Use of an Extended Monitoring Strategy in Patients With
Problematic Syncope
Andrew D. Krahn, MD; George J. Klein, MD; Raymond Yee, MD; Teri Takle-Newhouse, MSc;
Caro Norris; for the Reveal Investigators*
Downloaded from http://circ.ahajournals.org/ by guest on July 28, 2017
Background—The conventional investigation of patients who present with syncope involves short-term ECG monitoring
or provocative testing with head-up tilt and electrophysiological testing. A symptom-rhythm correlation is often difficult
to obtain during spontaneous syncope because of its sporadic, infrequent, and unpredictable nature.
Methods and Results—We used a prolonged monitoring strategy to determine the cause of syncope in 85 patients (age,
59618 years; 44 men) with recurrent undiagnosed syncope with an implantable loop recorder capable of cardiac
monitoring for up to 18 months. During a mean of 10.564.0 months of follow-up, symptoms recurred in 58 patients
(68%) 71679 days (2.362.6 months) after implantable loop recorder insertion. An arrhythmia was detected in 42% of
patients who recorded a rhythm during recurrent symptoms, with bradycardia present in 18 and tachycardia in 3. Five
of the 18 bradycardic patients and 2 additional sinus rhythm patients received a clinical diagnosis of neurally mediated
syncope. Patients who experienced presyncope were much less likely to record an arrhythmia during symptoms
compared with recurrence of syncope (24% versus 70%, P50.0005). There were no adverse events associated with
recurrent symptoms, and there were no sudden deaths. Inability to freeze after an event occurred in 8 patients, and pocket
infection occurred in 3.
Conclusions—The strategy of prolonged monitoring is effective and safe in patients with problematic syncope.
(Circulation. 1999;99:406-410.)
Key Words: syncope n arrhythmia n diagnosis
C
urrent investigation of patients who present with syncope involves short-term ECG monitoring or provocative testing with head-up tilt and electrophysiological testing.1– 4 The diagnostic yield of Holter monitoring in syncope
is disappointing,5–7 and provocative test results may be
negative or difficult to interpret.8,9 A prolonged monitoring
strategy has previously been difficult to use because of
waning patient compliance and motivation with external loop
recorder technology and the relatively short memory capabilities of these devices.7,10 –12 Prolonged monitoring is also
reliant on the spontaneous recurrence of symptoms, with
attendant risk of injury, concern regarding life-threatening
arrhythmias, and ongoing diagnostic uncertainty.
A symptom-rhythm correlation is often difficult to obtain
during spontaneous episodes because of the sporadic, infrequent, and unpredictable nature of syncope. Despite a wide
array of diagnostic tools, the cause of syncope is not determined after initial investigations in 38% to 47% of patients.6,13,14 Even after referral for tilt-table and electrophysiological testing, 10% to 26% of patients will remain
undiagnosed.2,15,16
Recent advances in loop recorder technology have permitted a longer duration of external ECG monitoring than
conventional Holter monitoring, improving the overall diagnostic yield.7,10 –12 We used a new insertable loop recorder
(ILR) that can provide monitoring for 14 months to assess the
utility and safety of a prolonged monitoring strategy in a
multicenter study of 85 syncopal patients without a diagnosis
after initial assessment.
Methods
Patient Population
Patients with undiagnosed syncope after initial assessment that
included a history, physical examination, ECG, and at least 24 hours
of ambulatory or in-hospital monitoring were approached to participate in a study using an ILR (Reveal ILR, Medtronic USA Inc) to
determine the cardiac rhythm during spontaneous syncope. Patients
were eligible for the study if they had had 2 syncopal episodes within
the previous 12 months or a single episode with a history of
presyncope as well. Patients were excluded if they were unlikely to
survive 1 year, were unable to give informed consent, had a
previously implanted programmable medical device, were pregnant,
or were women of childbearing potential not on a reliable form of
contraception. Eighty-five patients with unexplained syncope underwent insertion of the ILR (Table 1). The mean number of syncopal
episodes in the previous 12 months was 5.165.5 (median, 3). The
majority of patients had suffered from recurrent syncope for .2
Received April 21, 1998; revision received September 17, 1998; accepted October 9, 1998.
From the Division of Cardiology, University of Western Ontario, London, Ontario, Canada, and Medtronic, Minneapolis, Minn (T.T.-N.).
*See Appendix for list of investigators.
Reprint requests to Andrew Krahn, London Health Sciences Center, University Campus, 339 Windermere Rd, London, Ontario, Canada N6A 5A5.
E-mail [email protected]
© 1999 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
406
Krahn et al
TABLE 1.
January 26, 1999
407
Clinical Characteristics of the 85 Patients
Characteristic
Age, y
Mean6SD
Figure 1. Recorded rhythm during recurrent symptoms.
Symptom-rhythm correlation in
the 58 patients who experienced
recurrent syncope or
presyncope.
59618
Concomitant cardiovascular disease,* %
62
Sex, % male
52
Syncope
No. of syncopal spells in previous 12 months
5.165.5
Duration of symptoms, y
5.568.9
Symptoms .2 years, %
71
Symptoms .4 years, %
37
Investigations before enrollment
time of implantation. Patients were instructed to activate the device
in the event of syncope or presyncope. Follow-up was performed
after each event. The device remained implanted until syncope or
presyncope recurred unless the patient or investigator chose to
remove it sooner. Devices were removed after 18 months of
follow-up or at end of battery life.
Downloaded from http://circ.ahajournals.org/ by guest on July 28, 2017
Holter monitor, %
100
Echocardiography, %
70
Head-up tilt test, %
49
Electrophysiological study, %
43
Analysis
External loop recorder, %
24
Continuous variables were compared by Student’s t tests, and
categorical variables were compared by a x2 test. A value of P,0.05
was considered significant.
*Includes angina, prior myocardial infarction, previous cardiac arrest,
cardiomyopathy, cardiomegaly, congestive heart failure, and valvular, congenital, or pericardial heart disease.
Results
years. The study was approved by the institutional review board or
medical ethics committee at each study center.
Previous Investigations
Testing before patient enrollment in the study was performed at the
discretion of the investigator (Table 1). All patients underwent
clinical assessment, including ambulatory or in-hospital monitoring.
Of the 85 patients, 21 had been referred to an internist and 73 had
been referred to another cardiologist before assessment by the study
investigator. Most patients had several investigations for syncope
before ILR insertion, the most common of which were echocardiography, head-up tilt testing, and electrophysiological testing. One
patient had experienced a previous cardiac arrest and underwent
extensive investigation, including electrophysiological testing, before enrollment in the study.
Device
The ILR is a 6131938-mm recording device with 2 sensing bipoles
37 mm apart within its shell. It weighs 17 g and has a volume of 8
cm3, slightly smaller than a standard VVI pacemaker. The recorded
ECG signal is stored in a circular buffer capable of retaining 21
minutes of uncompressed signal or 42 minutes of compressed signal
in 1 or 3 divided parts. The memory buffer is frozen with a hand-held
activator provided to the patient at the time of device implantation.
The resultant programming can store a single episode of 21 minutes
(20 minutes before and 1 minute after “freeze”), a 42-minute
compressed episode (40 minutes before, 2 minutes after), three
7-minute episodes (6 minutes before, 1 minute after), or three
14-minute compressed episodes (12 minutes before, 2 minutes after).
The episodes are then downloaded after interrogation with a standard
pacemaker programmer (Medtronic 9790C).
Investigators performed device implantation in an operating room,
cardiac catheterization laboratory, electrophysiology laboratory, or
specialized procedure room at their discretion. The site of the
implant was generally in the left infraclavicular region but was
determined in each circumstance by patient and physician preference. Use of prophylactic antibiotics was left to the discretion of the
implanting physician. After the skin was infiltrated with local
anesthesia, a 2-cm incision was made. A pocket was fashioned, and
the device was inserted and anchored with a nonabsorbable suture.
The skin was closed with absorbable sutures, and a satisfactory
R-wave signal was verified with the programming head applied over
the implanted device. The patient, along with a spouse, family
member, or friend, was instructed in the use of the activator at the
Recurrent Symptoms
During a mean of 10.564.0 months of follow-up, symptoms
recurred in 58 patients (68%) 71679 days (2.362.6 months)
after ILR insertion (median, 51 days, or 1.7 months). One
patient had recurrence within a week of the implantation, and
3 patients had recurrence within the first month. Forty-nine of
85 patients (58%) had recurrence of symptoms within 6
months of implantation. Follow-up was .9 months in 68 of
85 patients. Failure to appropriately “freeze” after symptoms
occurred 24 times in 14 patients. No instance was attributed
to device failure. Six of these patients had an appropriate
freeze after spontaneous symptoms on a different occasion. A
total of 128 events were frozen by the remaining 50 patients
during the course of follow-up. The remaining 27 patients
have not had recurrence and continue to be followed up.
Symptom-Rhythm Correlation
An arrhythmia was detected in 21 of the 50 patients (42%)
who recorded a rhythm during recurrent symptoms, with
bradycardia being the most frequent (Figure 1). Of the 18
patients with bradycardia (heart rate ,50 bpm), 12 underwent
device removal and pacemaker implantation. Five of the 18
patients had heart rate slowing, which the investigator interpreted as the cardioinhibitory component of neurally mediated syncope. Two additional patients had relative slowing,
with a heart rate .50 bpm, and also received a clinical
diagnosis of neurally mediated syncope (Figure 2). Three
patients had tachyarrhythmias associated with recurrent
symptoms: sustained supraventricular tachycardia in 2 patients, who subsequently underwent catheter ablation, and
atrial flutter with a rapid ventricular response in 1 patient,
who received pharmacological therapy. The remaining 29
patients had sinus rhythm during symptomatic recurrence and
continue to be followed up. Devices remained implanted in
these patients to monitor subsequent episodes.
408
Use of Extended Monitoring in Syncope
TABLE 2.
Implant Data on 85 Patients Who Received an ILR
Implantation location
Figure 2. Clinical diagnosis in
50 patients with symptomrhythm correlation after recurrent
events with the ILR.
Electrophysiology laboratory
40
Operating room
22
Cardiac catheterization laboratory
23
Implant site
Left pectoral
54
Left inframammary
27
Other*
Syncope Versus Presyncope
Downloaded from http://circ.ahajournals.org/ by guest on July 28, 2017
Of the 50 patients with a symptom-rhythm correlation, 13 had
syncope, 10 had recurrence of syncope and presyncope, and
27 had presyncope alone. When patients experienced presyncope, they were much less likely to record an arrhythmia
during symptoms compared with recurrence of syncope (24%
versus 70%, P50.0005, Figure 3). When those patients with
a clinical diagnosis of neurally mediated syncope (n54) or
presyncope (n54) were excluded, the difference remained
significant (24% versus 63%, P50.006). Arrhythmias were
seen in 9 of the 13 patients (69%) who had recurrence of
syncope alone (without other presyncopal events), with bradycardia recorded in all 9 patients during syncope. In the 10
patients with both syncope and presyncope, syncope was
associated with an arrhythmia in 7 (bradycardia in 5,
tachycardia in 2), whereas presyncope documented an arrhythmia in only 4 patients (bradycardia in 2, tachycardia in
2). The 3 patients with an arrhythmia during presyncope had
the same arrhythmia during syncope.
Device
The majority of devices were implanted outside of an
operating room setting (Table 2). The device was inserted in
the left pectoral region near a traditional pacemaker implant
site in 64% of patients. Of the remaining 31 devices, 27 were
implanted in the left inframammary region. The mean implant
voltage was 4816279 mV for all 85 patients. An adequate
electrogram was obtained in all 85 patients (range, 58 to 1300
mV). The signal-to-noise ratio was 19:1. P waves were seen
in 37% of vertical implants, compared with 14% of horizontal
ones. The sensed amplitude was 8316343 mV at the single
center at which systematic surface mapping was performed
before implantation to optimize the sensed signal amplitude.
Two patients who did not receive prophylactic antibiotics
developed local infection requiring treatment with oral antibiotics after device removal. A second device was reim-
Figure 3. Diagnosis by recurrent symptom. Cause of symptoms
in patients with syncope versus presyncope. Syncope was
much more likely to correlate with an arrhythmia (P50.0005).
See text for discussion.
4
Implant electrogram amplitude, mV
4816279
*Included 2 left intercostal and 2 right parasternal implants.
planted in another site in 1 of these patients. A third patient
had persistent pain at a left inframammary implant site, which
resolved when the device was moved to the left pectoral
region. A fourth patient developed local erosion with infection 13 weeks after implantation. The device was explanted
without incident. No patient requested removal of the device
before recurrence of symptoms. The devices were removed at
the end of follow-up without complications.
Outcome
During the study, 1 patient died of myocardial infarction that
was not complicated by arrhythmias. A second patient died of
cancer of the lung, and a third patient suffered a cerebrovascular accident and withdrew from the study.
Discussion
The cause of syncope can be difficult to determine if it is not
obvious after initial assessment.6,13,14 Despite the good prognosis of patients whose investigations are negative, syncope
may recur, with attendant morbidity and even mortality.2,8,17–21 The current approach to the syncopal patient
involves a mixture of passive monitoring, which samples a
relatively small time frame, and provocative testing aimed at
actively reproducing the clinical situation. Both tilt-table and
electrophysiological testing are negative in as many as 70%
of cases8,9 and represent an artificial environment, making
interpretation of results particularly difficult. The reference
standard for establishing a diagnosis is the recording of
physiological parameters during a clinical episode. This
obviates the interpretation difficulties of extrapolating the
results of provocative testing to the clinical situation.
In a previous pilot study of 24 patients with syncope, a
prototype implantable loop recorder established the cardiac
rhythm in all 21 patients who had recurrent syncope after the
device was implanted.15 This population represented a difficult subgroup with refractory but infrequent syncope that was
not diagnosed after extensive testing. The present study
examined the utility of the ILR in a multicenter study. The
patient population was selected to be more representative of
those referred to cardiologists or electrophysiologists for
investigation of syncope after a workup that varied according
to physician preference.
The strategy of prolonged monitoring was successful in
establishing a symptom-rhythm correlation in 86% of the 58
patients who had recurrence during the follow-up period. The
Krahn et al
Downloaded from http://circ.ahajournals.org/ by guest on July 28, 2017
rhythm profile of patients during recurrent syncope reflected
an arrhythmic cause in 42% of patients, in keeping with the
findings of the pilot study (48%). In the remaining patients,
an arrhythmia was eliminated as a potential cause of symptoms, alleviating concerns of a life-threatening arrhythmia.
The absence of sudden death or significant morbidity
suggests that this observational approach was safe in the
population studied and did not place patients at risk during
spontaneous recurrence. This is of particular interest given
the prevalence of significant structural heart disease, the
major determinant of prognosis in syncopal patients.3 Sixtytwo percent of patients had some structural heart disease, with
19% having documented coronary artery disease, previous
cardiac arrest, or left ventricular dysfunction. Investigator
selection and preceding negative investigations, including
electrophysiological testing in some patients, may have
screened out those patients at higher risk of life-threatening
arrhythmias. This does not necessarily imply that a monitoring strategy is safe in all patients. For example, patients with
poor left ventricular function and inducible ventricular
tachycardia at electrophysiological testing have been shown
to receive appropriate shocks when managed with an implantable defibrillator.22 A proactive approach using electrophysiological testing in this population seems reasonable.
Symptoms did not recur in 32% of patients over 10 months
of follow-up. This spontaneous resolution is in keeping with
other series, which have noted a 57% to 85% resolution
during 10 to 40 months of follow-up after negative initial
investigations.1,2,21,23,24 This finding may relate to the spontaneous periodicity of syncope, a self-limited cause, or a
screening effect of the completed investigations, which have
identified the causes of syncope that are most likely to recur.
The occurrence of presyncope is often clinically interpreted as “imminent” syncope. It is tempting to use presyncope as a surrogate for syncope. The predictive value of
presyncope in establishing an arrhythmic cause for symptoms
was low. Excluding patients with a diagnosis of neurally
mediated syncope, only 24% of patients with presyncope
were found to have an arrhythmia (versus 63% for syncope).
The majority of patients (76%) reporting presyncope were in
sinus rhythm. In those patients with both presyncope and
syncope, presyncope was misleading in 3 of the 6 patients
with sinus rhythm during presyncope who subsequently had
an arrhythmia documented in conjunction with frank syncope. Others have similarly reported a low yield for external
monitoring in patients with presyncope,25 although data on
the relationship between presyncope and syncope in the same
patients remain scant.
Individual investigators each implanted 1 to 4 devices,
with the exception of a single site, at which 11 devices
were implanted. Despite the absence of a learning period
with respect to implantation technique, the relatively low
complication rate suggests that the procedure is readily
adopted by operators experienced with implantable devices. The unexpected infection rate may reflect the need
for routine antibiotic prophylaxis, which was not required
in the study. Programming and interrogation were performed with a pacemaker programmer, which is accessible
to most pacing centers. Patient-related difficulties with
January 26, 1999
409
freezing after events occurred in 16% of patients. Of these
patients, '50% subsequently froze appropriately. This
problem may be minimized in the future by development
of autodetection functions, improved patient education,
and expanded memory capacity. Similar difficulties with
freezing have been reported in 32% of patients using an
external loop recorder,7,10 in whom device malfunction,
patient noncompliance, or inability to activate the recorder
was responsible for the lack of success. External devices
suffer from insufficient memory for many patients who are
unable to activate the device within 4 to 6 minutes of
syncope, as well as waning patient compliance with
external electrodes in the absence of a diagnosis.
Limitations
The population under study represents a spectrum of individuals referred to a cardiologist or electrophysiologist for
evaluation. Although they may not represent a primary
syncope population, they served to test the utility of a
prolonged monitoring strategy in patients with recurrent
syncope. Second, obtaining a symptom-rhythm correlation
does not necessarily lead to a diagnosis. Nonetheless, exclusion of arrhythmia often alleviates the concerns of both the
patient and physician regarding the potential for lifethreatening arrhythmias and allows the focus of further
investigations (if necessary) to shift to other areas. Finally, a
small proportion of patients were unable to activate the
device after a spontaneous event. Future iterations should
include programmable automatic detection algorithms and
longer memory loops. In addition, monitoring of other physiological parameters, such as blood pressure and oxygen
saturation, is a feasible goal. Current development suggests
that device size may decrease by 30% to 60%, facilitating
implantation in an office setting by operators with less
surgical experience.
Conclusions
The strategy of prolonged monitoring is effective in establishing a symptom-rhythm correlation in the majority of
patients with problematic syncope. It obviates the need for
difficult interpretation of provocative testing. Presyncope is
much less likely to be associated with an arrhythmia than
syncope and did not prove to be an accurate surrogate for
syncope in establishing a diagnosis.
Appendix
Investigators
Dr D. Cameron, Toronto Hospital; Dr C. LeFeuvre, Hamilton
General Hospital; Dr H. Abdollah, Hotel Dieu Hospital; Dr R.
Leather, Royal Jubilee Hospital; Dr G. Klein and Dr A. Krahn,
London Health Sciences Center; Dr C. Kerr, St Paul’s Hospital; Dr
A. Gillis, University of Calgary; Dr L. Sterns, Queen Elizabeth II
Hospital; Dr M. Sami, Royal Victoria Hospital; Dr M. Talajic,
Montreal Heart Institute; Dr F. Philippon, Hôpital Laval; Dr M.
O’Reilly, Valley Regional Hospital; Dr A. Tang, University of
Ottawa Heart Institute; Dr R. Wald, Mt Sinai Hospital; Dr H.
Schmidinger, Allgemeines Krankenhuis Wien; Prof R. Stroobandt,
Sint Jozef Ziekenhuis Oostenende; Prof P. Brugada, Onze Lieve
Vrouwe Ziekenhuis Aalst; Dr E. Simonsen, Odense Universitets
Hospital; Prof S. Kacet, Hôpital Cardiologique Universitaire de
Lille; Dr T. Lavergne, Hôpital Broussais; Prof P. Coumel, Hôpital
410
Use of Extended Monitoring in Syncope
Lariboisière; Prof P. Touboul, Hôpital Louis Pradel; Prof P. Vardas,
Heraklion University Hospital; Dr J. Balkin, Shaare Zedek Hospital;
Dr E. Ovsyshcher, Soroka Medical Center; Dr A. Marchini,
Specedali Civili di Brescia; Dr C. D’Agostino, Ospedale Policlinico;
Dr C. Menozzi, Arcispedale Sante Maria Nuova; Dr F. Bracke,
Catharina Ziekenhuis; Dr R. van Mechelen, Sint Franciscus Gasthuis; Dr R. van der Heijden, Holy Ziekenhuis; Dr W. Beukema,
Ziekenhuis de Weezenlanden; Dr A. Ramdat Misier, St Sophia
Ziekenhuis; Dr I. Obel, Milpark Hospital; Dr F. Dateling, Johannesburg Hospital; Dr J. Fuhrer, Inselspital; Prof A.J. Camm, St
Georges Hospital.
Acknowledgments
This study was supported in part by the Heart and Stroke Foundation
of Ontario.
References
Downloaded from http://circ.ahajournals.org/ by guest on July 28, 2017
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.
2. Sra JS, Anderson AJ, Sheikh SH, Avitall B, Tchou PT, Troup PJ, Gilbert
CJ, Akhtar M, Jazayeri MR. Unexplained syncope evaluated by electrophysiologic studies and head-up tilt testing. Ann Intern Med. 1991;114:
1013–1019.
3. 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.
4. Manolis AS, Linzer M, Salem D, Estes NAM. Syncope: current diagnostic evaluation and management. Ann Intern Med. 1990;112:850 – 863.
5. Kapoor WN. Evaluation and management of the patient with syncope.
JAMA. 1992;268:2553–2560.
6. Kapoor WN. Evaluation and outcome of patients with syncope. Medicine.
1990;69:160 –175.
7. 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.
8. Klein GJ, Gersh BJ, Yee R. Electrophysiologic testing: the final court of
appeal for diagnosis of syncope? Circulation. 1995;92:1332–1335.
9. Kapoor WN, Smith NA, Miller NL. Upright tilt testing in evaluating
syncope: a comprehensive literature review. Am J Med. 1994;97:78 – 88.
10. Cumbee SR, Pryor RE, Linzer M. Cardiac loop recording: a new noninvasive diagnostic test in recurrent syncope. Southern Med J. 1990;83:
39 – 43.
11. 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.
12. Fogel RI, Evans JJ, Prystowsky EN. Utility and cost of event recorders in
the diagnosis of palpitations, presyncope and syncope. Am J Cardiol.
1997;79:207–208.
13. Martin GJ, Adams SL, Martin HG, Matthews J, Zull D, Scanlon PJ.
Prospective evaluation of syncope. Ann Emerg Med. 1984;13:499 –504.
14. 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.
15. Krahn AD, Klein GJ, Norris C, Yee R. The etiology of syncope in
patients with negative tilt table and electrophysiological testing. Circulation. 1995;92:1819 –1824.
16. Krahn AD, Klein GJ, Yee R, Norris C. The etiology of syncope in
patients with negative non-invasive and invasive testing: final results
from a pilot study with an implantable loop recorder. Am J Cardiol.
1998;82:117–119.
17. 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.
18. Gulamhusein S, Naccarelli GV, Ko PT, Prystowsky EN, Zipes DP,
Barnett HJM, Heiger JJ, Klein GJ. Value and limitations of clinical
electrophysiologic study in assessment of patients with unexplained
syncope. Am J Med. 1982;73:700 –705.
19. Doherty JU, Pembrook-Rogers D, Grogan EW, Falcone RA, Buxton AE,
Marchlinski FE, Cassidy DM, Kienzle MG, Almendral JM, Josephson
ME. Electrophysiologic evaluation and follow-up characteristics of
patients with recurrent unexplained syncope and presyncope. Am J
Cardiol. 1985;55:703–708.
20. 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.
21. 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.
22. Link MS, Costeas XF, Griffith JL, Colburn CD, Estes NAM, Wang PJ.
High incidence of appropriate implantable-defibrillator therapy in
patients with syncope of unknown etiology and inducible ventricular
arrhythmias. J Am Coll Cardiol. 1997;29:370 –375.
23. Freed LA, Eagle KA, Mahjoub ZA, Gold MR, Smith AJC, Terrell LB,
O’Gara PT, Paul SD. Gender difference in presentation, management, and
cardiac event-free survival in patients with syncope. Am J Cardiol.
1997;80:1183–1187.
24. Bass EB, Elson JJ, Fogoros 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.
25. Zimetbaum P, Kim KY, Ho KKH, Zebede J, Josephson ME, Goldberger
AL. Utility of patient-activated cardiac event recorders in general clinical
practice. Am J Cardiol. 1997;79:371–372.
Use of an Extended Monitoring Strategy in Patients With Problematic Syncope
Andrew D. Krahn, George J. Klein, Raymond Yee, Teri Takle-Newhouse and Caro Norris
for the Reveal Investigators
Downloaded from http://circ.ahajournals.org/ by guest on July 28, 2017
Circulation. 1999;99:406-410
doi: 10.1161/01.CIR.99.3.406
Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 1999 American Heart Association, Inc. All rights reserved.
Print ISSN: 0009-7322. Online ISSN: 1524-4539
The online version of this article, along with updated information and services, is located on the
World Wide Web at:
http://circ.ahajournals.org/content/99/3/406
Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published
in Circulation can be obtained via RightsLink, a service of the Copyright Clearance Center, not the Editorial
Office. Once the online version of the published article for which permission is being requested is located,
click Request Permissions in the middle column of the Web page under Services. Further information about
this process is available in the Permissions and Rights Question and Answer document.
Reprints: Information about reprints can be found online at:
http://www.lww.com/reprints
Subscriptions: Information about subscribing to Circulation is online at:
http://circ.ahajournals.org//subscriptions/