How and Why We Use Intravascular Ultrasound
Tell us about your lab.
The Medical University of South Carolina (MUSC) has 4 dedicated cath labs with 9 practicing interventionalists, 6 of whom are on faculty at MUSC. We do coronary, peripheral, and structural procedures.
How do you use intravascular ultrasound (IVUS)?
We use it primarily for optimization of the interventional technique, meaning vessel sizing and stent sizing, diameter, and length, and then to determine adequacy of stent deployment, which includes lesion coverage, stent expansion and apposition, and any edge injury.
What have you seen in terms of your outcomes with IVUS use?
Well, we certainly think we get better outcomes, but it’s hard to prove. It takes thousands of patients to truly show differences with regard to stent thrombosis, restenosis, or results with percutaneous coronary intervention (PCI) in general.
Does IVUS impact how you make decisions in the lab?
Absolutely. We use IVUS to determine stent length, diameter, and/or the need for adjunct therapy, meaning whether pretreatment of the lesion requires more aggressive pretreatment techniques, such as predilation with a cutting balloon or adjunctive treatment with rotational atherectomy. It gives us an idea of how the lesion will behave in response to direct stenting. If any adjunctive techniques are needed, we can optimize that, and make them more efficient.
What about after the stent is placed?
It’s always nice to see how you did! In our case, we would be looking specifically at lesion coverage, to make sure we didn’t miss anything, then also look at the edges, to make sure we didn’t cause any dissection, and then, of course, adequacy of stent expansion and apposition.
How frequently do you find that your post-stent IVUS prompts action?
I would say at least half the time we do something different. The question remains whether or not a simple post-dilation would have taken care of any issues. Some operators make the argument that if you are going to post dilate ½ mm up at high pressure throughout the whole stent, then you have, in many cases, covered whatever you would see on post-stent IVUS. Others argue that there is more still to be gained in terms of the edges and adequacy of lesion coverage, and that there is still benefit from routine IVUS post stent. Sometimes you may not even need to post dilate because IVUS shows the areas of coverage you have achieved are sufficient with the initial stent deployment.
So, in a sense, we need more data.
We can always say that. We always need more data. I would like to see a large-scale, randomized outcomes-based trial properly done that explores these techniques and evaluates outcomes. I think it’s difficult to do and those that have been done have had mixed results. I’m not sure there will be a definitive answer, but I certainly would like to see one. There is some evidence from a Washington Hospital series that was published in European Heart Journal that routine IVUS use in the drug-eluting stent era reduces the incidence of stent thrombosis.1 While we recognize that there is more than one way to ‘skin the cat’, we believe that routine IVUS use optimizes our equipment choices, optimizes our treatment strategies and optimizes our outcomes, although admittedly, we and most of the IVUS camp has had difficulty proving that in the drug-eluting stent era.
Do you use IVUS every time you stent?
I try to, unless there is a reason not to. Across our lab, we are at least 50% pre and post IVUS. I tend to be on the side of 85-90%.
In what patients would it not be appropriate?
Sometimes the IVUS catheter just won’t go because of vessel tortuosity or size. I tend not to use IVUS in vein grafts or through internal mammary grafts, just because I want to minimize the amount of instrumentation in those territories.
How do you use IVUS and FFR differently in your practice?
There was a time when many believed that anatomic lesion assessment was a good way of determining whether or not a lesion was significant. In the past few years, what we have learned, especially with the publication of the FAME trial2, is that FFR and the physiologic assessment it provides not only can reduce the number of stents that are implanted, but also improve outcomes. We don’t have that data with IVUS, and therefore, for the diagnosis of physiologically significant coronary disease that will benefit from treatment, an FFR-guided strategy is certainly preferred over an IVUS-guided strategy.
Today, we have come to the understanding that FFR and/or clinical reasoning tells us when to treat, while IVUS optimizes how we treat.
What about other imaging technologies, such as optical coherence tomography (OCT)?
OCT is a very exciting technology. It shows us things that, in truth, we haven’t seen before. What we still need to learn is whether routine strategy with OCT can provide the same information and/or better information than what can be provided by IVUS, and can further improve outcomes.
Do you think IVUS adds a significant amount of time to the procedure?
No. Once the lab is facile with the set up and everyone is comfortable with the equipment, it adds, at most, 5 minutes to the procedure.
What about interpretation of the images?
As with anything, it takes time. If it is only pulled off the shelf when there is clinical uncertainty, a question angiography is not answering and/or a sick patient, comfort level is going to be low. However, if IVUS is made part of routine use, comfort level will be high and interpretation will be uniform across the board.
How does your staff feel about IVUS use?
I think the majority of them are in favor. As their familiarity has increased and as their understanding of the modality and what we are visualizing has increased, their interest as well as their comfort with it has been enhanced, and now sometimes they look at me and wonder why we didn’t IVUS.
Do any particular patient populations especially benefit from IVUS use?
Any complex situation. In particular, ostial or bifurcation lesions, instent restenosis, stent thrombosis, long lesions, small vessels, or any time there is a question regarding the best manner in which to treat the lesion. I also feel that in STEMI patients, we tend to underestimate vessel size. Incomplete apposition has been shown to be greater in STEMI patients. After the stent is implanted, I like to IVUS in order to make sure we have accomplished expansion and apposition, as these issues can be overlooked in STEMI patients and then can lead to stent thrombosis and other untoward effects. Occasionally in large vessels we will also underestimate size, and have areas of incomplete apposition and underexpansion. Expansion is especially important in small vessels, where post stent area has been correlated with stent thrombosis, both early and late.
Dr. Steinberg can be contacted at steinbe@musc.edu.
Disclosure: Dr. Steinberg reports that he is a consultant for and has received an honoraria from Boston Scientific Corporation.
References
- Roy P, Steinberg DH, Sushinsky SJ, et al. The potential clinical utility of intravascular ultrasound guidance in patients undergoing percutaneous coronary intervention with drug-eluting stents. Eur Heart J 2008 Aug;29(15):1851-1857.
- Pijls NH, Fearon WF, Tonino PA, et al. Fractional flow reserve versus angiography for guiding percutaneous coronary intervention in patients with multivessel coronary artery disease: 2-year follow-up of the FAME (Fractional Flow Reserve Versus Angiography for Multivessel Evaluation) study. J Am Coll Cardiol 2010 Jul 13;56(3):177-184.
