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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 Duke National University of Singapore. Our feature discussion today is about the validation of a novel biomarker-based stroke risk score for atrial fibrillation, the ABC stroke score. But first, here's your summary of this week's journal.
The first paper provides experimental insights into endothelial nitric oxide synthase uncoupling in endothelial dysfunction. In this paper by first author Dr. Lee, corresponding author Dr. Wong and colleagues from Qilu Hospital of Shandong University in China, authors assessed endothelial function in animal models of hyperglycemia, hyperhomocysteinemia, and a dyslipidemia. They demonstrated that GTP cyclohydrolase 1 is the target of the microRNA-133a and that it's a topic expression and endothelial cells mediates endothelial dysfunction.
Furthermore, Lovastatin up-regulated GTP cyclohydrolase 1 and tetrahydrobiopterin and re-coupled endothelial nitric oxide synthase in stress endothelial cells. These actions of Lovastatin were abolished by enforced micro RNA 133A expression and mirrored by a mir-133a-antagomir. Finally, the beneficial effect of Lovastatin in mice were abrogated by in vivo mir-133A over-expression or by GTP cyclohydrolase 1 knockdown. In summary, this paper offers a mechanistic basis for targeting micro RNA 133A as a therapeutic approach to correct endothelial nitric oxide synthase dysfunction. It also provides further support to the role of statins in combating endothelial dysfunction.
The next study shows us that in hypertrophic cardiomyopathy, calcium mishandling may be the potential link between the primary genetic cause and downstream signaling cascade that leads to hypertrophy and arrythmias. In this study, Dr. Helms and colleagues from University of Michigan analyzed gene expression, protein levels and functional essays for calcium regulatory pathways in 35 human hypertrophic cardiomyopathy surgical samples with and without sarcomere mutations and compared that with 8 control hearts. They found a marked reduction in circa2 abundance, which correlated with reduced circa2 function in hypertrophic cardiomyopathy compared to controlled hearts regardless of the underlying genetic etiology.
However, calcium calmodulin depend protein kinase type 2 or cam2, which is a calcium sensing kinase, was deferentially activated only in the sarcomere gene mutation positive samples. Activation of chem kinase 2 was associated with an increase in phospholamb and phosphorylation in hypertrophic cardiomyopathy. However, neither calcineurin MRNA nor MEF2 activity was increased, suggesting that calcineurin pathway activation was not an upstream cause of increased chem kinase 2 protein abundance or activation.
In summary, this paper demonstrated that calcium mishandling occurs through both genotype specific and common pathways in human hypertrophic cardiomyopathy. Post-translational activation of chem kinase 2 pathway is specific to sarcomere mutation positive hypertrophic cardiomyopathy. While Sarco 2 abundance and sarcoplasmic reticulum calcium uptake are depressed in both sarcomere positive and negative hypertrophic cardiomyopathy. Thus, chem kinase pathway inhibition may improve aberrant calcium cycling in hypertrophic cardiomyopathy. This is discussed further in an accompanying editorial by Dr. Jill Tardiff.
The third study suggests that in patients with a dilated aortic route and trileaflet aortic valve, a ratio of aortic route area to height provides independent and improved stratification for prediction of death. First author Dr. Masry, corresponding author Dr. Desai and colleagues from the Center for Aortic Disease, Heart and Vascular Institute of Cleveland Clinic, studied consecutive patients with a dilated aortic route of greater or equal to 4 centimeters who underwent echocardiography and gated contrast enhanced thoracic aortic computer tomography or magnetic resonance and geography between 2003 and 2007.
A ratio of aortic route area over height was calculated on tomography and a cutoff of 10 squared centimeters per meter of height was chosen as abnormal. In 771 patients with trileaflet aortic valve and concomitant aortopathy, there was incremental prognostic value for indexing aortic route or ascending aortic area to patient height rather than using an unindexed aortic diameter. Incorporation of the ratio significantly and independently reclassified the risk for death and at normal ratio was independently associated with higher long-term mortality while cardiovascular surgery was associated with improved survival. Importantly, a sizable minority of patients with aortic route diameters between 4.5 and 5.5 centimeters had an abnormal aortic route when indexed to height ratio. 78 percent of deaths in this subgroup occurred in those with an abnormal aortic route area to height ratio. Findings were similar when ascending aortic measurements were considered. The take home message is that an aortic route area to height ratio above 10 squared centimeters per meter of height has significant and independent prognostic utility and may be used to re-stratify patients with trileaflet aortic valve and a dilated aorta.
The final study provides pre-clinical data to show that Ticagrelor reduces cardio damage post myocardial infarction to a greater extent than Clopidogrel by an adenosine induced organ protective response. First author Dr. Villaher, corresponding author Dr. Bademan and colleagues from the Cardiovascular Research Center in Barcelona, Spain studied a close-chest swine model of ischemia reperfusion in which myocardial infarction was induced by 1 hour balloon occlusion of the mid-left anterior descending coronary artery followed by 24 hours of re-flow. Prior to occlusion, the animals were randomly assigned to receive either placebo, a loading does of Clopidogrel, a loading does of Ticagrelor or a loading does of Ticagrelor followed by an A1 A2 receptor antagonist. Edema infarc size left ventricular size and left ventricular function were assessed by three T cardiomagnetic resonance imaging. Inhibition of platelet aggregation was the same between the groups receiving a P2Y-12 inhibitor.
Yet, Ticagrelor reduced infarc size to a significantly greater extent than Clopidogrel, reducing it by a further 23.5 percent, an effect supported by troponin eye assessment and histopathological analysis. Furthermore, compared to Clopidogrel, Ticagrelor significantly diminished myocardial edema by 24.5 percent, which correlated with infarced mass. Administration of an adenosine A1 A2 antagonist abolished the cardio protective effects of Ticagrelor over Clopidogrel. At a molecular level, aquaporin 4 expression decreased and the expression and activation of AMP kinase cyclin and COX-2 increased in the ischemic myocardium of Ticagrelor versus Clopidogrel treated animals. In summary, this study shows that Ticagrelor exerts cardio protective effects beyond its anti-platelet efficacy by adenosine dependent mechanisms, which reduce necrotic injury and edema formation. This is discussed in an accompanying editorial by Drs. Gerbel, Jung and Tantry. That wraps it up for the summaries. Now for our feature discussion.
Today, we are going to be discussing the performance of the ABC score for stroke in atrial fibrillation. And as a reminder for all our listeners there, ABC stands for A for age, B for biomarkers, that's NT-proBNP and high-sensitivity troponin, and C for clinical history of prior stroke. And again as a reminder, this risk score was originally derived in the Aristotle trial. However, we have new results about its performance and validation today from first and corresponding author Dr. Jonas Oldgren from Uppsala Clinical Research Center in Sweden. Welcome, Jonas.
Speaker 2: Thank you very much.
Carolyn Lam: We also have today the associate editor who managed this paper, Dr. Sandeep Das from UT Southwestern. Hi Sandeep.
Speaker 3: Hi Carolyn, thanks for having me.
Carolyn Lam: So Jonas, could you start off by telling us why you did this study and what you found?
Speaker 2: We did this study to validate the recently derived ABC stroke risk score. We have had risk scores for predicting stroke in patients with atrial fibrillation derived since the late 1990's and refined later on. But those risk scores have only used clinical markers for risk. We have for several years developed new risk prediction models with biomarkers and now we are combine them in a very simple biomarker based risk score, taking into account age as a clinical variable and the clinical history of prior stroke and only two common used biomarkers. And by that we can predict the risk of stroke with better precision than previous clinical risk scores.
Carolyn Lam: Yeah, I like what you said. I mean it is literally as simple as ABC. So tell us how you validated it and what you found.
Speaker 2: It was derived in a large cohort of patients participating in a clinical trial with new or relapsed coagulant compared to Warfarin and we now validated in almost a full size group participating it another clinical trial. So we have large data sets of very well described patients where we have good outcome data. Very solid data to rely on. Now we can see that the ABC risk score is now validated but the good precision and good collaboration of the discriminatory abilities is high and better than the previously used clinical risk scores.
Carolyn Lam: Could you give us some numbers behind that that are clinically meaningful? Everyone's going to be wondering compared to the chads-vasc score for example, how does this ABC score perform in that validation test set?
Speaker 2: We can adjust that by several different aspects. One is of course to calculate the C index which is a statistical method to see how good we can predict risk and the C indices for the ABC stroke score both in the duration and now in the validation cohort is higher than for the chads-vasc and atrial risk scores. But we can also look at what we have in this paper in circulation ... we can look at predicted outcome rates and observed outcome rates and can see that they clearly overlap both in the duration and validation court. So if you predict a risk that is less than 1 percent per year, it is observed also a risk that is less than 1 percent a year. Does this always ... the thing is when you derive risk or but when you validate it in another cohort, you need to show that it's a similar result.
Carolyn Lam: Yeah, that's true. Sandeep, you are managing this paper. It's very important. How do you think that clinicians should be taking the results?
Speaker 3: I think that clearly using anticoagulation and selected patients at high risk for stroke with atrial fibrillation is one of the best things we do in cardiology. You know in terms of reducing the risk of an important harm to patients. I think there's a fair bit of dissatisfaction out there with currently sort of standard, which is chads-vasc. Especially in people with a chads-vasc ... men with a chads-vasc of 1 or women with a chads-vasc of 1 to 2 where there's a bit of struggling over how to decide. So I think that one real advantage of this score in addition to the fact that it predicts better by the higher C statistic, which is fantastic and pretty uncommon, right? Lars sort of buried the lead a little bit by not emphasizing that it's relatively rare that we're able to move a c statistic by a point of 5 in the modern era.
But the other thing is that it helps give us an ability to come up with good estimates in people at low risk, which I think has been a challenge and something that people are a little concerned clinically. So I think that this is easily available, biomarkers that we routinely check all the time and it doesn't have the sort of gender challenge with chads-vasc where you're trying to figure out whether your low risk woman really needs to be on Warfarin or anticoagulation. So I think that it has a lot of clinical utility right out of the box, which is nice.
Carolyn Lam: Actually, Jonas could you let us know is there any sex differences in the performance of the score?
There are no differences in the performance of the score. So we looked ... the advantage of this score is when we derived it in the original model, we looked at all important clinical and biomarker risk factors and we can see that these were the foremost interesting markers. So we only used those. So we can predict much better and as pointed out so nicely by Sandeep, for patients at the lower end of the risk spectrum, we can find patients or have higher or lower risk even within patients with chads-vasc 1 or chads-vasc 2. And I think it's also important to see what about patients at higher risk despite proper anticoagulation. We did not know how to treat them but in the future we might perhaps tailor treatment also for those patients with residual high risk of stroke despite proper anticoagulation treatment. For instance, if the left atrial appendage occluded devices are shown in the future to be a good option for those patients, we can find them also by this risk score. So both in the higher and lower end of the risk spectrum.
Carolyn Lam: That's a really good point. On that note, I'm just curious. What do you think is in the future? What more knowledge do we need to address before we put this into practice or are you already using this? Or do you think it should enter guidelines for example? Maybe Sandeep, I could ask for your opinion first.
Speaker 3: We see a lot of biomarkers associated with increased risk kind of studies come out in the literature. You know probably every week you see several of these things come out. So what's really interesting about this is that it's obviously methodologically extremely well done but its been derived and validated in two large cohorts, which is pretty much best practice right? You want to see people validate these risk scores in large and distinct cohorts of patients to build up sort of clinical validity to the reader or consumer. So I think, from my standpoint, this is ready for prime time. I'm really intrigued by the fact that biomarkers, especially troponin, are predicting stroke in this population and there have been some observational reports out there that have showed an association between troponin and increased risk of stroke or worse outcomes after stroke. So I'd be really curious as to what Jonas thinks about why troponin would be predictive of stroke in this population.
Speaker 2: We were extremely intrigued by the finding when we first did those single observations of only troponin as a risk marker because we know that troponin is a very specific protein found in the myocardium. But the clinic predicts risk for stroke also and there are several explanations but they are mainly hypotheses about aging and myocardial function really to identify patients of risk. But the clear cut explanation is still not there.
Carolyn Lam: It's likely that these biomarkers are incorporating aspects that we don't fully understand, which is why they are better predictors isn't it? I mean to your point Sandeep.
Speaker 3: Yeah, no absolutely. And I think that's great.
Carolyn Lam: Exactly. It really opens a lot of other questions that need to be answered in the meantime. Jonas, any other last words about how you may be applying this clinically in your own patients?
Speaker 2: We have no solid data supporting the use of this clinical risk score and as already pointed out, which I think is very good, all clinic risk scores should of course be in the best world validated as useful decision support truth and really in clinics trial seeing that they improve outcomes. This is to my knowledge never been down with a clinical risk scores. We have never used them prospectively to guide treatment and to improve outcomes. Actually, we are aiming to do that. We hope to start a clinical trial next year with ABC score guided treatment compared to standard of care. But it's a very huge undertake of course to that we can improve treatment by risk or guided management.
Carolyn Lam: That's excellent. So remember everyone, you heard it right here. A new trial that they're engaging. I really congratulate you first for this study, as well as this future efforts which are clearly going to be very important.
Thank you very much both of you for joining us today and thank you listeners for listening. Don't forget to tune in next week.
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