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.
References
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:
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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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