A view from within

Thirteen years ago, an earlier report was published by Rosenfield et al. [1] on the use of three-dimensional reconstruction of human coronary and peripheral arteries from images recorded during two-dimensional intravascular ultrasound examination. In this current issue, we now have an article by Clark et al. on intravascular ultrasound examination of the carotid arteries during carotid stenting. In the interval, we have learned a great deal about the utility of IVUS in the coronary arteries from single and multicenter registries as well as randomized clinical trials. We have learned that IVUS provides tremendous images of the vessel wall. It can be used to select a specific treatment device, for example, rotational atherectomy, and to select the size of that specific treatment device. We have used IVUS to evaluate mechanisms and risks of restenosis and adequacy of stent deployment. The lessons we have learned from IVUS have improved outcome both early and longer term. Finally, we have learned that while often useful, IVUS is not routinely required [2]. We are at the beginning of the IVUS journey all over again, this time in the carotid arteries. In this new study, IVUS was performed in 98 consecutive high-risk patients undergoing carotid artery stent implantation. The results of stent implantation were similar to other series reported before the use of distal protection with 97% success and a 30-day combined endpoint of stroke or death of 5.6% (most frequently a minor stroke). Some familiar lessons were learned from the ultrasound as well as some new lessons. One, IVUS was safe even when performed prior to dilatation and stenting. Two, measurement of minimal lumen diameter of the distal internal carotid artery (ICA) reference segment was similar between IVUS and quantitative angiography (QA). This is in contrast of the typical findings in the coronary arteries; whether that is due to improved QA results in larger vessels with better boundary detection in nonmoving structures, or due to the fact that the distal ICA has usually a more normal reference vessel in contrast to the coronary arteries when diffuse disease may not be apparent angiographically but is apparent by IVUS, or is related to other issues is unclear. Three, as is true with coronary IVUS imaging, specific carotid lesion characteristics were detected more frequently (specifically calcification) and the extent of the calcification could be more readily quantitated with IVUS. Four, adequacy of stent deployment using as a criteria final stent minimal lumen diameter (MLD) could be enhanced with IVUS compared with angiography because in-stent MLD with IVUS was significantly smaller with IVUS at 3.65 0.68 vs. 4.31 0.76 mm with QA. In addition, stent malapposition was detected in 11%. Finally, and perhaps most importantly, the specific pattern and extent of calcification identified with IVUS was associated with a dramatic difference in stroke rate, although the numbers are very small. What we can conclude from this early experience of carotid ultrasound is that many of the lessons we learned in the coronary arteries with IVUS will be relevant in the carotid bed. There is much to learn and more data from registry studies and randomized clinical trials will be required. It may be too early to state with certainty as the authors do that “IVUS findings after an optimal angiographic result necessitate additional treatments,” but it certainly is not too early to begin gathering data such as those presented here.