Intravascular ultrasound (IVUS) is an imaging techniquewherein an ultrasound device is attached to acatheter, allowing images to be obtained frominside blood vessels. These images can be used asan adjunct to or as replacement of other imagingmodalities in the diagnosis and treatment of cardiovasculardisease.

One of the applications of IVUS in vascular surgery isduring the process of the endovascular placement of astent graft in the thoracic aorta. IVUS may especially beof benefit during the endovascular treatment ofpatients with a ruptured thoracic aortic aneurysm orwith a traumatic rupture of the thoracic aorta. This articledescribes the potential advantages and disadvantagesof IVUS in the endovascular treatment of patientswith a ruptured thoracic aorta.

IVUS AND ACUTE TEVAR
IVUS provides reliable real-time diameter and lengthmeasurements of the aorta (Figure 1).1 IVUS measurementsclosely agree with computed tomographic (CT) measurements,but IVUS images are in some cases even the reasonto alter a stent graft selection initially based on CT measurements.2 IVUS can therefore be of help in patients withindecisive CT angiography or magnetic resonance angiographyand in patients without any other imaging.

Thoracic endovascular aneurysm repair (TEVAR) isshown to decrease the mortality rate of patients withruptured aneurysms when compared with open repair.3The problem with TEVAR in the acute setting, however,is the preoperative need for cross-sectional images. Theacquisition of CT angiography images, which are generallyused, is time-consuming and requires patients to betransferred, thereby possibly reducing patients' survivalrates. IVUS might thus be of great value in hemodynamicallyunstable patients with a ruptured thoracicaorta wherein no preoperative images have beenacquired due to time restrictions. The decision to performTEVAR or open repair can be made with the useof IVUS in the operating room with no additionalpatient transfers required.

In addition, IVUS provides real-time images of thedynamic environment of the aorta, which is important, as the thoracic aorta is shown to expand significantlyper heartbeat.4,5 Diameter changes of the thoracic aortaduring the cardiac cycle of more than 20% are common,and not taking these movements into account mightlead to type I endoleaks or stent graft migration.4Moreover, it is also known that the diameter of the thoracicaorta decreases significantly during blood loss.6Images obtained before fluid resuscitation in patientswith a ruptured thoracic aorta and severe blood lossmay thus result in the measurement of aortic diametersthat do not represent the fully resuscitated diametervalues. With IVUS, images can be obtained before, during,and after fluid resuscitation. The use of IVUS mighttherefore lead to optimal stent graft sizing in patientswith a ruptured thoracic aorta.

During the deployment of a thoracic stent graft,given the real-time images IVUS provides, the mostoptimal site for proximal and distal landing zones of thestent graft can be chosen. IVUS is able to clearly visualizethe branches of the thoracic aorta and might help inpreventing unintentional coverage of side branches andstent graft sealing and fixation-related problems(Figures 2 and 3). In addition, IVUS will aid in coveringthe smallest part of the aorta as possible in patientswith an aortic rupture by identifying the exact site oftransection.

Besides these specific advantages of IVUS for patientsrequiring acute TEVAR, there are some other generaladvantages of IVUS. First, the use of contrast agents isnot required while performing IVUS; it currently is anattractive imaging alternative in patients with (minor)renal insufficiency or contrast allergy but might help inreducing the amount of contrast agent used in all EVARor TEVAR patients. Second, the exposure to radiation isreduced if IVUS is used instead of angiography.7 Thiscan be of importance to all patients that are beingtreated by EVAR or TEVAR, as the radiation burden inthese patients is already significant.8 Third, IVUS is capableof providing information about the alignment of thestent graft to the aortic wall and the existence ofendoleaks after the placement of a stent graft.9 The useof IVUS might thereby make the periprocedural use ofangiography unnecessary. In a study by von Segesser etal, it was shown that angiography could be replaced byIVUS while obtaining comparative EVAR results.7

There are certain cases wherein IVUS needs to besupported by angiographic images due to technicalfailure of the IVUS device. Another disadvantage ofIVUS, besides a potential technical failure, is that itadds time to the endovascular procedures, although itgenerally is not more than 10 minutes. In addition,guidewires, introducer systems, and stent grafts canmake the IVUS images less reliable. Finally, the interventionist should be aware that the IVUS device should beperfectly perpendicular to the aorta while measuringthe aortic sizes to prevent oblique measurements, whichis of special importance while measuring in the aorticarch. The IVUS technique is still evolving, and new developmentsare being made. Newer IVUS technologies,such as forward-looking IVUS and optical coherencetomography, are awaited with interest and might furtherimprove the technology.

Currently, IVUS is already capable of investigatingwhether patients are suitable for TEVAR. Moreover, it canbe used for optimal stent graft sizing measurements andis of help in deploying a stent graft at the most optimalsite. For these reasons, IVUS might be of great additionalvalue to patients with a ruptured thoracic aorta.

Jasper W. van Keulen, MD, is with the Section of VascularSurgery at Yale University School of Medicine in NewHaven, Connecticut. He has disclosed that he holds nofinancial interest in any product or manufacturer mentionedherein. Dr. van Keulen may be reached atjasper.vankeulen@yale.edu.

John Aruny, MD, is with the Section of InterventionalRadiology at Yale University School of Medicine in NewHaven, Connecticut. He has disclosed that he holds nofinancial interest in any product or manufacturer mentionedherein.

Bart E. Muhs, MD, PhD, is with the Section of VascularSurgery at Yale University School of Medicine in NewHaven, Connecticut. He has disclosed that he is a paidconsultant to Cook Medical, Medtronic, Inc., and W. L.Gore & Associates.

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