We learned a lot producing this episode and hope you do too! ACP members can claim CME-MOC Credit !

Time Stamps

  • 3:10 What are the big picture differences of functional stress tests and anatomical cardiac tests?
  • 7:48 What is coronary artery calcium scores’ role in managing coronary artery disease?
  • 16:20 How do coronary CTAs compare to stress tests?
  • 24:28 When should we avoid CTA?
  • 29:33 How do we communicate coronary CTA results with patients?
  • 36:02 Recap

Show Notes

Pearl 1

Pearl 2

Pearl 3

  • Coronary CTA is simply a gated arterial phase contrast CT study that allows us to visualize the coronary arteries.
  • We have randomized trial data that not only are these non-inferior to functional stress testing when it comes to death, myocardial infarction, hospitalization for unstable angina, or major procedural complication.
  • There is the potential to reduce death and non-fatal MI using coronary CTAs over standard care.  
    1. Patients undergoing coronary CTA as opposed to functional stress testing are more likely to be initiated on preventative, mortality-reducing therapies. 
  • Added benefits to coronary CT:
    1. Detect atherosclerotic disease that wouldn’t get picked up on with either stress test or even a  coronary angiogram because it’s also not encroaching on the lumen
    2. Coronary CTA also picks up plaque morphology, such as with thin-cap fibroatheroma or “soft plaques”
    3. Coronary CTAs can also be used to identify congenital anomalies and are routinely done prior to afib ablations to evaluation pulmonary veins and sizing for aortic valves for TAVR.

Pearl 4

  • Avoid coronary CTA in patients with elevated or irregular rates, frequent ectopy, or a history of prior stents. Also, it is generally a poor choice in the elderly or obese. 

Pearl 5

  • Coronary CTAs have a high negative predictive value and therefore, a CCTA without plaque burden can give reassurance that a patient’s symptoms are not from a cardiac source.
  • Coronary CTAs with obstructive coronary lesions, the decision should be made on a case-by-case basis with the cardiologist regarding revascularization and/or optimizing medical therapy.

Transcript

Pearl 1: Big Picture Functional vs. Anatomical Cardiac Testing

E: Guys, as you know, after reading so much about stress testing, I think I’ve identified an underappreciated concept that a lot of us don’t fully realize.   

M: Lay it on us bub

E: When we think about stress tests – like all the different iterations of stress tests that we labored through last episode – they’re actually only half of the story when it comes to diagnostic tests to risk stratify CAD.  

S: Wait, you gotta be kidding me. There’s more?!

E: Yes, yes – a whole episode worth more! There’s actually two broad categories for CAD testing: functional tests and anatomical tests. Functional tests was the last episode – studies like exercise ECG, stress echos, and nuclear tests.  There’s a whole other category of testing – anatomical tests

M: oh man I feel the stress bombs coming… 

S: for sure!  So maybe it’d be helpful to contrast the two types of testing… so what I took away from the last 5 Pearls is that functional stress tests tell us the physiological consequences of an obstruction. so when a patient undergoes a stressor, these test help me understand is there ischemia – which is shown with things like EKG changes or wall motion abnormalities.  But sounds like these functional stress might not give the most complete picture:

PAMELA DOUGLAS: the stress test you just have a no ischemia, but there could be, you know, the, the, the iceberg below the surface that you don’t know about and you absolutely visualize that with the CT.

E: As Dr. Douglas points out, these functional stress tests don’t tell us about the coronary anatomy of our patient or amount of plaque burden

M: Cue the anatomical tests! Typically we think of these as various types of coronary CT imaging.

E: Right – and we need to be careful about how we use the term “coronary CT” which often gets thrown around.  Coronary CT is an umbrella term that includes couple similar but separate tests, both of which involve: coronary artery calcium scoring and coronary CT angiography (or CTA). 

S:  Great so continuing with big picture framework – we talked about the downside of functional stress tests only tell half the story, are there any downsides to these anatomical testing? 

M: Right so while anatomical tests provide us information about a patient’s coronary anatomy and plaque burden, but they don’t give us info if that plaque is causing ischemia.

PAMELA DOUGLAS: It’s entirely possible to have a tight lesion – an anatomically tight leads in that does not cause flow disturbance and in fact is quite common.

S: So I am hearing so far from this pearl in terms of coronary artery disease risk stratification testing, we have in our arsenal the functional tests, which are the classic “stress tests,” which tells us about ischemia but NOT structure then we have  anatomical testing – such as coronary CTs that include calcium scores and coronary CTAs that help us better understand the plaque burden but don’t tell us necessarily about is that plaque is causing ischemia.

E: But not so fast with that recap, Shrey. Dr. Douglas is quick to remind us that with new technology, such as Fractional flow reserve CT, aka FFR-CT –we might actually be able to get both anatomical and functional information.  

PAMELA DOUGLAS: Ffr CT is obtained from, it’s not, um, is obtained from already acquired CT anatomic images, um, through, uh, big data process to model coronary flow. And it actually models, um, hemodynamic significance of lesions, much as invasive fractional flow reserve does, which is the invasive FFF, fractional flow reserve itself to be the gold standard for coronary lesion.

S: For us non-cardiologists, the invasive FFR Dr. Douglas is referring to happens in the cath lab. Remember,  in the cath lab, you’re trying to see a narrowing of the lumen, but during the procedure, cardiologists can also use something called “fractional flow reserve” – a special test tell that tells us the hemodynamic significance of a lesion – and that’s all done invasively. So that’s the cool thing about FFR-CT is that it’s NON-INVASIVE and uses high quality CT images, puts all those images together, does some crazy math, and gives us actual information about blood flow across lesions.

M: [Obnoxious “mind being blown sound” effect from Marty]. That’s the sound of my mind being blown. But a major caveat is that some of that FFR-CT technology is proprietary – meaning still super expensive.  We put it here for completeness sake but for the reminder of this episode, we’ll focus mostly on coronary artery calcium scoring and coronary CTA as these are the tests us internists are more likely to encounter on a day-to-day basis. 

Pearl 2: Coronary Calcium Scoring 

S: Let’s kick off the tour de coronary CT with calcium scoring.  I am a hospitalist these days and I see coronary calcium ordered from a patient’s prior clinic visits or sometimes its added to a coronary CTA, but frankly I really don’t know what to do with it. I’d really love a who, what, when, where, why run-down on all things coronary calcium score.  

M: Yeah let’s get into the basics here.  Coronary calcification generally means advanced atherosclerosis, and-it-matters…  coronary calcium has been demonstrated over and over again to be independently associated with coronary heart disease in asymptomatic people and poor prognostic factor in those folks who do have coronary disease.  

E: The test to detect coronary artery calcification is pretty simple – just a non-contrasted chest CT that takes only about 10-15 minutes and zooms in on the coronaries.  

S: Nice, but how does this non-CT come up with the coronary artery calcium (CAC) score? In order words, what does the coronary calcium score actually mean? 

E: Basically if there’s calcium-laiden plaques, its  density is measured in Hounsfield units and then multiplied by the area of the lesion. So the computer is really just adding up the total scores of all of the lesions to give us a composite score that reflects a patient’s total coronary plaque burden. 

S: Okay, great so if the score telling us, in a standardized way, the degree of calcified plaque burden, then what scores should worry us more than others?

M: The short answer here is that we should be concerned about anyone with a score greater than 0.  To help give you ranges, a lot of studies that stratify patients into groups – usually 0-100, 101-400 and above 400.  

E: It’s important to realize that the score isn’t the only thing we care about.  A calcium score of 50 in a 35 year old man is very different from a calcium score of 50 in an 80 year old woman.  To get a complete picture of someone’s risk of coronary disease, we have to also factor in a patient’s age, race, gender. So to the rescue is a calculator to help us do this: the Mesa calculator.  It’s generally thought that anything above the 75th percentile for the age, gender and race warrants a statin. 

M: Yes – Mesa calculators are super important in interpreting a CAC score.  Just to build out the differential benefits of statins as CAC scores increase, I want to mention a really nice  2018 paper published in JACC by Mitchell et. Al.  The authors showed that as CAC score increases, the NNT with a statin drops.  So, if a patient’s calcium score is relatively low, let’s say 1-100, the NNT with statins is 100 to prevent a patient’s 1st major adverse cardiovascular event (MACE). But,  if that score is >100, the NNT with a statin drops to 12 to prevent a patient’s first major cardiovascular event.

S: Nice, thanks for setting that up. What about the opposite end of the spectrum of the coronary calcium score? How does a calcium score of ZERO help us? 

E:  So a score of zero might be the most helpful score of all. There’s this really compelling idea coined by Dr. Nasir from Yale referred to as the “power of zero.” The TL;DR version of this is that patients with a CAC score of 0 don’t need to be put on statin therapy, and statins are not associated with a reduction in major adverse events in this group.

M: So this idea of power of zero is super important because a lot of factors for intermediate risk folks- (S: those 5-20% 10-year ASCVD risk) – that increase your concern for those patient – things like premature heart disease in the family or autoimmune disease like rheumatoid arthritis – all of those things increase risk, but there’s not a lot of things that decrease risk for a patient. There really isn’t anything that lets you decrease concern. A CAC score of 0 is one of those things! It lets us downgrade a person’s risk from intermediate to low risk, and that is really powerful. It basically lets us confidently identify previously-intermediate risk patients as low risk, and as such, NOT needing statins!

S: That is what Marty would call a Stress Bomb! 

E:  Oh boy, here we go . . . 

S: Yeah, that one was really well deserved. It was such an important point for me, too. Okay, let’s change gears to how we actually uses these calcium scores. Okay, putting my hospitalist hat back on, I’m thinking about patients who come in for chest pain and how do we use calcium scores in that? 

GREG KATZ: Calcium score has no role in the evaluation of chest pain. I’m gonna repeat that: calcium scoring has no role in the evaluation of chest pain. 

M: Alright then… 

E: Yeah, Greg was pretty unequivocal that calcium scoring is only for asymptomatic patients, and for good reason.

GREG KATZ: It [CAC] doesn’t tell you anything about soft plaque, it doesn’t tell you anything about obstruction, it doesn’t tell you anything about whether somebody’s symptoms are related to coronary disease or not.

M: What Greg is pointing out is that even a calcium score of 0 doesn’t necessarily mean absence of coronary disease – it just means absence of coronary calcification.  

S: Alright, it’s telling me just about the calcium, I get that. But wait – what does Greg mean with all this “soft plaque” business? 

E: Basically, plaques with a lot of calcium might actually be more stable compared to these quote unquote soft plaques sometimes called thin-cap fibroatheromas – or TCFA pronounced tick-fuh’s for those in the biz.  Unlike the calcium ladien plaques, these soft plaques have thin borders and large lipid cores, and are more likely to rupture.

M: Ohh lipid core, like twinkies in your LAD.  Maybe canolis are a better visual?  

S: I prefer to think of them more as poached eggs. Looks stable but can ruptures easily on you!

E: We may have just ruined brunch for everyone! Getting back on track, so while it’s rare to have vulnerable plaque without other calcified plaque around, the takeaway is that in a patient with active CP the calcium scoring can miss these so-called “soft plaques” which may very-well pose a high risk for a patient. 

S: Right, right, so in the spirit of high value care, what then is considered appropriate use getting CAC scores?

E: The current appropriate use criteria essentially only recommend calcium scoring in the risk stratification of asymptomatic patients who you are not sure about their cardiovascular risk or if they may or may not benefit from a statin.

M: And there are a bunch of situations where we find ourselves here – the patient who is skepetical about starting a statin despite a ASCVD risk score in the teens, or maybe that a middle-aged patient with a risk score of 5.5% but with a family history of premature heart disease.  The 2018 AHA/ACC cholesterol management guidelines (page 15) actually has some concrete examples where this test has really high yield so we’ll that in the notes of this show. 

E: Right, so calcium scoring is really is a clinic tool – not an emergency department tool – we’ll get to those in a minute.  

S: Last thing – any limitations we should know about before we wrap up calcium scoring? 

M: For sure. It’s worth noting that CAC might be less helpful in your elderly patients.  It’s common to have calcification as we age so it’s less useful differentiating low risk within that population.   

E: Another possible limitations that your patients may ask you about is the radiation exposure with these scans.  On average they are 0.9 mSv a pop, which is pretty low compared to annual background radiation of 3 mSv.

S: That is definitely handy to know, so let me recap what I’ve learned here: basically, calcium scoring  entails a quick non-con CT that tells us in a standardized way about a patient’s coronary calcium. The score can help us in our us in our asymptomatic patients who are intermediate risk for coronary disease and there is some question about the benefit of statin therapy – particularly, theres the “power of zero” coronary calcium score that can actually help me reclassify patients.  The caveat to using the score is that not as helpful for risk assessment in our elderly patients, say over 70s or 80s, who might already have a lot of calcification with age. And it’s also not helpful in patients with symptoms, i.e. chest pain, mark this test off the list aka watch out for the soft plaques. 

M: Or twinkles! Or poached eggs!

S: Team poached eggs!

Pearl 3: What is coronary CTA, and how does it compare to stress tests?

E: So let’s move on to coronary CT angiograms, which we’re going to shorten to coronary CTAs

M: Let’s make it happen Captain.  Alright, I feel like I’m seeing more and more patients in clinic who have had a coronary CTA – perhaps done in the ED when they presented with chest pain – but I gotta be honest it’s not something I routinely order. 

S: So let’s breakdown first what exactly a coronary CTA even entails.

E: So, again, we’re talking about putting the patient through the CT scanner, just like for coronary calcium scoring. The biggest difference here, though, is that the study needs to be gated – meaning synchronized to the EKG.  To do this patients will likely receive a splash of metoprolol to slow the HR, a hint of nitroglycerin to dilate coronary arteries, and a squeeze of IV contrast to visualize and virtually reconstruct the coronary vasculature. So, basically, nothing too crazy. 

M: It’s like easy bake CT cooking!!  Just add garnish and sprinkle with a generous portion of rosuvastatin… 

S: You really must be hungry… the part that I think is interesting how Coronary CTAs are being incorporated into guidelines. Dr. Douglass put this in perspective for us 

PAMELA DOUGLAS: the US guidelines, differ really dramatically from the European and even moreso from the UK guidelines. In the US, we say you should use a stress ECG unless the patient can’t exercise, then you use a pharmacologic stressor unless the ECG is uninterpretable. In the UK, there is no, the guidelines have no role for a stress test in that clinical scenario. None. Zero . . . and the first test is a CT angiogram.

S: What Dr. Douglas is referencing here are the National Institute for Health and Care Excellence, or “NICE” guidelines in the UK. (M: Niiiiiiiiiice) Thank you, Marty.  These guidelines were updated in 2016 to include coronary CTA as the first-line evaluation for stable chest pain.

E: This change was influenced in part by the PROMISE trial. This was a big deal in the Coronary CTA world – it was a RCT that randomized low-to-intermediate risk symptomatic patients in a 1:1 fashion to either a functional risk stratification strategy or a coronary CTA.

M: And what the PROMISE trial showed was that there was NO difference between the functional stress test group and coronary CTA group in the primary endpoint, which was a classic mash-up of cardiovascular badness after 12 months of follow-up. 

S: The real kicker is was looking into the people who did end up getting a left heart cath. So, the people who came from the functional stress testing group were significantly more likely to have a cath that showed no obstructive disease. So, in other words, you were less likely to go for a meaningless cath if you were in the coronary CTA group. 

M: Also NIIIIICE

E: Another compelling study to know is the SCOT-HEART trial. As the name implies, this study was conducted in Scotland, and looked at patients with chest pain being referred to ambulatory cardiology clinics. Patients were randomized to either a “standard care” group or a standard care plus coronary CTA group. 

M: This study was pretty shocking because it demonstrated a 1.6% absolute reduction in the primary endpoint of coronary heart disease death and non-fatal MI in the coronary CTA group, which translated into a whopping 40% relative risk reduction.  That is certainly nothing to sneeze at.

E: Is that a thing?  Do people sneeze at unimpressive trial results?

M: I don’t know Evan, it just felt right.    

S: Wait, but seriously, how could running a patient through a CT scanner alone reduce Coronary Heart Disease death and non-fatal MI by so much?? I mean, what are CT scanners made out of in Scotland??

M: Whiskey.  Kilts?… Bagpipes… [FREEEEEEDOOOOMMMM!!!]

E: Oh man, classic William of Orange… Now, subsequent analyses demonstrated that the reduction in the primary endpoint was driven primarily by the reduction in non-fatal MI. But, the results were still eye-opening to cardiologists. Why would simply putting a patient through a CT scanner have such a dramatic impact on mortality and MI? Great question Evan, I’ll answer that for you… As it turns out, patients in the coronary CTA group were far more likely to be started on evidence-based therapies like aspirin and statins than those in the standard care group.

M: There is something very powerful about being able to see the location and type of coronary plaques – for both physicians and patients!  It’s one thing to say ‘your stress test was positive’ and another to say ‘My man you have plaque and it’s RIGHT THERE.’ 

S: You guys can’t see Marty but he is emphatically pointing directly into the webcam… 

M: I’m pointing straight at my imaginary patient’s RCA…  Because studies show that’s the best way to get someone to take their statin… 

E: Please note, we have no evidence to support that claim.  Dr. Douglas helps us put these landmark trials into context

PAMELA DOUGLAS: there are very few times that we have a noninvasive test or diagnostic test that we can directly connect that with an improved outcome. Here we are able to directly connect by a randomized trial a better outcome

Both of those trials and a few other ones ( PACIFIC and SYNTAX ) clearly showed that use of a CT improved preventative care over use of stress testing, and that may well be the mechanism for the benefit. But needless to say, when you’ve got a real 40% reduction in hard endpoints, that’s kind of a hard effect to ignore and say, ‘You should use stress testing instead of CT.’

S: One reason coronary CTAs might be so useful is that they actually give us information that even traditional coronary angiography can’t.

PAMELA DOUGLAS: it’s a very important limitation of conventional angiography which you identified as that the lumen can be unchanged in spite of a significant plaque burden.

E: And this gets back to the pathophysiologic process of atherosclerosis itself:

GREG KATZ: CTA gives you information that cath doesn’t sometimes . . And the first thing that happens when you have the process of atherosclerosis is you have positive remodeling, meaning the atherosclerotic plaque grows out from the vessel, it doesn’t grow in. It’s only when there’s a certain amount of plaque burden that it starts to grow in. That might not be picked up on a cath, you can see pretty normal coronaries when someone still has atherosclerosis.

E: And just as coronary CTAs give us information about disease in the vessel wall, it can also give us information about plaque morphology. 

GREG KATZ: The other thing a CTA does for you is that it gives you information about plaque characteristics . . . there’s this idea of the vulnerable plaque being the one that’s more likely to rupture

M: Nice throwback to pearl 2 where we talked about those soft plaque TCFAs with their puny weak shells and lipid cores – I like to think of them Twinkies of the coronary world.

S: You guys, I haven’t looked at Twinkies or a poached eggs the same way since we started working on this! Let’s recap everything coronary CTA: Coronary CTA is simply a gated arterial phase contrast CT study that allows us to visualize the coronary arteries. We have randomized trial data that not only are these non-inferior to functional stress testing, but there is the potential to reduce death and non-fatal MI using coronary CTAs over standard care.  Added benefits to coronary CTA is that its lets us know about atherosclerotic disease that wouldn’t get picked up on with either stress test or even acath because it’s also not encroaching on the lumen, and coronary CTA also picks up plaque morphology.

Pearl 4: What are the limitations of coronary CTA?

S: Alright, guys, after all that, it sort of feels like the hype train for coronary CTAs is running full steam ahead. But should we be pumping the brakes a little bit? 

M:  Yeah honestly it’s starting to feel like the hype level is approaching Royal Wedding status. 

E: How dare you drag Harry and Meghan into this. 

S: Yeah that’s a low, Marty. Pretty low. 

E: Next thing you know Marty is going to be over here taking shots at The Bachelor. 

M: I mean, I think we can all agree that Colton ended up being the most vanilla Bachelor since season 18’s Juan Pablo, and Rachel was the best character in the franchise history.  But listen, I can see I’ve hit a nerve here. All I’m saying is that I think we should note that coronary CTA isn’t a great choice in all patients. 

S: Preach on Marty.  I think getting into what situations where coronary CTAs might not be a good choice can help us talk about the elephant in the room: I know a lot of people are probably wondering, “Hmmm . . . how do I choose between a functional stress tests vs. anatomical tests for a patient?” Spoiler alert: there is no right answer. But perhaps knowing which scenarios to avoid coronary CTAs can steer us in the direction of what times we should maybe be ordering functional tests more.

E: Well, the first big group of patients we should mention are those with a history of revascularization, for a couple reasons. First, functional stress testing can give you an idea about myocardial viability, which may be important if future interventions are being considered. Second, for those who have had stents placed, it’s important to know that coronary stents can create an imaging artefact which makes the image difficult to interpret. 

M: Another important point to remember is that the images during a coronary CTA are obtained coronary filling – which as we all know occurs during diastole. This is why we give that splash of metoprolol – or calcium channel blockers if beta blockers are contraindicated –  to reduce heart rate and lengthen diastole. 

E: So patients have to be able to tolerate metoprolol – and truthfully it’s actually a bit more than a splash – sometimes 150 mg of oral metoprolol.

S: And for the same reason of getting good images in diastole, we run into issues with patients whose tachycardia we can’t control – or people with irregular rhythms –  depending on your hospital’s radiology policy- things  like ventricular ectopy or even atrial fibrillation can interfere with getting the images we want. 

E: Finally, despite what the Got Milk commercials might have you believe, calcium is a bad thing, at least when it comes to coronary CTA. 

S: Wait, do they still make Got Milk commercials? 

E: Unfortunately they don’t, but we’re talking about coronary calcifications here. As it turns out, calcium deposits have attenuation on CT scans that approaches the density of metal. That means the greater the calcium deposition, the lower the diagnostic yield of coronary CTA

M: For this reason, we usually avoid coronary CTA in our elderly patients.  And Megatron, because his heart is made of steel… get it?!? 

S: Thank you for explaining that one . . . We also tend to avoid it in our extremely obese patients. A BMI > 40 may actually alter the quality of images obtained simply due to tissue density alone. 

E: The last and probably the biggest barrier to coronary CTAs currently is the patient’s insurance company and prior authorizations. And, I know both of you, as well as many of our listeners, take care of vulnerable populations who are often uninsured or underinsured. So in those patients, you may have to face the frustrating reality that coronary CTA was never an option in the first place. 

M: Hopefully as the already-robust data for coronary CTA continues to grow, that will become less of an issue. But, like the Bachelors and Bachelorettes yet to find love, I dream… 

S: I hope coronary CTAs have a better chance of making it than the Bachelors! But I think there’s one last possible limitation to touch on that’s important to our patients and they will probably ask you about: How big is the risk of radiation with CCTAs? 

E: This is a good one to mythbust! Yes, when first introduced, coronary CT did carry higher radiation risk, but now most scans are on the order of 2-3 millisieverts of radiation. To put that in perspective,  nuclear scans are on the order of 10-12 mvs.

M: Alright, guys, help me put all this together. 

S: Ok what i am hearing is that we probably want to steer clear of coronary CTAs in patients with prior stents bc that is gonna cause artifacts, patients with arrythmias that would prevent getting good images quality in diastole, elderly (say over >75 yo) who already a lot of calcium or obese patients where the tissue density alters image  Another roup of patients are those who can’t tolerate the splash – or perhaps generous portion – of beta blockade.  And, unlike Bachelor in Paradise, none of us live life in a bubble, and we need to remember that there’s always the unfortunate battle with insurance companies that might stand in the way of coronary CTA, at least for the time being. 

Pearl 5: Interpreting coronary CTAs

M: Alright, guys, I feel that I have a better grasp on what coronary CTAs are and their pros and cons, but the interpretation of coronary CT results is new territory for me. What  do I do with all the information I get from these tests? And even more importantly, how am I going to talk to my patients about it?! 

E: Obviously, just like anything in medicine, there isn’t a straightforward answer. It’s not  going to be “If the Coronary CTA result is this, then do this.” Everything needs to be considered on a case by case basis. 

M: Okay, but coronary CTA is an anatomical test, so these should be straightforward to communicate, right? I mean, coronary disease is either there or it’s not. 

E: Well, yes and no. Let’s start by tackling the extremes of what we might find on coronary CTA, with the help of Dr. Douglas. First, there are the patients whose scans look great:

PAMELA DOUGLAS: If the CT angiogram shows no blockages at all and shows no plaque, I think it can be very reassuring to the patient that they do not have any blockages in the coronary arteries and they are incredibly unlikely to have a heart attack due to plaque erosion or plaque rupture because they don’t have any plaque. 

S: There is a 97-99% NPV for coronary CTA so if a patient has chest pain but clean arteries on a coronary CTA, you can assure them their symptoms are not coming from their heart. We probably can’t say the same thing about functional stress testing

PAMELA DOUGLAS: Stress test is an approximation, but they’re roughly 80 percent sensitive and 80 percent specific, which means that one, that one in five patients will have a false positive or false negative diagnosis . . . four out of five will be accurate.

S: To me, the ability to really reassure patients cardiac-wise if they have no blockages on a CTA is the biggest advantage clinically. Some studies suggest that a normal coronary CTA may confer up to a 7 year warranty when it comes to mortality. 

PAMELA DOUGLAS: You know, there are definitely high-risk groups in which a small number of people have no plaque, for example in PROMISE 18% of diabetics had no plaque. I would still treat them for secondary prevention as the guidelines say as they’re diabetic, but it doesn’t mean they can go out and smoke now or whatever or eat bacon three times a day, but I think it’s very reassuring. 

S: The caveat here is the sensitivity of coronary CTA for things like (coronary dissection) spontaneous coronary artery dissection or myocardial infarction in the absence of obstructive coronary artery disease – aka MINOCA – is unclear – this disproportionately happens in women and is an evolving area of study. 

M: Definitely important caveats to point out.  Ok, so let’s move from patients with low risk coronary CTA results to patients on the other end of the spectrum who with high risk results.   Here, we’re talking about >70% blockages in major vessels other than left main and >50% in the left main artery itself. 

E: Again not a straightforward answer but sometimes cath and PCI ends up being the best choice.  Dr Douglas told us about how she discusses this intervention with her patients.  

PAMELA DOUGLAS: We can say well your chest pain or your exertional symptoms seem to be due to blockages that are limiting blood flow to the heart muscle, we want to open that up. I always tell them that is a palliative procedure, it does not cure the disease. We are not getting rid of the plaque, we are just pushing it out of the way, or we’re bypassing it, and it’s on them to work with us in cardiac rehab and in their lifestyle adjustments and with our medications over the rest of their life to keep this from becoming a problem for them.

S: Let’s pause here for a second there, because I just love how Dr. Douglas frames this: revascularization isn’t a curative procedure, it’s a palliative one. This is an important reminder that even after obstructive disease has been intervened upon, there is a lot of work left to do. 

M: Moving on, in between those patients with no blockages and those with significant plaque are those patients caught in the middle. Specifically, we’re talking about intermediate blockages of less than 70% in the major vessels other than the left main, and in the left main, less than 50%. 

E: In these folks, again there is no algorithm and its always a case by case basis. Dr. Douglas speaks broad strokes about how she approaches patients with intermediate blockages: 

PAMELA DOUGLAS: In general for those people I would do aggressive secondary prevention. They’ve demonstrated they do have atherosclerosis, even if it’s not at this level of clinical coronary artery disease.

E: Greg also gives us his take on knowing the nuanced information that a coronary CTA can give: 

Greg: Even if it’s not obstructive, it might change the way that I manage their risk factors that might give me a lower LDL goal. It might make me more eager to add on ezetimibe or up the dose of their statin and it might make me push them harder on prevention. They were just like so many subtle things that happen in the interaction with the patient. And if you show them a picture of a CTA and you say, look at all of your heart, that is at risk. If this plaque were to rupture, if this pimple were to pop and you obstruct all of this flow. it’s very hard to capture in trials the subtleties of the one on one interaction. And also the way that you’re framing it for yourself dictates how you talk about how you talk about the disease to the patient. It changes the tone that you use. It changes the level of concern And I think that subconsciously knowing what someone’s disease burden is like gives you a different sense of how you should be approaching them.

M: Wow, that is an awesome thought to end with.  Let’s wrap up this pearl focusing on interpretation of coronary CTA: If your patient has a clean coronary CTA, then it’s “Keep up the good work” and gives them reassurance and up to a 7 year warranty.  If they have coronary artery disease, then management is some mix of secondary prevention versus intervention. And as Dr. Douglas and Greg pointed out nicely is that anatomical testing can really be a powerful motivator for behavior change and affects the patient-physician interaction in meaningful and measurable ways.  

References

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  • https://www.forbes.com/sites/harlankrumholz/2015/10/05/this-test-might-tell-you-if-you-dont-need-a-statin/#39617ede242d
  • https://www.acc.org/~/media/Non-Clinical/Files-PDFs-Excel-MS-Word-etc/Guidelines/2018/Guidelines-Made-Simple-Tool-2018-Cholesterol.pdf
  • https://www.nice.org.uk/guidance/cg95/evidence/full-guideline-245282221
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