Journal of Surgical Research 180, 43–44 (2013)doi:10.1016/j.jss.2011.11.1016

COMMENTARY

Working Towards a Better Understanding of the

Biomechanics of the Carotid Artery

Originally submitted November 15, 2011; accepted for publication November 18, 2011

Perhaps no other arterial bed and itsmanagement have been as intenselystudied as the carotid artery. Whether to patch or not following carotid end-arterectomy (CEA), what type of patch to use, complications associatedwithpatching, and long-term results with the various methods of treatment arestill not resolved. Added to the treatment options are carotid artery stents(CAS), which have their own attendant complications. Understanding thebiomechanics of the carotid artery is essential in our ongoing efforts to treatcarotid artery disease in the most effective way.

The authors of the current study are to be commended for reminding us ofthe mechanical properties of the carotid artery that are important in themanagement of patients undergoing CEA [1].

As they have noted, circumferential or hoop stress is an important factorin the development of atherosclerosis. In addition, hoop stress plays a signif-icant role in the development of pseudoaneurysms that are occasionallyseen following CEAs and other complications, including carotid artery‘‘blowouts’’ that may occur following saphenous vein patch angioplasty ofthe carotid artery.

What is somewhat unusual in this series is that all patients had primaryclosure of the carotid artery following CEA. My personal preference, and Ibelieve that of most surgeons, is to patch the carotid artery following theendarterectomy. AbuRahma and colleagues reported both a lower risk ofpostoperative strokeanda lower risk of recurrent stenosis inpatients receiv-ing carotid artery patches compared with those with primary closure [2].

In 2005, we reported a series of 76 patients in whom porcine biologicpatches (SIS-small intestinal submucosa) were implanted following CEA[3]. The rationale behind the biologic patch is to provide a lattice work sothat the patient’s own tissues replace the patch. Extensive animal testinghad demonstrated the effectiveness of the SIS patch in terms of strengthand durability. In addition, histologic examination of the SIS patches hadconfirmed that the SIS patches were indeed replaced by the host’s owntissues. Mechanical testing was done on these patches, including measure-ment of the patch thickness, tensile strength, and suture retentionstrength. Multiple layers were then fashioned to form a patch that wasthought to have adequate strength to withstand arterial pressure. Theclinical results of the first 60 patients were outstanding without evidenceof pseudoaneurysm formation or rupture.

However, in the latter part of the series, seven patients developed pseu-doaneurysms and the trial was immediately suspended. Extensive testing

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of the two lots of animals from the patches in which pseudoaneurysmsdeveloped indicated that these patches were thinner and demonstratedmore variable tensile strength and suture retention strength than thepatches that did not develop pseudoaneurysms. In those patients whodevelop pseudoaneurysms, we believe that the physiologic stresses encoun-tered by the patch exceed its mechanical integrity. From this data, weestimated that the minimum thickness for the SIS patch or any biologicpatch is 3 mm.

Rupture of saphenous vein patches is an uncommon but disastrous com-plication following CEA. The common denominator among the rupturedvein patches was harvesting of the vein from the ankle [4, 5]. In an elegantstudy on saphenous vein patching of the carotid artery, Archie noted thatvein patch rupture correlated with the diameter of the vein, although therewas wide variability [5]. Archie noted thatmaterial fatigue and thickness ofthe vein wall may also play a role. Accordingly, Archie advised that onlysaphenous veins with a greater than 3.5 mm distended diameter be usedfor carotid patch angioplasty. He also advised that the CEA reconstructionbe tailored to keep the carotid bulb major diameter axis less than 13 mm.

Further testing along the lines of this studymay allow us to developmoreeffective treatment of carotid artery disease, including better carotid arterystent design.

Robert Alan McCready, M.D.1

Clarian Health PartnersDepartment of Vascular Surgery1801 North Senate Blvd, Suite 755Indianapolis, IN

REFERENCES

1. Kamenskiy AV, Dzenis YA, MacTaggart JN, et al. Nonlinear mechanical behavior of thehuman common, external, and internal carotid arteries in vivo. J Surg Res 2012;176:329.

2. AbuRahma AF, Robinson PA, Saiedy S, et al. Prospective randomized trial of carotid end-arterectomy with primary closure and patch angioplasty of the saphenous vein, jugularvein, and PTFE: Long-term follow-up. J Vasc Surg 1998;27:222.

3. McCready RA, Hodde J, Irwin RJ, et al. Pseudoaneurysm formation in a subset of patientswith small intestinal submucosal patches after carotid endarterectomy. J Vasc Surg 2005;41:782.

4. O’Hara PJ, Hertzer NR, Krajewski LP, et al. Saphenous vein patch rupture after carotidendarterectomy. J Vasc Surg 1992;15:504.

5. Archie JP. Carotid endarterectomy saphenous vein patch rupture revisited: Selective useon the basis of the vein diameter. J Vasc Surg 1996;24:346.

1 Towhomcorrespondence and reprint requests should be addressed at ClarianHealthPart-ners, Department of Vascular Surgery, 1801 North Senate Blvd, Suite 755, Indianapolis, IN46202. E-mail: rmccready@clarian.org.