**EP218: Update on Cardiac CT** Welcome to Dr. Warwick's podcast channel. Warwick is a practicing cardiologist and author with a passion for improving care by helping patients understand their heart health through education. Warwick believes educated patients get the best health care. Discover and understand the latest approaches and technology in heart care and how this might apply to you or someone you love. Hi, my name's Dr. Warwick Bishop, and welcome to my podcast and videocast station. Today, I would like to talk about an update on cardiac CT imaging. A number of studies have come out recently which, to some degree, have validated some of the approaches I've taken over the years and some of the observations I've made over the years. Now, of course, we do medicine through trials, and you can't just have a philosophical position on something. But this is really interesting, and what I'd like to share with you are two studies that have just come across my desk in recent time. The first is the use of CT coronary angiography in risk. Now, there's been almost nothing done in that space to any degree, and what I'd like to talk about is a trial called the SCAPIS study (S-C-A-P-I-S). Don't expect you to remember it, and in fact, I'll probably forget it myself, but it was a Swedish study that looked at over 25,000 people between the ages of 50 and 64 years. What they wanted to do was look at calcium scoring, which involves no injection of contrast, but they also wanted to compare it using injection of contrast, which is a CT coronary angiogram. When they scanned this population, they found about 40% of them had plaque. Well, off the top, that's not particularly surprising. We would expect that if coronary disease kills about one in two to one in three people, that 40% of the population probably should have plaque. So there's no surprise there. To my mind, having the opportunity to evaluate that and image there is really an incredibly powerful tool. The other thing that they found was that men seemed to have nearly twice as much plaque as women, and that there was a decade delay between the amount of plaque that women had compared to men. Now, that fits in almost perfectly with an idea that I've been carrying for a number of years, and that is that there is approximately a 10-year difference between the onset of coronary disease in men compared with women, with women being about 10 years behind. Now, that's useful because I tend to try and think of a perfect screening time for men at about 50 years of age and women, therefore, at about 60 years of age. That coincides with risk calculator estimates of average 50-year-old men and average 50-year-old women falling into pretty well an intermediate risk category. Now, if there were things going on that could be risk enhancers, that would make me think about imaging those individuals sooner. So, a woman, for example, at 60 who has a terrible family history of premature coronary artery disease within her family, I might look to image that person five or ten years earlier. And vice versa, if a woman comes to me and says her father had a heart attack at 60 and she's 55, then I could give her some reassurance that maybe we don't have to rush because nature would dictate that his event at 60 means that her at 55 probably has to wait to nearly 70 to have the same event. Doesn't mean that I wouldn't screen sooner than that 70-odd years of age, but you can see that that 10-year gap between the genders is an important thing to put into the context of consideration of imaging. So what else did they find on the SCAPIS study? Well, it was a very interesting trial in that what they looked for was to try and understand the difference between the calcium score results and the CT coronary angiography results. What they found is that in the patients who had a zero score—this is considered a very low-risk feature—5.5% of those individuals had some plaque, the fatty plaque that you can only see when you inject contrast, demonstrated when they had their CT coronary angiogram. Of those, 0.4%, so less than half a percent, had any significant stenosis. So the chance of having a zero score and any significant stenosis is extremely low, but not zero. I don't know what the subfractions are or the interpretation of the individuals who were found to have the 0.4% stenosis; they may well have had other risk enhancers, whether it be raised triglycerides or prediabetes—I'm not sure. The important part, though, is that we are not surprised that a small but recognizable number of patients will have non-calcific plaque if they've got a zero score. And of course, that makes perfect sense because the first process in atherosclerosis is the deposition of cholesterol. It's not until the cholesterol has been in there for a period of time that some stabilization to the plaque occurs. As that stabilization to the plaque occurs, then calcium gets formed, secondary to micro scarring. So it has to be the case that a zero score will show non-calcific plaque in a small number of immature and early plaques. Still, all the data for a zero calcium score is extremely robust for the average population. My own practice, in fact, is to use a zero calcium score as a gatekeeper. If that score is zero, then we know from all our research that the chance of an event is very low in the next three to five years. I don't tend to do a CT coronary angiogram unless there's really a significant drive or, of course, if there are any symptoms. This same study showed that with scores over about 400, there was about 40% of cases that had a significant narrowing within one of the arteries. I guess that pretty well correlates to what I see in my own practice. I regularly see scores that are above zero. Once you're above zero, I think it's really important to know what plaque is there. Even a small amount of calcium might be associated with a significant amount of fatty plaque, and that, in terms of management strategies, becomes important. Well, now I've talked about using CT angiography, or literally injecting contrast to try and understand better what's going on in the arteries. One situation that could be really important is trying to delineate if someone's a really high risk or not so high risk based on their calcium score. That leads me into the second study that I wanted to talk about, and it's a Korean study that was run between 2011 and 2017, looking at over 25,000 people again, a bit like the SCAPIS study. Interestingly, these Korean researchers came to a conclusion that calcium scores tended to be higher and progressed faster in people who did exercise. And that is a paradox. Because the paradox is this: we know that as calcium scores increase, we see a greater likelihood of coronary events. But we know, as people exercise, we see a lower rate of coronary events. So how does that all match up? Well, what these researchers did was they took their cohort, their population of people. They had about 45% who were said to be inactive, about 40% who were moderately active, and the remainder were under a health-enhancing, physically active program. They did some serial scans on these people, and the two active groups demonstrated not only higher calcium scores but a higher rate of progression of calcium compared to the inactive group. What does that all mean? Well, there are two processes occurring that can be driving calcium. Of course, the first is that calcium can be a marker of plaque formation and stabilization. So we can simply use calcium as an indicator of what fatty plaque is going into the arteries. The more fatty plaque that goes into the arteries, the greater the amount of calcium that will end up being demonstrated as that fatty plaque becomes, if you like, stabilized and becomes an atherosclerotic plaque. The other thing that's important to understand is that if we do have a fatty plaque, then one of the things that really brings that plaque to more stability, i.e., a lower chance of having a heart attack, is that fatty plaque becoming calcified. That's a process of stabilization. So calcium presence will tell us about the deposition of cholesterol and how much, and is an appropriate indicator of propensity to put cholesterol in the arteries. But similarly, calcium can also show us the process of stabilization. Interestingly, although this study demonstrated that exercise might be associated with an increased amount of calcification, we also know that if we give people statin therapy and potentially stabilize the plaque within their arteries, then that increases the calcification as well. So it's a paradox to some degree, but really the previous study, if we inject contrast, should illuminate exactly where we are in that space. That's what I see in my own practice. If we see someone with a calcium score of whatever it is—several hundred—we inject contrast and we're looking for the fatty plaque, which is the one that causes problems. So if we took a calcium score of 200 and there was lots and lots of fatty cholesterol-dominant plaque present, we would know that person's at very high risk. But we could equally take someone with the same calcium score who's been a marathon runner and inject contrast and see no evidence of fatty plaque whatsoever, i.e., the calcium is really just sitting within the arteries looking very benign and unlikely to cause any problems. Well, what an interesting process, and certainly one that I see within my own practice. There is no question that the complexity around calcium going into arteries, cholesterol being in arteries, and the process of unstable plaque remains a mystery, which often makes me laugh because I do have patients from time to time who have done a lot of Google research and feel very confident that they fully understand the process of coronary artery disease and statins for that matter. Nonetheless, I remain humbly open to learning, and I hope you do too. So this interesting journey on CT coronary angiography and the paradox of raised calcium scores, I hope you found it interesting. If you have, drop us a note; I would love to hear from you. If you have any ideas for any future podcasts, please let us know. For now, I'm going to wish you the very best to stay as well as possible for as long as possible. Until next time, take care and bye for now. You have been listening to another podcast from Dr. Warwick. Visit his website at drwarwickbishop.com for the latest news on heart disease. If you love this podcast, feel free to leave us a review.