Journal of Neuro-Ophthalmology, September 1989, Volume 9, Issue 3

Noninvasive testing of suspected carotid artery disease.

Journal of Clinical Nroro- aphthalmology 9( 3): 205- 208, 1989. Noninvasive Testing of Suspected Carotid Artery Disease Peter J. Savino, M. D. © 1989 Raven Press, Ltd., New York , Why not do carotid arteriography on all patients WIth suspected carotid artery disease? The reason is that not all suspected patients actually have ca­rotid artery disease. More importantly, carotid ar­teriography is not without complications ( stroke and death) ( 1). Given these complications much attention has been given to methods of determin­ing carotid patency, flow, and morphology with­out exposing the patient to the risks of carotid ar­teriography. IDEAL CRITERIA FOR A NONINVASIVE TEST What are the criteria for a good noninvasive test? First, the test must provide reliable anatomic and hemodynamic data. Even with carotid arteriogra­phy, which is said to be the " gold standard," only morphologic or anatomic information is obtained, not hemodynamic data. Secondly, the test should be safe, relatively inexpensive, rapidly performed, and easily repeatable. A variety of noninvasive tests are available. Some are direct and some are indirect. TYPES OF NONINVASIVE TESTING Periorbital Doppler At Wills Eye Hospital, periorbital Doppler stud­ies, which determine carotid artery flow by analyz­ing the direction of flow in the periorbital arteries ( supratrochlear and supraorbital), are not done be­cause of the low sensitivity in detecting carotid ste­notic disease. From the Neuro- Ophthalmology Service, Wills Eye Hospital, Philadelphia, Pennsylvania. Address correspondence and reprint requests to Dr. P. J. Savino, Neuro- Ophthalmology Service, Wills Eye Hospital, Philadelphia, PA 19107, U. S. A. 205 Ocular Pneumoplethysmography ( OPG) This is a type of ophthalmodynometry wherein a suction cup is applied to anesthetized sclera to in­crease the intraocular pressure above systolic pres­sure. Then the vacuum is decreased. As the suc­tion is decreased, the intraocular pressure de­creases. At a certain lowering of intraocular pressu. re, the systolic pressure is determined ( Fig. 1). ThIS test actually measures choroidal systolic FIG. 1. T~ chn. ician with suction cup on patient's eye. Pressure IS raised to the point where the graph shows no ocular pulse ( arrow). Pressure is lowered until eye pulse is recordable ( arrowhead). 206 P. J. SAVINO FIG. 2. The technician holds the B- scan probe over an area in the neck that corre­sponds to the area of the carotid that is to be evaluated. The common carotid, the bifurcation, and the internal and external carotid arteries are viewed on a screen and recorded on videotape. A specific area of the carotid system is identified, and the Doppler cursor is held in that specific area. pressure, and not central retinal artery pressure ( 2). It is sensitive for high- grade stenosis at any point along the carotid system, including the in­tracranial vessels, which are not easily visualized by ultrasound. For this reason, OPC should be used in combination with duplex scanning. Ultrasound Imaging Real- time ultrasound has progressed to provide high- resolution images of the carotid system from the low neck to the angle of the jaw ( common ca­rotid to above the carotid bifurcation) ( Fig. 2). A picture of the carotid lumen can be constructed in cross- section. The major advantage of this tech­nique is that plaque ulceration and hemorrhage may be detected. Doppler Imaging The frequency of an administered sound wave of flowing blood produces a change in frequency 0f thl:' r,... fh: terl ,,;"" nd The frequency change : t" the ,:, peed of the flowing blood. This test is most useful in evaluat­ing hemodynamically significant lesions ( 3). INVASIVE TESTS Intravenous Digital Subtraction Angiography ( DSA) Over the last several years, there has been great interest in intravenous digital subtraction angio­graphy." This was initially touted as the method ' Although there is variation, one technique of DSA will be described. A catheter is inserted into an arm vein and passed into the vena cava, so as to provide an entry for the injection of a bolus of contrast medium. The entire process is viewed with the fluoroscope. The resultant views are converted by the com­puter into digital images, which are stored in the computer. Hence, the term " digital." Initially, an image is obtained before the contrast medium is injected. Then a large bolus of contrast medium is injected into a proximal vein. As the contrast me­dium passes through the lung, heart, arteries, etc., digital im­ages are recorded. Then the computer takes the initial image and " subtracts" the background. This enhances the final im­ages. The background has been subtracted; hence, the term " subtraction. " NONINVASIVE TESTING OF SUSPECTED CAD 207 of the future in detecting carotid artery disease. In fact, however, this has not been so because of several limitations of the test ( 4). A large bolus of dye is given, which rapidly passes through the ve­nous circulation, so seb~ ctive views ( as seen with intraarterial injection) are not available. Second, many of these patients have poor cardiac output, so the contrast medium is not rapidly pumped out of the lungs. Thus, the contrast is diluted. For these reasons, true intravenous digital angiogra­phy is not done in many institutions in the Phila­delphia area. Intraarterial Digital Subtraction Angiography Intravenous digital subtraction angiography is relatively noninvasive, but does not provide adequate information regarding the arterial ves­sels. Thus, the technique has been modified by injecting the dye intraarterially and recording the images with a digital technique. With this combi­nation, it is possible to obtain better studies ( 5). However, such arteriography is very invasive test­ing. ROUTINE AT WILLS HOSPITAL At Wills Eye Hospital, a combination of three tests is done. Good noninvasive testing for carotid artery disease should include duplex scanning. A duplex scan is a B- scan ultrasound image of the carotid artery combined with a pulse Doppler wave that gives hemodynamic information, so that with one test, two pieces of information are ob­tained that are essential to the evaluation of sus­pected carotid artery disease. It is a true ultra­sound B- scan, which provides excellent anatomic views of the carotid artery in its surgically accessi­ble portion. Duplex scanning ( Fig. 3) compares favorably to arteriography ( Fig. 4). Duplex scan­ning also can delineate ulceration and hemor­rhage in a plaque. The data may be displayed in a variety of ways, so that lateral as well as trans­verse views are possible. The flow data may also be color coded and displayed, with blue indi­cating the highest amount of stenosis and red the lowest. Oculoplethysmography ( OPG) is also routinely FIG. 3. Carotid ultrasound with line cursor in the area of carotid stenosis. Light gray ( white arrow) represents soft plaque; white area is harder plaqu~ ( arrowhead). Bla~ k area under the plaque is the hemorrhage ( H). The area of ulceration ( curved arrow) In the plaque is seen easily. JClin NeuTo- ophlhalmol, Vol. 9. No. 3. 1989 208 P. J. SAVINO FIG. 4. Carotid arteriogram demonstrating high- grade stenosis of internal carotid artery. performed, as it is the most reliable indicator of hemodynamically altered carotid flow. It may also be the only abnormality detected with disease at the origin of the ophthalmic artery. I Clin Neuro- ophthalmol, Vol. 9, No. 3, 1989 CANDIDATES FOR NONINVASIVE TESTING Who, therefore, should have noninvasive test­ing? For those radical physicians who think every­one with suspected carotid disease needs surgery and requires arteriography preoperatively, nonin­vasive testing is superfluous. For those who be­lieve that no one requires carotid surgery, any test of carotid patency is not indicated. For those who believe that all patients with suspected carotid ar­tery disease should be studied, noninvasive test­ing of the carotid system gives excellent anatomic and hemodynamic information. It is safe and ac­curate. It is so accurate, and the advances have been so great, that at some point, this testing may replace cerebral arteriography as the " gold standard" in the investigation of carotid disease ( 6). REFERENCES 1. Faught E, Trader SO, Hanna GR. Cerebral complication of angiography and transient ischemia and stroke: prediction of risk. Neurology 1979; 29: 4. 2. Gee W. Ocular pneumoplethysmography. SUT" V Ophthalmol 1985; 29: 276. 3. Humphrey PRO, Bradbury PG. Continuous wave Doppler ultrasonography in the detection of carotid stenosis and occlusion. I Neural Neurosurg Psychiatry 1984; 47: 1128. 4. Ball lB, Lukin RR, Tomsick TA, Chambers A. Complica­tions of intravenous digital subtraction angiography. Arch NeuroI1985; 42: 969. 5. Brant- Zawadzki M, Gould R, Norman 0, et al. Digital sub­traction cerebral angiography by intra- arterial injection: comparison with conventional angiography. Am I Radiol 1983; 140: 347. 6. Bosley TM. The role of carotid noninvasive test in stroke prevention. Semin Neurol 1986; 6: 194.