Yield of Transcranial Doppler in Acute Cerebral Ischemia
Yield of Transcranial Doppler in Acute Cerebral Ischemia
abstract & commentary
Source: Alexandrov AV, et al. Yield of transcranial Doppler in acute cerebral ischemia. Stroke 1999;30:1604-1609.
The ability to identify the location and severity of arterial obstruction in acute stroke stands crucial in making accurate pathophysiological diagnoses and triaging patients for emergency therapies. Transcranial Doppler (TCD), a portable tool with bedside availability for rapid screening in the emergency setting, can accomplish this goal.
Alexandrov and associates used TCD in 130 consecutive patients with symptoms indicating acute cerebral ischemia. Vascular occlusions were documented in 69% of thrombolysis-eligible patients compared with 24% of patients with strokes and none with TIAs. Of the 130 patients, 84 (65%) also underwent either digital subtraction angiography (DSA), MR angiography (MRA), or CT angiography (CTA). Patients with presumed proximal arterial occlusions were more likely to undergo DSA. Using a combination of DSA, MRA, and CTA, Alexandrov et al found TCD to be 87.5% sensitive and 88.6% specific for detection of a vascular abnormality.
As Alexandrov et al point out, information from TCD may help select patients for angiography and possible intra-arterial thrombolysis. In the Prolyse in Acute Cerebral Thromboembolism Trial (PROACT), 105 thrombolysis-eligible patients with clinically suspected MCA occlusion underwent cerebral angiography, which showed no M1-M2 occlusion in 59 patients (56%). Such unnecessary angiography might be avoided by TCD. Given a negative predictive value of 89%, according to Alexandrov et al, a normal TCD provides reasonable assurance of vessel patency.
Commentary
With the recently reported results of the PROACT showing a significant benefit for intra-arterial pro-urokinase over placebo, intra-arterial thrombolysis with agents such as urokinase or tPA will come into increasing use. It is, therefore, crucial to use techniques such as TCD to make a rapid vascular diagnosis.
Although Alexandrov et al’s results are encouraging, few neurologists in the community practice TCD. Results depend on the examiner’s skill. Even in the hands of Alexandrov et al, false negatives did occur. Furthermore, the paper does not state how many TCD studies were confirmed by DSA, the only true gold standard in this setting.
Other techniques may be of use. MRA may be performed but can be time consuming and difficult for an agitated acutely ill patient. CTA is another method of rapid diagnosis. It requires a helical CT scanner, present in many ERs, and limited interpretive skill. —azs (Dr. Alan Z. Segal is Assistant Professor, Department of Neurology, Weill-Cornell Medical College, Attending Neurologist, New York Hospital.)
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