Carotid Arteries

The role for carotid endarterectomy in the prevention of stroke is well established. Randomized trials have confirmed its effectiveness when compared to best medical treatment. However, surgery needs to maintain high-level standards; in fact morbidity and mortality should be under 7% for symptomatic, and under 3% for asymptomatic, disease. To be able to obtain these results technical perfection is mandatory.

Angiography was the first method tested as quality control. In 1978 Anderson et al. [3] reported on 131 angiographies. Seven patients (5.3%) had major defects, which were revised. Only three with complications related to angiography were observed: all of them required surgical correction (for carotid occlusion), and one of them resulted in a stroke. None of the patients revised for the presence of defects had complications.

Coubier et al. [8] published a comparison between two consecutive series before and after the introduction of intraoperative angiography. Out of 100 patients in the second series, only 5 were revised due to major defect, while another 37 had minor defects (3 were spasms) and 58 had normal results. Among patients with normal angiography only 3.5% were found to have a restenosis at a mean follow-up of 19 months. When comparing clinical outcome in the two series, patients undergoing intraoperative angiography had 2% stroke rate; patients without angiography, 8.2%. However, there is a substantial differ

1.12.4 Carotid Arteries

ence in the preoperative characteristics: only 38% were asymptomatic in the old series compared to 58% in the new one.

When ultrasounds were first introduced, they did not obtain the expected results: Seifert and Blackshear [31] used CW Doppler on 229 carotid endarterectomies and found 30 abnormal cases: in 10 of them the internal carotid artery was involved. Two underwent immediate revision, while in 8 an angiography was performed. Five defects were confirmed, thus leading to 70% sensitivity only when compared to angiography. Dilley used B-mode echotomography to detect anomalies after endarterecto-my and compared it to angiography [9]. Twelve defects were found in 158 patients (8.3%); four were found by both techniques, three by B-mode only and five by angiography only. These results confirmed angiography as the gold standard.

In 1988 Bandyk compared angiography and duplex in 235 patients undergoing 250 CEA [5]. Duplex found 20 severe defects, but only 10 were confirmed by angiog-raphy. These patients were promptly revised and surgery confirmed the diagnosis. In another 10 carotids duplex indicated the presence of a severe flow disturbance, while no defect was visible at angiography. For this reason none was revised. Two of them experienced major neurological deficit in the recovery room and were revised. Both had a complete thrombosis and experienced a stroke; one patient died. Eight patients were asymptomatic, but developed restenosis of >50% in three cases and of <50% in the remaining five. This study showed that the more the ultrasound technology improved, the more this was able to overcome angiography.

The problem encountered with duplex was that a lot of minor defects were visible and physicians were not sure about the behaviour of these lesions. Sawchuck studied the fate of 21 unrepaired minor defects found at duplex [30]. Only one flap of the external carotid artery occluded. Among nine defects on the internal, seven resolved and two developed a stenosis of <30%.

An elegant paper from University of California, San Francisco (UCSF) reported in 1990 on 131 carotids where a completion duplex was performed at the end of the procedure [25]. They divided the carotid bifurcation into operated and nonoperated segments. They recorded if any segment was not visible or poorly visualized. They also classified the defects detected according to their size. Any defect in a nonoperated segment was defined as residual disease, while defects in the operated ones were flaps. Excluding the external carotid artery, only 10% of the com mon-internal segments were not visualized. This rate further reduced down to 5% if the proximal common carotid was not taken into consideration. The percentage of narrowing and length of the flap relative to segment diameter classified the defects. Fifteen arteries were found to have at least one defect at intraoperative control and were therefore revised. In seven cases the internal carotid was involved; the common carotid artery in three. Follow-up studies were performed at 1, 3 and 6 months. Restenosis was classified according to the percentage of narrowing from 0 (no restenosis) to 6 (100%). The authors built an ordinal logistic regression model using several local and systemic factors to predict the severity of restenosis. Among technical factors only intraoperative size defect predicted severity of restenosis (p=0.0175). Among systemic factors hypertension, smoking and cholesterol were positively associated with restenosis.

Similar results were found by Kinney a few years later [17]. Among 461 carotids operated in 430 patients, 410 (89%) received an intraoperative duplex scan. An angi-ography was added in 268 of them, while the remaining 51 patients received physical examination and clinical inspection only. Twenty-six carotids were revised based on the classification in Table 1.12.6 (Figs. 1.12.3, 1.12.4). Three of them had moderate flow disturbance at redo duplex scan. After all revisions 337 arteries had normal flow, 73 moderate disturbance and 51 were unknown, not having had any test. At 1 month no strokes were recorded in the group not receiving any test. Seven strokes occurred in the 337 patients in the normal-flow group, compared to 3/73 (4.1%) among the moderate abnormal flow one (p=NS). This difference increased at 5 years (3.9% versus 9.3%) but still it was not statistically significant. Estimated survival analysis for freedom from restenosis showed a significant difference between normal duplex arteries when compared to either the untested group or the abnormal one. Multiple regressions indicated that female gender had 2.8 relative risk of developing carotid restenosis (95% CI 1.21-6.723; p=0.024), while normal completion duplex had a protective effect (RR 0.276; 95% CI 0.126-0.604; p=0.0015). Only normal duplex was significantly inversely related to long-term ipsilateral stroke (RR 0.173; 95% CI 0.031-0.965; p=0.037).

Baker et al. [4] reviewed 316 carotids operated in 283 patients. They patched 153 vessels (48.4%), the remaining being primary closure. A 3-mm cut-off was used to distinguish between major and minor defects at intraoperative duplex (Fig. 1.12.5). This was positive in 254 arteries (80.4%) and abnormal in 62 (19.6%). Nine of

Fig 1.12.3 Normal intraoperative duplex scan of a carotid artery. PSV reaches 60 cm/s
Fig. 1.12.4 Abnormal velocities recorded during intraoperative duplex following carotid endarterectomy. A platelet aggregate is clearly visible. The PSV right after the defect is about 300 cm/s

them were major defects (14.5%); all of them were revised and the abnormality was confirmed at surgery in all but one (only turbulent flow). None of the 53 minor defects (85.5%) was reopened. Early stroke rate was 1.6%; duplex follow-up was done at 1 day, 6 months and then every 12 months. Among normal carotids four patients experienced a stroke (1.3%); this was not significantly different from the percentage for the group with unrepaired defects (1 stroke - 1.9%). Recurrent stenosis occurred in eight patients with normal intraoperative findings (3.1%),

Fig. 1.12.5 Small flaps inside an operated internal carotid artery
Table 1.12.6 Classification of intraoperative duplex findings for carotid endarterectomy. (SB Spectral broadening)

Grade

Diameter reduction (%)

(cm/s)

Spectral analysis

Normal

0-15

< 100

No or minimal SB

Mild

16-49

100-125

SB only in diastole

Moderate

50-75

126-150

SB in systole and diastole

Severe

> 75

> 150

SB in systole and diastole

Modified from [17]

Modified from [17]

four of them on the first postoperative day and four at late controls. Nine restenoses occurred among those 52 patients who had unrepaired defects (17.5%). The difference was highly significant (p=0.002). No neurological complications were recorded among patients revised and only one restenosis was seen at 6 months. A significant difference in restenosis rate was noted when patched arteries were compared to primary closure technique (2.6% versus 9.2%, p=0.025).

Another recent study confirmed the correlation between unrepaired minor defects and restenosis. Paday-achee studied 244 arteries [23]; in 76 cases a shunt was used and only 37 cases were patched. Intraoperative duplex found 52 stenoses: according to flow velocity 18 were severe stenosis of the internal carotid, but they re vised only 9 of them where a flap was associated with the increased PSV. This left 41 arteries with an untreated defect for follow-up and 172 with normal findings. In the latter group restenosis rate was 23%, significantly lower (p<0.0001) than the 51% observed in the normal one. It is interesting to note that all the nine arteries with severely increased flow velocity that were left untreated showed some kind of stenosis regression at follow-up. No correlation was shown between the presence of defects at intraoperative control and postoperative stroke or occlusion.

A comparison between intraoperative duplex and angiography was the aim of a study by Valenti et al. [33]. They reported on 141 CEA on 138 patients. All arteries received an intraoperative duplex and angiography at the end of the procedure. The operating surgeon read the results. Thirty-six defects were detected, but only four were major defects, which required revision. Among 32 minor defects, duplex was able to pick up 28 of them, while only 19 were visible at angiography. These results led to 100% sensitivity and specificity for both techniques, but 87% specificity for duplex compared to 59% of angiography for minor defects.

To conclude, the reported studies underline the importance of coupling morphology and physiological parameters. Flaps alone are often benign lesions, which improve with time and usually disappear during the remodelling that occurs after endarterectomy. At the same time increased flow velocity without visible defects might be caused by spasm or calibre change and rarely threaten the operated artery. Duplex scan can provide both kinds of information. It is relatively cheap, safe and accurate. The major flaw is that the operator needs adequate training and experience to be able to discriminate between small benign lesions and the others that can really jeopardize the short- and long-term results of the operation.

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