Published online before print November 29, 2004, doi: 10.1161/01.STR.0000150496.27584.e3
(Stroke. 2005;36:32.)
© 2005 American Heart Association, Inc.
Original Contributions |
Yield and Accuracy of Urgent Combined Carotid/Transcranial Ultrasound Testing in Acute Cerebral Ischemia
From the Stroke Treatment Team (OYC, ZG, JS, MSC, EAN, HS, C-IC, YI, JCG, AVA), the University of Texas-Houston, Texas; and the Department of Neurology (S.C.), Hospital Central Universitario de Asturias, Oviedo, Spain.
Correspondence to Dr Andrei V. Alexandrov, University of Texas-Houston Department of Neurology, 6431 Fannin Street MSB 7044, Houston, Texas 77005. E-mail avalexandrov{at}att.net
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Abstract |
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Background and Purpose— We routinely perform an urgent bedside neurovascular ultrasound examination (NVUE) with carotid/vertebral duplex and transcranial Doppler (TCD) in patients with acute cerebral ischemia. We aimed to determine the yield and accuracy of NVUE to identify lesions amenable for interventional treatment (LAITs).
Methods— NVUE was performed with portable carotid duplex and TCD using standardized fast-track (<15 minutes) insonation protocols. Digital subtraction angiography (DSA) was the gold standard for identifying LAIT. These lesions were defined as proximal intra- or extracranial occlusions, near-occlusions, 
50% stenoses or thrombus in the symptomatic artery.
Results— One hundred and fifty patients (70 women, mean age 66±15 years) underwent NVUE at median 128 minutes after symptom onset. Fifty-four patients (36%) received intravenous or intra-arterial thrombolysis (median National Institutes of Health Stroke Scale (NIHSS) score 14, range 4 to 29; 81% had NIHSS 10 points). NVUE demonstrated LAITs in 98% of patients eligible for thrombolysis, 76% of acute stroke patients ineligible for thrombolysis (n=63), and 42% in patients with transient ischemic attack (n=33), P<0.001. Urgent DSA was performed in 30 patients on average 230 minutes after NVUE. Compared with DSA, NVUE predicted LAIT presence with 100% sensitivity and 100% specificity, although individual accuracy parameters for TCD and carotid duplex specific to occlusion location ranged 75% to 96% because of the presence of tandem lesions and 10% rate of no temporal windows.
Conclusions— Bedside neurovascular ultrasound examination, combining carotid/vertebral duplex with TCD yields a substantial proportion of LAITs in excellent agreement with urgent DSA.
Key Words: carotid stenosis • embolism • stroke, acute • thrombolysis • ultrasonography, Doppler
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Introduction |
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Bedside neurovascular ultrasound can play an important role in the diagnostic work up of acute stroke patients.1–6 Urgent detection, localization, and grading severity of the arterial obstruction help triage patients with acute cerebral ischemia and patient selection for invasive angiography. Several reports evaluated the accuracy of either transcranial Doppler (TCD) or carotid duplex ultrasound (CD) in acute stroke setting.2,7,8 Few studies reported the combined use of TCD and CD in stroke patients.3,9–11 None reported both the yield and accuracy of combined ultrasound assessment in acute cerebral ischemia. Combined TCD and CD can be used as a screening test for lesions amenable for interventional treatment (LAITs).12
Considering previous publications2,3,5,7,13 and our own experience, we developed a fast-track neurovascular ultrasound examination (NVUE) protocol for an experienced sonographer to urgently evaluate acute stroke patients at bedside. We also developed detailed diagnostic criteria for normal, stenosed, and acutely occluded intracranial and extracranial vessels.13–17
We routinely perform urgent bedside NVUEs with both standard fast-track TCD and carotid/vertebral duplex in patients with acute cerebral ischemia. We aimed to determine the yield and accuracy of these combined modalities to identify LAITs.
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Subjects and Methods |
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To perform NVUE at bedside, we used portable 2 MHz power-motion or single-channel TCD (PMD 100, Spencer Technologies; Ez-Dop, DWL; Companion III, Nicolet) and portable carotid duplex ultrasound (Sonosite 180 Plus) equipped with B-mode, power-mode, angle-corrected spectral Doppler and 5 to 10 MHz linear probe.
An experienced sonographer and stroke neurologist arrived concurrently. The former performed and the latter evaluated urgent bedside NVUE results. To avoid delays in routine patient evaluation and thrombolytic therapy, bedside ultrasound examination was carried out simultaneously with clinical assessment, blood draws, computed tomography (CT), and chest x-ray, etc. Sonographers used standardized fast-track (<15 minutes) insonation protocols (Table 1) to identify suspected arterial obstruction. The neurological evaluation guided the sequence of vessels targeted by NVUE. Ultrasound results were interpreted at bedside without knowledge of angiographic results using previously published diagnostic criteria13–19 (Table 2). In patients with no temporal windows, we performed a non-contract–enhanced TCD examination of the orbital and posterior circulation vessels and carotid/vertebral duplex.
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Patients received recombinant tissue plasminogen activator intravenously within 3 hours in a dose of 0.9 mg/kg as the standard of care.20 Patients were also screened for eligibility for experimental intra-arterial rescue using institutional review board (IRB)–approved protocols. At our center, both ultrasound studies are initiated emergently without specific written informed consent in order not to delay institution of appropriate therapies or management strategies or select patients for experimental treatment. IRB approval was obtained in all cases when patients participated in our experimental protocols. All IRB approvals of our hyperacute experimental treatment protocols have mention of ultrasound tests as part of initial evaluation for symptoms of stroke. Patients presenting with sustained neurological deficits outside protocol time windows from symptom onset or hypoattenuation on CT scan did not receive interventional treatment. Patients with resolved neurological deficits at the time of examination were considered having transient ischemic attacks (TIAs).
Stroke neurologists decided to perform digital subtraction angiography (DSA) if patients either met clinical CT criteria for an IRB-approved experimental intra-arterial rescue protocol or ultrasound showed persisting arterial occlusion or reocclusion after full-dose intravenous recombinant tissue plasminogen activator therapy. DSA was the gold standard for the diagnosis of LAIT. LAIT was defined as an occlusion or near-occlusion, or 50% stenoses or thrombi in an artery (arteries) supplying brain area(s) affected by ischemia. Hence, current definition of LAIT may include chronic lesions, and caution should be exercised if these lesions are directly responsible for current patient symptoms. Patients with TIA, lacunar syndromes, and normal ultrasound findings were least likely to undergo urgent DSA.
After neuroradiologists dictated DSA reports, we compared NVUE results to DSA to determine true-positive, true-negative, false-positive, and false-negative ultrasound results. We calculated accuracy parameters, including sensitivity, specificity, and positive and negative predictive values. We used 
2 analysis for dichotomous variables, Student t test for normally distributed continuous variables, and Wilcoxon 2-sample test for variables with nonparametric distribution. We determined statistical significance at a 2-tailed P<0.05.
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Results |
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We studied 150 consecutive patients (80 men, 70 women, mean age 66±15 years) with NVUE on average 238±323 minutes (median time 128 minutes) after symptom onset.
Fifty-four patients (36%) received either IV (n=24) or intra-arterial (IA, n=5) thrombolytic therapy or both (n=25). Their median National Institutes of Health Stroke Scale (NIHSS) score was 14 points (range 4 to 29); 81% had NIHSS 10 points. No delay in treatment resulted from ultrasound testing. Sixty-three (42%) patients were found ineligible for thrombolysis. Thirty-three patients (22%) had TIAs.
NVUE showed abnormal results consistent with our ultrasound criteria for LAIT in 98% of patients eligible for thrombolysis, 76% of acute stroke patients ineligible for thrombolysis, and 42% in patients with TIA, P<0.001 (Figure 1). In the thrombolysis group, 44% had internal carotid artery (ICA) lesions with or without middle cerebral artery (MCA) lesions, 52% had isolated MCA lesions, 2% had lesions in the vertebrobasilar (VB) system, and 2% had normal ultrasound findings. In patients ineligible for thrombolysis, 44% had ICA lesions; 30%, isolated MCA lesions; 2%, VB lesions; and 24% had normal findings. In the TIA group, 25% had isolated ICA lesions; none had tandem ICA+MCA lesions; 7%, isolated MCA lesions; 10%, VB lesions; and 58% had normal findings (Figure 1).
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A total of 30 patients (20%) underwent urgent DSA at mean time of 230±207 minutes (maximum delay 308 minutes) after initial NVUE. DSA demonstrated LAIT presence in all patients with abnormal NVUE without false-positive ultrasound studies (sensitivity and specificity for LAIT presence 100%). DSA localized LAIT to the MCA in 10 patients, ICA in 4 patients, tandem ICA/MCA in 15 patients (Figure 2), and VB circulation in 1 patient (Figure 3).
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Compared with DSA, the accuracy parameters for each component of NVUE were as follows: TCD 96% sensitivity, 75% specificity, 96% positive, and 75% negative predictive values (given the observed 10% rate of absent temporal windows). Carotid/vertebral duplex had 94% sensitivity, 90% specificity, 94% positive, and 90% negative predictive values (Table 3).
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TCD and carotid/vertebral duplex ultrasound each showed 1 false-negative and 1 false-positive study (Figure 3). Tandem ICA/MCA lesions were responsible for these errors because of difficulties identifying the unilateral MCA occlusion with delayed collateral flow in the presence of bilateral carotid diseases and unilateral distal ICA stenosis beyond the reach of carotid duplex scanning area.
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Our study showed that an urgent combined intra- and extracranial ultrasound examination yields a substantial number of vascular lesions in patients with acute cerebral ischemia. Nearly all patients receiving thrombolysis had lesions amenable for intervention likely due to preponderance of severe strokes and earlier arrival times. Three quarters of patients who had strokes, but did not qualify to receive thrombolysis, still had detectable lesions. These rates are higher than previously reported in studies using solely TCD or CD for stroke evaluation1,3,7,21,22 likely due to combined testing at the earliest possible time after symptom onset (ie, on admission). NVUE also showed large arterial lesions in 42% of patients with TIAs. Previous studies carried with TCD or CD alone showed detection of arterial lesions in 25% to 35% of these patients.7,23 Diagnostic tests have even lower yield if done electively.24,25 Identification of an arterial lesion that persists outside the time window or despite symptom resolution may have serious prognostic implications and deserves further studies regarding acute management of these patients. These findings may ascertain stroke mechanism at bedside and may select most appropriate management or next most informative test. Perhaps, these vascular abnormalities can help to identify the "high-risk TIA" group for early stroke recurrence.
The accuracy of NVUE demonstrated in this study is based on a relatively small sample of urgent invasive angiograms, and the selection bias introduced by abnormal ultrasound findings cannot be ruled out. Therefore, our findings should be interpreted with caution. However, TCD and CD taken separately have lesser accuracy parameters within the same patient sample. Knowledge of shortcomings of each test and the complimentary value of information derived from extra- and intracranial vessels helped to compensate for these shortcomings. Patients with posterior circulation symptoms, greater variability of posterior circulation vessels, and technical difficulties may further affect the performance of these tests.18,26 In our study, accuracy parameters were largely driven by findings in the anterior circulation. Individual accuracy parameters for TCD and CD were comparable to previous studies.2,3,5,7,27,28
Our study has limitations, including the need for considerable sonographer skill and expertise to complete testing promptly and efficiently. Other factors that can affect the yield and accuracy of NVUE include potential selection bias for diagnostic angiography and greater preponderance of patients with severe stroke symptoms or admitted very early after symptom onset. Also, our study had an average delay of over 3 hours between initial ultrasound and DSA that may provide ample time for thrombus propagation, dissolution, or reocclusion to occur. Our study also identified clinical situations when neither TCD nor CD could be reliably interpreted, including tandem lesions with poor collateral flow, limited arterial visualization, and absent temporal windows. Some of these shortcomings can be overcome by using ultrasound contrast agents.5,19,29–31
Clinical implications of our findings affirm that rapid bedside ultrasound screening can be used in patient selection for interventional treatment.32–34 With further developments in portable noninvasive technology, such examination can be feasibly taught to vascular neurologists, emergency physicians, and vascular technologists. The small devices required can become the new "stethoscope" for bedside evaluations.
In conclusion, urgent bedside NVUE yields a substantial proportion of LAITs in patients with acute cerebral ischemia. Transcranial and carotid ultrasound tests, if performed together by experienced sonographers, compensate for each other’s shortcomings and can achieve 100% accuracy in detection of lesions amenable for intervention.
Received June 20, 2004; revision received October 26, 2004; accepted October 27, 2004.
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References |
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