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Justin E. Davies MBBS, MRCP, PhD

Dr. Justin Davies is a Walport Clinical Lecturer in Cardiology at the National Heart and Lung Institute of Imperial College London. His work has led to development of the reservoir pressure model, which has been shown to be highly predictive of cardiovascular events in 2069 patients in the CAFE sub-study of the ASCOT trial, and to describe the minimum pressure needed to overcome the compliance and resistance of the aorta.

Dr. Davies is principal investigator for the ADVISE (ADenosine Vasodilator Independent Stenosis Evaluation) study which is testing the development of new methodologies for determining the severity of coronary stenoses and measuring fractional flow reserve (FFR) without the need for administration of pharmocological vasodilators.



Justin E. Davies MBBS, MRCP, PhD
Dr. Justin E. Davies

Q: You have developed iFR -- a new way to measure intracoronary pressures that does not require the use of adenosine infusion. What is the difference between standard FFR (Fractional Flow Reserve) and iFR (Instant Wave-Free Ratio™) in terms of the patient's experience?

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Dr. Davies: With FFR, it's not a very nice experience. You warn the patients beforehand. They become short of breath. It only lasts for the duration of the infusion and it wears off very very quickly, but for that period of time, it's not very pleasant. So if you're performing an assessment using an infusion line, that may mean one or two minutes of the patient not feeling great. You may then want again to repeat it because you're not sure you've got the stability. So often you've got two, three, four minutes of the patient not feeling great. Now most people can tolerate that, but obviously in cardiology we're always trying to improve things. And the huge difference with iFR is that once we've got the wire into position to make the measurement, whereas with standard FFR you normally would just start the adenosine infusion, here with iFR we would be in a position just to push the button, make a recording of five beats and that's it! So with iFR, for the patient, they are unaware the measurements are even being made. For them it doesn't make any difference.

"...without some kind of documentation now, [doctors] may not get reimbursed or, even worse, they may have legal cases brought against them."    

Q: If you can't use adenosine, necessary in standard FFR, aren't you excluding a subset of patients who are typically much sicker and might benefit from intracoronary pressure measurement?
Dr. Davies: You're absolutely right. For example, if you've got the potential for bronchospasm or asthma, people who may have some block in the conduction systems for the heart, which adenosine could actually make worse, and which can cause the heart to go into heart block. Then you've got people whose blood pressure is low-ish already.

If their blood pressure is less than a mean of 60mm mercury, recommendations are that you have to infuse fluids an get their blood pressure up to 80, 90. Because we know that if you don't do that, the relationship between pressure measurements begins to fall apart and your FFR measurements can become unreliable.

Most multivessel disease patients have some LV impairment so their pressures are a bit lower. People aren't widely aware of these things although they are in the guidelines, but if you look in the physiology writings of Nico [Pijls] and Bernard [De Bruyne] you'll see that the linear relationship towards the end of the curve starts to deviate off and that's why there's a caution in the AHA guidelines for this exact reason. So iFR has applicability to all of these groups of sick people.

Q: My understanding is that the iFR wire is in fact just like a standard guide wire, so you can utilize an IVUS or OCT catheter over this iFR guide wire. Can you also use the FFR during the procedure to assess your progress?
Dr. Davies: Absolutely right. I expect long term this would be the kind of vision not only to make your initial assessment using an iFR type wire, but then to do your angioplasty and then at the end or maybe in between angioplasty get values to see how your treatment is going.

So, for instance, you may have two lesions, even though you're starting iFR at 0.6, you put one stent in and then literally all you have to do is connect up, wait 5 seconds and you get a value of 0.8, and you know you haven't reached the 0.9 threshold yet, and then you put another stent in. connect up again and take another measurement. And maybe it's 0.93. Of course you can do with adenosine but no one does it because it all takes so long. You have to do an infusion every time, get more drugs up from the pharmacy.

What this does is facilitate better practice. And this, I suspect, is helpful in the U.S. where you have the appropriate practice guidelines. You know, people were just putting stents in just because they think the lesion looks tight on angiography -- and without some kind of documentation now, they may not get reimbursed or even worse, they may have legal cases brought against them.

But the other thing, apart from just making that diagnostic assessment, is that at the end of the cases we currently look at angiogram images and we say, "Oh it looks like a good result, an excellent result," or whatever. But there's no measure, which is strange for cardiologists because normally we like to put numbers on things. You could do this with FFR, but it takes too long. But if you're using the iFR wire to do angioplasty and you don't need to give drugs, literally in this case, you just make a measurement. So one advantage of using this technology that at the end of the case, every single case, you have a value, 0.9, 0.93, whatever it is. And that gets documented in the patient's notes and maybe people even get judged by that as to how successful they are.

Q: There's a saying that if you don't want to stent, use FFR, if you do, use IVUS. But from what you are saying, you can use iFR as a way of helping you do the procedure better, not just to judge whether you should do the procedure or not.
Dr. Davies: Personally I feel there's a role for both IVUS and FFR, and iFR. There's all the comparison studies between IVUS and FFR: you know the relationships are there but they're not great. And the reason for this is that they're trying to focus on one tight lesion and, of course, doing that they ignore all the small little lesions which affect the pressure all along the length of the vessel. Functional measurement (FFR or iFR) takes into account all of those things, but it's not great to see if you've got good wall apposition, have you pushed the center up to the really high pressures to know you've deployed the stent. That's where a tool such as IVUS is really the gold standard. So really I think a combination of FFR, iFR for physiological assessment, and IVUS assessment for seeing how the stents are being deployed will give you all the information you need.

Q: When Andreas Gruentzig invented coronary angioplasty, he always measured intracoronary pressures before, during and after the balloon dilatation. He felt it would be impossible to judge the procedure without them. Are we going "Back to the Future" here?
Dr. Davies: He was absolutely right. Of course, Gruentzig was very limited by the technology and the tools of the day that he had. Now we have these fantastic pressure wires which Bernard [De Bruyne] and Nico [Pijls] didn't have when they developed FFR and that's why they really went down the route they did in terms of having to use mean resistance reductions and giving a drug.

We don't have that. And we also have a huge concentration of computing power. You know all our mobile phones have got so much power compared to the most advanced computers 10, 15 years ago, so it's relatively easy for us to develop algorithms that are quite complex but can be put on a console which works in a very simple robust and reliable way to give us effectively a measure of the severity of stenosis. iFR is taking on board all of the advances of technology over the last 20 or 30 years while still sticking to the basic physiological principles of which FFR or pressure flow relationships are founded upon.

Q: The device is called iFR™ -- is that a reference to the iPhone, iPad, etc? And how is it that Apple hadn't already taken the trademark?
Dr. Davies: Hah, right! We called it that because it's an "instantaneous wave-free ratio. It's instantaneous because it's very quick. But you also can actually make the measurements at any moment in time over the wave-free period effectively. We've chosen to make it over the whole period because it gives us a lot of robustness and stability. But it is instantaneous which means that you could potentially do all kinds of other assessments to get an idea of serial stenoses. I think this is one of the areas which this technique will probably be potentially important, because we don't have the problem of having to give adenosine or of distal pressure reduction. The problem with serial stenoses is you have one stenosis after another and they both effectively affect the pressure on either side. Whereas if you are looking at the entire length of the vessel, it's just the whole mass of the stenosis resistance effectively. This is an area that we are doing work on right now and will be talking about more in the near future.

This interview was conducted in November 2011 by Burt Cohen of Angioplasty.Org.