TCD and Carotid Endarterectomy (CEA): Lessons for the Vascular Laboratory

Merrill P. Spencer MD, Spencer Vascular Laboratory, Seattle, WA USA

Introduction: Accuracy in grading the severity of carotid artery stenosis is of utmost importance in selecting patients who will benefit from CEA. Additional pre and postoperative TCD information, provided by the vascular laboratory, can assist the management of surgery.

Methods: Our experience with monitoring more than 1000 CEA operations has provided tips for our vascular laboratory technologists performing ultrasonic carotid Duplex evaluations. We compared stenosis severity provided by regional laboratories with our results using the additional criteria of intracranial collateral, MCA pulsatility, and velocity ratios between the proximal and distal ICA. In addition we explored the prevalence and rate of perioperative microemboli relative to preoperative stenosis and postoperative restenosis.

1. We found frequent preoperative overestimation of severity of carotid artery stenosis. Explanations appear to be incorrect Doppler angle, inappropriate use of single criteria such as cross section area measurements, and failure to use additional Doppler methods for grading stenosis including carotid collateral effects in stenoses >= 70%.
2. The need for shunting can be anticipated preoperatively by attention to low MCA pulsatility.
3. Preoperative MCA microemboli are diagnostic of plaque ulceration and increase the urgency for surgery when other criteria are met. Postoperative microemboli provide warning of thrombosis and restenosis and can be successfully treated with infusions of Dextran 40 and glycoprotein IIB/IIIA inhibitors.

1. Complete agreement between angiographic measurements of carotid stenosis and Doppler criteria is not possible because the former is a morphologic measurement and the latter is a hemodynamic assessment.
2. The accuracy of the vascular laboratory should be validated by seeking agreement between multiple methods of grading carotid stenosis and by high resolution angiography, when available.
3. The need for shunting can be predicted by attention to MCA pulsatility.
4. Plaque ulceration can be diagnosed by finding ipsilateral microemboli in the MCA.
5. Postoperative microemboli can predict complications of restenosis and cerebral insufficiency and can be successfully treated with Dextran and new antiplatelet agents.