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(Circulation. 1995;92:1819-1824.)
© 1995 American Heart Association, Inc.

Articles

The Etiology of Syncope in Patients With Negative Tilt Table and Electrophysiological Testing

Andrew D. Krahn, MD; George J. Klein, MD; Caro Norris, RN; Raymond Yee, MD

From the Department of Medicine, Division of Cardiology, University Hospital, University of Western Ontario, London, Ontario, Canada.

Correspondence to Dr Andrew Krahn, Division of Cardiology, University Hospital, 339 Windermere Rd, London, Ontario, Canada N6A 5A5.

	Abstract

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Background Patients with syncope of unknown etiology after negative noninvasive and electrophysiological testing may suffer from recurrent disability. Syncopal episodes are often too infrequent and unpredictable for detection by conventional ambulatory monitoring techniques.

View this table: [in this window] [in a new window]   Table 1. Demographic Profile of Patient Population

Methods and Results A long-term subcutaneous monitoring device was implanted in patients with negative ambulatory monitoring, tilt table and electrophysiological testing to establish cardiac rhythm during spontaneous syncope. Sixteen patients aged 57±19 years with a mean of 8.4±4.4 previous episodes of syncope underwent device implantation. Fifteen patients (94%) had recurrent syncope 4.4±4.2 months after implantation. The remaining patient has not had recurrent syncope and continues to be followed. A diagnosis was obtained in every patient who had recurrent episode. Syncope was secondary to sinus arrest in 5, atrioventricular block in 2, ventricular tachycardia in 1, supraventricular tachycardia in 1, and nonarrhythmic in 6. Successful therapy was implemented in all 15 patients, without recurrence of syncope during 13.0±8.4 months of follow-up.

Conclusions Unexplained syncope in patients with negative investigations has a broad spectrum of etiologies, the most common of which is bradycardia. An implantable long-term monitoring device is useful for establishing a diagnosis when symptoms are recurrent but too infrequent for conventional monitoring techniques.

Key Words: syncope • electrophysiology

	Introduction

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The etiology of recurrent syncope is often difficult to determine if the diagnosis is not evident from initial clinical and laboratory investigations.^{1 2 3 4} The major obstacles to diagnosis are the periodic and unpredictable frequency of events and the high spontaneous remission rate.^{5 6} Clinicians often rely on abnormal laboratory results to make inferential decisions regarding the etiology and treatment of this disorder. It is generally accepted that electrophysiological testing is the final arbitrator when noninvasive testing is negative or inconclusive.^{1 2 7 8 9} Nonetheless, electrophysiological testing is negative in 14% to 70% of patients in major studies.^{9 10 11 12 13 14 15 16 17 18} These patients may have ongoing morbidity from recurrent syncope. We present the long-term findings in 16 patients with unexplained syncope and negative laboratory investigations.

	Methods

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Patients
Patients with recurrent unexplained syncope referred to University Hospital for assessment between September 1992 and September 1994 underwent standard investigations, including a resting electrocardiogram, ambulatory monitoring, myocardial imaging, and tilt table testing. If noninvasive investigations were negative, electrophysiological testing was performed. Syncope was defined as sudden transient loss of consciousness that resolved without cardioversion or defibrillation; patients were not included if they only had presyncope. Patients with negative or nondiagnostic tilt table and electrophysiological testing during this period were approached and asked to participate in a trial involving the implantation of a long-term subcutaneous monitoring device to establish cardiac rhythm during spontaneous syncope. All patients gave informed consent. The study was approved by the University of Western Ontario Research Review Committee.

Laboratory Investigations
Patients underwent a minimum of 48 hours of ambulatory or in-hospital monitoring as well as cardiac imaging with transthoracic echocardiography or radionuclide ventriculography. An exercise treadmill test or neurological investigations were also performed in selected cases. Tilt table testing was performed with the use of 60° head-up tilt for 15 minutes with continuous ECG and noninvasive blood pressure monitoring (Finipres). If no response occurred, intravenous isoproterenol was administered at 1 µg/minute and titrated to a 25% increase in heart rate for an additional 15 minutes. A positive test was defined when syncope or presyncope occurred, accompanied by a significant fall (>30 mm Hg) in blood pressure with or without a drop in heart rate. This protocol has previously been shown to have 61% sensitivity and 93% specificity in our laboratory.¹⁹

Electrophysiological studies were performed in the postabsorptive, nonsedated state. Standard multipolar catheters were inserted into the right femoral vein and placed in the high right atrium, right ventricle, and near the His bundle. Sinus node recovery time, sinoatrial conduction time, and antegrade and retrograde AV node function were assessed using atrial and ventricular pacing and extrastimuli.²⁰ Programmed electrical stimulation was performed at the right ventricular apex at a drive cycle length of 600 and 400 ms for 8 beats, followed by up to 3 extrastimuli. This protocol has been found to be 90% sensitive for induction of sustained monomorphic ventricular tachycardia in patients with spontaneous ventricular tachycardia in our laboratory.²¹ A positive test was defined as induction of ventricular tachycardia longer than 30 seconds in duration or requiring urgent intervention, sustained supraventricular tachycardia, a corrected sinus node recovery time greater than 550 ms, or an HV (His to ventricle) interval greater than 75 ms.

Device
The implantable syncope monitor is a pacemaker-sized device (53x60x8 mm, 2.1x2.4x0.3 in) with 2 electrodes 32 mm (1.25 in) apart within its shell (Fig 1). It continuously records a single-lead electrocardiogram (Medtronic USA Inc.). The ECG signal is stored in a circular buffer capable of retaining either one 15-minute or two 7.5-minute segments of recorded rhythm. Using a magnet, the patient, family member, or friend "freezes" the device during or after a spontaneous syncopal episode, storing the preceding 7.5- or 15-minute segment, which is retrievable at a later date. The syncope monitor has a battery life of approximately 2 years.²²

View larger version (182K): [in this window] [in a new window]   Figure 1. Photograph of implantable syncope monitor. Arrows point to sensing electrodes.

A subcutaneous pocket was fashioned in the left pectoral region under local anesthesia. The device was placed within the pocket and rotated through 360° to optimize the magnitude of the recorded R-wave electrogram. It was then fastened to the underlying tissue at opposite corners of the device with nonabsorbable sutures. The incision was then closed with absorbable sutures, and a satisfactory electrogram was verified after wound closure. Devices were explanted after a diagnosis was obtained.

Follow-up
All patients were followed in the pacemaker clinic at 1, 2, and 4 weeks after device implantation and subsequently at monthly intervals. Each visit included a patient interview and device interrogation. Patients were seen immediately if they had activated the device.

	Results

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From September 1992 to September 1994, 209 patients were assessed for syncope. A presumptive diagnosis was obtained in 146 patients after a history, physical examination, ECG, and tilt table test. Forty-one of the remaining patients underwent electrophysiological testing. Sixteen patients with negative electrophysiological testing and unexplained recurrent syncope who were able to return for follow-up and capable of informed consent were approached to participate in the study. All patients approached consented to participate. Before enrollment 15 patients had recurrent syncope (8.7±6.1 episodes, mean±SD) and 1 patient had a single episode of syncope with serious injury in a motor vehicle accident (Table 1). The mean age was 57±19 years. There were 12 men. Concomitant heart disease was present in 8 patients; ischemic heart disease in 5, hypertension in 1, cardiac transplantation in 1, and hypertrophic cardiomyopathy in 1. One of the remaining 7 patients had mitral valve prolapse with mild mitral regurgitation on echocardiography. Repeated ambulatory or in-hospital monitoring was negative in all patients. Tilt table testing and electrophysiological studies were negative in all patients. All patients in whom device implantation was attempted had satisfactory ECG sensing, with a mean sensed QRS amplitude of 265±130 µv.

Spontaneous syncope occurred in 15 of 16 patients (94%), a mean of 4.4±4.2 months after device implantation (range, 6 days to 14 months). The remaining patient has not had syncope and continues to be followed.

Table 2 summarizes the etiology and treatment of syncope in the 15 patients with recurrence during follow-up. Syncope was secondary to bradyarrhythmia in 7 patients (47%); sinus arrest in 4, complete heart block in 2, and sick sinus syndrome in 1. In this group, the mean baseline corrected sinus node recovery time was 280±105 seconds, and the HV interval was 57±8.1 ms. Syncope was secondary to tachyarrhythmia in 2 patients (17%). Patient 5 had AV node reentrant tachycardia and underwent AV node modification. Repeat electrophysiological study showed only single AV node echo cycles after addition of isoproterenol and atropine. Spontaneous syncope was associated with a narrow complex tachycardia at a rate of 180 beats per minute. The patient underwent repeat AV node modification and has had no further syncopal episodes during 15.5 months of follow-up. Patient 6 had nonsustained ventricular tachycardia at a rate of 240 beats per minute during spontaneous presyncope. No ventricular arrhythmias (including nonsustained ventricular tachycardia) were induced at baseline electrophysiological study.

View this table: [in this window] [in a new window]   Table 2. Clinical Correlates for Etiology of Recurrent Syncope

Syncope was nonarrhythmic in 6 patients (40%), in whom a presumptive clinical diagnosis was made. In patients 10 and 14, vasodepressor syncope was diagnosed because of a reasonable prodrome and gradual slowing of heart rate to a minimum of 50 and 45 beats per minute during spontaneous syncope. Patient 16 had repeat tilt table testing which confirmed the clinical diagnosis of vasodepressor syncope. In patient 4, spontaneous syncope associated with normal heart rate and blood pressure occurred during a clinic visit. Syncope has subsequently resolved with psychotherapy. In patient 3, syncope was presumed to be on the basis of hemodynamic obstruction from hypertrophic cardiomyopathy after sinus rhythm was documented during an episode of spontaneous syncope. This patient has not had recurrence after treatment with ß-blockade. Patient 7 had witnessed syncope with seizure-like activity and normal heart rate, and is undergoing neurological evaluation.

Fig 2 illustrates the results of device interrogation after an episode of spontaneous syncope in patient 2. The upper tracing shows sudden onset of complete atrioventricular block lasting 17 seconds, confirmed on the lower magnified tracing showing atrioventricular dissociation. Fig 3 illustrates recurrent nonsustained ventricular tachycardia in patient 6, associated with near syncope. Fig 4 illustrates sinus arrest lasting 22 seconds associated with syncope in patient 13.

View larger version (41K): [in this window] [in a new window]   Figure 2. Monitor rhythm strip in patient 2 during episode of syncope. A, Single-lead ECG demonstrating sinus rhythm for 2.5 minutes before syncope. B, Magnified view demonstrating complete atrioventricular block.

View larger version (54K): [in this window] [in a new window]   Figure 3. Monitor rhythm strip in patient 6 during episode of near syncope. A, Single-lead ECG demonstrating sinus rhythm interrupted by nonsustained ventricular tachycardia. B, Magnified view demonstrating ventricular tachycardia.

View larger version (35K): [in this window] [in a new window]   Figure 4. Monitor rhythm strip in patient 13 during episode of syncope. A, Single-lead ECG demonstrating the rhythm before and during syncope. B, Magnified view demonstrating a ventricular escape beat during sinus arrest.

The 12 patients in whom a diagnosis was obtained were divided into three groups based on the etiology of syncope (Table 2). A univariate comparison of clinical risk factors failed to reveal any significant baseline characteristics that predicted the etiology of syncope.

A diagnosis was obtained in every patient who had recurrent syncope. Seven of 9 first-generation devices provided by the manufacturer were subject to inappropriate "freezing" of data. In 5 patients, a diagnosis was not obtained after the initial recurrence of symptoms, although a diagnosis was obtained after programming changes. Modification to the device software resulted in resolution of this problem. No patient had difficulty "freezing" the device.

Therapy for the underlying cause was instituted in all patients (Table 3). No further episodes of syncope have occurred during a mean of 13.0±8.4 months of follow-up. No complications were encountered during or after device implantation or explantation. No patient requested premature explantation. Fourteen of 15 patients had their device explanted after a diagnosis was obtained. Patient 6 requested the device be left in until sotalol therapy for ventricular tachycardia was considered effective. No complications were encountered during or after device implantation or explantation. No patient requested premature explantation or declined explantation after a diagnosis was obtained.

View this table: [in this window] [in a new window]   Table 3. Follow-up in 15 Patients With Recurrent Syncope

	Discussion

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The etiology of syncope of unknown origin can be elusive, even after rigorous noninvasive and invasive testing. A cause is not determined after a standardized diagnostic evaluation in 38% to 47% of patients.^{4 23 24 25} Tilt table and electrophysiological testing provide additional information upon which to make a clinical diagnosis. These forms of testing may be described as active measures that induce changes in cardiac rhythm or vasomotor tone aimed at reproducing the patient's symptoms or provide data upon which to make an inferential decision regarding the etiology of syncope. Patients with negative investigations for syncope are said to have a good prognosis.^{9 10 26 27} Despite this, they continue to suffer from recurrent syncope (19% to 43% over an 18- to 36-month follow-up period) with significant morbidity and a small risk of arrhythmic death.^{2 9 10 11 26 27} Many of these patients are unable to drive and can suffer serious injuries associated with recurrent syncope. Little is known regarding the etiology of syncope in patients with negative investigations who continue to lose consciousness.

Conventional ambulatory monitoring is frequently undertaken in patients with syncope, but symptoms correlating with a significant rhythm occur in only 2% to 4%.^{28 29 30} Asymptomatic arrhythmias occur in 13%, and symptoms occur without arrhythmia in 17%.³⁰ Linzer et al³¹ reported the use of long-term (up to 1 month) ambulatory monitoring with the use of a patient-activated loop recorder. Despite recurrence of symptoms in 32 of 57 patients, a diagnosis was obtained in only 14. Device malfunction, patient noncompliance, or inability to activate the recorder was responsible for the lack of diagnosis in the remaining 18. Similar results have been reported by Brown et al.³² Loop recorders were not used in this study because of the infrequent and unpredictable nature of syncope in this population. Undoubtedly, the etiology of syncope would have been discovered in some patients with use of these devices. The syncope monitor we implanted functioned as a long-term implantable loop recorder.

Electrophysiological testing is negative in 14% to 70% of patients investigated for syncope.^{9 10 11 12 13 14 15 16 17 18} This wide variation is strongly influenced by the prevalence of structural heart disease in the population under study. Electrophysiological studies may have low sensitivity and specificity for syncope related to intermittent bradycardia.³³ In one series, the underlying cause of unexplained syncope was not determined in 26% of patients after both tilt table and electrophysiological testing.²

We utilized a long-term subcutaneous ECG monitoring device to determine the cause of syncope in 16 consecutive patients with negative investigations. Fifteen of the 16 patients (94%) developed syncope during follow-up, a higher rate than in the above-mentioned series. The ability to "freeze" the current and preceding rhythm after a spontaneous event allowed us to determine the etiology of syncope in all patients in whom syncope recurred. Implantation of the syncope monitor largely eliminated the issue of patient compliance and operator error, although patients or others were still required to "freeze" the loop. Thirteen of the 15 patients had a cardiovascular etiology for syncope, with bradycardia or tachyarrhythmia the cause in 9. There were no prospectively identifiable clinical risk factors that predicted etiology. The small number of patients with each etiology of syncope precludes definitive identification of risk factors in a pilot study such as this. Bradyarrhythmias tended to predominate in the elderly. All had normal sinus node recovery times and HV intervals at baseline electrophysiological testing. Three other patients, aged 71, 74, and 80 years, were diagnosed with vasodepressor syncope and subsequently did well on ß-blockers. Thus, a presumptive diagnosis of bradyarrhythmia would have been incorrect in 3 of the 7 patients over age 70. In addition, structural heart disease did not predict the etiology of syncope, in particular ventricular arrhythmias.

The determination of the etiology of syncope has obvious therapeutic significance. All diagnoses were amenable to intervention, with resolution of syncope in all patients after etiology was determined. This series reflects a subgroup of the overall syncope population, since we investigated only those patients referred to the arrhythmia service with recurrent but infrequent syncope with negative noninvasive and invasive investigations. The primary utilization of a long-term monitoring device may be appropriate in others, such as patients without structural heart disease in whom the yield of electrophysiological testing is low.^{2 3 9}

This study has important limitations. Any strategy that requires recurrence of a spontaneous episode undertakes the risk of morbidity or sudden death accompanying that recurrence. This was not encountered in this series. This small risk may be balanced by the ability to arrive at a more precise diagnosis and avoid potentially nonbeneficial speculative therapy. In addition, the etiology of nonarrhythmic syncope is presumptive, although the spectrum of diagnoses is considerably narrowed, and unnecessary treatments are avoided. Ultimately, recording devices capable of monitoring other physiologic parameters such as blood pressure may lessen this problem.

Received February 28, 1995; accepted April 1, 1995.

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Kapoor WN, Hammill SC,Gersh BJ. Diagnosis and natural history of syncope and the role of electrophysiologic testing. Am J Cardiol. 1989;63:730-734. [Medline] [Order article via Infotrieve]
   
2. Sra JS, Anderson AJ, Sheikh SH, et al. Unexplained syncope evaluated by electrophysiologic studies and head-up tilt testing. Ann Intern Med. 1991;114:1013-1019.
   
3. Morady F, Shen E, Schwartz A, Hess D, Bhandari A, Sung RJ, Scheinman MM. Long term follow-up of patients with recurrent unexplained syncope evaluated by electrophysiologic testing. J Am Coll Cardiol. 1983;2:1053-1059. [Abstract]
   
4. Kapoor WN, Karpf M, Weiand S, Peterson JR, Levey GS. A prospective evaluation and follow-up of patients with syncope. N Engl J Med. 1983;309:197-204. [Abstract]
   
5. Manolis AS, Linzer M, Salem D, Estes NAM. Syncope: current diagnostic evaluation and management. Ann Intern Med. 1990;112:850-863.
   
6. Kapoor WN. Evaluation and management of the patient with syncope. JAMA. 1992;268:2553-2560. [Abstract]
   
7. Akhtar M, Shenasa M, Denker S, Gilbert CJ, Rizwi N. Role of cardiac electrophysiologic studies in patients with unexplained syncope. PACE Pacing Clin Electrophysiol. 1983;6:192-201. [Medline] [Order article via Infotrieve]
   
8. Sharma AD, Klein GJ, Milstein S. Diagnostic assessment of recurrent syncope. PACE Pacing Clin Electrophysiol. 1984;7:749-759.[Medline] [Order article via Infotrieve]
   
9. Denniss AR, Ross DL, Richards DA, Uther JB. Electrophysiologic studies in patients with unexplained syncope. Int J Cardiol. 1992;35:211-217.[Medline] [Order article via Infotrieve]
   
10. Doherty JU, Pembrook-Rogers D, Grogan EW, et al. Electrophysiologic evaluation and follow-up characteristics of patients with recurrent unexplained syncope and presyncope. Am J Cardiol. 1985;55:703-708. [Medline] [Order article via Infotrieve]
    
11. Muller T, Roy D, Talajic M, Lemery R, Nattel S, Cassidy D. Electrophysiologic evaluation and outcome of patients with syncope of unknown origin. Eur Heart J. 1991;12:139-143. [Abstract/Free Full Text]
    
12. Teichman SL, Felder SD, Matos JA, Kim SG, Waspe LE, Fisher JD. The value of electrophysiologic studies in syncope of undetermined origin: report of 150 cases. Am Heart J. 1985;110:469-479. [Medline] [Order article via Infotrieve]
    
13. Olshansky B, Mazuz M, Martins JB. Significance of inducible tachycardia in patients with syncope of unknown origin: a long term follow-up. J Am Coll Cardiol. 1985;5:216-223. [Abstract]
    
14. Click RL, Gersh BJ, Sugrue DD, Holmes DR, Wood DL, Osborn MJ, Hammill SC. Role of invasive electrophysiologic testing in patients with symptomatic bundle branch block. Am J Cardiol. 1987;59:817-823. [Medline] [Order article via Infotrieve]
    
15. Twidale N, Heddle WF, Ayres BF, Tonkin AM. Clinical implications of electrophysiologic study findings in patients with bifascicular block and syncope. Aust NZ J Med. 1988;18:841-847. [Medline] [Order article via Infotrieve]
    
16. Denes P, Uretz E, Ezri MD, Borbola J. Clinical predictors of electrophysiologic findings in patients with syncope of unknown origin. Arch Intern Med. 1988;148:1922-1928. [Abstract]
    
17. Lacroix D, Dubuc M, Kus T, Savard P, Shenasa M, Nadeau R. Evaluation of arrhythmic causes of syncope: correlation between Holter monitoring, electrophysiologic testing, and body surface potential mapping. Am Heart J. 1991;122:1346-1354. [Medline] [Order article via Infotrieve]
    
18. Bachinsky WB, Linzer M, Weld L, Estes NAM. Usefulness of clinical characteristics in predicting the outcome of electrophysiologic studies unexplained syncope. Am J Cardiol. 1992;69:1044-1049. [Medline] [Order article via Infotrieve]
    
19. Morillo CA, Klein GJ, Zandri S, Yee R. Diagnostic accuracy of a low-dose isoproterenol head-up tilt protocol. Am Heart J. In press.
    
20. Gulamhusein S, Naccarrelli GV, Ko PT, Prystowsky EN, Zipes DP, Barnett HJM, Heger JJ, Klein GJ. Value and limitations of clinical electrophysiologic study in assessment of patients with unexplained syncope. Am J Med. 1982;73:700-705. [Medline] [Order article via Infotrieve]
    
21. Li HG, Thakur RK, Yee R, Klein GJ. The value of electrophysiologic testing in patients resuscitated from documented ventricular fibrillation. J Cardiovasc Electrophysiol. 1994;5:805-809. [Medline] [Order article via Infotrieve]
    
22. Murdock CJ, Klein GJ, Yee R, Leitch JW, Teo WS, Norris C. Feasability of long-term electrocardiographic monitoring with an implanted device for syncope diagnosis. PACE Pacing Clin Electrophysiol. 1990;13:1374-1378. [Medline] [Order article via Infotrieve]
    
23. Kapoor WN. Evaluation and outcome of patients with syncope. Medicine. 1990;69:160-175.[Medline] [Order article via Infotrieve]
    
24. Martin GJ, Adams SL, Martin HG, Mathews J, Zull D, Scanlon PJ. Prospective evaluation of syncope. Ann Emerg Med. 1984;13:499-504. [Medline] [Order article via Infotrieve]
    
25. Day SC, Cook EF, Funkenstein H, Goldman L. Evaluation and outcome of emergency room patients with transient loss of consciousness. Am J Med. 1982;73:15-23. [Medline] [Order article via Infotrieve]
    
26. Bass EB, Elson JJ, Fogors RN, Peterson J, Arena VC, Kapoor WN. Long-term prognosis of patients undergoing electrophysiologic studies for syncope of unknown origin. Am J Cardiol. 1988;62:1186-1191. [Medline] [Order article via Infotrieve]
    
27. Kushner JA, Kou WH, Kadish AH, Morady F. Natural history of patients with unexplained syncope and a nondiagnostic electrophysiologic study. J Am Coll Cardiol. 1989;14:391-396. [Abstract]
    
28. Gibson TC, Heitzman MR. Diagnostic efficacy of 24-hour electrocardiographic monitoring for syncope. Am J Cardiol. 1984;53:1013-1017. [Medline] [Order article via Infotrieve]
    
29. Clark PI, Glasser SO, Spoto E. Arrhythmias detected by ambulatory monitoring: lack of correlation with symptoms of dizziness and syncope. Chest. 1980;77:722-725. [Abstract/Free Full Text]
    
30. DiMarco JP, Philbrick JT. Use of ambulatory electrocardiographic (Holter) monitoring. Ann Intern Med. 1990;113:53-68.
    
31. Linzer M, Pritchett ELC, Pontinen M, McCarthy E, Divine GW. Incremental diagnostic yield of loop electrocardiographic recorders in unexplained syncope. Am J Cardiol. 1990;66:214-219. [Medline] [Order article via Infotrieve]
    
32. Brown AP, Dawkins KD, Davies JG. Detection of arrhythmias: use of a patient-activated ambulatory electrocardiogram device with a solid state memory loop. Br Heart J. 1987;58:251-253. [Abstract/Free Full Text]
    
33. Fujimara O, Yee R, Klein GJ, Sharma AD, Boahene KA. The diagnostic sensitivity of electrophysiologic testing in patients with syncope caused by transient bradycardia. N Engl J Med. 1989;321:1703-1707.[Abstract]
    

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				R A Kenny and A D Krahn Implantable loop recorder: evaluation of unexplained syncope Heart, April 1, 1999; 81(4): 431 - 433. [Full Text]

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				J. Sagrista-Sauleda, B. Romero, G. Permanyer-Miralda, A. Moya, T. Rius-Gelabert, L. Mont Girbau, and J. Soler-Soler Clinical usefulness of head-up tilt test in patients with syncope and intraventricular conduction defect Europace, January 1, 1999; 1(1): 63 - 68. [Abstract] [PDF]

				R. A. Kenny and for the SAFE PACE 2 study group SAFE PACE 2: Syncope and Falls in the Elderly -- Pacing and Carotid Sinus Evaluation: A randomized controlled trial of cardiac pacing in older patients with falls and carotid sinus hypersensitivity Europace, January 1, 1999; 1(1): 69 - 72. [Abstract] [PDF]

				Causes of Syncope Determined with Implanted Monitor Journal Watch Cardiology, November 1, 1995; 1995(1101): 12 - 12. [Full Text]

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