TCD in Acute Stroke
To the Editor:
We read with great interest the Stroke article by Alexandrov and colleagues.1 This study stresses the importance of transcranial Doppler ultrasonography (TCD) for the rapid assessment of patients with acute cerebral ischemia. Expeditious measurement of cerebral hemodynamics with TCD in the emergency room offers new insight into the process of acute stroke and provides guidance for and monitoring of therapeutic interventions. Regarding their findings and interpretation, we would like to make the following comments.
(1) It is our understanding that the authors used digital subtraction angiography (DSA), MR angiography (MRA), and CT angiography (CTA) for calculation of sensitivity, specificity, and overall accuracy of TCD findings. However, the “angiographic studies” (DSA, MRA, and CTA) were performed within 48 hours after admission. We think that the use of delayed angiographic studies to determine accuracy of TCD is questionable. The time difference and sequence between TCD and angiographic studies may change the sensitivity of early TCD if recanalization occurred between TCD completion and angiographic studies. Although spontaneous recanalization of thrombosed extracranial and intracranial vessels is known to occur, the timing of spontaneous recanalization is unknown. The cumulative experience suggests a spontaneous recanalization frequency between 14% and 24% during the first 24 hours after onset of cerebral ischemia.2 3 4 The timing of MRA and TCD investigations could influence the findings of Alexandrov and his coworkers.1 Ideally, angiographic studies and TCD comparisons should be made using studies performed within 2 to 4 hours of each other to limit discrepancies caused by the natural history of thrombosis.
(2) Another consideration is the fact that the authors used 3 different angiographic methods (DSA, MRA, and CTA) to evaluate specificity and sensitivity of TCD. TCD is likely to have different sensitivity and specificity when compared with each of these 3 angiographic methods. The use of the combination for this comparison is therefore arguable.
(3) It is accepted that the specificity and sensitivity of TCD varies from one segment to another.5 6 We have shown that in the first 24 hours after acute stroke, overall TCD specificity in detecting abnormal cerebral blood flow velocity (CBFV) in all affected vessels (anterior and posterior circulation) is 33%.7 When we analyzed only the middle cerebral artery territory lesions, the specificity increased to 100%, which is in keeping with the higher values noted by Camerlingo et al8 (92%) and Alexandrov et al1 (88.6%). We would be interested to know whether the results of Alexandrov et al.1 showed any difference in specificity according to the location of the arterial lesion.
Finally, we had significant difficulty obtaining methodological information (the Appendix with the description of fast-track protocol and diagnostic criteria for the location of arterial obstruction) using the Internet (http://www.strokeaha.org). We would suggest that important information pertinent to the paper should be published in the body of work.
We agree with Alexandrov et al1 that CBFV quantitative measurements using TCD will provide a powerful tool for the selection of patients for reperfusion therapy.
- Copyright © 2000 by American Heart Association
Alexandrov AV, Demchuk AM, Wein TH, Grotta JC. Yield of transcranial Doppler in acute cerebral ischemia. Stroke. 1999;30:1604–1609.
Toni D, Fiorelli M, Bastianello S, Falcou A, Sette G, Geschin V, Sacchetti ML, Argentino C. Acute ischemic strokes improving during the first 48 hours of onset: predictability, outcome, and possible mechanisms: a comparison with early deteriorating strokes. Stroke. 1997;22:10–14.
Del Zoppo GJ, Higashida RT, Furlan AJ, Pessin MS, Rowley HA, Gent M, and the PROACT Investigators. PROACT: A phase II randomized trial of recombinant pro-urokinase by direct arterial delivery in acute middle cerebral artery stroke. Stroke. 1998;29:4–11.
Toni D, Fiorelli M, Zanette EM, Sacchetti ML, Salerno A, Argentino C, Solaro M, Fieschi C. Early spontaneous improvement and deterioration of ischemic stroke patients: a serial study with transcranial Doppler ultrasonography. Stroke. 1998;29:1144–1148.
Ley-Pozo J, Ringelstein EB. Noninvasive detection of occlusive disease of the carotid siphon and middle cerebral artery. Ann Neurol. 1990;28:640–647.
Babikian V, Sloan MA, Tegeler CH, DeWitt LD, Fayad PB, Feldman E, Gomez CR. Transcranial Doppler validation pilot study. J Neuroimaging. 1993;3:242–249.
Razumovsky AY, Gillard JH, Bryan RN, Hanley DF, Oppenheimer SM. TCD, MRA and MRI in acute cerebral ischemia. Acta Neurol Scand. 1999;99:65–76.
Camerlingo M, Casto L, Censori B, Ferraro B, Gazzaniga GC, Mamoli A. Transcranial Doppler in acute ischemic stroke of the middle cerebral artery territories. Acta Neurol Scand. 1993;88:108–111.
We appreciate the comments of Drs Razumovsky and Oppenheimer and would like to reply to the points made.
(1) We had to use all available angiographic imaging modalities (ie, DSA, MRA, or CTA), since these tests are often used to judge TCD performance in clinical practice and time delays between TCD and angiography are unavoidable outside of a rigorous trial. We agree that arterial recanalization, clot propagation, or reocclusion may have occurred after TCD was performed, thereby decreasing its accuracy compared with that of angiography. We provide additional data regarding time delays from TCD to angiographic studies: 19% of the angiograms were performed within 2 hours after TCD; 29% within 2 to 6 hours; 19% within 6 to 24 hours; and 33% were delayed by more than 24 hours after TCD.
(2) Despite these shortcomings, we demonstrated that TCD accurately reflects arterial patency in 88% of patients when compared with a combination of DSA, MRA, and CTA. Although this combination may not be an adequate standard, individual management decisions are often based on an angiographic test obtainable or when the risks associated with DSA were justified. An overall good agreement between TCD and various angiographic modalities indicates that TCD can be used as a reliable screening or complimentary test when emergent angiography can not be performed or serial angiography is impossible.
(3) Drs Razumovsky and Oppenheimer correctly pointed out that TCD accuracy varies with different arterial segments involved. In our decisions drawn from bedside TCD studies, we consider that TCD accuracy is the highest for the proximal anterior circulation lesions and is less for the posterior circulation. So far, we have analyzed 190 patients with variable duration of symptoms of cerebral ischemia who had TCD and DSA or MRA and have calculated the accuracy parameters for TCD in identifying arterial occlusions at different segments.R1 For the middle cerebral artery occlusions, TCD had sensitivity of 93%, specificity 98%, positive predictive value 93%, and negative predictive value 98%. For occlusions located at other arterial segments, the accuracy parameters were as follows: distal internal carotid artery 81%, 96%, 81%, 96%; proximal internal carotid artery 94%, 97%, 94%, 97%; basilar artery 60%, 96%, 60%, 96%; and vertebral artery 55%, 96%, 71%, 92%.R1 Although sensitivity for posterior circulation occlusions was low, a normal TCD examination excluded major arterial occlusion at any level with at least 92% certainty. The high specificity values achieved in our study resulted from a large number of consecutive patients who had patent vessels on DSA or MRA (75%) and may also be attributed to the use of detailed diagnostic criteria for TCD developed for the assessment of stroke patients.R1 We also appreciate the comment regarding the access to the Web site that contains the Appendix to our article. It had been suggested that we shorten the article by placing the fast-track insonation protocol and diagnostic criteria on the Internet. Since the article has been published, several people have had difficulty accessing this web location, which apparently requires an online subscription to Stroke. We hope that this issue will be resolved and online publications in the future will have an easy and free access.
We are also glad that Drs Razumovsky and Oppenheimer are on the same wavelength with us regarding the usefulness of TCD in acute stroke management.
Editor’s Note: We apologize to readers for any difficulty they had while trying to access the appendix. The website problem has been repaired and we hope access will now be simple and direct. This appendix can now be accessed in several ways. One way is to click on the title of the article. When the article appears on your screen, a box on the right hand side of the title will list various links, including “Appendix.” Click on “Appendix” and it will appear on your screen.
Demchuk AM, Christou I, Wein TH, Felberg RA, Grotta JC, Alexandrov AV. The accuracy and criteria for localizing arterial occlusion with transcranial Doppler. J Neuroimaging. In press.