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What are the chances of a 24 hour tape detecting the causes for collapse in a patient? What other alternative monitoring devices are now available?

 Syncope is a common medical problem accounting for up to 6% of

emergency medical admissions. In older patients presenting to

casualty this may be as high as 20% when evaluated with a full

cardiovascular work up. The annual recurrence rate is as high as

30%.1 Syncope due to cardiac causes is associated with a high

mortality (>50% at 5 years) compared with 30% at 5 years in

patients with syncope due to non-cardiac syncope and 24% in

those with unexplained syncope.2 However, in the elderly, even

“benign” syncope can result in significant morbidity and

mortality due to trauma, anxiety or depression, which may lead to

major changes in lifestyle or financial difficulties.3

Syncope is often unpredictable in onset, intermittent and has a

high rate of spontaneous remission making it a difficult diagnostic

challenge. Thus even after a thorough work up, the cause of

syncope may remain unexplained in up to 40% of cases.4

Prolonged ambulatory monitoring is often used as a first line

investigation. Documentation of significant arrhythmias or

syncope during monitoring is rare. At best, symptoms correlating

with arrhythmias occur in 4% of patients, asymptomatic

arrhythmias occur in up to 13%, and symptoms without

arrhythmias occur in up to a further 17%.5–7 Prolonged monitoring

may result in a slight increase in diagnostic yield from 15% with 24

hours of monitoring to 29% at 72 hours.8

Patient activated external loop recorders have a higher diagnostic

yield but do not yield a symptom-rhythm correlation in over 66% of

patients, either because of device malfunction, patient noncompliance

or an inability to activate the recorder.9,10 In addition

such devices are only useful in patients with relatively frequent

symptoms. In a follow up by Kapoor et al,11 only 5% of patients

reported recurrent symptoms at 1 month, 11% at 3 months and 16%

at 6 months. Thus this type of monitoring is likely to be useful only

in a small subgroup of patients with frequent recurrence in whom

initial evaluation is negative and arrhythmias are not diagnosed by

other means, such as 24 hour ECG or electrophysiology studies.

The diagnostic yield from cardiac electrophysiology ranges

from 14–70%. This variability is primarily dependent on the characteristics

of patients studied, in particular the absence or

presence of co-morbid cardiovascular disease.12 Thus despite the

use of investigations such as head up tilt testing, ambulatory

cardiac monitoring, external loop recorders and electrophysiological

testing, the underlying cause of syncope remains

unexplained and continues to pose a diagnostic problem.

The implantable loop recorder (ILR) is a new diagnostic tool to

add to the strategies for investigation of unexplained syncope.12 It

permits long term cardiac monitoring to capture the ECG during a

spontaneous episode in patients without recurrence in a

reasonable time frame. It should be considered in those who have

already completed the above outlined investigations that have

proved negative, and in those in whom the external loop recorder

has not yielded a diagnosis in one month. The ILR is implanted

under local anaesthetic via a small incision usually in the left

pectoral region. It has the ability to “freeze” the current and

preceding rhythm for up to 40 minutes after a spontaneous event

and thus allows the determination of the cause of syncope in most

patients in whom symptoms are due to an arrhythmia. The

activation device, used by the patient, family member or friend

freezes and stores the loop during and after a spontaneous

syncopal episode. This is retrievable at a later stage using a

standard pacemaker programmer. The ILR specifically monitors

heart rate changes. Hypotensive syndromes including vasovagal

syncope, orthostatic hypotension, post-prandial hypotension and

vasodepressor carotid sinus hypersensivity may also cause

syncope. An ability to record blood pressure variation in addition

to heart rate changes during symptoms would be a very helpful

and exciting addition to the investigation of people with syncope.


1 Brady PA, Shen WK. Syncope evaluation in the elderly. Am J Geriatr

Cardiol 1999;8: 115–24.

2 Kapoor W. Syncope in older persons. J Am Geriatr Soc 1994;42: 426–36.

3 Lipsitz L. Syncope in the elderly. Ann Intern Med 1983;99: 92–105.

4 Kapoor W. Diagnostic evaluation of syncope. Am J Med 1991;90: 91–106.

5 Gibson TC, Heitzman MK. Diagnostic efficacy of 24 hour electrocardiographic

monitoring for syncope. Am J Cardiol 1984;53: 1013–17.

6 Clark PI, Glasser SO, Spoto E. Arrhythmias detected by ambulatory

monitoring; lack of correlation with symptoms of dizziness and

syncope. Chest 1990;77: 722–5

7 DiMarco P, Philbrick JT. Use of ambulatory electrocardiographic

(Holter) monitoring. Ann Intern Med 1990;113: 53–68.

8 Bass EB, Curtiss EI, Arena VC. The duration of holter monitoring in

patients with syncope: is 24 hours enough? Arch Intern Med 1990;150:


9 Linzer M, Pritchett ELC, Pontiueu M et al. Incremental diagnostic

yield of loop electrocardiographic recorders in unexplained syncope.

Am J Cardiol 1990;66: 214–19.

10 Brown AD, Dawkins RD, Davies JG. Detection of arrhythmias; use of

patient-activated ambulatory electrocardiogram device with a solid

state memory loop. Br Heart J 1989;58: 251–3.

11 Kapoor W, Peterson J, Wieand H et al. Diagnostic and prognostic

implications of recurrences in patients with syncope. Am J Med

1987;83: 700–8.

12 Kenny RA, Krahn AD. Implantable loop recorder: evaluation of

unexplained syncope. Heart 1999;81: 431–3.

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