Application of ultrasound in carotid endarterectomy

Release date: 2007-08-13

Application of ultrasound in carotid endarterectomy is one of the main causes of disability and death in middle-aged and elderly people, 75% of which is due to ischemic cerebrovascular disease. Carotid stenosis and emboli detachment are the main causes of ischemic stroke. It is reported that about 70% of stroke patients over 60 years old in the United States have carotid atherosclerosis, indicating ischemic stroke and atherosclerosis. Carotid stenosis caused by sclerosis is closely related. In our hospital, vascular surgery and neurosurgery performed carotid endarterectomy (CEA) and carotid stenting (CAS) earlier in China, and achieved significant results. Clinical data show that CEA can make narrow carotid canal Path recovery, increased cerebral blood flow, and elimination of micro-emboli sources caused by extracranial carotid atherosclerosis are effective surgical methods for preventing and treating ischemic stroke.
The diagnosis of carotid stenosis has always relied on digital subtraction angiography (DSA), which is still regarded as the “gold standard”, but DSA has certain trauma, and sometimes it can cause local atherosclerotic plaque or thrombus detachment. Serious complications such as cerebrovascular spasm. With the development of ultrasound technology, cranial vascular ultrasound has made great progress, especially the detection of extracranial carotid artery disease is gradually replacing DSA, and the accuracy of detecting severe carotid stenosis and occlusion is over 90%. [1]. Ultrasound can be used for screening, intraoperative monitoring and postoperative follow-up of patients with CEA. According to foreign literature, if CEA is performed on the basis of ultrasound alone, the risk of surgery will be reduced by half, making the benefits of CEA more attractive than medical treatment [2]. The application of ultrasound in preoperative, intraoperative and postoperative CEA is summarized as follows.
First, the application of ultrasound before CEA
CEA is currently recognized as a good surgical method for the treatment of carotid stenosis, and has a significant effect on severe carotid stenosis with cerebral ischemia. Two-dimensional color Doppler ultrasound (2D-CDUS) can accurately display and detect the extracranial carotid artery. For example, two-dimensional ultrasound can show the carotid artery, wall echo, lumen size, plaque and Plaque properties, tunable intima-media thickness, plaque size, color Doppler can be used to show lumen filling and assessment of stenosis, spectral Doppler can measure hemodynamic parameters and blood at plaque Changes in flow dynamics parameters. Ultrasonography plays an important role in the screening of preoperative patients, the timing of surgery and the prevention of cerebral ischemia after surgical blockade of carotid blood flow.
(1) Application of ultrasound in screening patients before surgery
The North American Symptomatic Carotid Endartereetomy Trial (NASCET) and the European Carotids Surgery Trial (ECST) concluded that patients with severe carotid stenosis (70% to 99%) CEA is effective, and its efficacy can be maintained for an average of 8 years, but the effect on mild and moderate stenosis is not obvious [3], showing how to properly screen patients to become an important part of CEA before surgery.
Ultrasound estimation methods for carotid stenosis rate include morphological index estimation (% reduction in inner diameter or percentage of area stenosis), hemodynamic index method (Doppler flow curve blood flow parameters), and the like. 2D-CDUS can measure the length of plaque in the lumen of the long axis of the vessel, and can measure and calculate the stenosis rate of the lumen from the short-axis section. When the two-dimensional image is not satisfactory, it can be further advanced by color Doppler. Determine the narrowness of the lumen. The calculation of the stenosis rate by the vascular diameter method is applicable to the distribution of the plaque ring rule. This method has been reported in previous articles by scholars and will not be described. The area method is a unique method for ultrasonic detection, and is particularly suitable for the case where the plaque is irregularly distributed, and the accuracy of evaluating the stenosis is high. The basic method is to first measure the original lumen cross-sectional area (A) of the stenosis section, and then measure the residual lumen cross-sectional area (B), and then calculate by the formula stenosis rate = (A-B) / A × 100%.
Ye Ming et al. showed that compared with the DSA results, the accuracy of the stenosis rate of 79% to 69% was 79%, and the accuracy of the stenosis rate of 70% to 99% was 91. %[4], patients with CEA indications are often patients with a stenosis rate >70%, so ultrasound has good specificity for screening patients with preoperative CEA. According to the principle of hemodynamics, the degree of arterial stenosis is proportional to the blood flow velocity within a certain range. The Australian Austin Vascular Surgery Laboratory (Austin, Australia) has shown that when the rate of common carotid stenosis is between 75% and 89%, the carotid blood flow velocity increases significantly, and the stenosis rate reaches 90%. When the stenosis is more than 95%, the blood flow velocity in the luminal is obviously blocked, and the blood flow velocity of the carotid artery is decreased, which indicates that the change of blood flow velocity can reflect the degree of carotid stenosis within a certain range. Austin's criteria for determining the blood flow velocity of internal carotid artery stenosis: mild stenosis is 20% to 40%, PSVICA is <100 cm/s; moderate stenosis is 40% to 60%, PSVICA is 100 to 140 cm/s; severe stenosis is At 60% to 80%, PSVICA>140cm/s, EDVICA (endarterial end-diastolic velocity) <140cm/s, stenosis at 80%-99%, PSVICA>140cm/s, EDVICA>140cm/s. At the same time, accurate measurement of blood flow velocity at stenosis should be more sensitive and specific to color Doppler detection. When the blood vessels are narrow, the normal blood flow disappears, eddy currents or turbulence appear, and the color blood flow is characterized by "multicolored inlay". The color stenosis can clearly observe the stenosis and accurately locate the Doppler sampling.
Three-dimensional power Doppler ultrasound imaging (3D-PDI) is an advanced ultrasound detection technique for diagnosing carotid stenosis. It can perform stereoscopic imaging and reconstruct and reconstruct the stenosis area in a complete image, showing the lumen and blood flow of blood vessels. The degree of stenosis is judged more accurately, and the test results are highly correlated with DSA [5]. At present, some hospitals at home and abroad have applied 3D-PDI to the detection of preoperative carotid stenosis in CEA.
CEA surgical indications are not only related to the degree of arterial stenosis caused by atherosclerotic plaque, but also closely related to the pathology of atherosclerotic plaque. A number of data suggest that unstable plaques (thin or broken fibrous caps, ulcer formation, more lipid components in the plaque, or bleeding) are prone to symptoms than stable plaques. According to the characteristics of ultrasound images, plaques are generally divided into three types: type I is a smooth small plaque or flat plaque, the incidence of stroke is 0.5% per year; type II is large and deep or inlaid in Endometrial plaques cause an incidence of strokes of 2.0 to 4.5% per year; type III is a large, uneven plaque that causes an incidence of strokes of 5 to 7% per year [ 6,7]. Studies by Tegos et al. have shown that cortical or subcortical infarction is associated with microemboli formation of unstable plaques. In addition, plaques with ulcers on the surface are prone to thrombus adhesion, resulting in rapid increase of plaque in a short period of time, narrowing of the lumen, and insufficient cerebral blood supply. It is particularly important to follow up the size and echogenicity of the plaque by ultrasound follow-up [8] ].
Ultrasound detection of carotid stenosis directly affects the choice of treatment methods, especially the choice of surgical treatment, and is closely related to the prognosis of severe carotid stenosis. In addition to determining the stenosis of the lumen and showing the nature of the plaque, ultrasound examination also provides effective information for preoperative CEA in specific areas of vascular stenosis and the number of diseased vessels. For example, different stenosis sites may determine different surgical methods. A large number of foreign literature reports, the use of ultrasound examination results can be used as the main indicator of surgical treatment, pointing out that high-level, high-quality carotid ultrasound results are the basis of CEA, according to clinical manifestations and carotid ultrasound results, Implement CEA.
(B) the application of ultrasound in the timing of surgery
Cervical artery occlusion can lead to a reduction in total cerebral blood flow. According to Austin Hospital studies, cerebral blood flow begins to decline rapidly when carotid stenosis is >75%, and cerebral blood flow is reduced to 10% when stenosis reaches 95%. At this time, the nerve cells stop moving. If they are not relieved in time, the patient will be disabled. At this time, surgery and how to relieve the symptoms more quickly are the key issues to solve the ischemic cerebrovascular disease. The risk of stroke in TIA patients depends on a number of clinical and plaque-related variables, and evidence has been shown that patients with recurrent and severe or irregular carotid stenosis should be treated as early as possible [9]. 2D-CDUS has good sensitivity and accuracy to the location, size, nature and morphology of carotid plaques, which plays an important role in the timing of CEA surgery.
The occlusive cerebral ischemic disease of acute internal carotid artery thrombosis is acute, and the mortality rate is high. Once the thrombus is formed, it rapidly causes ischemia and necrosis of the cerebral hemisphere in the occlusion side, and there is a risk of death at any time. Clinically, the best time for surgery is less than 2 hours. If the delay is too long, it is not suitable for surgery. This requires a simple and convenient imaging diagnosis. Ultrasound can dynamically detect the carotid artery and is easy to operate. Ultrasound two-dimensional sonogram of carotid artery thrombosis showed vascular lumen widening, local sound transmission and probe compressibility were poor, color showed no obvious color blood flow signal in the blood vessel, spectrum Doppler detection occlusion segment no flow rate The curve is displayed.
(C) the application of ultrasound in the evaluation of preoperative brain blood supply
Most patients with carotid stenosis have intracranial Willis ring dysfunction, bilateral carotid artery and vertebral-basal artery with different degrees of disease. Accurate diagnosis of these lesions for CEA preoperative preparation, anesthesia selection and intraoperative diversion Applications have played an important role.
Transcranial color Doppler flow imaging (TCCD) has the functions of traditional transcranial Doppler (TCD) and adds two-dimensional images and color flow display. When one side of the internal carotid artery was stenosis, the intracranial blood supply was reduced by the 2D-CDUS, the intracranial arterial perfusion pressure was decreased, and the Doppler flow velocity curve showed low flow velocity and low resistance. As the disease progresses, the cranial collateral circulation is established and corresponding intracranial hemodynamic changes occur. There are three general collateral circulation pathways: 1 anterior communicating artery opening, contralateral internal carotid artery blood flow compensation, increased anterior cerebral artery flow rate, reversal of anterior cerebral artery blood flow direction; 2 affected lateral carotid artery passing eye The artery supplies blood to the internal carotid artery, and the direction of blood flow of the ophthalmic artery is reversed. 3 The posterior communicating artery of the affected side is open, and blood is supplied to the middle cerebral artery of the affected side through the posterior cerebral artery, which is characterized by an increase in blood flow velocity of the posterior cerebral artery. TCCD can display the ophthalmic artery, middle cerebral artery, anterior cerebral artery, posterior cerebral artery, vertebral artery and basilar artery in real time, and can measure its diameter and hemodynamic parameters. Through the analysis of blood flow direction and blood flow velocity, the intracranial arterial perfusion can be understood to determine whether there is open establishment of collateral circulation. The establishment of collateral circulation suggests that the degree of proximal vascular stenosis is >70%, indicating that good compensatory capacity has been established, suggesting that the prognosis is good; if the collateral circulation is not well established, cerebral ischemia and cerebral infarction are prone to occur. By compressing the stenotic lateral cranial carotid artery and observing the changes of intracranial arterial blood flow velocity and direction, it is possible to predict the degree of decrease of middle cerebral artery blood flow velocity during carotid artery clipping during CEA operation, and to infer the possible intracranial intraoperative The low perfusion condition provides the intracranial hemodynamic information for the surgeon to use the shunt technique to prevent the occurrence of cerebral ischemia [10,11].
Second, the application of ultrasound in CEA surgery
CEA is a good surgical method to alleviate and even cure ischemic cerebrovascular disease, but a variety of objective factors can also cause complications of surgery. Most of the causes of stroke caused by CEA are acute thromboembolism or thrombosis of the internal carotid artery. Intraoperative application of 2D-CDUS can show the residual lumen of the internal carotid artery occlusion or significant stenosis, and can be found immediately after CEA. There are technical errors, such as the formation of a valve-like embolization after CEA and the mechanical vascular stenosis caused by surgical suture after the formation of the intimal flap. The superiority of CEA preoperative TCCD for intracranial and extracranial cerebral vascular detection has been as described above. In CEA, due to the use of general anesthesia and partial excision of the extracranial carotid artery, it is impossible to understand the blood supply of the cerebral circulation by the nervous system and DSA examination. At present, there are many reports on the monitoring of TCD in CEA at home and abroad.
Scholars believe that TCD can monitor the blood flow of the middle cerebral artery in CEA surgery, which can monitor the ipsilateral middle cerebral artery and observe the changes of the basic blood flow velocity of the cerebral artery in real time. During the operation, the blood flow velocity of the middle cerebral artery is greatly reduced, which is generally caused by blood pressure drop, insufficient blood supply to the brain, distortion of the diversion tube and thrombosis. It is necessary to take corresponding measures for the patient, such as increasing blood pressure, placing the diversion tube, and adjusting Twisted diverter tubes, etc. TCD can also monitor the formation of microemboli. During CEA, microemboli is most likely to occur in the following stages: before carotid incision, the blood vessels are generally clamped first. At this time, if small plaques are not strong enough, they tend to fall off to form microemboli; after carotid artery incision When the diverting tube is placed, if the implanted part is formed as existing plaque, the plaque is easy to fall off and form a micro-emboli; when the end of the operation releases the non-invasive blocking forceps, if the original clamped part has a spot The block is formed, and at this time, the micro-emboli is also easily formed. It has been reported that the number of microemboli signals in CEA surgery is closely related to the new ischemic injury revealed by magnetic resonance imaging and postoperative deterioration [12]. In the carotid incision and clipping stages, the following three factors are closely related to the occurrence of stroke: the number of microemboli detected by TCD is >50% per hour, and the middle cerebral artery flow rate is reduced by >90% when the carotid artery is clamped. The pulsation index increased by >100% when the clamp was not damaged. A study of 500 patients with CEA who underwent TCD surgery showed that the first 100 patients had a stroke rate of 7%. Because of the correlation between the TCD monitoring results of the top 100 patients and the stroke of the patients, The stroke prediction of 400 patients played a certain guiding role, which reduced the incidence of stroke in the last 400 cases to 2%, indicating that the application of TCD in CEA surgery can actually reduce the incidence of stroke.
Monitoring CEA during TCD can provide important information about intracranial hemodynamics and emboli occurrence, and help to take appropriate measures at various stages to reduce the occurrence of intraoperative stroke, but because of the blind detection of intracranial arteries by TCD, Compared with color Doppler under two-dimensional image display, it lacks obvious localization and accuracy. With the improvement of ultrasound technology and the improvement of probe performance, it is believed that the monitoring effect of TCCD in CEA and postoperative will be more comprehensive and accurate.
Third, the application of ultrasound after CEA
Complications after CEA were classified into short-term complications and long-term complications. The recent complications mainly refer to complications within three months, including neck hematoma, carotid pseudoaneurysm, neck thrombosis, etc.; long-term complications mainly refer to complications after three months, mainly the formation of restenosis, etc. . 2D-CDUS can display the stripping of the intima of the wall in real time after CEA, the fixation of the residual endometrium, whether the lumen is smooth, etc., which has a good detection and follow-up effect on the complications of CEA.
(1) Ultrasound detection of carotid pseudoaneurysm after operation
Carotid pseudoaneurysm after CEA is common in arterial patch formation, and occurs within 30 days after surgery. The identification of carotid pseudoaneurysms and aneurysms is difficult to find. 2D-CDUS can clearly show the morphology and internal conditions of pseudoaneurysm: pseudoaneurysm is mostly cystic mass in two-dimensional images, the boundary is still clear, but there is no clear three-layer structure of normal arteries. A fine sand-like, echo-like echo that is echoless or moving. Color shows that the carotid artery has a breach that communicates with a pseudoaneurysm or is connected by a tortuous channel. In the systolic tumor, red and blue eddy currents are seen in the body. In some tumors, multicolored inlaid eddy currents can be seen. The peripheral part of the diastolic phase away from the neck can be free of blood flow, and even blood flow back into the diseased artery. Spectral Doppler shows that the blood flow in the systolic flow to the tumor is high and sharp, and the blood flow in the diastolic phase away from the tumor is relatively low, which is a special manifestation of its ultrasonic detection.
(2) Ultrasound detection of neck hematoma and thrombus after operation
The neck hematoma after CEA can be life-threatening, and early detection and localization are particularly important. 2D-CDUS can clearly show the location and size of the hematoma, and even the source of the hemorrhage. There is no pulsation in the hematoma. The two-dimensional image shows a substantial and cystic mass. The boundary is clear. The color shows no blood flow signal. The Doppler test shows no flow velocity curve. When the proximal artery of the tumor is compressed, There was no change in the size of the hematoma. In view of the convenient and accurate ultrasound detection, the formation of hematoma can be dynamically observed, which can be checked at any time.
Carotid artery thrombosis is often formed within 7 days after surgery. If it can be examined within 2 hours, the thrombus can be relieved in time, and the brain function can be restored. In the two-dimensional image, the carotid thrombus mainly appears as a weak echo or equal echo filled in the lumen, and the inner diameter of the lumen is slightly widened. Color Doppler detection showed a sudden interruption of color flow in the thrombus obstruction on the long axis of the carotid artery, and there was a short, transient color flow reversal phenomenon, which can determine the beginning of the thrombus, and the bloodless part of the thrombus The flow signal is displayed. Spectral Doppler detection of the proximal arterial flow velocity curve generally has no abnormal changes, and the flow velocity curve is not detected in the thrombus site and the distal artery. At the same time, TCCD detects intracranial blood vessels. When the blood flow in the middle cerebral artery is significantly decreased or the blood flow of the ophthalmic artery is obviously weakened or disappeared, the combination of clinical symptoms can further explain the formation of carotid thrombosis.
(3) Ultrasound detection of carotid artery restenosis
The restenosis lesions within 2 years after CEA were arterial intimal hyperplasia, and the restenosis lesions more than 2 years after surgery were recurrence of carotid atherosclerosis. The difference between neonatal arterial intimal thickening and atherosclerotic recurrence in ultrasonography is that the former migrates more to the normal annular stenosis in the common carotid artery or the internal carotid artery, while the latter appears to be irregular in the lumen. Stenosis with focal ulcers. In a more systematic report on CEA complications, mild restenosis (stenosis rate <50%) accounted for 59% to 72% of total restenosis; greater than 50% of restenosis occurred at approximately 12%, 8% The patient's stenosis rate is over 80%. 50% to 96% of patients with restenosis were detected within 1 to 2 years after surgery, and it was found that follow-up after CEA became extremely important. At present, most of the postoperative follow-up of CEA is performed by ultrasonography. The follow-up time is 1 time, 1, 3, 6 and 12 months after surgery. Once every year, the restenosis standard is based on the University of Washington index, which is the maximum blood flow during systole. The speed is >125cm/s, and the waveform is widened, and the lumen stenosis rate exceeds 50% [13].
Ultrasound examination of the extracranial arteries has the advantages of economical, convenient, non-invasive, repetitive dynamic observation, and hemodynamic information. Therefore, it plays a very important role in the screening, intraoperative monitoring and postoperative follow-up of patients with CEA. Important role. With the development and improvement of ultrasound technology, some new technologies, such as three-dimensional ultrasound technology and ultrasound contrast imaging, will be applied to the ultrasound detection of carotid arteries. The accuracy of ultrasound examination will be further improved, and the current stroke rate of CEA surgery will be reduced. Postoperative stenosis rate and long-term recurrence and restenosis will play a greater role. —Midi Medical Network

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