Ron Blankstein, MD, FACC, FASNC, MSCCT, FASPC, discusses evolving CTA imaging approaches and new evidence.
Hi, my name is Ron Blankstein. It's a great pleasure to be part of today's program. I will be speaking about coronary ct angiography. Now, chances are if you are a cardiovascular imager and you're reading cardiac ct, you're a lot busier today than you used to be just a couple of years ago. Um If we look at this slide here, this shows data from Medicare beneficiaries showing that in the last decade, in the US whether you're a cardiologist reading cardiac cTR radiologist, reading cardiac cT, you have noticed a dramatic expansion in volume. And if you haven't been paying attention to this field, you may ask, well, why is it, why has there been such a dramatic expansion? And I'd argue there's a couple of reasons for this. First is the fact that cT scanners are simply better today. The technology today allows for much better spatial resolution, much better temporal resolution, which allows us to freeze the motion of the heart. As a result, it's actually easier to acquire cardiac cT scans today. If you have a modern contemporary scanner, you can get very good image quality far better quality than what was possible a decade ago. We've also seen studies and I'll get to those in my talk today that have shown that the use of CT may lead to better patient outcomes. And ultimately this also translates into better value value actually is whether we can improve outcomes relative to cost. And the fact is that CT costs far less than other modalities, there's of course a flip side to that because of the techniques such as C. T. Does not pay well when we look at reimbursement for it. Uh It also means that the physicians are working hard to do cardiac ct. They're probably not generating as many RV US as physicians who may be involved in other exams that that pay better as a result of the improved outcomes. We have seen adoption of C. T. In numerous international guidelines where C. T. Now has a class one indication both in the U. S. And europe and asian guidelines. Um And ultimately also an adoption by clinicians where there's now better understanding of how to use cardiac cT and patient management. Uh In this used to be problematic. I think physicians who maybe were not used to C. T. Would get the results and see mild plaque and they wouldn't really know what should I do as these results. Well today we have a lot more information on that. So let's go over some of the basics. The advantages of coronary cT A still remain as this was the case 10 or even 15 years ago that it's a it's a rapid exam. It's very safe. We actually don't stress the heart. We do give beta blockers often to slow down the heart rate. We give nitroglycerin to dilate the coronary arteries. Uh C. T. A. Is very accurate. It has a high negative predictive value for ruling op stenosis. So when we see a scam such as this where there's no plaque, no stenosis, it's very reassuring. It's associated with a very low event rate but but also allows us to completely exclude any any obstructive disease as the cause of someone's chest pain. The other advantage of C. T. However is the fact that it can detect plaque. This is the type of plaque that we would call non obstructive plaque and this plaque that cT can identify. But a lot of other techniques and stresses would not be able to identify this. Now in the recent chest pain guideline in the US we have recognized that the detection of plaque is actually important. Um You don't always need a coronary cT A for doing this calcium sport can identify calcified plaque into that matter. If you have an old chest ct and you look at that and you see a lot of plaque there. That's also very important information. Regardless of how you identify it. We now have a class one indication in our guideline that when patients have non obstructive C. A. D. It is recommended to optimize preventive therapies. In fact in the recent chest pain guideline we for the first time now categorized non obstructive C. A. D. As being coronary artery disease. What was all that I wanted to share with you why it is actually important to identify plaque. Um well there's a couple reasons first is the fact that in the US most of the stress tests that we do our normal in fact this uh study which is almost a decade old from Cedars Sinai showed that among stable patients the likelihood of finding ischemia in patients referred for a nuclear stress test was only 5%. Not only are most trust as normal but we know from studies such as promise that most patients who have a stress test and go on to develop an event. The most likely finding on that stress test is that the stress test will be normal. And it's not that the stress test was wrong is just that a stress test can be normal even when there's extensive plaque if that plaque is not limiting the blood flow. And because the normal stress tests are the most common result statistically speaking most events end up happening in these patients because these are the most frequent findings on a stress test and often defining even in patients who have a large plaque burden. In fact we have learned that plaque burden is such a strong predictor of future events that in some studies that predicts future events better than stenosis. So once you account for how much plaque individuals have whether they have stenosis doesn't always add to future risk assessment. In fact this is so important that in the recent cad rob statement. This is a statement put together by the S. E. C. T. Um which gives information on how to report ct findings. We actually now recommend that in every cardiac ct report when there is plaque assigned from estimating how much stenosis this is there is we also give a quantification of plaque and this is called the P. Score as P one P two P. Three P. Four corresponding to mild moderate severe extensive plaque. You can do this using a calcium score if one is available a segment involvement score which is a score of how many segments of the coronary tree have plaque or even just a visual assessment of plaque. Of course down the road there's also quantitative assessments but this is not something that we still use in prime time. So regardless of the technique uh clinicians to now report how much plaque there is in every corner. The C. T. A. So it's not just good enough to say how much stenosis but overall how much plaque is there in the study. But I would tell you that the most important reason why we should be reporting a plaque is the fact that when we use this we can actually improve the outcomes. In fact when coronary cT A. Is added to stress testing. As was done in the scott heart study there was a 41% reduction in incident M. I. Or coronary heart disease death in the following five years. So coronary cT A. Was associated with a reduction in hard endpoints. Hard endpoints being M. I. Or CHD death in the US promised study was was designed a little bit differently in that study there was no significant difference in events in patients who were randomized to C. T. A. Or stress testing. However, in a pre specified sub study looking at patients with diabetes would be higher risk patients. There was a lower event rate observed in the patients who ended up having C. T. A. Versus stress testing. So again this is not randomized. This is a retrospective look at these two groups but still shows a signal here that the use of C. T. A. Was associated with a lower event rate. Now in the scott heart uh study the investigators did go back and try to see what drove the reduction in events when C. T. A. Was used in the conclusion was that the reason why C. T. A. Lead to better outcomes is because of better use of preventive therapies particularly in patients was corner disease, that patients who had a plaque. Not only were they more likely to be treated with preventive therapies but that was maintained throughout the study. So you can say okay see ta can show us who has plaque and maybe we'll treat them better and maybe we'll use stems. But I'll share with you that today when we talk about identifying high risk patients was uh who have plaque, it's not just about lipid lowering therapy. There's a whole slew of therapies that I know will be discussed in this course uh that we can give patients who are higher risk when patients have a large amount of plaque, were more likely to use anti platelet therapy. Uh There have been some studies showing that once you have at least a moderate plaque or council score over 100 you're more likely to benefit from aspirin therapy compared to patients who have less plaque. This is based on modeling data. So this is not a prospective trial, but still the concept is that if you have a lot of plaque, your risk is higher. You're more likely to benefit from aspirin than to be harmed from it. If you have a large amount of plaque will probably treat you more aggressively when it comes to blood pressure targets the use of some of the newer agents to treat diabetes. We should be advocating more aggressive lifestyle therapies. Uh of course you don't need plaque to to tell you that lifestyle therapies we should recommend for everyone but patients was a large amount of black. We may want to be even more aggressive and also more aggressive when it comes to lipid lowering therapy and getting the LDL down even more at times using add on therapies like PCSK nine inhibitors. Um, is that a mine or perhaps epidemic acid in the future? So, these would all be agents that we may want to think of. So I talked about plaque and prevention. I want to talk about another potential advantage of coronary ct a and that is in patients who we are thinking of sending to the cath lab. This is a recent study published in the new England Journal Medicine called a discharge trial and enrolled stable patients with chest pain was an intermediate pretest probability of obstructive disease. In patients were randomized to go directly to the cath lab or to have a coronary CT A. Instead in the use of coronary cT A. Was associated with fewer complications. Perhaps not surprising after all, going to the cath lab does have more complications in a non invasive test. When you looked at long term outcomes, it was similar between the two groups and specifically this was cardiovascular desk. M. I. Or strokes are similar, suggesting that the use of C. T. A. Did not lead to worse outcomes because maybe miss disease. Uh So sometimes doing the less expensive, easier tastic coronary ct it leads to just as good as an outcomes. In fact in a one of the endpoints that was looked in this study looked at not just the heart events but also the procedural complication. And if that was taken into account the use of CT actually was associated with a lower event rate. But of course that's not the primary um endpoint of the study. So we cannot really uh pay too much attention to it but still important. But I think another piece of information that is important is that patients who are randomized to coronary CT A. Um In the initial era, only 22% of them actually underwent invasive angiography suggesting that the use of C. T. A. Actually leads to far fewer invasive angiograms and this of course has important cost implications. So with all this information perhaps with the exception of discharge trial which is a more recent trial we have seen in the U. S. A. New guideline. The chest pain guideline for the evaluation of patients is both stable and acute chest pain For the purposes of today's talk. I'm just gonna share with you some of the recommendations for stable chest pain and specifically we now recommend imaging only in intermediate to high risk patients. These are patients that have more than 15% pretest probability of obstructive disease. If you are low risk for recommending deferring test specifically in stable chest pain. But if you have more than a 15% pretest probability you can have a test in coronary CT A. Now has the strongest level of evidence. A um level class of recommendation of one and the level of evidence uh of a which is higher than the stress test where the level of evidence was. B. Um And specifically the recommendation for coronary cT A. Is that it is effective for the diagnosis of coronary disease for risk stratification and for guiding treatment decisions. So at the end of the day you can say that all our tests really have a class one indication which is great but for clinicians that challenges well how do we choose between C. Ta versus stress testing and obviously a lot of this depends on the local availability and expertise. Um You know my talk today is on coronary ct and it's a great test but it's only a good test if you can get good image quality. So if you happen to be at the institution where maybe corner C. T. Is not very good with respect to quality you can get very good pet or stress M. R. I. Then perhaps that would be a better test. But assuming you can get all the tests how do we choose between them? Well in the guideline generally we state that Corner CT may be preferable and younger individuals who are not an optimal preventive therapies. And the reason for this is the fact that most of the time when we do a test like C. T. A. We may find non obstructive plaque. The type of plaque that will not require more tests or invasive angiography but the type of plaque that may prompt more aggress preventive therapies. And if we would have done another test and seen a normal result that change in therapy might have not occurred. So that's why C. T. Is preferable in this particular population. And on the converse individuals who are older have a high likelihood of having ischemia uh stress test may be preferable. Ultimately we favor the use C. T. A. For our objective is to rule out obstructive disease network to identify non obstructive disease. And we favor the use of stress testing in the guidelines. If our objective is to perform what's called ischemia guided management where we try to identify if the patients have ischemia and if they have more ischemia generally we would be more inclined to send them for invasive angiography. So let's say you start with C. T. A. Because you have a patient who is not an adequate preventive therapies. Um And you may now ask, well what about after the coronary cT A. When should you go for invasive angiography? And in the guideline um we now state that really the only patients that we should proceed for invasive angiography or patients who have high risk anatomy or frequent angina. So this is patients with obstructive disease who have frequent angina. They should go to invasive angiography or high risk anatomy which is defined at the bottom of this slide here as patients who have three vessel disease or left main disease. What if you have obstructive corner disease and you don't have frequently engine or you don't have high risk C. A. D. Uh Should you still go for invasive angiography. And at this point you have an option you can do a stress test which would have a level to a evidence. Or you can do an F. F. R. C. T. Also level to a evidence specifically when it comes to FFR CT. We in the guidelines state that this may be useful if the anatomical legions are in the proximal of mid vessels. And this may be useful for legions that have a 40 to 90% stenosis. This is not to say that every 40 to 90% legion needs an F. F. R. C. T. But if you are uncertain if that patient would benefit from revascularization, If you are uncertain if this is a flow limiting legion. This is where a stress test or an F. F. R. C. T. May be helpful in deciding on the role of invasive angiography uh in hence revascularization moron moron effort for uh C. T. I think some folks may be familiar with this. But this is a uh noninvasive technique that uses the same coronary cT A data. So there's no need for any more uh imaging or any more radiation. And it takes that coronary cT data and uses computational fluid dynamics to estimate what the invasive FFR would be in multiple studies, including several multi center studies showing a high accuracy of the FFR CT to invasive FFR. But beyond just the accuracy. I think one of the important pieces of data comes from the advanced registry and this is a registry uh that really looked at what happened in the real world and importantly when patients have an F. F. R. C. T. That is more than 0.8 which we would call negative. They do very well with a very low event rate. So this data at least tells us that it's safe to take these patients who have stenosis who have legions that maybe flow limiting. If the FFR CT is more than 0.8 we can defer invasive angiography and do so safely. One piece of data that I think is very uh exciting as a trial. Known as the precise trial. This is a trial that actually randomized uh patients to corner C ta with FFR CT versus standard of care. We don't know the results of this trial but this will be presented at the H. A. Meeting later this month. So stay tuned. I think that will be another piece of information that will be important for us to understand how FFR CT performs when we compared to standard of care. So when we talk about the chest pain guideline, I mentioned that uh there's several principles that are important. One of them is that we try to defer testing and low risk patients. Uh The guideline now is based on a lot more evidence than we ever had in prior guidelines to. That's good. We try to be more selective in choosing between different tests. We are recommending imaging as a gatekeeper to the Cath lab specifically among patients who have stable chest pain who generally should always have imaging before going to the cath lab coronary artery disease Now also includes non obstructive plaque and throughout the guide lenders really a lot of emphasis on prevention and plaque imaging in the fact that patients who have plaques should be implemented on preventive therapies. Before I end, I just want to share with you a couple of other kind of exciting things about coronary CT A for the future. One potential application is something known as the fat attenuation index and this is the ability to look at the fat around the coronary arteries, look at the hands field unit and specifically come up with these maps that looked at the fat attenuation index and identify patients who are more likely to have inflammation in that fat and that usually is a signal that there's inflammation in the coronary arteries. So the ability to look at coronary ct A data and look at two patients who have the same amount of plaque but identify that one of them is far has a far higher level of inflammation. I think this is exciting. It may tell us why some patients progress more than others. It may ultimately be used to identify patients who may benefit from anti inflammatory therapy. I did not get too much into high risk plaque features. And there's still some debate that these really gonna add on top of quantitative plaque on top of how much plaque individuals have. But we do have various um plaque features that we look when we read coronary cT ace such as positive remodeling or low attenuation plaque. These generally show us legions that have a larger burden of plaque, a larger burden of lipid rich plaque and those are associate was was higher risk. These are these are important as well. And finally there's also down the pipe uh multiple vendors that will have the option to quantify plaque and it's going to be a fully quantitative score. So just like we have a calcium score today when we do a calcium score will have a score that tells us how much plaque and what type of plaque individuals have. This may enhance our ability to identify higher risk paid. Even though we need more studies on this. And this may also help us identify how patients are responding to therapy. So for example here's a slide courtesy of one of my colleagues. Andrew choi A. G. W. Showing at baseline of 55 year old male who has a plaque here in the L. A. D. And then two years later on preventive therapy showing actual regression of plaques, a certain reassuring to this patient as opposed to a patient who may progress over time and the patient and progresses. Maybe we would then want to implement even more aggressive therapies or at least be aware that our therapies are not working specifically when we do so. In this case we can see a reduction in stenosis from 68% to 31% but also regression in the non calcified plaque. So a lot of parameters that will be able to follow in the future certainly will need more trials to show us what all these mean. But I think this is gonna be the future that when we look at the corner of C. T. A. It's not just going to be about the visual estimation of plaque, but we're actually gonna have a quantitative assessment of the burden of with all that. Thank you all very much. I'll be happy to take any questions during the discussion.