Vascular Imaging Solutions

What is the clinical value of intravascular ultrasound (IVUS)? The primary benefit of IVUS is that it offers a tomographic, 360-degree view of the vessel wall from the inside, allowing a more complete and accurate assessment of a vessel than possible with angiography. Interventionalists who routinely rely on angiograms alone are probably going to miss a significant number of diagnoses, particularly in regards to hazy lesions, ostial lesions and left main disease. Once one becomes accustomed to IVUS, it is amazing how many of these cases become quite clear to the operator. Furthermore, routine use of IVUS improves angiographic interpretation skills because you are able to more accurately diagnose the cases in which you previously had doubts when performing procedures just based on angiography. IVUS also allows you to get an accurate assessment of plaque composition. This is particularly important in vessels with potential calcification, often seen in elderly patients with kidney failure or diabetes. Aorta ostial lesions also tend to be calcified. IVUS is important in these patients for optimization of the procedure, as you need to know the exact plaque composition in order to determine a plaque modification strategy, such as rotational atherectomy or cutting balloon angioplasty. Finally, IVUS can guide your procedure more effectively by helping you determine the right balloon size and length, the number of required stents and the stent length - information that is much harder to obtain precisely with angiography. When is it most important to use IVUS? The most valuable use for IVUS is the assessment of hazy angiograms - angiograms that are ambiguous from multiple angles. In left main disease, for example, hazy angiograms are a potentially critical issue in accurate diagnosis. Left main disease frequently involves eccentric stenosis, and the uncertainty of whether or not you see a tight lesion may persist despite multiple angiographic views. Misinterpretation of an angiogram in the case of left main disease can result in unnecessarily sending a patient to a bypass operation or, even worse, mistakenly sending a patient with a tight lesion home. After stent placement, angiograms can show haziness in the proximal or distal edge of the vessel, making it hard to determine whether the cause is a plaque dissection or extrusion or a calcified lesion, all which are treated differently. The eccentricity of some intermediate lesions also poses a problem for accurate angiographic assessment. With intermediate lesions, IVUS is only useful when assessing vessels >2.5 mm in diameter due to the size of the ultrasound catheter. Because of their angulation and trajectory, ostial and bifurcation lesions are also more difficult to evaluate with angiography, since it can be very difficult to get the perpendicular view that is necessary for an accurate assessment. In bifurcation lesions, IVUS allows you to evaluate the true compromise of each individual branch vessel so you can determine whether it is possible to protect the side vessel with a single stent or if you should instead use a bifurcation technique. In ostial lesions, it allows you to determine whether a stenosis is related to catheter engagement. In-stent restenosis is another important indication for IVUS. Fortunately, this is now less of an issue with drug-eluting stents (DES). With DES, we usually attribute restenosis to a mechanical issue, such as an unexpanded stent or unapposed struts, rather than intimal hyperplasia. It’s very difficult to assess this based on angiography, whereas IVUS answers these questions immediately. Similarly, IVUS is an obligatory test in patients with subacute thrombosis which, although rare, has been a concern with DES. Again, IVUS allows you to determine whether the problem is unapposed struts, unexpanded stents, unrecognized disease in the stented segment or dissections that were left behind. Can you discuss the use of IVUS for the optimization of stent deployment? This falls into a second group of situations in which the use of IVUS is perhaps a little more debatable. In the bare-metal stent (BMS) era, restenosis was thought to be inversely related to stent size; in other words, the smaller the stent, the more likely it was to restenose. Therefore there was a lot of interest in optimizing the stent diameter for each individual vessel, and IVUS was thought to offer an advantage over angiography because it provided more accurate measurements of the vessel wall. However, data from multiple studies have failed to show a true benefit of routine IVUS in all BMS cases, since the likelihood of restenosis is so low. Rather, IVUS appears to be useful for optimizing BMS placement in particular situations, such as small vessels (20 mm in length), diabetic patients and patients undergoing saphenous vein grafts. There hasn’t been a lot of data regarding the use of IVUS for optimization of DES placement. My feeling is that since you’re allowed a smaller stent area with DES, you’re not so compelled to optimize the stent to the vessel, and therefore IVUS would be less important in this category. However, we do know that when DES are placed in very small areas, there is a risk for subacute thrombosis or restenosis, especially in diabetic patients, so hopefully future studies will shed some light on the true indications for IVUS in the deployment of DES. What are some key barriers to regular IVUS use? The need for training on image interpretation is by far the most important reason for the slow adoption of IVUS in many cath labs. Operators can often perform the procedure correctly, but they don’t know how to interpret the images, and this makes them feel that the technique is not useful. Another key barrier to adoption is that it is often perceived to be time-consuming to set up IVUS equipment, which discourages some operators. However, with education and practice, this barrier can be overcome, and therefore adding minimal time to the procedure. What is Boston Scientific doing to address these barriers? Boston Scientific’s next-generation iLab IVUS Imaging System can be installed into the cath lab, reducing set-up time and giving interventionalists control of the system via a tableside controller. This enables operators to browse through the whole image and obtain measurements without having to rely on other team members who may not be skilled in image interpretation. Additional technical improvements include a Dynamic Review feature, which animates static images for enhanced image interpretation, and an easy-to-use and intuitive touch panel. Education is also a key component in improving the uptake of IVUS in cath labs. To address this need, Boston Scientific has designed the iLearn IVUS Education Series to provide training on IVUS for physicians, fellows, nurses and technologists of all levels of experience. Sponsored by Boston Scientific.

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