International Circulation: What is the optimal indication of IVUS? Do you think IVUS should be a routine test during PCI procedures?

Prof. Mintz: There are a few institutions that use PCI routinely， Japan， most noticeably， but maybe couple of other institutions in U.S. It is hard to argue that it should be used in all procedures because quite frankly， certain patients and certain lesions are so low risks for events， that it will be impossible to prove that IVUS adds benefits in terms of reducing patients’ complications. The way I try to explain it， is whenever you have a high risk patient with a lesion subset， that IVUS makes sense. And it is well documented what situations are high risks for restenosis， or high risks for stent thrombosis， or whenever you have a clinical scenario， where you have one or more of those risk factors. That is when IVUS makes the most sense.

International Circulation: Is it a cost versus the benefits as well as in the low risk patients? the extra cost of complications?

Prof. Mintz: Complications are not an issue. Cost and course is an issue but even just proving benefit. For example， if you are dealing with a clinical situation， where the combined risk of restenosis and stent thrombosis is 5% or 6%， how are you going to prove that IVUS helps， unless you do a study of thousands and thousands patients. There are now three studies that have shown that IVUS doesn’t prove a patient outcome， but they have been used in more complex patient with lesion subsets.

International Circulation: Is it really not that all probable to use IVUS to replace angiography to evaluate the therapeutic effect of PCI in the future? Or it will be a replacement?

Prof. Mintz: That is a complicated question. In U.S.， for device of approval， you have to approve clinical efficacy and safety. The FDA clearly wants clinical benefit. But the FDA is also very interested in mechanistic information and the safety information. So what now typically is happening， is you have a large clinical study， you have an angiography sub-study， and then an IVUS sub-study of the angiography study. So it is almost here to approach， a big clinical group， a smaller angiography group， and a smaller IVUS group. Obviously， you can’t do IVUS without doing angiography. So to say that IVUS will replace angiography， I think it is unlikely especially if we are talking about accessing future therapeutic techniques. However， there are all circumstances where IVUS adds information that is simply not available angiographically. The Drug-eluting stent issue such as stent malaposition is not detectable by angiography. Or looking at vascular effects， or looking at edge effects. In this progression regression arena， IVUS holds the tech-plaque progression regression that can not be detected angiographically. But as I said what seems to be happening as it is here to approach， large clinical studies， angiographic sub-studies， and then either sub-studies of the angiography population.

International Circulation: Would IVUS cut down the incident of stent thrombosis while using DES stent?

Prof. Mintz: First， we talk about stent thrombosis. The arc definition talks about early， late， and very late， early within a month， late within a year and very late beyond a year. There are now at least two studies clearly showing that IVUS will reduce early stent thrombosis. However， it probably would not reduce very late stent thrombosis which I believe is a biologic phenomenon， not a mechanical phenomenon. What IVUS does improve is the implantation procedure and eliminates any mechanical problems with the stent. The mechanical problems have more effect early， and the impact disappears over time. I don’t know what the exact cut-off is， but somewhere between a month and a year the effect of IVUS in reducing stent thrombosis probably would taper. And beyond a year probably has no effect， what’s so ever.

International Circulation: Sometimes IVUS could help to identify potentially high-risk lesions with thin-cap fibroatheromas that were considered non-culprit by angiography. How to deal with those lesions if there is not significant relationship with the patient’s condition? How to identify the vulnerable plaque by IVUS?

Prof. Mintz: Well， grasculivous? can not identify vulnerable plaque. Grasculivous? is not to identify thin-cap fibroatheromas. So that is just not a possibility. Some of the newer techniques such as virtual histology can identify lesions with a large necrotic core close to a surface. The question is whether those lesions will be at higher risk of events. There is currently a study that our group has led by Grastone is the personal investigator called “Prospect”. It’s a three vessels IVUS virtual histology study in which about 7 hundred patients either ST-segment elevation or non-ST elevation. And mine underwent IVUS and VH of the culprit arteries and all three arteries have been followed up for several years. And we just about finish to follow up and we will look to see whether the virtual histology detection of the large necrotic core close to the surface predicts the events. I don’t know if it will， I suspect not. And I suspect IVUS per se will not be available to detect the vulnerable plaque if by that you mean the plaque is slightly the cause of event over the next year. And certainly if we see such a lesion now clinically without any hard data showing that this type of lesion will in fact cause an event over the next year. There is no indication to treat it preemptively.

 International Circulation: What is the difference between the intracoronary OCT and IVUS? What is the advantage or the disadvantage of the intracoronary OCT?

Prof. Mintz: Intracoronary OCT should be thought of as the light analogue of iris. That is not really a correct statement but it’s an easier way to understand. Light has very short wave compare to ultrasound. And anytime you have an imaging technique with very short wave length， the resolution increases but penetration decreases. So OCT has incredible near field resolution on the order of 10 microns， which is at least 10 times better than IVUS. However it cannot see through blood field which means you have to flush the artery before doing OCT. And that has limited penetration. But within its limited view， you can look at plaque composition. It can access lipid， fibrous tissue and calcium. It can even detect macrophages， because it can detect very thin structures. It can look at very thin fibrous caps that maybe more rupture prone.  And after stent implantation， it can look at subtle findings of malaposition， plaque prolapse， thrombus information， and edge trisection. And if followed up， it can detect small amounts of new intimal coverage that is simply not visible by IVUS. It is currently been highly touted， as a way of accessing stents of follow up， particularly the ability to access the amount of new intimal coverage and also the amount of thrombus. IVUS for example is very poor in detecting thrombus. OCT can not only detect thrombus but can differentiate red thrombus from white thrombus. The two techniques in truth are complimentary. The problem is no one is going to do both techniques. I have seen designs where manufacturers and engineers indicate that they should be able to combine both imaging technologies in a single catheter. So they can actually be done on the same imaging run. That case will be able to merge two technologies and get the best out of both. But in terms of routine use in the catheter， the current time it really was very little place for OCT， because everything that we do in the catheter， in terms of sizing stents and so on， requires penetrat