Intra-operative control of carotid thromboendoarterectomy by Doppler spectrum analysis

The authors report their experience with intraoperative Doppler spectrum analysis of carotid flow after thromboendoarterectomy. The method seems to be useful in the early localisation of technical defects potentially responsible for postoperative stroke. In 22 patients operated on consecutively, three major abnormalities were detected, one of the internal and two of the external carotid. This enabled immediate reexploration of the involved artery with restoration of normal flow. This kind of examination is also safe, quick and highly accurate. The authors propose it as a substitute to intraoperative arteriography which is routinely performed by some surgeons after carotid thromboendoarterectomy.     

Evaluation of the color coded Doppler ultrasound in detecting carotid bifurcation disease

The color coded continuous wave doppler ultrasound was compared with angiography in 201 arteries, 83 with greater than 50% diameter stenosis and 118 with less than 50% stenosis. Overall accuracy in identifying hemodynamically significant (greater than 50% diameter stenosis) was 87% in the presence of peak velocities greater than 5000 Hz and a blue color coded image. Negative predictive value was 94.5%. False positives were mainly due to the presence of severe external carotid stenosis and increased flow due to contralateral carotid occlusion. Within the limitations of the test being an indirect method, it is a reliable screening method for detecting hemodynamically significant carotid artery disease.     

Detection of carotid occlusive disease by ultrasonic imaging and pulsed Doppler spectrum analysis.

Ultrasonic imaging of the cervical carotid arteries by ultrasonic arteriography and duplex scanning combined with pulsed Doppler spectrum analysis were investigated in a series of patients undergoing arteriography. By using the ultrasonic image as a guide for precise placement of the pulsed Doppler sample volume, the characteristics of blood flow at points of interest in the carotid arteries could be determined. Audible analysis of the Doppler signal permitted correct diagnosis of 23 of 26 (88%) high-grade stenoses or occlusions with ultrasonic arteriography and 24 of 26 (92%) with duplex scanning. Spectrum analysis of Doppler signals obtained with the duplex scanner detected all of the 22 high-grade stenoses. Spectral abnormalities of a lesser degree also were detected in 18 of 23 vessels (78%) with atherosclerotic plaques which should not have reduced cerebral blood flow. These techniques permit the accurate detection of and the distinction between high-grade stenoses and occlusion, as well as the identification of many plaques which are not large enough to affect intracranial hemodynamics.     

Continuous-wave versus range-gated pulsed Doppler power frequency spectrum analysis in the detection of carotid arterial occlusive disease

Two types of ultrasonic Doppler velocity metering devices currently used in the detection of extracranial carotid artery disease, the continuous-wave (CW) and the range-gated pulsed (RP) Doppler systems, were compared in the present study. Power frequency spectrum analysis (PFSA) was performed on 130 carotid arterial bifurcations with a CW Doppler and 81 carotid arteries with an RP Doppler system. All results were compared with angiographic findings. The frequency bandwidth at 50% peak power (f50%), a quantitative index for defining spectral broadening, detected stenoses equal to or greater than 50% diameter reduction with 93% sensitivity, 92% specificity, and 92% accuracy with the CW system. With the RP Doppler, the same degree of stenosis was identified with 94% sensitivity, 93% specificity, and 93% accuracy. Compared with angiographic classification into 0-24%, 25-49%, and 50-99% diameter reduction categories, CW Doppler PFSA and an 85% overall accuracy, and the RP Doppler overall accuracy was 86%. CW Doppler also correctly identified 15 of 16 internal carotid artery (ICA) occlusions; 8 of 8 ICA occlusions were correctly identified with the RP Doppler. Thus, both techniques detected carotid artery disease with comparable results. For research and ease of operation, an RP Doppler system with a variable sampling volume appears to be most desirable. However, a standard CW system is superior if utility and cost-effectiveness are of prime importance.     

Duplex Doppler investigation of suspected vascular lesions at the carotid bifurcation

This prospective study was undertaken to evaluate the role of duplex Doppler (DD) scanning in the diagnosis of masses of suspected vascular origin at the carotid bifurcation. We also assessed the different DD signs of carotid body tumors, especially the difference in resistance index (RI) in the external carotid artery on the side of the tumor. Over a 3-year period (1987–1991) all patients (n=50) with masses of suspected vascular origin at the angle of the mandible underwent DD investigation. The clinical diagnoses included carotid body tumors and carotid bifurcation area aneurysms. Arteriography was also performed in all patients. DD examination diagnosed carotid body tumors in 11 patients, aneurysms in 5, nonvascular lesions in 11, carotid artery kinks in 10, and a prominent carotid bifurcation in 13 patients. In 23 of 50 patients (46%) no pathology (kinks and prominent vessels) was present. DD imaging proved to be 100% accurate in diagnosing these lesions as determined by arteriography. The DD findings in carotid body tumors demonstrated a wineglass bifurcation containing a lesion with echoes as well as pronounced and turbulent multidirectional flow (hypervascular tumor flow). Low-resistance flow was present in the external carotid artery in 80% of patients, indicating the blood supply of the tumor. Patients with lumps of suspected vascular origin at the carotid bifurcation should be initially investigated by DD examination, which can accurately exclude the diagnosis of carotid body tumors and carotid aneurysms and clearly eliminate arteriography in these patients.Presented at the Congress of the Vascular Society of Southern Africa, Durban, South Africa, June 26–28, 1991.     

Effect of carotid bifurcation location on the length of internal carotid disease

Background: A relationship between the height of the carotid bifurcation and the extent of disease in the internal carotid artery has not been reported. The aim of the present study was to determine if such a correlation exists. Methods: Fifty‐one patients undergoing carotid endarterectomy had measurements made of the height of the carotid bifurcation from the sternoclavicular joint. The length of disease removed distal to the bifurcation after carotid endarterectomy was also measured. Correlation analysis was performed. Results: There is a statistically significant negative correlation between the extent of disease in the internal carotid artery and the height of the bifurcation. Conclusions: A low carotid bifurcation correlates with a longer extent of disease in the internal carotid artery.     

Early results of carotid stent placement for treatment of extracranial carotid bifurcation occlusive disease

OBJECTIVE: The purpose of this study was to review the initial results of carotid artery angioplasty with stenting (CAS) performed by vascular surgeons to treat bifurcation occlusive disease. Most patients were selected for CAS if they had indications for endarterectomy (CEA) but were considered at high risk for surgery. METHODS: Since December 2000, 74 carotid arteries in 69 patients underwent CAS, with distal balloon embolization protection in 96%. Mean patient age was 72 years; 82% of patients were men. Indications for CAS included asymptomatic disease (62%), transient ischemic attack (TIA; 23%), and cerebrovascular accident (15%). Mean internal carotid artery diameter stenosis was 82%. CAS was chosen over CEA because of cardiac (49%) or pulmonary (4%) comorbid conditions, hostile neck (25%), distal extent of disease (6%), and contralateral cranial nerve injury (1%). CAS was performed in 15% patients who were good surgical candidates, because of patient preference. Pathologic conditions were primary atherosclerosis (81%), recurrent carotid stenosis (18%), and dissection (1%). Procedures were transfemoral in 95% of cases and transcarotid in 5%. In 30% of cases the contralateral carotid artery had 80% or greater stenosis or was completely occluded. RESULTS: Technical success was achieved in 96% of cases. There were no deaths, no major strokes, one minor stroke (National Institutes of Health Stroke Scale, 3), and one TIA (neurologic event rate, 2.6%). The single minor stroke resolved completely by 1 month. One patient (1.3%) had a perioperative myocardial infarction. Transient neurologic changes occurred in 8% of patients during the protection balloon inflation, and all resolved with deflation. Bradyarrhythmia requiring pharmacologic treatment occurred in 14% of patients. At mean follow-up of 6 months there have been two instances of recurrent stenosis greater than 50% as noted at duplex scanning. During the same period, 266 carotid CEAs were performed, with a neurologic event rate of 0.8% (major stroke, 0.4%; no minor strokes; TIA, 0.4%) and a myocardial infarction rate of 3%. Combined stroke and death rate was 1.3% in patients who underwent CAS and 0.5% in patients who underwent CEA. CONCLUSION: CAS with cerebral protection can be performed safely in patients at high surgical risk, with low perioperative morbidity and mortality. The durability of the procedure must be determined with longer follow-up.     

Measurement of carotid bifurcation pressure gradients using the Bernoulli principle

Current randomized prospective studies suggest that the degree of carotid stenosis is a critical element in deciding whether surgical or medical treatment is appropriate. Of potential interest is the actual pressure drop caused by the blockage, but no direct non-invasive means of quantifying the hemodynamic consequences of carotid artery stenoses currently exists. The present prospective study examined whether preoperative pulsed-Doppler duplex ultrasonographic velocity (v) measurements could be used to predict pressure gradients (ΔP) caused by carotid artery stenoses, and whether such measurements could be used to predict angiographic per cent diameter reduction. Preoperative Doppler velocity and intraoperative direct pressure measurements were obtained, and per cent diameter angiographic stenosis measured in 76 consecutive patients who underwent 77 elective carotid endarterectomies. Using the Bernoulli principle (ΔP = 4v²), pressure gradients across the stenoses were calculated. The predicted ΔP, as well as absolute velocities and internal carotid/common carotid velocity ratios were compared with the actual ΔP measured intraoperatively and with preoperative angiography and oculopneumoplethysmography (OPG) results. An end-diastolic velocity of ⩾ 1 m/s and an end-diastolic internal carotid artery/common carotid artery velocity ratio of ⩾ 10 predicted a 50% diameter angiographic stenosis with 100% specificity. Although statistical significance was reached, preoperative pressure gradients derived from the Bernoulli equation could not predict actual individual intraoperative pressure gradients with enough accuracy to allow decision making on an individual basis. Velocity measurements were as specific and more sensitive than OPG results. ΔP as predicted by the Bernoulli equation is not sufficiently accurate at the carotid bifurcation to be useful for clinical decision making on an individual basis. However, end-diastolic velocities alone as well as internal carotid artery/ common carotid artery velocity ratios are highly specific in the prediction of clinically significant carotid stenoses. An end-diastolic velocity of ⩾ 1 m/s accurately identifies a 50% or greater diameter stenosis, and thus may in some cases be sufficient for operation.     

Endovascular repair using vein-covered stents in the carotid artery bifurcation

The treatment of a bleeding carotid artery pseudoaneurysm in a patient using endovascular repair is described. Vein-covered stents were successfully employed. There were no neurological complications and no recurrent bleeding during 8 months follow up and carotid artery continuity was achieved.Stents covered with saphenous vein may be considered a treatment option for endovascular repair of pseudoaneurysm of the carotid artery.     

Prediction of early cerebral outcome by transcranial Doppler monitoring in carotid bifurcation angioplasty and stenting

OBJECTIVE: The outcomes of carotid angioplasty and stenting (CAS) are, in addition to patient baseline characteristics, highly dependent on the safety of the endovascular procedure. During the successive stages of CAS, transcranial Doppler (TCD) monitoring of the middle cerebral artery was used to assess the association of cerebral embolism and hemodynamic changes with transient (amaurosis fugax and transient ischemic attack) and persistent (minor and major stroke) cerebral deficits, and death. METHODS: By use of a prospectively completed database of 550 patients, the association of various TCD emboli and velocity variables with periprocedural cerebral outcome 5) at postdilation after stent deployment (odds ratio [OR] 2.6, 95% confidence interval [CI], 1.3 to 5.1), particulate macroembolus (OR, 27.0; 95% CI, 4.5 to 157), and massive air embolism (OR, 51.4; 95% CI, 5.4 to 492), as well as angioplasty-induced asystole and prolonged hypotension with a >70% reduction of middle cerebral artery blood flow velocities (OR, 6.4; 95% CI, 2.3 to 17.8) were independently associated with cerebral deficits. The ROC area of this model was 0.72. Of the patient characteristics, only preprocedural cerebral ischemia (OR, 5.0; 95% CI, 2.4 to 10.4) was associated with outcome. Adding this patient characteristic to the model, the area under the ROC curve increased to 0.80. CONCLUSIONS: In CAS, in addition to such obviously adverse events as particulate macroembolism and massive air embolism, multiple microemboli (>5 showers) at postdilation after stent deployment and angioplasty-induced asystole and hypotension with a significant reduction of middle cerebral artery blood flow velocities are associated with periprocedural cerebral deficits. In combination with the presence of preprocedural cerebral symptoms, these four TCD monitoring variables reasonably differentiate between patients with and without adverse cerebral outcome. TCD monitoring provides insight into the pathogenesis of CAS related adverse cerebral events.     

The effect of contralateral disease on carotid Doppler frequency

Continuous-wave Doppler frequency analysis is one standard of noninvasive evaluation for stenotic carotid disease. Interpretation is most commonly based on frequency recorded at the site of stenosis. If flow velocity is increased because of contralateral disease, this criterion may overstate the degree of stenosis. To investigate this, three centers contributed 167 patients to a study of carotid Doppler frequency analysis. Each patient underwent bilateral carotid studies by a standard protocol with use of continuous-wave 5 MHz Doppler probe. There were 309 patent and 25 occluded internal carotids seen on subsequent angiographs. Each patient side was categorized by the severity of ipsilateral disease (less than 45%, 45% to 70%, 71% to 99%, occlusion) and then subgrouped by contralateral disease. For all carotid arteries, the optimal peak frequency to detect 45% or more stenosis was 5500 Hz, with an overall accuracy of 92.2%. Within the three classifications of ipsilateral stenosis, a trend was noted that related increasing peak frequency to greater degrees of contralateral disease. This was most apparent when the contralateral internal carotid artery was occluded. Of all false-positive errors, 43% were accounted for by this subset that represented 15% of the total population. For the 25 patients with occlusion opposite a stenosis, the 5500 Hz cutoff of Doppler peak frequency yielded only 76% accuracy; an ROC curve showed that a cutoff value of 8500 Hz improved overall accuracy to 92% for these patients. By applying two cutoff criteria--5500 Hz for those with patent contralateral internal carotids and 8500 Hz for those in whom a contralateral Doppler signal was not detected--the overall accuracy for all patients improved to 93.3%. It is concluded that contralateral occlusion affects Doppler peak frequency by increasing the velocity in the companion carotid artery, whereas severe contralateral stenosis did not result in a consistent pattern of increased velocity.     

Carotid endarterectomy: still the standard of care for carotid bifurcation disease

Current treatment guidelines of symptomatic and asymptomatic carotid stenosis are based on studies performed over a decade ago. Since that time, significant advances have been made in medical management, namely high dose statin therapy and improved antiplatelet agents, and in carotid interventions, namely the advent of carotid artery stenting. Especially with carotid stenting, the technology has grown by leaps and bounds and continues to advance at a rapid pace. These advances have necessitated new studies to compare these treatments with the gold standard of carotid endarterectomy. In asymptomatic patients, the current data does not justify medical management alone for severe (>80%) carotid stenosis. Furthermore, in both asymptomatic and symptomatic patients current studies have failed to demonstrate equivalence of CAS to CEA for significant carotid stenosis. Clearly additional studies comparing CAS, CEA, and medical management are needed to further clarify this issue. In the future, advances in CAS technology and techniques may greatly expand the role of CAS beyond its current role in certain high-risk patient subsets. However, for the time being CEA still remains the gold standard for carotid intervention.     

The spectrum of carotid artery disease in asymptomatic patients

A spectrum of asymptomatic patients with carotid bifurcation disease exists, with varying degrees of risk for each sub-group. With Duplex scanning we studied the carotid arteries of several asymptomatic populations: volunteers at a health fair, patients referred to our vascular laboratory because of cervical bruits or associated vascular disease, and the contralateral asymptomatic vessels in those patients who had previously undergone endarterectomy. Volunteers had an extremely low incidence of carotid disease, possibly reflecting a bias of more healthy individuals attending a health fair. The contralateral asymptomatic vessels and vessels in the hospital asymptomatic group both had similar disease, with mainly fibrous or calcific plaques. Occurrence of new carotid territory symptoms was low in each hospital group. However, there were more strokes in the territory of the contralateral asymptomatic vessels, suggesting a greater risk for these patients. Symptomatic vessels tend to have plaques that are heterogeneous and echolucent. Change in plaque morphology may eventually become the best predictor of stroke risk, but longer follow-up studies of plaque progression are needed. In the meantime, the characteristics of asymptomatic populations in carotid artery studies must be carefully defined.     

Computational analysis of effects of external carotid artery flow and occlusion on adverse carotid bifurcation hemodynamics

OBJECTIVE: This is a computational analysis of the effects of external carotid artery (ECA) flow, waveform, and occlusion geometry on two hemodynamic wall parameters associated with intimal hyperplasia and atherosclerosis.Study design Transient three-dimensional fluid mechanics analysis was applied to a standard carotid artery bifurcation. Mean internal carotid artery (ICA) flow was maintained at 236 mL/min with a normal waveform. ECA flow was increased from zero to 151 mL/min (64% of ICA flow) with both a normal biphasic waveform and a damped waveform. Geometry of five ECA occlusions was studied: distal, proximal stump, smooth, smooth without carotid sinus, and optimal reconstruction.Primary outcome measures Two time-averaged and area-averaged hemodynamic wall parameters were computed from the velocity and wall shear stress (WSS) solutions, ie, wall shear stress angle gradient (WSSAG) and oscillatory shear index (OSI). Both local and area-averaged hemodynamic wall parameters were computed for the distal common carotid artery (CCA) and the proximal ICA. RESULTS: When ECA flow with a normal waveform is increased from zero to 151 mL/min, area-averaged WSS values increase in the CCA, from 3.0 to 4.4 dynes/cm(2) (46%), and in the ICA, from 16.5 to 17.1 dynes/cm(2) (4%); minimum local WSS values in the carotid sinus remain less than 1 dyne/cm(2); maximum local values of WSSAG and OSI are observed in the carotid sinus and increase from 3.5 to 9.1 radian/cm (160%) and 0.23 to 0.46 (100%), respectively; CCA plus ICA area-averaged WSSAG increases by 52%, and OSI increases by 144%; and damping of the ECA waveform has little effect on local or area-averaged WSSAG but reduces OSI to 68%. When the ECA is occluded, the minimum local WSS in the carotid sinus is less than 1 dyne/cm(2). However, if the carotid sinus is removed or the CCA-ICA geometry hemodynamically optimized, the minimum WSS is approximately 4 dynes/cm(2). Similarly, eliminating the carotid sinus markedly reduces local maximum WSSAG, from 3.0-3.5 radian/cm to 0.3 radian/cm, and reduces local maximum OSI from 0.22-0.49 to 0.04. Area-averaged WSSAG and OSI over the CCA and ICA are reduced by approximately 50% with elimination of the carotid sinus. CONCLUSIONS: The degree of adverse carotid bifurcation hemodynamics as measured with WSSAG and OSI is directly proportional to ECA flow. The marked difference in normal ICA and ECA flow waveforms does not contribute to adverse wall hemodynamics. Location of an ECA occlusion (distal, proximal, stump, smooth) does not affect adverse carotid hemodynamics; however, marked improvement is obtained with elimination of the carotid sinus.