Interview with Michael C. Foster, M.D., F.A.C.C.

Dr. Foster is past president of the American Heart Association's South Carolina affiliate, and has served on its board of directors. He also has served as the chief of the Department of Cardiology and Director of Cardiac Rehabilitation at Providence Hospital, Columbia, South Carolina, as well as President of the South Carolina Heart Center. He is a clinical assistant professor of medicine at the University of South Carolina School of Medicine.

As principal investigator in a number of clinical trials, Dr. Foster has been involved in assessing numerous innovations in cardiology. He is a strong proponent of intravascular ultrasound, which he feels can make a signficant addition to the armamentarium of the interventionalist. In this interview, Dr. Foster discusses how IVUS can make a difference in procedural success, drug-eluting stent safety and better results for patients.

Michael C. Foster, MD
South Carolina Heart Center

Q: In what percentage of cases do you use intravascular ultrasound (IVUS)?
Dr. Foster: I personally use IVUS on at least 90% of my cases. My IVUS use is very high, perhaps one of the highest in the country. I’d preface that by saying I’m still about 90% drug-eluting stents, and my interventional population tends to be a more complex population than average. That just sort of reflects the way our practice runs. I’ll often do cases that are passed on by some of the other interventionalists in the practice and other cardiologists around the hospital or at other hospitals – they will refer cases to me that maybe they’re less comfortable in doing. So I’m intervening in a higher, more complex population than may be average.

In general I recommend IVUS for complex lesions: bifurcation lesions, long lesions, diabetics, left main and particularly restenosis lesions. But I think there are very few cases where IVUS is not useful. I never see it as a liability to get the best information I can and I think IVUS gives me that.

The lesions I would avoid doing IVUS in are situations where we have calcified tortuous anatomy, maybe hemodynamically unstable patients where it’s an emergency and you just need to get in there and get it fixed. Maybe a situation where we’re dealing with a small, very small artery, and there isn’t much doubt that the only size stent I’m going to be able to use is a 2.5mm drug-eluting stent and going in there and IVUS-ing a baseline is probably not going to change my mind.

Q: Can you give me an example of how the use of IVUS changed your treatment of a patient?
Dr. Foster: Sure. A young female with chest pain had seen several cardiologists and finally had a cardiac catheterization. It showed a small blockage and the patient was sent to our practice. Her cardiologist’s colleagues had determined from the angiogram that she need to be stented, but when we IVUS-ed her, we discovered no disease whatsoever. It turned out that what looked like a stenosis on the angiogram was an anatomical feature -- her artery made a somewhat sharp turn, but there was no disease at all.

So we did not place a stent. We showed her the IVUS and the angiogram and explained how she had no disease in her coronary arteries at all and she was discharged. It seemed her chest pain was an anxiety reaction and she was treated for that instead. If IVUS had not been used, she would have been implanted with a drug-eluting stent and would have had to be on aspirin for life and clopidogrel for at least 6 months to a year. So IVUS changed the intended treatment for this woman and she avoided all the complications and expense that would have occurred.

Dr. Foster working in cath lab at Providence Hospital in
Columbia, South Carolina

Q: You have a system where IVUS is integrated into the cath lab. How does this impact cost and time?
Dr. Foster: I think the studies we had in the past illustrate pretty well that IVUS is cost-neutral, and some studies may even indicate that it’s a cost saving. These were bare metal stent days – you included the fact that they seem to restenose less, come back less frequently. You factored that into the cost of IVUS.

Now if we use an integrated system, there really is no significant increase in the procedure time, and you’re not adding the personnel costs. You don’t necessarily have to have an extra person in the room to look at these studies. The physician can run that right at the tableside, or the technician right beside them could do that, or a nurse that’s in the room. It’s extremely flexible. I have a controller under a sterile drape right beside me, and I do all the measuring and the manipulation of the controls myself, as I’m standing in the laboratory.

There’s no bringing in a machine, turning it on, waiting for the computer to boot up, and then a technician adding the name, the age, birth date, none of that has to be done. Our system is a Volcano system integrated into a GE Innova 2100 lab, so the IVUS is always on -- if the cath lab’s on, the IVUS is on.

So when I start my procedure, and I get to the place where I’m ready to IVUS, it’s literally handing the end of the ultrasound catheter off the side of the table to a technician who plugs it in, and you’re ready to go. I would call it a plug-and-play environment, and you instantaneously have your pictures. In about one minute, I can get the IVUS set and do a pull-back into the artery that I’m interested in. And, of course, I’m looking at the images as I’m pulling back, and I’ll usually spend another minute or two, on an interesting case, manipulating images, maybe making some measurements, and so forth. So from soup to nuts, we’re talking about three minutes to do IVUS.

Q: WHat is the main advantage for you in your practice of using IVUS?
Dr. Foster: The advantage, I think, is better results for the patient. I mean that’s the bottom line to me: better results.

Particularly if one has become so uncomfortable with drug-eluting stent technology and their results and is going back to bare metal stent technology, which we know means a restenosis rate of at least double what we’re getting with drug-eluting stents.

Dr. Foster with a patient

Q: Tell me technically about the integrated cath lab – can an existing lab be retrofitted or does this have to be built-in from the start?
Dr. Foster: These labs can be retrofitted, and we’ve done that. At least two of the labs at Providence Hospital have been retrofitted. The only difference I can think of between a retrofitted lab and a brand new integrated lab is that the IVUS images don’t go directly on the same bank of monitors as the angiographic images. Usually in the retrofitted lab, they’ll put a small monitor across the table for the IVUS images.

Q: How does the integration of IVUS and fluoroscopic angiographic images help?
Dr. Foster: When I do an IVUS pullback and I have my foot on the fluoroscopy, I can have the technician injecting the artery, so I can see angiographically the landmarks that I’m dealing with where my IVUS catheter is, and I’m seeing the corresponding IVUS image on the monitor right beside it: in real time! And you get a tremendous sense of what you’re dealing with.

It really helps me figure out where to land my stent. We’ve known for a long time that you want to land the distal end of your stent in as normal an artery segment as you can. Of course, the problem with angiography is we underestimate mild disease. So sometimes the vessel looks pretty good just beyond the lesion, but when I’m looking at that same region on ultrasound, many times I can see pretty severe disease in there. So I actually mark the area of artery in my mind that’s really pristine by IVUS. And then I know I’ve landed that stent into the best possible segment I can.

In the future there will probably be this type of integrated IVUS-angiographic system called AIM, which stands for Angiographic IVUS Mapping, I believe, so you could look at the angiogram and see where your lesion is, put a cursor on there and the IVUS image would automatically link right to that spot. That’s sort of what I’m doing in my mind, when I do these pullbacks in the integrated lab. Once I finish that 1 min, 90 sec, baseline run, I know exactly where I want to put my stent. I know exactly the size of the vessel I’m dealing with. I know my vessel’s 4.0mm, and I’m putting in a 3.5mm drug-eluting stent which is the largest we have available, so I know I’m going to have to go in after I deploy that stent with a 4.0mm balloon and I can do that very rapidly before I even bother to take any more angiograms to assess my results. So I get a tremendous amount of information for a 1-2 minute assessment that guides the rest of my case. And, of course, when I finish my stent, I always re-ultrasound to be sure that the stent is deployed like we want.

I just think the integration speeds up the IVUS time so quickly that I think it will lend itself to more expanded uses of the system. Because time, I think, is really a prime obstacle for many people using ultrasound.

IVUS VH™ Virtual Histology screenshot (courtesy of Volcano Corporation) shows both vessel and lumen diameters (top left) and type of tissue (top middle)

Q: A feature of the Volcano IVUS system that you are using is Virtual Histology, or VH, which uses color-coding to characterize tissue and differentiate soft plaque from calcified, for example. How do you use Virtual Histology?
Dr. Foster: There are essentially four instances where I will use it. One, if I’m treating a distal right lesion, for example, that is symptomatic and, if I see a moderate lesion more proximal, I'll IVUS it. It may be that it looks moderate angiographically, but there may be a substantial necrotic core -- a so-called thin-capped necrotic core or “vulnerable plaque” -- I then might treat that with a stent, as well, to prevent what might be a potentially more serious event in the future.

Two, I would use IVUS and VH as another data point to determine in a borderline lesion, say 60%, whether to treat or not. Although angiographically it may look borderline, it may also have a necrotic core.

Three, I use the Virtual Histology feature to quickly measure the vessel diameter and lumen diameter because the software automatically performs edge-detection and gives me this info at the touch of the VH button.

Finally I sometimes use VH to plan out my stent strategy. If there is a calcified plaque, or fibro-fatty atheroma, I might pre-dilate or use a cutting balloon to remodel the vessel prior to stenting and give the stent a better situation to expand in. Also, I will get the diameter information, so I know ahead of time that I might, for example, have a 4.5mm vessel diameter, so I’m going to need an extra 4.5mm balloon to completely expand the stent.

Q: Are there any other ways in which IVUS has impacted your treatment decisions?
Dr. Foster: Yes. IVUS is also very useful in treating in-stent restenosis. We find that 1/3 of the time, what is called “in-stent restenosis” angiographically, is really not an growth of intimal hyperplasia, but is simply that the original stent was not fully deployed or expanded, in which case all we do is re-dilate the stent with a larger balloon, using the IVUS diameter measurement as a guide. The procedure is less expensive because no second drug-eluting stent is used and the result is excellent.

Q: Speaking of drug-eluting stents (DES), has your use of IVUS in these cases made you more comfortable about using them?
Dr. Foster: You’re exactly right. I feel very comfortable in using the drug-eluting stent as long as I IVUS. If I’m confident that I’m getting that stent well-expanded, and all those struts nicely opposed, I’m not worried about stent thrombosis in that setting. My experience has been extremely good, extremely positive in placing DES with virtually 100% IVUS usage. And historically that goes back to sort of day one, when drug-eluting stents came out in April of 2003. At that time my IVUS use was pretty low. In the first 30 days of placing these stents, I had two sub-acute stent thromboses. And one of my partners had one or two as well. And that bothered me a lot, because we’d just not been seeing that since the very early days of bare metal stents. So we sort of said, “Well, why is that?”

Michael C. Foster, MD

So we started IVUS-ing and I saw that many of these stents were just not well-expanded in the artery. So we addressed that, went to more aggressive post-dilation, and after many months went by, we realized we had not seen any more stent thrombosis. That really started my curiosity as well as my habit of IVUS-ing these drug eluting stents. Because our experience is that these stents are harder to expand than the thin-strutted bare metal stents.

Q: Why are drug-eluting stents harder to expand?
Dr. Foster: [Drug-eluting stents] are older stent technologies: they’re thick-strutted and encased in a polymer which I believe must add some sort of resistance to expansion. So we found that we had to work a little bit harder than we did with the thin-strutted, highly expandable bare metal stents that we had gotten used to. I just felt like we were dealing with a different sort of animal with drug-eluting stents as far as the deployment. I don’t think this message has been generally well-appreciated by the interventional community at large. But, in fact, I think we’ve seen in the last year that this is probably part of what we’re dealing with in the DES thrombosis issue. I’ve seen data that says that well over 60% of Cypher stents are under-expanded when deployed at 14 atmospheres.

Q: Dr. Marco Costa recently published a study stating the figure for under-expanded Cypher stents at 66%. Is this really accurate?
Dr. Foster: That was my own experience when I started IVUS-ing in the early days of DES. The problem is, you put these things up to 10, 12, 14 atmospheres and they look perfectly fine angiographically. But they’re really not fine and in an under-expanded state. I think these drug-eluting stents are a little bit of a time bomb in there. Perfectly expanded, they do great. I’ve felt for some time that some of the issues we’re having are not necessarily the fault of the drug or the technology, although that’s certainly playing a role here, but there’s very little discussion about the technique of deployment of these stents.

It sort of reminds me of the early days of when we started putting in bare metal stents. We had this absolutely amazing anti-coagulation regimen. We’d use Dextran in the lab, heparin in the lab. Then, as soon as we put the stent in, we’d pull the sheath. Then we’d go on Ticlid, Coumadin and continue on heparin intravenously until the Coumadin was therapeutic. And for the first six months that we were putting these stents in, the average hospital stay was 7-8 days. It exceeded bypass surgery. There were tremendous bleeding problems, and so forth. And I thought, “These stents are just unacceptable.”

Then Antonio Colombo discovered using IVUS that we were under-expanding those bare metal stents -- that if you really expanded them out well in the artery, you didn’t have to do the heparin, you didn’t have to be on Coumadin. You could just be on aspirin and Ticlid (subsequently we used Plavix) and you could get patients out in 24 hours. It totally changed the way we thought of stents when this was discovered.

I think in a sense we’re going through this same situation with the drug-eluting stent. I don’t think we’ve had quite an appreciation of how to optimize its implantation and I think once we’ve discovered how, we’ll see the true potential of drug-eluting stents in the clinical realm.

And with what’s happening now with the integrated system, it’s going to be harder to ignore IVUS or excuse not using it because the time factor to do an IVUS examination becomes essentially negligible.

This interview was conducted in June 2007 by Burt Cohen of Angioplasty.Org.