Angiography

Blaisdell and colleagues were the first to recognize the potential of intraoperative testing to decrease the morbidity of carotid endarterectomy. They found a 26% incidence of technical error using completion arteriography, with most of the defects being strictures. Others have also found technical errors following carotid endarterectomy, and the rate of reoperation when completion arteriography has been used has ranged from 2.4% to 26%.

Owing to the relatively low stroke rate associated with carotid endarterectomy, it has been difficult to demonstrate that the use of intraoperative arteriography actually decreases the complication rate because of the large number of patients required to assure a statistically reliable result. An exception is the report by Scott’s group, which showed a significant difference in the stroke rate when 146 procedures in which intraoperative arteriography was not used were compared with 137 endarterectomies in which intraoperative arteriography was used. These authors found that the stroke rate was reduced from 6.8% to 3.8%, and the mortality rate was reduced from 4.8% to 1.5% when intraoperative completion arteriography was employed. However, the groups were concurrent rather than randomized.

Another potential benefit of using intraoperative arteriography is the prevention of recurrent disease. Courbier and colleagues demonstrated that defects that were seen on intraoperative arteriography and that were not corrected led to a higher than usual incidence of recurrent disease. By performing arteriography a mean of 19.2 months postoperatively, Courbier and colleagues documented disease recurrence in only 3% of internal carotid arteries that had normal intraoperative arteriographic studies. This rate was considerably less than the 28% recurrence rate of when residual defects were left uncorrected.

Intraoperative completion carotid arteriography is performed before reversing the heparin effect, so that any defect that requires correction can be repaired without the need to administer heparin to the patient again. An x-ray cassette is placed under the patient’s head and neck. The head is maintained in the turned position to allow optimal separation of the internal and external carotid arteries in the anteroposterior view. The common carotid artery is punctured with a 19-gauge needle attached to a long extension tubing and a 25-mL syringe. It is most important to be sure that no air bubbles or other debris are present in the line. Just before injection, the common carotid artery is clamped as far proximal as the wound edge allows. The surgeon, standing behind a lead shield, injects 12 mL of full-strength contrast medium, and the film is exposed. The common carotid artery clamp is then removed. The needle is usually left in place until a satisfactory film has been obtained. A figure-of-eight suture is placed at the needle base, and the needle is removed as the suture is tied. Numerous variations of the technique have been described, most of which give satisfactory results. The use of a dental film placed within the wound also has been shown to be satisfactory.

Doppler Studies

Doppler spectrum analysis was one of the first noninvasive techniques to be used in evaluating carotid artery disease. Barnes and others have demonstrated that the technique also is useful intraoperatively to detect technical errors. Initially, continuous-wave devices were employed for this purpose, but subsequently it has been demonstrated that pulsed Doppler is probably more sensitive. High-frequency pulsed Doppler allows the sampling of small volumes of blood flow within the vessel being insonated. Although tight stenoses may be detected by the audible interpretation of the Doppler frequency shift, hard copy spectral analysis is much more sensitive. Zierler and coworkers demonstrated that pulsed Doppler, using a 20-MHz pulsed device, was as accurate as arteriography in detecting intraoperative defects in internal carotid arteries.

The Doppler probe is a 20-MHz pulsed device mounted in a 16-gauge needle. The sample volume is very small and can be positioned at discrete points within the vessel. The probe is connected to a real-time, fast-Fourier transform spectrum analyzer that puts out a visual spectrum. The probe is held at a 60-degree angle to the vessel, and saline is placed in the wound for acoustic coupling. Examination is performed both before and after endarterectomy. Velocity patterns are measured at several sites in the common, external, and internal carotid arteries.

Flow abnormalities are classified into three categories. Mild disturbances show peak systolic frequencies up to 16 kHz and spectral broadening in late systole only. Also, any spectrum with minimal spectral broadening is characterized as a mild disturbance. Moderate disturbances show peak systolic frequency up to 16 kHz and spectral broadening throughout most of systole. Severe flow disturbances show peak systolic frequency above 16 kHz and spectral broadening throughout most of systole. It is important to realize that these criteria are only good for the incident frequency (20 MHz) used.

Although pulsed Doppler is very sensitive in detecting flow disturbances, it is not able to identify the defect responsible for the disturbance, and it thus requires the addition of an imaging test to identify the defect and to assist the surgeon in the decision to reopen the vessel to correct the defect.

Duplex Scanning

The advent of high-resolution imaging ultrasonography was a major advance in the noninvasive evaluation of carotid artery disease. It is not surprising that the technique was quickly adopted for intraoperative evaluation during carotid endarterectomy. Duplex scanning, which combines both imaging ultrasonography and pulsed Doppler, has been used more recently.

Before ultrasonic imaging was used in the operating room the utility of the technique was assessed in the canine laboratory. At the University of Illinois, Coelho and colleagues created technical defects consisting of strictures, thrombi, intimal flaps, and intimal dissections in the aortas of dogs and then imaged the defects using a high-resolution small parts scanner (Figure 1). Scans were interpreted by observers who were blinded to the defects. The observers were able to identify all but 1-mm intimal flaps 100% of the time. The 1-mm flaps were correctly identified 67% of the time. The correlation between real and measured flap size was r = .84. In a follow-up study, Coelho and colleagues then compared ultrasonographic imaging to single-plane and biplane portable arteriography. Both ultrasonography and arteriography were accurate in detecting arterial strictures; however, ultrasonography was superior to both single-plane and biplane arteriography in detecting intimal flaps and intraluminal thrombi.

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