Asymptomatic Embolization Predicts Stroke and TIA Risk in Patients With Carotid Artery Stenosis
To the Editor:
It was very interesting to read in Stroke the article of Molloy et al,1 as well as those of other investigators, concerning embolic signals (ES).2 3 Since we believe that the use of transcranial Doppler (TCD) will contribute to the stratification of the high-risk patients who are candidates for sustaining a stroke, we would like to first congratulate the authors and to add certain observations and knowledge that might prove to be useful in such a future program.
I would like to enlarge upon the following points. (1) The investigation with TCD of patients depicting embolic signals (ES) of 60-minute duration has given an interesting outcome. The results may be more beneficial if the evolution of the method will finally permit its application on a 24-hour basis, similar to the Holter method used in cardiology. (2) The evaluation of the patients under everyday working conditions (hypertension period) might add profitable informative data. (3) Not only the quality but also the quantity of ES might be related to the frequency and gravity of the ensuing cerebral episode. (4) The placing of probes concomitantly on the thoracic wall and along the neck area will also signal the focus of origin of emboli (heart, aortic arch, carotid). (5) The intraoperative application of the method with preoperative and postoperative mapping with MRI of the brain will also proffer an answer for the value of various other technique at the aortic arch and its branches, relative to the presence of ES.
We would like to remark that the heart, as an embologenic focus, in the beginning of the study does not exclude, for example, 774 days later an ES of cardiac origin, because the cardiac cause might have ensued during the investigation.
A more sophisticated development of the method and its application in the form of a large multicenter study would render it a remarkable method that might alter the refined and current indications for surgery and, moreover, the prognosis for these patients.
- Copyright © 2000 by American Heart Association
Molloy J, Markus HS. Asymptomatic embolization predicts stroke and TIA risk in patients with carotid artery stenosis. Stroke. 1999;30:1440–1443.
Vacton L, Larrue V, Pavy Le Traon A, Massabuau P, Geraud G. Microembolic signals and risk of early recurrence in patients with stroke or transient ischemic attack. Stroke. 1998;29:2125–2128.
Furui E, Hanzawa K, Ohzeki H, Nakajima T, Fukura N, Takamori M. “Tail sign” associated with microembolic signals. Stroke. 1999;30:863–866.
I thank Drs Dimakakos and Arapoglou for their comments. I agree that TCD detection in cerebral emboli is an exciting technique to stratify risk in patients with cardiovascular disease. Studies to date have provided most evidence for the clinical significance of Doppler embolic signals in patients with carotid artery stenosis, as described in our article and in previous studies. A number of previous studies have looked at patients with cardiogenic sources of emboli. The frequency of embolic signals in patients with atrial fibrillation appears to be lower than that found in carotid stenosis, and we were unable to find any association between the presence of embolic signals in patients with atrial fibrillation and clinical marks of increased risk.R1 More studies are required in this area. There has been relatively little work studying embolization in patients with aortic arch atheroma although current studies are underway. It certainly is possible to localize the source of embolization in patients by recording from multiple sites along the arterial system. We have performed such studies in patients with acute stroke and have localized the embolic source to the carotid bifurcation in individual patients.R2 However, such studies can be technically difficult. It is relatively easy to record for prolonged periods of time from the middle cerebral artery, as good probe fixation can be achieved using a head band. However, maintaining probe position on the common carotid artery is more difficult, because the position of the vessel may vary during swallowing and other normal activities. It is possible with improved technology that some of these difficulties may be overcome.
The prospective studies to date, including our own, have not been sufficiently large to determine whether there are particular thresholds or frequencies per hour of embolic signals that confer increased risk. Although our study and those of Valton et alR3 and Siebler et alR4 have shown that asymptomatic embolization predicts stroke risk in patients with large-artery disease, the confidence intervals are wide. For these reasons we are now carrying out a much larger international multicenter study to determine the predictive value of Doppler embolic signals in patients with asymptomatic carotid stenosis. This study, which will recruit 600 patients, is supported by the British Heart Foundation. If any centers are interested in taking part, they are encouraged to contact me at the address below.
Cullinane M, Wainwright R, Brown A, Monaghan M, Markus HS. Asymptomatic embolization in subjects with atrial fibrillation not taking anticoagulants: a prospective study. Stroke. 1998;29:1810–1815.
Kaposzta Z, Young E, Bath, PMW, Markus HS. The clinical application of asymptomatic embolic signal detection in acute stroke: a prospective study. Stroke. 1999;30:1814–1818.
Valton L, Larrue V, Le Traon AP, Massabuau P, Gerard G. Microembolic signals and risk of early recurrence in patients with stroke or transient ischemic attack. Stroke. 1998;29:2125–2128.
Siebler M, Nachtmann A, Sitzer M, Rose G, Kleinschmidt A, Rademacher J, Steinmetz H. Cerebral microembolism and the risk of ischaemia in asymptomatic high-grade internal carotid artery ischemia. Stroke. 1995;26:2184–2186.