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Head and Neck Imaging |
1 From the Departments of Radiology (J.A.V., J.C.v.d.B., T.T.C.O., H.P.M.v.H.), Cardiology (S.M.P.G.E., M.J.S.), Neurology (H.W.M., O.J.M.V.), and Clinical Neurophysiology (O.J.M.V., R.G.A.A.), St Antonius Hospital, Koekoekslaan 1, 3435 CM Nieuwegein, the Netherlands; and Departments of Vascular Surgery (F.L.M.), Clinical Epidemiology (Y.v.d.G.), and Radiology (W.P.T.M.), University Medical Center Utrecht, the Netherlands. Received January 22, 2004; revision requested March 31; revision received April 29; accepted June 2. Address correspondence to J.A.V. (e-mail: j.a.vos@antonius.net).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: This study was approved by the institutional human research committee. Written informed consent was obtained for all patients. Patients were divided into three groups: 161 patients treated before filtering CPDs had become available (group 1), 151 patients treated with filtering CPDs (group 2), and 197 patients treated without CPDs after CPDs had become available (group 3). Clinical end points were cerebral ischemic events and death. Transcranial Doppler US end points included isolated microemboli, microembolic showers, macroemboli, and distal thrombus. The procedure was divided into five phases: wiring, predilation, stent deployment, postdilation, and CPD handling. Data not distributed normally were analyzed with the Mann-Whitney U statistic. For binomial data, the 
2 test was used. P < .05 indicated statistical significance.
RESULTS: For each phase, median and interquartile range (IQR) for isolated microemboli in group 2 versus group 3 were as follows: wiring, 51 (IQR, 31–69) versus 27 (IQR, 15–48); predilation, 19 (IQR, 13–33) versus 13 (IQR, 8–19); stent deployment, 64 (IQR, 46–82) versus 48.5 (IQR, 33.25–66); and postdilation, 24 (IQR, 14–39) versus 16 (IQR, 11–27.5) (P < .001 for each phase). Median and IQR for microembolic showers were as follows: wiring, 0 (IQR, 0–3) versus 0 (IQR, 0–0); predilation, 1.5 (IQR, 0–4) versus 0 (IQR, 0–2); stent deployment, 22 (IQR, 11–36) versus 11 (IQR, 6–17); postdilation, three (IQR, 0–9) versus one (IQR, 0–4); (postdilation phase, P = .001; all other phases, P < .001). Median for isolated microemboli in group 1 versus groups 2 and 3 combined were as follows: predilation, 10 (IQR, 5–22.75) versus 16 (IQR, 9–25) (P = .001); stent deployment, 32 (IQR, 15–58) versus 54 (IQR, 40.5–74) (P < .001); and postdilation, 11 (IQR, 6–19) versus 18 (IQR, 12–33) (P < .001). Median for microembolic showers during stent deployment were six (IQR, 1–14) versus 13 (IQR, 7–26) (P < .001). Five patients died, and five major strokes and 14 minor strokes occurred. Eight macroemboli occurred in unprotected procedures; six distal thrombi occurred in protected procedures.
CONCLUSION: Carotid angioplasty and stent placement yielded more microemboli in patients treated with filtering CPDs than in unprotected procedures. The infrequent occurrence of cerebral sequelae did not allow comprehensive statistical comparison between groups.
© RSNA, 2004
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Over the past few years, an alternative treatment for carotid stenoses has emerged: carotid angioplasty and stent placement (CAS) (4–7). This procedure obviates anesthesia and a surgical approach and may, therefore, be employed to treat high-risk surgical patients. It does have its drawbacks, however. The major hazard of CAS is the dislodgment and distal embolization of plaque material, a process that may result in a stroke. Several options for the prevention of distal embolization have been proposed (8–11). Cerebral protection devices (CPDs) can be divided into three categories: filtering CPDs, obstructing CPDs, and flow reversal CPDs.
Few studies have compared the different categories of CPDs (10,11) or compared patients treated with cerebral protection with patients treated without cerebral protection (12–16). Only one of these studies (12), which focused on a small series of patients who were treated with distal occluding balloons, analyzed transcranial Doppler ultrasonography (US) as a modality that could be used to assess the efficacy of the CPD. To the best of our knowledge, no series has compared transcranial Doppler US data between patients treated with filtering CPDs and patients treated without filtering CPDs.
The intended advantage of filtering CPD use during CAS is the prevention of cerebral embolic complications. Potential disadvantages include a more cumbersome procedure; the possibility of the filter filling with embolic material, thereby resulting in subsequent stasis in the internal carotid artery (ICA); thrombus formation on the filter; damage to the vascular wall; and costs.
Thus, the purpose of our study was to prospectively evaluate emboli detected at transcranial Doppler US, to assess the outcome of CAS, and to compare these findings in patients treated with the use of filtering CPDs with findings in patients treated without the use of filtering CPDs.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The study population was divided into three groups. Group 1 comprised all patients treated before filtering CPDs had become available, group 2 comprised all patients treated with filtering CPDs, and group 3 comprised all patients treated without CPDs after filtering CPDs had become available. Two separate statistical analyses were conducted. In the first analysis, group 2 was compared with group 3 (ie, patients treated with CPDs were compared with patients treated without CPDs during the same period). In the second analysis, group 1 was compared with groups 2 and 3 combined (ie, patients treated before the advent of filtering CPDs were compared with patients treated after the advent of CPDs).
Study Population
Of the 509 patients included in the study, 360 (70.7%) were men (age range, 47–88 years; median age, 70 years) and 149 (29.3%) were women (age range, 50–89 years; median age, 73 years). All patients had a stenosis at the carotid bifurcation of more than 70% according to criteria from the North American Symptomatic Carotid Endarterectomy Trial (1). The degree of stenosis had been assessed by using duplex US imaging and intraarterial digital subtraction angiography prior to therapy. Prior ipsilateral symptoms (eg, amaurosis fugax, transient ischemic attack, or minor stroke) were present in 166 patients (32.6%).
Stent Placement
All procedures were performed by an experienced, board-certified endovascular specialist who was chosen from a pool of two interventional radiologists (J.C.v.d.B., T.T.C.O.) and two interventional cardiologists (S.M.P.G.E., M.J.S.), each with experience in endovascular procedures ranging from 8 to 30 years. A femoral approach was used in all patients. If necessary, predilation was performed by using a 2.5–3.5-mm balloon, and a self-expandable stent was introduced. Finally, postdilation was performed by using a balloon with a size ranging from 5 to 8 mm. Size selection depended on the diameter of the ICA, which was determined at preprocedural duplex US imaging. Several types of self-expandable stents were used: Easy Wallstent (Boston Scientific, Natick, Mass) (84 stents), Carotid Wallstent (Boston Scientific) (332 stents), Peripheral Wallstent (Boston Scientific) (four stents), Acculink (Guidant, Indianapolis, Ind) (23 stents), Carotid SE (Medtronic, Minneapolis, Minn) (13 stents), Protege (EV3, Plymouth, Minn) (one stent), and Precise (Cordis J&J, Miami Lakes, Fla) (37 stents).
In 15 patients (2.9%), no angioplasty or stent placement was performed. Of these patients, 11 had technical or anatomic impediments, and two had a stenosis that was less severe than anticipated. In one patient, the procedure was discontinued because the ICA had asymptomatically become occluded in the 3 days between the last preprocedural duplex US examination and the procedure. In the final patient, the procedure was discontinued because a major stroke occurred at angiography prior to stent placement. This was one of the major strokes in patient group 3.
Filtering CPDs
A filtering CPD was used in 151 patients. After 2
years in which 161 patients were treated without cerebral protection, the first filtering CPD was used in July 2000. During the procedure, the filtering CPD was introduced before stent placement and, if possible, before predilation. The filtering CPD was removed at the end of the procedure after postdilation and postprocedural angiography. In two of 153 patients (1.3%), placement of the filtering CPD was unsuccessful. Because the actual stent procedure was performed without cerebral protection, these two cases were regarded as unprotected procedures and were therefore included in group 3 for statistical analysis. The various types of filtering CPDs used are listed in Table 1.
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For each phase of the procedure, we registered the number of isolated microembolic signals in the middle cerebral artery, as well as all microembolic showers (ie, a cardiac cycle with too many microembolic signals to be counted separately), that were detected at transcranial Doppler US. The microemboli were identified according to the criteria described in the literature (18). A macroembolus was defined as an embolus partially or completely obstructing flow in the middle cerebral artery, as evidenced by decreased flow at transcranial Doppler US and confirmed by findings at angiography. If a macroembolus was found, this was recorded separately. Also, any angiographically demonstrated thrombus formation on the guidewire or CPD distal to the site of stent placement was recorded.
Medication
All patients received platelet aggregation inhibitors: aspirin (Aspirin; Bayer, Leverkusen, Germany) (250 mg daily) and clopidogrel (Plavix; Bristol-Myers Squibb, New York, NY) (75 mg daily), starting the day before the procedure. During the procedure, 5000–10 000 IU of heparin was administered intravenously. Before balloon inflation, 1 mg of atropine sulfate (Department of Clinical Pharmacy, St Antonius Hospital, Nieuwegein, the Netherlands) was given intravenously to reduce bradycardia and/or hypotension induced by carotid body compression.
Monitoring
The neurologic status of the patient was monitored throughout the procedure by an independent neurologist from a pool of two neurologists with more than 10 years of experience in cerebrovascular diseases. Systemic blood pressure, heart rate, and peripheral arterial oxygen saturation were continuously monitored.
Evaluations before Intervention and during Follow-up
Patients were examined according to a standardized protocol, which included neurologic examination by using the modified Rankin Scale (19) and carotid duplex US imaging. These examinations were performed before and directly after the intervention, on the day after the intervention, and subsequently on day 7. Any neurologic deficit persisting for more than 24 hours was regarded as a stroke. A deterioration in the clinical situation of three or more categories on the Rankin Scale (19) was regarded as a major stroke.
Statistical Analysis
In group 1, 141 of 161 patients (87.6%) had an adequate acoustic temporal bone window for transcranial Doppler US monitoring. In group 2, 125 of 151 patients (82.8%) had an adequate acoustic temporal bone window for transcranial Doppler US monitoring. In group 3, 161 of 197 patients (81.7%) had an adequate acoustic temporal bone window for transcranial Doppler US monitoring.
Data that were not distributed normally were presented with median and interquartile range; differences were tested by using the Mann-Whitney U statistic. For binomial data, the 2 test was used. In all cases, P < .05 was regarded as indicating a statistically significant difference. Statistical analyses were performed by using a statistical software package (version 11.5; SPSS, Chicago, Ill).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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When group 1 is compared with groups 2 and 3 combined, there was a statistically significant difference for isolated microemboli observed during predilation (P = .001), stent deployment (P < .001), and postdilation (P < .001). For microembolic showers, there is a statistically significant difference during stent deployment only (P < .001). There is also a statistically significant difference in the total number of microembolic showers observed during the entire procedure (P < .001). In all instances, the microembolic load was higher in groups 2 and 3 combined than it was in group 1.
Adverse Events
A comparison of the nonclinical adverse events that occurred during the procedure is presented in Table 5 for all groups. There were six patients with particulate macroemboli in group 1, no patients with particulate macroemboli in group 2, and two patients with particulate macroemboli in group 3. Of the eight patients with a macroembolus, three had a transient ischemic attack during the procedure (two patients in group 1 and one patient in group 3), two had a major stroke (one patient in group 1 and one patient in group 3), and the remaining three did not have cerebral symptoms. Remarkably, all cases of macroembolism occurred during the first 186 procedures. In the more than 300 procedures performed since then, no macroemboli were found, regardless of whether a filtering CPD was used.
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Complications
Cerebral outcome at 1 week is presented in Table 6. In group 1, there were two deaths (1.2%), two major strokes (1.2%), and three minor strokes (1.9%). In group 2, there were no deaths, two major strokes (1.3%), and five minor strokes (3.3%). In group 3, there were three deaths (1.5%), one major stroke (0.5%), and six minor strokes (3.0%).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The higher microembolic load in the filtering CPD group is counterintuitive and puzzling. Recently presented findings from a small, randomized series (21) also demonstrated more microemboli in patients who underwent protected procedures than in those who underwent unprotected procedures—a finding that parallels our own. A theoretic explanation for this might be that a macroembolus may be propelled into the filter and subsequently disintegrated into smaller particles that can pass through the micropores, thereby leading to an increase in the number of microemboli. This could also account for the lower number of macroemboli found.
A different theory would be that filtering CPDs do not adequately cover the entire ICA, thus allowing some emboli to pass by. Findings from an in vitro study (22) proved that embolic material can be found distal to all four types of filtering CPDs studied. One of the devices evaluated in that study was the Filterwire EX (Boston Scientific), which was the most frequently used filtering CPD in our series. The investigators found a gap between this device and the vascular wall during CPD deployment, which was performed according to the manufacturer’s specification. Investigators had to manually adjust the position of the filtering CPD to optimally cover the ICA in their model. The higher microembolic load might also be explained by a more cumbersome procedure as a result of filtering CPD use.
Another theoretic explanation might be thrombus formation on the distal filter surface or on the tip of the filtering CPD wire, thereby resulting the possibility of subsequent embolization. We observed a thrombus that was large enough to be seen at angiography in six filtering CPD cases. Smaller thrombi may be present in more cases and may lead to an increased embolic load. Another explanation for the increased embolic load in protected procedures might be the considerable movement of the filtering CPD in the distal ICA. This movement, which was observed during our procedure, has been described before (11) and might be the cause of microtrauma to the vascular wall, which in turn might lead to increased embolic load.
Two studies (23,24) have been published that involved the use of diffusion-weighted magnetic resonance (MR) imaging to assess filter-protected CAS. New ipsilateral lesions were observed at postprocedural diffusion-weighted MR imaging in three of 16 patients in one study (23) and in 10 of 42 patients in the other (24). Findings from these two studies apparently confirm that a filtering CPD does not prevent all emboli from reaching the cerebral circulation during CAS.
A limitation of our study is the gradual introduction of filtering CPDs in our patient population. Also, the use of filtering CPDs depended both on the availability of each device and on operator preference. Some selection bias for filtering CPD use may therefore have been introduced. At first we analyzed the findings from all patients in our series who were treated after filtering CPDs had been introduced and compared data from patients treated with cerebral protection (group 2) with data from patients treated without cerebral protection (group 3). We also compared the two groups of patients (groups 2 and 3) that were treated during the same time frame. As shown, we observed more microemboli in the filtering CPD group, and this finding was determined to be statistically significant.
Our analysis, however, might contain the possible selection bias mentioned before. To preclude the possibility of bias, we compared data from the patients treated before the advent of filtering CPDs (group 1) with data from all other patients (groups 2 and 3 combined). This analysis, in effect, compared patients treated without a choice for cerebral protection with patients treated with a choice for cerebral protection. We thereby "diluted" the filtering CPD group considerably. Nevertheless, the significantly higher microembolic load in the group containing patients treated with filtering CPDs remained.
More important than the transcranial Doppler US data is the clinical outcome. Fortunately, the complication rate of CAS was low in all three patient groups. This low event rate, however, precludes comprehensive statistical conclusions about clinical outcome. A nonrandomized study (13) compared the clinical outcome in 75 patients treated without cerebral protection with the clinical outcome in 75 patients who underwent procedures with Neuroshield (MedNova) filter protection. No statistically significant difference in cerebral outcome was observed. A different study (14) compared early outcome in 125 unprotected CAS procedures with early outcome in 150 protected CAS procedures (147 filters); no deaths or major strokes were found. There were three minor strokes, one transient ischemic attack, and one subarachnoid hemorrhage in the unprotected group, and there was one minor stroke and one subarachnoid hemorrhage in the protected group. Although this difference is described as a 79% reduction in "the acute neurologic event rate" in the group treated with CPDs, this difference can easily be calculated not to be statistically significant.
The same authors more recently published the results of protected CAS in 442 patients (25). Findings from this study also demonstrated a low complications rate, and investigators concluded that the use of cerebral protection is feasible and effective in preventing distal embolization. Because the investigators did not use transcranial Doppler US, pre- and postprocedural computed tomography, or MR imaging, they concede that their study does not provide objective information on the degree of embolization during the procedure. The editorial comment (26) on this publication puts the findings of the study in a broader perspective and concludes that, to date, real evidence either for or against the use of cerebral protection during CAS is still lacking.
The low event rate during CAS means that only a trial with a large number of cases could potentially yield a statistically significant difference in cerebral outcome between patients treated with cerebral protection and those treated without cerebral protection. Two such studies (15,16) have evaluated a large number of cases. One of these (15) reviewed all CAS series reported in the literature to date. In this report (15), the authors conclude that "the use of protection devices appears to reduce thromboembolic complications during CAS." The other publication (16) is based on a survey from the global carotid artery stent registry. The authors found a reduction in stroke and procedure-related death from 5.29% in unprotected procedures to 2.23% in protected CAS. Although both studies are based on a large number of cases, both studies are hampered by a difference in time frame. The unprotected procedures in both studies were, on average, performed earlier than the protected procedures. Other substantial improvements, such as dedicated catheters, sheaths, stents, and a more dedicated medication regimen, were introduced in the meantime, and all of these may have contributed to the steady decline in the event rate during CAS. Furthermore, the nature of both publications probably means that there is considerable overlap in patient populations. One of the studies (16), however, did find that eight of 28 medical centers had worse results with protected procedures than with unprotected procedures.
We used transcranial Doppler US to assess the efficacy of filtering CPDs in preventing embolic material from passing through to the cerebral circulation during CAS. The applicability of transcranial Doppler US to assess microembolic load is limited by the inability to differentiate between the sizes of the various depicted microemboli. There is a correlation between increase in particle size and increased likelihood of adverse outcome (27). It is therefore possible that, although the total number of microemboli in our filtering CPD group is higher, the number of clinically relevant emboli is not higher. The occurrence of particulate macroemboli is also correlated to adverse outcome (17). In the current study, we found more microemboli but fewer particulate macroemboli in protected patients. Conversely, thrombus formation distal to the site of stent placement was observed only in patients treated with a filtering CPD; this finding may also be correlated with adverse outcome.
Our study population contains a substantial number of asymptomatic patients. The high number of asymptomatic patients in our series is caused by the fact that many CAS procedures were performed in the workup before major cardiothoracic surgery. A combined surgical procedure for coronary artery bypass grafting and carotid endarterectomy has been employed in our institution for several years. Over the past few years, carotid endarterectomy has progressively been replaced by CAS in these patients. Although controversy remains regarding the optimal management of the multisystem disease in such patients, this strategy of staged CAS and coronary artery bypass grafting has successfully been employed elsewhere (28,29). Consequently, the majority of patients in our series had a relatively high surgical risk as a result of cardiac and pulmonary comorbidity. The high number of asymptomatic patients and the large fraction of patients with substantial comorbidity may have influenced results in our series.
In our study, only filtering CPDs were analyzed. In a transcranial Doppler US controlled study (12) of CAS that was performed by using distal occlusion balloon protection, significantly less microemboli were found during protected procedures versus during unprotected CAS. The third category of CPDs includes flow reversal devices. A small study (10) compared all three different categories of CPDs (six filters, 10 distal occlusion balloons, and nine flow reversal devices) in 25 patients treated without a CPD. The investigators used transcranial Doppler US whenever an acoustic temporal bone window was available (75%), but the results are mentioned nonquantitatively. With the use of flow reversal devices, however, "no embolic signals were detected." The use of occluding CPDs or flow reversal CPDs may consequently yield an embolic load different from our findings and, indeed, a different cerebral outcome.
In conclusion, the findings from our study on filtering CPDs do not support the commonly held view that cerebral protection is required for all CAS procedures; in our series, more microemboli were found in patients who underwent protected procedures than were found in those who underwent unprotected procedures. The filtering CPD group also had more cases of distal thrombus formation, whereas the unprotected group had a higher number of particulate macroemboli. Only a large multicenter randomized trial can resolve the issue of cerebral protection during CAS. Such a trial may also provide insight into the question of which patients might benefit from cerebral protection and which type of CPD provides the most adequate protection for the brain.
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FOOTNOTES |
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Authors stated no financial relationship to disclose.
Author contributions: Guarantor of integrity of entire study, J.A.V., J.C.v.d.B.; study concepts, J.A.V., J.C.v.d.B., S.M.P.G.E., M.J.S., T.T.C.O., H.P.M.v.H., H.W.M., O.J.M.V., R.G.A.A.; study design, J.A.V., J.C.v.d.B., R.G.A.A., Y.v.d.G., W.P.T.M., F.L.M.; literature research, J.A.V., J.C.v.d.B., R.G.A.A.; clinical studies, H.W.M., O.J.M.V., R.G.A.A., F.L.M.; data acquisition, J.A.V., R.G.A.A., J.C.v.d.B., S.M.P.G.E., M.J.S., T.T.C.O.; data analysis/interpretation, J.A.V., R.G.A.A., J.C.v.d.B., Y.v.d.G.; statistical analysis, J.A.V., R.G.A.A., Y.v.d.G., W.P.T.M.; manuscript preparation, J.A.V., J.C.v.d.B., R.G.A.A., Y.v.d.G., O.J.M.V., H.P.M.v.H.; manuscript definition of intellectual content, all authors; manuscript editing, J.A.V., R.G.A.A., J.C.v.d.B.; manuscript revision/review and final version approval, all authors
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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