whatâ€™s new in vascular ultrasound - vanderbilt university

Surg Clin N Am 84 (2004) 1113–1126

What’s new in vascular ultrasound

William H. Pearce, MDa,b,*,Patricia Astleford, BSN, RN, RVTb

aNorthwestern University, Feinberg School of Medicine, 201 E. Huron, #10-105,

Chicago, IL 60611, USAbVascular Laboratory, Northwestern Memorial Hospital, 251 E. Huron, #8-305,

Chicago, IL 60611, USA

Traditionally, the vascular laboratory is used to diagnose a wide varietyof vascular diseases and to provide objective tools to assess operativeinterventions. Duplex ultrasound scan is the method of choice for di-agnosing deep venous thrombosis, evaluating patients for carotid arterystenosis, and monitoring lower extremity bypasses for neointimal hyperpla-sia. However, the role of the vascular laboratory is now changing with theintroduction of new technology. Arterial mapping of the lower extremity iscurrently replacing contrast angiography (CA) and magnetic resonanceangiography (MRA) as the sole imaging modality for lower extremitybypass procedures. This approach has followed what in many centers hasbeen the standard for patients with carotid artery stenosis (Figs. 1 and 2). Inaddition, new procedures such as carotid stenting and endovascularaneurysm repairs have created new applications for duplex ultrasound indetecting in-stent stenosis and endoleaks. The duplex ultrasound is alsobeing used intraoperatively to evaluate in situ vein bypasses and to monitorendovenous procedures such as lasers and radiofrequency ablation. Finally,duplex ultrasound is used to treat common femoral pseudoaneurysms, eitherby compression or to guide thrombin injections.

Duplex arteriography (DA)

In patients with lower extremity ischemia, a variety of imaging techniquesare used to define the inflow and outflow vessels. CA is generally consideredthe gold standard. However, in recent years the gold standard has been

* Corresponding author.

E-mail address: [email protected] (W.H. Pearce).

0039-6109/04/$ - see front matter � 2004 Elsevier Inc. All rights reserved.

doi:10.1016/j.suc.2004.04.006

mailto:[email protected]

1114 W.H. Pearce, P. Astleford / Surg Clin N Am 84 (2004) 1113–1126

challenged by the use of prebypass intraoperative arteriography, MRA, andduplex scanning. Huber et al suggested that intraoperative arteriography isperhaps the most accurate way of identifying distal targets in patients withsevere distal ischemia when compared with CA [1]. However, timing and siteof injection greatly influence the accuracy of both CA andMRA. In addition,the quality of MRA studies varies greatly depending upon local expertise.

Duplex arteriography (DA) has been advocated as the sole method forevaluating patients undergoing lower extremity bypass by a number ofauthors [2–6]. Unfortunately, to scan the entire arterial tree from the aorta to

Fig. 1. B-Mode image of a right internal carotid artery stent.

Fig. 2. B-Mode image of the distal attachment of an internal carotid artery stent.

1115W.H. Pearce, P. Astleford / Surg Clin N Am 84 (2004) 1113–1126

the pedal vessels is time-consuming (average times ranging from 75minutes tomore than 150 minutes). Furthermore, imaging the iliac vessels may bedifficult in patients who are obese or who have bowel gas or tortuous iliacarteries (Figs. 3 and 4). In these cases, the arterial waveforms may be useful inidentifying a proximal occlusive stenosis. Mazzariol reported that a severely

Fig. 3. Duplex scan of the common femoral and proximal profunda femoris and superficial

femoral (SFA) arteries. There is some evidence of plaque present in the proximal SFA, but it is

hemodynamically insignificant (less than 60% diameter reduction).

Fig. 4. Duplex scan of the common femoral and proximal profunda femoris and superficial

femoral (SFA) arteries. There is some evidence of plaque present in the proximal SFA, but it is

hemodynamically insignificant (less than 60% diameter reduction).


abnormal common femoral artery waveform was 100% predictive fordetecting stenosis greater than 50% [7]. Mildly abnormal common femoralartery waveforms unfortunately did not exclude significant proximal stenosisand, therefore, additional imaging modalities were required. Mazzariolconcluded that DA was able to provide enough information for surgery inmore than 83% of patients. For infrainguinal disease, a significant stenosis isdefined as a twofold or greater increase in peak systolic velocity (PSV) or theabsence of blood flow consistent with an occlusion. In similar studies, Proaiand Grassbaugh reported that DA was predictive in 88% of patientscompared with 93% of patients undergoing CA [3,4]. These investigatorsused PSV, end diastolic velocity, and transverse images of the arteries todetermine arterial diameter and wall calcification. The majority of tibial andpedal vessels can be visualized using DA. However, heavy calcification ornonvisualization of the peroneal artery may limit usefulness. Also, painfululcers precluded distal imaging. Proai found that graft patency was greaterwhen the PSV was 30 cm/s or greater in the distal artery [4]. In evaluatinglong-term results, he found that patency was also increased for patients withhigh PSV, when compared with those patients with lower values. Similarly,end diastolic velocity was less in the group that failed (14 � 8 cm/s versus22� 7 cm/s;P=0.08). Ultrasound contrast agents are being used to improveimaging in the lower extremity. Eiberg and colleagues from Denmark wereable to improve overall accuracy by 70% in poorly visualized segments usingcontrast agents [8]. Unfortunately, the short half-life of these agents requirerepeated dosing or continuous intravenous infusion.

When comparing the results of MRA versus DA, it appears that MRAhas a greater sensitivity for detecting arterial disease of the lower extremity.In a meta-analysis comparing MRA and DA, the authors concluded that thesensitivity for MRA was 97.5% compared with 87.6% for DA [9]. Thespecificity of the two tests was similar, 96.2% versus 94.7%. Unfortunately,gadolinium-enhanced MRA is not available in all institutions, and thetechnique varies widely. Furthermore, gadolinium may be nephrotoxic inpatients with borderline renal function [10]. In these instances, DA mayprovide a better alternative to either CA or MRA.

Intraoperative duplex scanning

Following arterial reconstruction, completion angiography has beenrecommended to detect technical flaws, which may limit long-term patency.Single-shot arteriograms or fluoroscopy is currently used in most institu-tions. However, a high concentration of contrast may hide a significantdefect. Johnson et al have reviewed intraoperative duplex monitoring asa completion technique [11]. At completion, the entire bypass graft isscanned for anatomic and flow abnormalities. Measurements of PSV andratio at the lesion divided by proximal velocity are used as criteria todetect defects. In addition, postoperative management of perioperative


anticoagulation was based upon graft flow velocity (cm/s). PSV of morethan 25 cm/s was generally the threshold for detecting a graft abnormality.However, this velocity may be recorded from small diameter grafts. Thedefect was more closely examined if the velocity ratio (VR) was greaterthan 2 VR. Revision of the graft occurred when the PSV was greater than180 cm/s and a VR of greater than 2.5 (Fig. 5). In venous segments withborderline velocities, the scan was repeated following administration ofpapaverine. If the PSV increased more than 200 cm/s, the graft was exploredor revised. In patients with impaired outflow (a PSV of less than 45 cm/s),postoperative anticoagulation was given. In this study, Johnson founda 15% revision rate that was comparable to that detected by CA.Reintervention was only 2.5% in 30 days. Continued postoperativesurveillance was also performed.

Surveillance duplex scanning is an essential component of patient follow-up following lower extremity revascularization. Other studies by Mills [12]and Bandyk [13] have demonstrated the utility in detecting hemodynamic-ally significant lesions. Identification of these lesions and intervention hasincreased secondary patency and limb salvage.

Venous ablation

The treatment of varicose veins has changed dramatically over the pastseveral years. Percutaneous or intraoperative ablation of the greater

Fig. 5. Duplex scan of the distal anastomosis of a bypass graft. Increased flow at the distal

anastomosis warrants reexploration or revision at the site.


saphenous vein can be accomplished using radiofrequency or laser energy[14,15]. Using these devices, the groin incision is avoided. A catheter is placedunder ultrasonic guidance to within 1 cm of the saphenofemoral junction.Before using this technique, the vein must be evaluated to assure appropriatevenous anatomy and vein diameter. Large varicosities greater than 2 cm,venous aneurysms, and varicosities at the saphenofemoral junction arecontraindications. These procedures are performed in the office using localanesthesia. To avoid thermal injury to the skin, the anesthesia agent isinjected in the space directly above the varicose vein, again using ultrasoundguidance. The device is placed from the knee to the groin. The location of theprobe is identified just below the saphenofemoral junction, and ablationoccurs by pulling the device distally and monitoring venous occlusion.

Preoperative evaluation of patients undergoing varicose vein strippingand venous ablative surgery is needed to assure that the deep system iscompetent and without clot. Preoperative duplex scanning also providesinformation regarding the location of perforators and accessory veins andthe presence of lesser saphenous reflux. Many techniques have been used todefine reflux and are detailed elsewhere [16].

Endovascular aneurysm repair (EVAR)

Endovascular repair of abdominal aortic aneurysms (EVAR) wasdescribed more than a decade ago by Juan Parodi, MD [17]. Since then,a variety of graft manufacturers have developed endovascular prostheses(Fig. 6). The basic principal of these devices is to bridge the aneurysm defectusing a modular graft system. The devices require adequate landing zones,both proximally and distally (aortic leg 1.5 cm and iliac 1 cm), minor degreesof neck angulation, and adequate iliac diameter and tortuosity. Each deviceis slightly different, and the reader is referred to specific manufacturer’sinstructions for use. Currently, helical CT is the imaging technique of choicefor determining suitable aortic morphology. However, once the graft hasbeen placed, long-term follow up is mandatory. Long-term follow up isneeded to determine whether the aneurysm sac has shrunk and to monitorfor the presence or absence of an endoleak. Between 15% and 25% ofpatients will develop an endoleak. The most common endoleak, Type II,is of uncertain significance, particularly if the sac is stable or shrinking.Types I and III endoleaks, on the other hand, are dangerous and requirereintervention. Early experience with these devices relied upon contrast CTscans with delayed venous filling. Even in these instances it was sometimesdifficult to identify the exact source of endoleak. As a result, some patientswith continued pressure within the arterial sac but without demonstrableendoleak are labeled as having endotension. Because of the expense andpotential contrast nephrotoxicity associated with repeated CT scans, manyinvestigators have used duplex ultrasonography as a method to determineendoleaks. Type I endoleaks are characterized by arterial flow outside of the


graft at either the proximal or distal attachment system. Retrograde branchflow Type II endoleaks are characterized as periprosthetic flow, which ischaracterized as biphasic (high resistant) or monophasic (bi-directional)(Figs. 7–10). Using this criteria Carter et al evaluated 89 EVARs in whom 12had endoleaks [18]. Two patients were found to have false-positiveendoleaks by CT scan, probably due to artifact either from calcium oradjacent hardware. Of the 12 patients, 10 had branch endoleaks, while 2 hadboth attachment system and branch vessel endoleaks. Although a smallseries, the endoleaks that persisted exhibited biphasic arterial flow. Mono-phasic arterial flow was more likely to occlude. In a more recent study byBendick, conventional duplex scanning was only 60% accurate in detectingthe nature of the endoleaks [19]. However, an infusion of ultrasonic contrastagent increased the sensitivity 100% when compared with CT scans. Theseresults are similar to those reported by McWilliams, who found improve-ment in the diagnostic accuracy of ultrasound using contrast-enhanced colorDoppler [20]. The value of duplex ultrasound scanning in patients withEVARs is that repeated studies can be performed frequently. Repeated CTscans and CTAs are not only expensive but also increase the likelihood ofcontrast-induced nephropathy. In addition, metal artifacts, from adjacentspinal hardware or the attachment systems, may make interpretation of theCT scan difficult.

Femoral pseudoaneurysms

Femoral pseudoaneurysms are relatively uncommon following cardiaccatheterization (1% to 2%). Pseudoaneurysms occur more often with

Fig. 6. B-Mode image of an aortic endograft.


catheters, sheaths, and antiplatelet agents. Kent et al reported that, althoughmany of these pseudoaneurysms thrombosed spontaneously, repeatedduplex scanning was necessary for their diagnosis [21]. In 1991, ultra-sound-guided compression of pseudoaneurysms replaced watchful waiting.Using this technique, the pseudoaneurysm is externally compressed to

Fig. 7. Aortic endograft with a Type 2 endoleak originating from the inferior mesenteric artery.

This leak lies anterior to the graft.

Fig. 8. All suspected leaks need to be confirmed by spectral Doppler analysis. The Doppler

signal will be able differentiate between a true leak and a spurious artifact caused by the metal

appliance. Type 2 endoleaks of the inferior mesenteric artery and lumbar arteries have

a characteristic to-and-fro waveform.


promote thrombosis. Compression times ranged from 10 to 90 minutes. Coxreported an overall success rate of 94% with a mean occlusion time of33 minutes (range 10 to 120 minutes) [22]. Pseudoaneurysms occluded inmore than 98% of patients receiving anticoagulation. However, there were10 recurrent pseudoaneurysms; 6 of these occurred in patients receivinganticoagulation. Recurrence developed within 24 hours. There were no

Fig. 9. Type 3 aortic endoleak. There is evidence of a leak coming from the left common iliac

artery modular connection.

Fig. 10. Type 3 aortic endoleak. There is evidence of a leak coming from the left common iliac

artery modular connection.


other complications. Two patients required surgical repair. Due to patientdiscomfort and long periods of time required for compression, Kangintroduced the use of duplex ultrasound-guided thrombin injection. In theinitial report, 20 of 21 patients were successfully treated with thrombininjections [23]. Under ultrasound guidance, thrombin (0.5 to 1 mil thrombinsolution; 1000 units/mL) was injected into the aneurysm. There were noprocedure-related complications. A later study performed by Kruger foundthat the mean dose of thrombin could be reduced to under 500 units ina majority of cases [24]. Primary success (closure) for simple pseudoaneu-rysms was 97% and 61% for complex pseudoaneurysms. Secondary successrate in this group, however, was 100% (Figs. 11 and 12). There were nothromboembolic, infectious, or allergic complications during this study.Similarly, Kruger also studied antithrombin II complex and found slightelevations following thrombin injection. Unfortunately, others have re-ported serious complications following thrombin injections. There are casereports of extravasation of the thrombin into the arterial system leading toarterial embolization or thrombosis of the femoral artery. Complex andmultilobe pseudoaneurysms are often difficult to treat, and may requiremultiple injections. In addition, we have been cautious in using thistechnique for patients with short, wide communications between the arteryand the pseudoaneurysm (Fig. 13). The likelihood for infusing the thrombininto the arterial lumen is greater in such instances. We have seen one case inwhich additional compression of the thrombosed pseudoaneurysm forcedthrombotic debris into the arterial lumen with distal embolization.

Fig. 11. Right groin pseudoaneurysm originating from the superficial femoral artery. A

pseudoaneurysm will have the characteristic to-and-fro Doppler signal.


Carotid stenting

Carotid artery stenting (CAS) is currently being clinically evaluated as analternative to carotid endarterectomy (CEA). Duplex ultrasound (DU) iscommonly being used to monitor restenosis in patients following CEA. ForCAS to be compared with CEA, a similar follow-up must be performed.Recent reports of DU follow-up of CAS suggest that critical restenosis is lowand that DU velocity criteria may be inaccurate, particularly in patients withless than 20% stenosis [25]. Lal found that a PSV of 130 cm/s or greater wasless specific (63%) than a value of 150 cm/s (specificity 96.4%). In addition,the positive predictive value rose from 16.2% to 60%. Lal suggests that thehigher velocities may be normal in a stented artery and that arterialcompliance is decreased by the stent, increasing velocity. Further studies willbe needed to validate this observation and to determine the restenosis ratefollowing CAS.

Comment

The vascular laboratory has adapted to changing technology. Virtually allperipheral arterial and venous structures may be imaged with color duplexultrasound. The identification of occlusions, the characterization of plaques,and the monitoring of vascular interventions are just a few examples. The lowcost and noninvasive aspect of duplex ultrasound make it the technique ofchoice for the repeated studies that these technologies require.

Fig. 12. Right groin pseudoaneurysm originating from the superficial femoral artery. A

pseudoaneurysm will have the characteristic to-and-fro Doppler signal.


The vascular laboratories will be playing a greater role in the detection andprevention of asymptomatic vascular disease. The Society for VascularSurgery has launched a national effort to screen large populations for carotidartery stenosis, abdominal aortic aneurysms, and lower extremity arterialdisease. The screening program consists of a truncated carotid artery scan, anabdominal ultrasound to detect abdominal aortic aneurysms, and an ankle–brachial index. In addition, a rhythm strip is obtained to identify patientswith atrial fibrillation. Flinn recently reported the finding of unsuspectedaneurysms in 2.2% of patients, carotid stenosis[50% in 7.6% of patients,and peripheral arterial disease in 7% patients [26]. Furthermore, he foundthat less than 50% of patients with peripheral arterial disease were onantiplatelet agents or lipid-loweringmedication. Hopefully, the United Statesgovernment will recognize the importance of screening for vascular diseaseand provide funding. At present, screening studies are not reimbursed.

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and wide and unsuitable for a thrombin injection.


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