If there is the suggestion of retrograde vertebral artery flow, examine the subclavian artery for a tight stenosis or occlusion that could result in subclavian steal syndrome. In the United States, carotid US may be the only diagnostic imaging modality performed before carotid endarterectomy. 4. The ICA Doppler spectrum typically shows a low-resistance pattern. This is better appreciated on the far wall than for the near wall of the CCA.2 There is a close correlation between histology and ultrasound-based measurements of the intima-media thickness.1,3. 8.3 How can color Doppler help to distinguish the internal from the external artery. Use of a 3-6MHz curvilinear probe is useful for distal ICA in patients with high bifurcations, very thick necks and vertebral areties in arthritic necks. Cerebrovascular duplex ultrasound for carotid disease is a powerful tool that has become an invaluable resource in the decision making process. Although the so-called NASCET method may not truly reflect the degree of luminal narrowing at the site of stenosis, this method has the advantage of minimizing interobserver error. In a normal carotid US examination, the color velocity scale should be set between 30 and 40 cm/sec (mean velocity). Is the ICA high or low resistance? The true ICA has parallel walls above (distal to) the sinus. Therefore, if the CCA velocity for the ratio is obtained from the proximal portion of the artery, the ratio may be low, potentially causing an underestimation of the degree of stenosis based on this parameter. External carotid artery. The external carotid arteryhas systolic velocities higher than the internal carotid artery, and its waveform is characterized by a sharp rise in flow velocity during systole with a rapid decline toward the baseline and finally return to diminished diastolic flow. 2015;5(3):293-302. Imaging conventions stipulate positioning of the probe such that the head of the patient is at image left for longitudinal views, and the patients right is at image left on transverse views as if viewed standing at the foot of the patient. Fig. In addition, on average, the common carotid blood flow velocity in the low neck is 10 to 20 cm/sec higher than near the bifurcation.11 This observation is of considerable importance, as the measured peak systolic velocity ratio (ICA peak systolic velocity/CCA peak systolic velocity; see Chapter 9) will depend on the location where velocities are sampled in the CCA. Check for errors and try again. You can use Radiopaedia cases in a variety of ways to help you learn and teach. (you can feel the pulse of the temporal artery anterior to the ear). Long-axis view of the carotid bifurcation. When considering an individual patient, the great variation in the PSV and EDV in any population must be taken into consideration. As discussed in, Peak systolic ICA velocities as high as 120 cm/sec have been reported in some normal adults, but these values are exceptional, and an ICA velocity exceeding 100 cm/sec should be viewed as potentially abnormal in older individuals. The relationship between the systolic and diastolic maximal velocities is intermediate. Lancet. The normal range of velocities in the carotid branches varies as a function of age. Trials combining CEA with statin therapy started on hospital admission for surgery showed a decrease in neurologic events such as ischemic stroke and decreased mortality after CEA. Given that the two velocity values are taken from the same vessel involved by the stenosis, Hathout etal. Modified from Grant EG, Benson CB, Moneta GL, etal. 7.7 ). 1. The transition between media and adventitia also corresponds to the external elastic lamina as seen on pathologic studies. 24. You may only be able to see a few cm of the ICA if there is a high bifurcation. In contrast the presence of side branches clearly denotes that the vessel is the external carotid artery. Vertebral Arteries Next chapter: 9. Introduction to Vascular Ultrasonography. Other studies, both here and abroad, confirmed the benefit of CEA and validated the role of this procedure. 1995; 273(18):1421-1428. Similarly, if there is low systolic, high diastolic flow in the common carotid artery this may be related to CCA origin or subclavian pathology. Elevated blood flow velocities in the ECA are not considered clinically important except that they can explain the presence of a clinically detected carotid bruit. 8.5 How does the spectrum of the vertebral arteries and the common carotid artery look? The normal range of velocities in the carotid branches varies as a function of age. In general, however, PSV in the normal CCA ranges from 70 to 100 cm/sec and decreases gradually as one samples distally. Methods of measuring the degree of internal carotid artery (. After endarterectomy, the lumen-intima interface is less prominent at the surgical site because the intima has been removed. A, This diagram shows the key landmarks of the carotid artery bifurcation. Material and Methods. The ICA origin incoporates the bulb which may create a degree of turbulent flow. From these, the ICA/CCA ratio can be automatically calculated, typically with the PSV measurement from the distal CCA in the ratio, because velocity measurements in the proximal CCA may be slightly elevated because of the proximity of the thoracic aorta. Hathout etal. Thwin SS, Soe MM, Myint M et-al. 7.1 ). Average PSV clearly increases with increasing severity of angiographically determined stenosis. Several different methods have been utilized in the past to measure carotid stenosis. In addition, any benefit of a cerebrovascular screening study depends on the expected risk reduction of any intervention based on screening results. Blood flow velocities can therefore be artificially elevated as the blood flows into and out of the curved segment. However, the standard deviations around each of these average velocity values are quite large, suggesting that Doppler velocity measurements cannot predict the exact degree of vessel narrowing ( Fig. The vertebral artery is typically identified in the longitudinal plane, between the transverse processes of the cervical spine. There are several observations that will help you identify the arteries. if tortuous) and the presence of any intimal thickening or plaque. Similarly, the CCA waveform is a combination of both ICA and ECA waveforms. Unable to process the form. The common carotid artery (CCA) lies deep to the sternocleidomastoid and jugular vein. Previous studies have shown the importance of internal carotid plaque characterization (see Chapter 6 ). The arrows indicate the dicrotic notch, the transition from systole to diastole. They should always demonstrate antegrade flow (toward the brain) and be low resistance similar to the ICA. The vascular diagnostic community is divided into two groups: 1) those that perform duplex Doppler examinations using a 60 degree Doppler angle between the ultrasound beam and the vessel axis, and 2) those that use a convenient angle less than or equal to 60 degrees [ 28 ]. Analysis of the combinations of low ICA velocity, abnormal ICA Carotid Ultrasound Case Series: What's the Diagnosis? Since the ultrasound transducer typically measures 4 cm, it can be used to help locate this point by placing one end at the level of the bulb and sampling at the mid transducer, or approximately 2 cm below the beginning of the bulb. The internal carotid artery supplies the brain while the external carotid artery supplies extracranial structures of the head and neck. For a table showing criteria for ICA stenosis classification. Unable to process the form. It is routinely examined as part of carotid duplex ultrasound, but criteria for determining ECA stenosis are poorly characterized and typically extrapolated from internal carotid artery data. Your CME credits are available at any time in your Online CME Control Panel. The black (relatively echolucent) region peripheral to this reflection represents the media of the artery (arrowhead). The external carotid artery suppliesa high resistance vascular bed, while the internal carotid artery supplies the brain which has a low resistance vascular bed. In addition, the Doppler blood flow velocities should always be compared with the degree of plaque, if present. ADVERTISEMENT: Supporters see fewer/no ads. The CCA shares the appearance of both waveforms. Distal ICA scan plane. The standard position is the posterolateral projection, in which the transducer is placed longitudinally along the vessel at an angle of 45 degrees from the horizontal. However, carotid stenting was associated with a higher incidence of periprocedural stroke, while CEA patients had a higher risk of perioperative myocardial infarction. 7.1 ). It should be noted that the ECST continued to rely on the conventional method of stenosis measurement, and, although both the original NASCET and ECST confirmed the effectiveness of CEA, their methods of measuring ICA stenosis were quite different. Up to 30% of all major hemispheric events (stroke, transient ischemic attacks [TIA], or amaurosis fugax) are thought to originate from disease at the carotid bifurcation. ICA: The ICA waveforms have broad systolic peaks and a large amount of flow throughout diastole. Carotid ultrasound: Carotid (kuh-ROT-id) ultrasound is a safe, painless procedure that uses sound waves to examine the blood flow through the carotid arteries. The ECA begins at the level of the upper border of the thyroid cartilage (at the level of the fourth cervical vertebra). HTN, young people) 3. The carotid sinus originates along the medial wall of the proximal ICA where it is adjacent to the external carotid artery (ECA). Ultrasound of the CCA will have a doppler trace that is representative of both upstream and down stream influences. Ability to use duplex US to quantify internal carotid stenoses: fact or fiction? Positioning for the carotid examination. ECA: External carotid artery (ECA) waveforms have sharp systolic peaks, pulsatility due to reflected waves from its branches, and relatively little flow in diastole as compared to the internal carotid artery (ICA). velocity ratio (ICA peak systolic velocity/CCA peak systolic velocity; see Chapter 9) will depend on the location where velocities are sampled in the CCA. The CCA peak systolic velocity should therefore be obtained before the beginning of the bulb, ideally 2 to 4 cm below. An important technical point to be made when calculating the ICA/CCA PSV ratio is that the denominator must be obtained from the distal CCA approximately 2 to 4cm proximal to the bifurcation. What is normal peak systolic velocity? What does ICA CCA mean? The ICA (located inferiorly and to the right) is typically larger than the ECA (located to the left and upward). The ACAS (Asymptomatic Carotid Atherosclerosis Study) also showed a reduction in incident stroke for asymptomatic patients with 60% or more stenotic lesions but, like the moderate range of stenoses in the NACSET, there was only a 5.8% reduction over 5 years. The identification of carotid artery stenosis is the most common indication for cerebrovascular ultrasound. ), have velocities that fall outside the expected norm for either PSV or EDV. The test is done to help diagnose: Arteriosclerosis of the arms or legs. Barnett HJ, Taylor DW, Eliasziw M, et al. Begin proximally in transverse and follow distally to the bifurcation. Off-axis view of the carotid wall. This longitudinal image of the common carotid artery demonstrates a sharp line (specular reflection) that emanates from the intimal surface (arrow). Arrows indicate the flow direction in a right sided subclavian steal syndrome. In a diseased artery, however, the color velocity scale should be shifted up or down according to the mean velocity of blood flow to demonstrate aliasing only in systole. The ECA also usually has a smaller diameter, arises laterally and has a higher resistance waveform (ie lower diastolic flow than a normal ICA). FIGURE 7-2 Off-axis view of the carotid wall. For example: you can use both Power Doppler and color Doppler to visualize side branches. ICA = internal carotid artery. Criteria for duplex diagnosis of internal carotid stenosis [6]. The ICA and ECA can be distinguished by the low-resistance waveforms (higher diastolic flow) in the ICA as compared with the high-resistance waveforms in the ECA (lower diastolic flow) ( Fig. The features of the common, external, and internal carotid spectral Doppler waveforms are distinct from each other, and changes in the Doppler tracings can offer clues as to the presence of occlusive disease. The structure above these two branches is a partly collapsed internal jugular vein (IJV). Sometimes, arteriography and venography may be needed later. The SRU consensus conference proposed the following Doppler velocity cut points: An internal to common carotid peak systolic velocity ratio <2.0, 125cm/s but <230cm/s peak systolic velocity of the ICA, An internal to common carotid PSV ratio 2.0 but <4.0, An end-diastolic ICA velocity 40cm/s but <100cm/s. In others, magnetic resonance angiography (MRA) or computed tomographic angiography (CTA) may be performed in combination with sonography in cases where significant luminal narrowing is identified on the ultrasound examination or when the sonographic results are equivocal. Is 70 blockage in artery bad? The original studies validating intervention in asymptomatic patients showed absolute risk reductions at 5 years of 5-6%, but this number remains in question with continuing improvements in medical management of asymptomatic patients and the lack of recent data [5,6]. The Asymptomatic Carotid Surgery Trial 1 (ACST-1) demonstrated a 10-year benefit in stroke reduction in asymptomatic patients who underwent CEA for severe stenosis between 70% and 89%. c. demonstrate a high-resistance Doppler signal. One of the most frequently asked questions, in carotid ultrasound is: how can I tell if the vessel I am imaging is the internal- or the external carotid artery?" Patients with peak systolic velocities between 175 and 260 cm/s may represent a group at higher risk for future neurologic event, but this has not yet been definitively shown [7]. Hemodynamically significant stenosis of the internal carotid artery (ICA) is usually diagnosed by elevated velocities in a region of luminal narrowing. THere will always be a degree of variation. Changes that affect blood velocity like hypertension, pregnancy, overactive thyroid, infection etc could affect the results to a certain extent. Ultrasonographic study of 48 renal collecting systems in 24 healthy children (age range 3 days to 12.6 years). Anatomy of the carotid bifurcation; intima-media thickness (IMT) protocol. Especially, since the location of the vessels (and their relationship to each other) vary greatly. Large, multicenter trials both in North America and Europe confirmed the effectiveness of CEA in preventing stroke in patients with ICA stenoses compared with optimized medical therapy. The mean peak systolic velocity in the ECA is reported as being 77 cm/sec in normal individuals, and the maximum velocity does not normally exceed 115 cm/sec. Elevated velocities can be seen in normal carotid arteries that diverge from a straight line and become curved. 7.1 ). As the temporal artery is a branch of the ECA, velocity deflections caused by the tapping should be seen on the ECA waveform (Fig. Normal changes in flow dynamics throughout the course of the common carotid and the absence of ultrasound windows for imaging the proximal left common carotid also contribute to the diagnostic uncertainties. FIGURE 7-3 Anatomy of the carotid bifurcation; intima-media thickness (IMT) protocol. This test is done as the first step to look at arteries and veins. Several studies have identified a peak systolic velocity of 230 cm/s as a reasonable threshold for determining 70% stenosis, and this has been suggested as a suitable screening threshold as well [5,6]. Stenoses of the external carotid artery (ECA) are not considered clinically important but should be reported because they may explain the presence of a bruit on clinical examination and need to be considered by the surgeon at the time of carotid endarterectomy (CEA). There are several ways how both color Doppler and spectral Doppler can help to tell if the vessel you are imaging is the internal or the external artery. Be sure that you are really tapping the temporal artery! The ICA is usually posterior and lateral to the ECA. Enter the password that accompanies your e-mail. IMPORTANTLY, this angle may not correspond to the course of the vessel. Velocities vary widely between patients but peak systolic velocities around 77 cm/s have generally been accepted as normal [1]. As discussed in Chapter 3, the Doppler spectral waveforms are almost always altered in the region of the bulb (see Figure 7-4), a reflection of the complex flow dynamics that occur at this location.6, Peak systolic ICA velocities as high as 120 cm/sec have been reported in some normal adults, but these values are exceptional, and an ICA velocity exceeding 100 cm/sec should be viewed as potentially abnormal in older individuals. ; 1998. A PSV of 35 cm/s is unequivocally normal, whilst a PSV of <25 cm/s following adequate stimulation indicates definite arterial insufficiency. All three layers can be visualized on ultrasound images (Figure 7-1). Take Doppler samples in the proximal and distal segments and anywhere else that pathology or an altered waveform is detected. Variations of the origin and branches of the external carotid artery in a human cadaver. The ICA will have low resistance flow, with constant forward flow during diastole. 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