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Is carotid duplex scanning sufficient as the sole investigation prior to carotid endarterectomy?

¹ Department of Radiology and ² Department of Vascular Surgery, University of Aberdeen, Grampian NHS Trust, Ward 36, Aberdeen Royal Infirmary, Foresterhill, Aberdeen AB25 2ZN, UK

	Abstract

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Carotid endarterectomy (CEA) is the accepted treatment for certain patients who have had, or who are at risk of having, a stroke if they have a significant narrowing of the internal carotid artery. Rapid and accurate classification of the degree of stenosis is important as the benefit of surgery is highly dependent on this. The aim of this study was to assess whether the addition of angiography to duplex scanning resulted in a change in patient management in a unit where duplex scanning was used as the sole imaging investigation prior to CEA. The study population consisted of 64 patients with significant internal carotid artery stenosis on duplex scanning who were suitable for, and wished to be considered for, CEA. All patients underwent an angiogram. In this study 9 (14%) patients did not proceed to surgery on the basis of angiography and in a further 11 (17%) patients insufficient views of the distal vessel were obtained on duplex scanning. Three of these patients had extensive disease which excluded surgery. One patient experienced a transient ischaemic attack (TIA) at the time of angiography. In conclusion, this audit has highlighted the limitations in performing duplex scanning alone, and the costs that this can incur on the patient who may undergo an unnecessary operation. We cannot recommend duplex scanning as the sole investigation prior to CEA. There is need to evaluate the role of additional non-invasive carotid imaging such as magnetic resonance angiography or CT angiography in the assessment of these patients.

	Introduction

Top Abstract Introduction Materials and methods Results Discussion References

 
Carotid endarterectomy (CEA) is the accepted treatment for certain patients who have had, or who are at risk of having, a stroke if they have a significant narrowing of the internal carotid artery. Rapid and accurate classification of the degree of stenosis is important as the benefit of surgery is highly dependent on this.

The European and North American carotid trials have clearly shown a significant reduction in the rate of further stroke and mortality in patients undergoing surgery and best medical therapy compared with best medical therapy alone [1, 2]. Screening of patients for inclusion into these trials was performed with duplex scanning, but conventional angiography was required prior to randomization [1, 2]. Although angiography is considered to be the gold standard, it is an invasive technique which has been shown in a systematic review to have an associated 0.1% risk of death and 1% risk of permanent neurological sequelae [3].

Duplex scanning is a non-invasive, accurate and cost effective means of screening for carotid artery stenosis [4, 5]. However, concern has arisen over the accuracy of duplex, interobserver and machine variability [6]. Its role is also limited in the presence of subtotal occlusions, heavily calcified vessels and tandem lesions. Despite these limitations, there has been a move in many centres to perform duplex scanning as the sole imaging investigation prior to performing CEA [4].

It is generally accepted that each centre should validate duplex against other imaging modalities [7]. In our teaching hospital, as in the case of many other centres, this has not previously been performed, yet we have moved on to using duplex scanning as the sole imaging modality prior to proceeding to CEA. The aim of this study was to validate duplex ultrasound performed by our fully accredited technicians against angiography and to determine whether the addition of angiography to duplex scanning altered the clinical management of our patients.

	Materials and methods

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Elective patients referred to the vascular unit with significant internal carotid artery stenosis on a vascular laboratory duplex scan and who were suitable and wished to be considered for CEA were referred for angiography. The primary outcome measure was to assess if the addition of angiography to duplex scanning resulted in a change in clinical patient management. All duplex scans were performed by fully accredited vascular technicians using Bluthe criteria [8]. Angiograms were reported by a consultant radiologist using the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria [2].

The duplex and angiography findings were discussed at a multidisciplinary meeting. Over a 2 year period, 64 patients were recruited. The median patient age (range) was 70 years (38–82 years) with a male to female ratio of 1.5 to 1. The majority of patients were symptomatic with 25 patients having had a previous cerebrovascular accident, 28 had a transient ischaemic attack (TIA), 9 had amaurosis fugax and 2 were asymptomatic.

	Results

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64 patients underwent carotid duplex scanning and angiography. In one patient, a young man of 38 years, the angiography images could not be interpreted due to a technical problem. In the majority (67%) of patients there was concordance between the imaging modalities, and no change in decision making occurred as a result of the addition of angiography. In 5 (8%) patients, duplex overestimated the degree of stenosis, and in 1 patient it underestimated the extent of the disease (Table 1). In 22 patients, the vascular technologists were unable to view the distal internal carotid sufficiently beyond the stenosis in order to exclude distal disease and thus were unable to determine if lesion was suitable for surgery. In three of these patients no normal distal internal carotid artery was seen on angiography and surgery was not performed. The duplex scan suggested the possibility of distal disease in two of these patients who had greater than 80% stenosis and showed trickle flow in the third patient. Angiography also showed the presence of proximal vessel disease in three patients in this study, but this was not severe enough to prevent surgery (Figure 1). One patient sustained a TIA as a result of angiography. This occurred during the procedure, affecting the previously asymptomatic side which had no significant underlying stenosis.

View larger version (23K): [in this window] [in a new window]   Figure 1. Results of carotid angiography and duplex scanning and subsequent outcome.

	Discussion

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In this audit 5 (8%) patients who would have had CEA on the basis of duplex scanning alone did not merit surgery as the angiography detected stenosis was 50% or less. Thus these patients avoided unnecessary surgery, which is associated with a 3.1% major stroke and mortality rate. A further patient, who would have had CEA on the basis of duplex scanning alone, had a very high inoperable lesion on angiography and surgery was therefore cancelled. Thus angiography resulted in a direct and unexpected change in clinical management in 6 (9%) of patients in this study. Only patients with significant stenosis in whom surgery was indicated were included in this study and thus we cannot comment on whether duplex scanning may have underestimated the degree of stenosis. Clearly this may result in the potential risk of patients developing a further stroke because they were denied appropriate surgery.

Surprisingly, in 14 (22%) of patients the vascular laboratory technicians were unable to exclude distal disease, necessitating further imaging. In these patients, 11 had no distal disease on angiography and underwent surgery and 3 had extensive disease on angiography which excluded surgery. Overall, in this study 9 (14%) patients did not proceed to surgery on the basis of angiography and in a further 11 (17%) of patients insufficient views of the distal vessel were obtained on duplex scanning. This is lower than a recently published study comparing carotid angiography and duplex scanning which showed that the use of duplex alone would have resulted in 28% of clinical decisions being changed [9]. A meta-analysis of non-invasive carotid artery testing has also shown that duplex scanning results in significant misclassifications of the degree of stenosis and thus should not be substituted for carotid angiography [10]. However, angiography is an invasive procedure and in this study did result in one patient experiencing a TIA. Ideally, duplex scanning should be combined with another non-invasive imaging modality such as CT angiography. With new developments in technology and software, CT angiogram images can rapidly be produced. The sensitivity and specificity of CT angiography has been shown to exceed 80% and 90%, respectively, in a number of studies [11, 12].

In summary, this audit has highlighted the limitations in performing duplex scanning alone, and the cost that this can incur on the patient who may either undergo an unnecessary procedure or develop a further stroke because they were denied appropriate surgery. Duplex scanning as the sole investigation prior to CEA cannot be recommended on the basis of this audit, and the value of non-invasive carotid imaging such as magnetic resonance angiography or CT angiography needs to be explored.

Received for publication December 20, 2004. Revision received February 23, 2005. Accepted for publication May 23, 2005.

	References

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