From the Department of Clinical Neurosciences, King's College
School of Medicine and Dentistry and the Institute of Psychiatry, London, UK.
Correspondence to Dr Hugh Markus, Department of Clinical Neurosciences, Institute of Psychiatry, De Crespigny Park, London, SE5 8AF, UK. E-mail h.markus{at}iop.bpmf.ac.uk
Background and Purpose—Although
asymptomatic embolization can be detected in patients with
carotid artery stenosis, its temporal variability is unclear.
An understanding of this is important in designing optimal
recording protocols for future prospective studies of the
predictive value of embolic signals (ES). We determined the effect of
repeating and extending recording times in patients with
symptomatic and asymptomatic carotid
stenosis.
Methods—In 20 asymptomatic and 20
symptomatic subjects with >60% carotid stenosis,
we used transcranial Doppler ultrasound to record
for ES in the ipsilateral middle cerebral artery. Three 1-hour
recordings were performed on three separate days, and on one
occasion (not necessarily the first) the recording was extended
to 2 hours. The recordings were saved onto digital tape for
subsequent blinded analysis.
Results—Marked temporal variability was seen in
symptomatic patients in whom the cumulative proportion of
subjects with ES increased from 10 (50%) after a single hour of
recording to 12 (60%) and 15 (75%) after two and three
recordings, respectively. Extending the recording to 2
hours increased the yield of ES-positive patients from 6 (30%) to 8
(40%). In symptomatic patients there was excellent
agreement between whether patients were positive for ES during each of
two consecutive 1-hour recordings (
Conclusions—The temporal variability of ES needs to be
taken into account in the design of optimal recording protocols
and comparisons of results from different studies. Extending the
duration of recording beyond an hour in symptomatic
stenoses is of less value, but repeating the recording
on a different day will often identify additional subjects with ES. In
intervention studies in symptomatic patients, the time
since last symptoms must be considered. In asymptomatic
stenosis, extending the duration of recording beyond an
hour will increase the proportion of patients positive for ES.
© 1998 American Heart Association, Inc.
Original Contributions
Temporal Variability of Asymptomatic Embolization in Carotid Artery Stenosis and Optimal Recording Protocols
=0.78,
P=0.0003) but poor agreement between the results of two
single-hour recordings performed on different days (=0.22,
P=0.27). In asymptomatic patients, 4 (20%)
were ES positive during the first hour; this increased to 5 (25%)
after the recording was repeated once, with no further increase
after the third recording. Extending the recording to 2
hours increased the yield from 3 (15%) to 7 (35%). In contrast to
symptomatic stenoses, in patients with
asymptomatic stenoses there was fair agreement
between whether patients were ES positive on two consecutive 1-hour
recordings (=0.49, P=0.01) or two single-hour
recordings performed on different days (=0.48,
P=0.02). Symptomatic subjects were more
likely to have ES (when all 1-hour recordings were considered,
24/60 versus 10/60; P=0.0046). ES in
symptomatic subjects had a higher relative intensity
increase than in asymptomatic subjects
(P=0.01).
Key Words: carotid artery diseases • cerebral embolism • ultrasonography, Doppler
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