Value of intraoperative duplex imaging during supervised carotid endarterectomy

Carotid Endarterectomy: A Review

Background:

Since the validation of carotid endarterectomy (CEA) as an effective means of stroke prevention, there has been renewed interest in its best indications and methods, as well as in how it compares to carotid angioplasty and stenting (CAS). This review examines these topics, as well as the investigation of carotid stenosis and the role of auditing and reporting CEAresults.

Investigation:

Brain imaging with CTor MRI should be obtained in patients considered for CEA, in order to document infarction and rule out mass lesions. Carotid investigation begins with ultrasound and, if results agree with subsequent, good-quality MRAor CTangiography, treatment can be planned and catheter angiography avoided. An equally acceptable approach is to proceed directly from ultrasound to catheter angiography, which is still the gold-standard in carotid artery assessment.

Indications:

Appropriate patients for CEA are those symptomatic with transient ischemic attacks or nondisabling stroke due to 70-99% carotid stenosis; the maximum allowable stroke and death rate being 6%. Uncertain candidates for CEA are those with 50 - 69% symptomatic stenosis, and those with asymptomatic stenosis ≥ 60% but, if selected carefully on the basis of additional risk factors (related to both the carotid plaque and certain patient characteristics), some will benefit from surgery. Asymptomatic patients will only benefit if surgery can be provided with exceptionally low major complication rates (3% or less). Inappropriate patients are those with less than 50% symptomatic or 60% asymptomatic stenosis, and those with unstable medical or neurological conditions.

Techniques:

Carotid endarterectomy can be performed with either regional or general anaesthesia and, for the latter, there are a number of monitoring techniques available to assess cerebral perfusion during carotid cross-clamping. While monitoring cannot be considered mandatory and no single monitoring technique has emerged as being clearly superior, EEG is most commonly used. “Eversion” endarterectomy is a variation in surgical technique, and there is some evidence that more widely practiced patch closure may reduce the acute risk of operative stroke and the longer-term risk of recurrent stenosis.

Carotid angioplasty and stenting:

Experience with this endovascular and less invasive procedure grows, and its technology continues to evolve. Some experienced therapists have reported excellent results in case series and a number of randomized trials are now underway comparing CAS to CEA. However, at this time it is premature to incorporate CAS into routine practice replacing CEA.

Auditing:

It has been shown that auditing of CEA indications and results with regular feed-back to the operating surgeons can significantly improve the performance of this operation. Carotid endarterectomy auditing is recommended on both local and regional levels.

Training for Carotid Intervention: Preparing the Next Generation

BACKGROUND

Carotid interventions are performed to reduce the cumulative risk of stroke. The success of the procedure is dependent upon maintaining low operative risk. This article reviews the current state of training for both carotid endarterectomy (CEA) and carotid angioplasty and stenting (CAS).

METHODS

Medline searches were performed to identify articles with the combination of the following key words: carotid, endarterectomy, stent, training, assessment and simulation. Manual searches of the reference lists and related papers was conducted.

RESULTS

Training and assessment for CEA and CAS follows the traditional apprenticeship model. There is no formal training protocol or objective means of assessment for either carotid endarterectomy or stenting. Models and simulators to allow for training and assessment away from the operative theatre have been developed, and exist for both CEA and CAS.

CONCLUSION

The technology exists to allow for both training and assessment of competency to take place in a controlled and objective environment for both CEA and CAS. The use of simulation needs to be robustly evaluated and assessed to both complement and augment existing training programs to ensure that the highest standards of care are maintained for treatment of carotid territory disease. Objective competency based training and assessment is no longer unattainable. Simulators augment this process and without them operative exposure is sporadic and crisis management infrequent.

Cost-effectiveness of Intraoperative Imaging in Carotid Endarterectomy

OBJECTIVE:

There has never been a large, randomized controlled trial to assess the impact of intraoperative imaging on the success of carotid endarterectomy (CEA). This comparison involves cost-effectiveness analysis.

METHODS:

We constructed a decision-analytic model to compare effectiveness and costs of intraoperative ultrasound (IUS) and completion angiography as adjuncts to CEA. Data on procedural mortality, morbidity, and costs were obtained from the English-language literature. The review included a total of 52 reports, encompassing more than 22,000 patients. The main components of costs were those of the monitoring interventions and the care of perioperative stroke.

RESULTS:

Mean perioperative outcome without completion imaging is approximately 96.7% of what it would be in the absence of perioperative stroke or death. IUS and completion angiography each result in approximately 2% improvement in expected outcome. Mean perioperative costs are $396.50 for IUS, $721.30 for no monitoring, and $840.90 for completion angiography. Because IUS is significantly more effective at detecting technical errors that would likely result in perioperative stroke than no imaging and is significantly less costly than angiography, this strategy dominates the other two (i.e., it provides greater effectiveness at lower cost).

CONCLUSION:

Although surgical complications are uncommon, IUS substantially lowers the rate of perioperative stroke and mortality and thus is significantly more cost-effective than either completion angiography or no operative imaging.

Internal carotid artery flow volume measurement and other intraoperative duplex scanning parameters as predictors of stroke after carotid endarterectomy

PURPOSE

Intraoperative duplex scanning (IDS) after carotid endarterectomy (CEA) has been shown to reliably identify major defects either by significant changes in peak systolic velocities or by B-mode imaging. To evaluate whether IDS could also predict postoperative strokes in technically flawless CEAs, we analyzed several hemodynamic parameters and correlated them with patient outcome.

METHODS

From March 2000 to February 2001, 226 consecutive primary CEAs were performed in 208 patients (120 men). Of these, 153 lesions were asymptomatic. General anesthesia and synthetic carotid artery patches were used routinely. Intraluminal shunts were used when internal carotid artery (ICA) back-pressures were <50 mm Hg (35% of cases). IDS consisted of B-mode and color-flow imaging and spectral analyses of the common, external, and internal carotid arteries. Volume flows were measured three times, and the mean flow rate was used for this study.

RESULTS

The first set of data was analyzed when the twenty-ninth patient had the second immediate postoperative stroke. It was noted that the two patients who had postoperative strokes had mean ICA volume flows (MICAVF) of 48 mL/min and 85 mL/min. Only two additional patients had MICAVF <100 mL/min. The remaining 25 cases had MICAVF ranging from 102 to 299 mL/min, with a mean of 165 +/- 57 mL/min (+/-SD) (P <.02). Although there was a significant correlation between MICAVF and ICA peak systolic velocity (P <.01), the latter was not found to be a significant predictor of postoperative stroke. Moreover, end-diastolic velocities, resistive index, ICA diameter, and ICA back-pressure also did not correlate with neurologic events. These findings led us to change our protocol for patients with MICAVF <100 mL/min. This included a repeat set of volume flow measurements after 15 to 20 minutes, withholding the reversal of heparin, and the liberal use of completion arteriography. Of the following 197 CEAs, 26 (13%) were found to have MICAVF <100 mL/min (range 55 to 99 mL/min; mean 79 +/- 18 mL/min). Of these, five had arteriography that documented spasm of the intracranial portion of the ICA in four and a small-diameter ICA (<2 mm) in one. Except for the five cases, the remaining 21 cases had MICAVF >100 mL/min (range 105 to 158 mL/min, mean 127 +/- 20 mL/min [+/-SD]) on repeat study. Four patients with persistent ICA low flow (70 to 99 mL/min) were treated with postoperative anticoagulation. One of the last 197 patients had a stroke caused by hyperperfusion syndrome 2 weeks after operation. Overall, six of 226 cases (2.7%) required revision on the basis of abnormal B-mode imaging results or peak systolic velocities >150 cm/s. There were two common carotid artery flaps, two ICA stenoses, one ICA flap, and one localized thrombus. All six were successfully revised and had repeat normal IDS study results, and none of these patients had a postoperative stroke.

CONCLUSIONS

IDS is helpful in identifying residual lesions or defects that may contribute to postoperative neurologic deficits. MICAVF <100 mL/min are suggestive of spasm that could lead to thrombus formation and stroke, particularly in the presence of synthetic patches. We suggest that heparin reversal should not be used unless ICA flow rates are >100 mL/min. ICA spasm is short lived in most patients undergoing CEA.