Circulation July 11, 2017 Issue


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Dr. Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. I'm Dr. Carolyn Lam, associate editor from the National Heart Center and Youth National University of Singapore. Coming right up, we will be discussing fascinating new data on the prevalence of subclinical coronary artery disease in masters endurance athletes but first, here's your summary of this week's journal. The first paper provides insight into ischemic cellular post conditioning. Now, we know that cardiosphere derived cell therapy has been utilized as a strategy to treat ischemic heart disease and reduce chronic scar burden when administered months after myocardial infarction. In the current study, by first author Dr. de Couto, corresponding authors Dr. Marban and Berman from Cedars-Sinai Heart Institute in Los Angeles, California, the authors used rat and pig models of myocardial infarction to show that exosomes, which are nanosize lipid bi-layer vesicles, actually mediate the cardio protective effects of cardiosphere derived cells when administered after reperfusion of myocardial infarction.

They further show that treatment with either cardiosphere-derived cells or their secreted exosomes reduce infarct size and improved functional recovery. Using RNA sequencing to determine exosome content and alterations in gene expression profiles on macrophages from cardiac tissue or bone marrow, they found that a specific micro RNA species miR 181-B within the exosomes, acted on macrophages and was implicated as a key mediator of the cardio-protective benefits. Thus, this study gives new reason to test the idea that allogeneic cardiosphere-derived cells may be efficacious in preventing scar formation and improving cardiac function, when given in the earlier reperfusion period. The data further support that exosomal transfer of miR 181-B from these cardiospheric-derived cells into macrophages underlie the cardio-protective effects after reperfusion.

The next study describes a potential new therapeutic strategy for vasoproliferative retinopathy which can underlie age-related macular degeneration, the leading cause of blindness in industrialized nations. First author, Dr. Bucher, corresponding authors Dr. Yea and Friedlander, from the Scripps Research Institute in La Jolla, California used rodent models of retinal neo-vascular disease to show that Tspan-12, beta-catenin signaling plays an important role in the development of vasoproliferative retinopathy. As background, Tspan-12 belongs to the Tetraspanin family, which mainly includes cell surface proteins characterized by four transmembrane domains and two extra cellular domains.

Members of the Tspan family participate in a diverse cellular processes and act as signaling platforms by forming Tspan-enriched micro domains in plasma membranes. The authors went further to use a novel phage display combinatorial antibody library to specifically design a Tspan-12 blocking antibody which is capable of interacting with human and mouse Tspan-12 antigen. They then provided strong evidence that the Tspan-12 blocking antibody prevents developmental pathological neovascularization in murine models of vasoproliferative retinopathy. Combination therapy with a known anti-VEGF agent demonstrated significant synergy supporting the potential clinical use of the anti-Tspan-12 antibody as a novel angiomodulatory agent.

The next study addresses the paradox that blacks have higher coronary heart disease mortality compared with whites, but non-fatal coronary heart disease risks may be lower for black versus white men. To address this paradox, first author Dr. Colantonio, corresponding author, Dr. Safford and colleagues from Weill Cornell Medical College in New York, compared fatal and non-fatal coronary heart disease incidents and case fatality among blacks and whites in three studies. The Atherosclerosis Risk in Communities or ARIC study, cardiovascular health study, and reasons for geographic and racial differences in stroke or regards study, all stratified by gender.

They found that the incidents of non-fatal coronary heart disease was consistently lower among black versus white men, although black men have a higher burden of unfavorable social determinants of health and cardiovascular risk factors and a higher fatal coronary heart disease incidents. Following adjustment for social determinants of health and cardiovascular risk factors, black men and women had a similar risk of fatal coronary heart disease, but a lower risk of non-fatal coronary heart disease compared with white men and women respectively. Finally, blacks with incident coronary heart disease had a higher case fatality compared with whites and the difference remained similar after adjustment for social determinants of health and risk factors. Thus, there is an apparent lower risk for non-fatal coronary heart disease among black versus white men and women, which needs to be further studied. Blacks have a higher risk of their initial coronary heart disease event being fatal compared with whites, highlighting the need for reinforcing primary prevention in this population.

The next study provides important information on the burden of re-admissions after hospitalization for critical limb ischemia. First author, Dr. Kolte, corresponding Dr. Aronow and colleagues from Brown University in Providence, Rhode Island, used the 2013/2014 nationwide re-admissions databases to identify almost 61,0000 hospitalizations for primary diagnosis of critical limb ischemia during which patients underwent endovascular or surgical therapy. They found a 30-day re-admission rate of 20.4%. Independent predictors of 30-day re-admission included presentation with an ulcer or gangrene, age above 65 years, females, large hospital size teaching hospital status, known coronary artery disease, heart failure, chronic kidney disease, anemia, coagulopathy, obesity, major bleeding, acute myocardial infarction, vascular complications, and sepsis. Interestingly, mode of revascularization was not independently associated with re-admissions.

The most common reasons for re-admissions included infections, persistent or recurrent manifestations of peripheral artery disease, cardiac conditions, procedural complications, and endocrine issues. Finally, the costs of 30-day re-admissions for critical limb ischemia during the study period were 624 million U.S. dollars. Thus, this study provide knowledge of independent predictors and reasons for re-admissions that will help clinicians and hospitals to identify, develop, and implement strategies to reduce re-hospitalizations and healthcare costs associated with critical limb ischemia.

The final study tells us that there may be a direct relationship between life-long exercise volume, and coronary atherosclerosis in athletes. Dr. Aengevaeren and colleagues from Radboud University Medical Center in the Netherlands, studied 284 middle-aged men engaged in competitive or recreational leisure supports, using contrast enhanced CT to assess coronary artery calcification and plaque characteristics.

Participants also reported life-long exercise history patterns and exercise volumes were quantified as metabolic equivalent of task or met minutes per week. They found that participants in the more than 2,000 met minutes per week group had a higher prevalence of coronary artery calcification and atherosclerotic plaques. The most active group did, however, have a more benign composition of plaques with fewer mixed plaques and more often, only calcified plaques. These observations may explain the increased longevity typical of endurance athletes, despite the presence of more coronary atherosclerotic plaques in the most active participants. Well, that wraps it up for your summaries. Now for our featured discussion.

Our current physical activity guidelines recommend 150 minutes of moderate exercise and that's supposed to protect against cardiovascular disease and increase longevity. However, what do we really know about the dose response relationships and the effects of exercises doses that exceed current recommendations. Well, recent data, including a paper in this week's issue, suggests that long-term, high volume endurance exercise may actually accelerate, rather than reduce coronary atherosclerosis. To discuss this exciting paper, we have the corresponding author, Dr. Sanjay Sharma, from Saint George's University of London, as well as editor of digital strategies and associate editor at UT Southwestern who handled this paper, Dr. Amit Khera. Welcome, gentleman.

Dr. Amit Khera: Good morning.

Dr. Sanjay Sharma: Thanks for having us.

Dr. Carolyn Lam: First, Sanjay, oh yikes! As a runner and as a person who strongly advocates regular exercise, please, please, put us out of our misery. Tell us what you've found and what you think are the possible explanations.

Dr. Sanjay Sharma: I'm a runner too, and I don't think anyone would argue that the benefits of exercise on the cardiovascular system are unrivaled. People who exercise regularly do reduce their risk of an adverse event from a heart attack by 50% when they're in their 5th and 6th decade and they live around three years longer than people who don't exercise at all. Now as you rightly point out, the current recommendation suggests 2 1/2 hours of moderate physical activity per week and by that I would mean, at maximum, a 15-minute mile pace. Clearly, our endurance athletes exercise much, much more than that. They exercise 10 to 20 times greater than that volume and in parallel with this has been the emergence of a large number of people participating in marathon runs. For example, in Europe, there were two million marathon runs per annum and that figure's going up by about 5%.

Coinciding with this burgeoning increase in endurance exercise, is the development of several reports that show that exercise may cause release of biomarkers of cardiac damage. Animal experiments have shown that exercise may cause scaring in the heart and human studies have shown that some marathon runners have more calcium in their coronary arteries compared to relatively sedentary individuals. One of the problems with these studies is firstly, the biomarker release is very transient, it goes away after about two days. Animal experiments cannot really reflect what goes on in human beings because they're artificial and animals are forced to exercise with electrical shocks, et cetera. The studies in human beings have been conducted in runners who have been former smokers.

In fact, the most commonly reported study or cited study, contained individuals of whom 50% had risk factors for coronary artery disease. What we decided to do was to do a clean study, where we took 150 individuals who had none of the risk factors for coronary artery disease and 92 relatively sedentary controls who exercise within the normal limits. We have to exclude a lot of people because we have to exclude anyone that had ever smoked, anyone that had high blood pressure, high cholesterol, or a family history of permanent cardiac disease. We actually subjected them to all sorts of investigations and we found that a small number of male runners had more calcium in their arteries compared to sedentary individuals.

Dr. Carolyn Lam: Wow! Please tell us that there's something good that you can say about that. First of all, I really want to congratulate you on this most elegant study and Amit, I'm sure you put in what the editor's thought but we're just so proud to be publishing such a high quality study here. Amit, is there anything you might want to add of what the editors thought?

Dr. Amit Khera: Sure, I first want to congratulate Dr. Sharma and his colleagues. This was a carefully done study and we've talked a bit about the coronary calcium but there was extensive investigation and I really think this advanced the field. Sounds like all three of us are runners, so this hit home to all of us and as he mentioned, this has been a very hot area and one that's been very controversial. I think here what we have is a manuscript that really helped move the field forward, helped us better understand the biology. The one thing I'll comment on that we found very interesting was the observation that those that were the masters athletes actually had more of a calcific phenotype, where as those that were not looked like a soft plaque phenotype, if you will. Actually, if you look, we have a companion article in circulation looking at sort of dose dependent finding a similar finding. My question, now turned back to Dr. Sharma is, what do you counsel your patients now with these findings? Has it changed now how you recommend exercise or your thoughts on how you counsel them?

Dr. Sanjay Sharma: Well, we examined 152 different athletes, or masters athletes in 92 controls. These athletes were aged 56 years old, who'd been training for 36 years and had immediate marathon number of 13. Now, what we've found in these individuals is that a small number of males, that's 11%, had a coronary artery calcium score of more than 300. Some men had more plaques than sedentary individuals and these plaques were distributed throughout all three coronary arteries. When we looked at the pathology of the plaques very carefully, we found that the plaques in the athletes were calcified. Indeed, 72% of athletes had very calcified plaques. We know that such calcified plaques are stable, they're less likely to fissure and are less likely to cause coronary thrombosis and therefore, acute myocardial infarction.

This led us to propose that although exercise may be causing some atherosclerosis through the sheering and stressful source during exercise of the bending and kicking of vessels, we believe that the repair mechanism here is different to that seen in people who smoke or who have high cholesterol or high blood pressure. The repair mechanism results in very calcified and stable plaques in athletes and this may actually mitigate the risk of acute myocardial infarction and may explain why the number of people who actually suffer an acute myocardial infarction during a marathon run is very small, around 1 in 50,000, and no different to the number of people who suffer a sudden cardiac arrest playing football or basketball, due to congenital or inherited abnormalities of the heart.

Dr. Carolyn Lam: Sanjay, those are just such important points to keep in mind as we read your paper. It did strike me as a significant minority, actually, of these long term endurance athletes who develop significant coronary artery calcification and it could potentially be a clinically benign phenotype. At the end of the day, this is a cross-sectional study, isn't it? We can't, I suppose, extrapolate into the clinical events. What are your postulations there and what could be future work that you're planning?

Dr. Sanjay Sharma: Well, you make a good point. This is a cross-sectional study and the demonstration of an increased cardiopathy calcium does not necessarily reflect future cardiac events. We have followed these individuals up for the last 18 months. These masters athletes and have not demonstrated a single one to develop an acute event that would last 18 months. We really don't know what the meaning of these plaques is. I think the only thing to do now, being we've got the liberty of having so many people that do marathon runs and so many people who've been exercising for three or four decades, we can actually do a prolonged follow up study, so the answers will be a while coming. To follow these people up with high calcium, just to see whether they do go on to develop adverse events in the future. All our study has shown is that some male athletes who've exercised lifelong get an increasing number of plaques. These plaques appear to be calcified and stable and the long term effects of such plaques is unknown.

Dr. Carolyn Lam: Sanjay, just circling back to Amit's question earlier and maybe Amit, you could take it to after this. What do we recommend to our athletes who come in and have a high coronary artery calcium score? Do we tell them to stop?

Dr. Sanjay Sharma: I certainly wouldn't and I'm much less worried about an increase coronary calcium score in a lifelong runner or cyclist than I was 10 years ago. It appears that these plaques are there in some individuals, they are calcified, they appear stable. Given the fact that we know that coronary events during marathon running in experienced runners are very, very low indeed. I don't think I would be keen to do anything about it, not even consider stacking therapy based on our findings at present. As I said before, we do need longitudinal follow up to really identify all ascertain the precise implications of these plaques in masters athletes.

Dr. Carolyn Lam: Right, and this is again recognizing that your particular population was free of traditional cardiovascular disease. Of course, if we were to find these risk factors in our athletes, we would most certainly treat the traditional risk factors. Amit, anything to add there?

Dr. Amit Khera: I think that was an excellent point about his approach to counseling patients. I will mention on the editorial staff, we felt like this was such an interesting area with emerging data and fast moving, that it was warranting of an editorial. I recommend people to look at the one by Aaron Baggish and Ben Levine. I think they had a very similar conclusion and that was that they don't necessarily proscribe exercise in patients with high coronary calcium but rather, focus on risk mitigation strategy, focusing on risk factors as we normally would do. I think the conclusions are similar and the thoughts in that editorial were insightful, pairing both of these papers and helping us make sense out of this really evolving field.

Dr. Carolyn Lam: Well, thank you Sanjay and Amit for this wonderful discussion. I learned so much as I'm sure our listeners did. You've been listening to Circulation On The Run. Tune in next week.

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