma RE, Esquinesy S, Sanatamarina NO: Evaluation of sinoatrial node function Since submission of this manuscript, we have learned of another through the use of transesophageal atrial pacing. In study: Stery H, Prager H, Koller H: Transesophageal rapid stimu- Proceedings of VI World Symposium on Cardiac Pacing, lation of the left atrium in atrial tachycardias. Z Kardiol 67: 136, edited by Meere C. Montreal, Pacesymp, 1979, ch 5, section 7 1978 13. Kraska T, Sadowski Z, Szwed H: Assessment of sinus node recovery time and sinoatrial conduction time in patients with sick sinus syndrome. In Proceedings of VI World Symposium on Cardiac Pacing, edited by Meere C. Pacesymp, Montreal, 1979, ch 5, section 6 14. Santini M, Rocchi M, Massini V: Study of sinus node recovery time and sinoatrial conduction time in patients with sick sinus syndrome. In Proceedings of VI World Symposium on Cardiac Pacing, edited by Meere C. Montreal, Pacesymp, 1979, ch 8, section 1 15. Gallagher JJ, Smith WM, Kasell J, Smith WM, Grant AO, Benson DW: The use of the esophageal lead in the diagnosis of mechanisms of reciprocating supraventricular tachycardia. PACE 3: 440, 1980 16. Furman S, Escher DWJ: Principles and Techniques of Cardiac Pacing. New York, Harper and Row, 1970, p 38 17. Novick TL, Pritchett ELC, Campbell RWF, Rogers GC, Wallace AG, Gallagher JJ: Temporary, catheter-induced block in accessory pathways. Circulation 58: 932, 1978