Sep 20, 2016
Welcome to Circulation on the Run. Your weekly podcast summary and backstage pass to the journal and it's editors. I'm Dr. Carolyn Lam, Associate Editor from The National Heart Center and Duke National University of Singapore. Have you wondered which anti-platelet agent you should use in your patients with diabetes and coronary artery disease? Well, our feature paper deals with just this topic, so stay tuned, I'll be write back with it's author and associate editor. First, here's your summary of this week's journal: The first paper unravels novel peptides involved in atrial extracellular matrix remodelling in atrial fibrillation. This is work from first author Dr. Barallobre-Barreiro, corresponding author Dr Mayr from King's College London, and colleagues. They used novel mass spectrometry methods to analyze extracellular matrix in human atrial appendages from patients undergoing coronary artery bypass surgery.
Now, previous proteomic studies have examined the cellular proteome, but this is the first study to comprehensively characterize extracellular matrix proteins in human cardiac tissues, including the identification of glycosylation sites. They found extensive cleavage in the protein core of decorin which is a small leucine-rich proteoglycan that regulates collagen fibrillogenesis and a variety of other extracellular matrix cell signalling molecules. Decorin processing differed between human ventricles and atria and was altered in disease. It's C-terminus which is important for the interaction with connective tissue growth factor was predominantly detected in ventricles compared to atria. In contrast, atrial tissues from patients in persistent atrial fibrillation had higher levels of full length decorin, but also harbored a unique cleavage site that was not found in atrial appendages from patients in sinus rhythm. This unique cleavage site preceded the M-terminal domain of decorin and altered the binding capacity for myostatin, this altering muscle growth.
The cleaved decorin peptide antagonized myostatin, such that myostatin expression was decreased in atrial appendages of patients with persistent atrial fibrillation and in hearts of decorin-null mice. Furthermore, a synthetic peptide corresponding to this decorin region, those dependently inhibited the response to myostatin in cardiomyocytes and in perfused mouse hearts. This is clinically important because mystatin inhibition has been implicated as a substrate for atrial fibrillation. This study therefore provides first evidence that peptides generated from the cleavage of extracellular matric proteins such as decorin, constitutes a local regulatory mechanism for growth factors in human cardiac tissue.
The next study looked at therapeutic hypothermia in patients with out of hospital cardiac arrest, and questioned if it may be most effective when induced early during cardiopulmonary resuscitation or CPR, in contrast to prior trials that looked at therapeutic hypothermia induced only after return of spontaneous circulation and hospital admission. This is the RINSE trial from Professor Bernard and colleagues from Ambulance Victoria Australia, which was a multi center randomized controlled trial which assigned adults with out of hospital cardiac arrest undergoing CPR to either a rapid intravenous infusion of up to two liters of cold saline, or standard care. The primary outcome measure was survival at hospital discharge. Secondary end points included return of spontaneous circulation.
The trial was unfortunately closed early at forty-eight percent of the recruitment target, due to changes in temperature management protocols at the major receiving hospitals. Still, a total of one thousand, one hundred and ninety-eight patients were randomized. Six hundred and eighteen to therapeutic hypothermia during CPR, and five hundred and eighty to standard pre-hospital care. Overall there was no difference in outcomes at discharge. In patients with an initial shockable cardiac rhythm there was lower rate of return of spontaneous circulation in patients who received cold saline compared with standard care. Thus, although this trial was stopped early, the data suggests that induction of mild therapeutic hypothermia using a rapid infusion of large volume intravenous cold saline during CPR did not affect outcomes at hospital discharge and may in fact cause harm in the subset of out of hospital cardiac arrest patients who present with shockable rhythm.
The last study provides the first generalizable risk score for sudden cardiac death among American adults from the general population without a history of cardiovascular disease. This large study from Dr. Deo of University of Pennsylvania, and colleagues, derived a sudden cardiac death prediction model using the Atherosclerosis Risk in Communities or ARIC cohort, and validated it in the Cardiovascular Health Study or CHS cohort. They found that the twelve independent risk factors in the ARIC study included age, male sex, African American race, current smoking, systolic blood pressure, use of [anti-hypotensive 00:06:00] medication, diabetes, serum potassium, serum albumin, HDO, estimated GFR, and QTC interval. Over a ten year follow up period this model combining these risk factors showed good to excellent discrimination for sudden cardiac death risk. In fact the model slightly outperformed that of the 2013 ACC AHA pooled cohort risk equations.
Finally, they also showed in the echocardiographic sub-cohort that a left ventricular ejection fraction less than fifty percent was present in only 1.1 percent of these participants and did not enhance sudden cardiac death prediction. This study importantly contributes to the distinguishing of sudden cardiac death risk across the general population, and the results can help target future strategies aimed at sudden cardiac death prevention for the highest risk subgroups in the American general population. That does it for the summaries. Now for our feature paper.
For our feature paper today we are discussing the super important issue of anti-platelet therapy in type 2 diabetes with coronary artery disease. Joining me today are the corresponding author, Dr. Dominick Angiolillo from the University of Florida College of Medicine - Jacksonville, as well as Dr. Gabriel Steg, Associate Editor from Paris, France. Welcome gentlemen.
Thanks for having us.
Dominick, I'd really like to start with you. Your paper entitled the OPTIMUS-4 Study, is really a study of the pharmacodynamic comparison of Prasugrel versus Ticagrelor in these patients with type 2 diabetes and coronary artery disease. The whole question is, what was the rationale to look at the pharmacodynamics?
As the title of the study says, OPTIMUS-4, it means that there was an OPTIMUS-1, 2 and 3 in the past, which means that there's a lot of thought that went into this and a lot of background information. The rationale for this specific study was that we're all well aware of the fact that patients with diabetes have high platelet reactivity, which may be one of the reasons why they have a higher risk of recurrent atherothrombotic events. Therefore, the need to define ways to optimize their anti-platelet effects, their levels of platelet inhibition. In this specific study we took an approach of looking at the novel, although we cannot call them novel nowadays, but the newer P2Y12 receptor inhibitors Prasugrel and Ticagrelor. Looking at them in a head to head comparison from a pharmacodynamic standpoint to see if one drug would be superior than the other, again, in terms of a platelet inhibitory effect.
This is the rationale, and just to expand a little bit on this, there's been a perception, again I want to underscore a 'perception' that based on subgroup analysis of the larger clinical trials, that Prasugrel is a superior drug for patients with diabetes. We do know that there's a benefit also with Ticagrelor compared with Clopidogrel, although the absolute risk reductions in the studies led to a perception that Prasugrel would be a better drug. We said to ourselves, "Well, we're never going to have a large scale head to head clinical comparison, why don't we do a head to head pharmacodynamic comparison to see if there are any differences?" This was the overall rationale for conducting this specific study.
That really sets a background perfectly. Tell us about the main findings.
The main finding was as follows, we conducted a very detailed pharmacodynamic study, this was a prospective randomized double-blind double-dummy crossover study, with all patients on the background of aspirin therapy. We looked at platelet reactivity, using a variety of assays, I like to say it in every possible salsa that you can imagine. The primary end point which is platelet reactivity at one week into two drugs, using an [ADP 00:10:00] specific assay, actually showed that Ticagrelor was superior to Prasugrel in terms of platelet inhibitory effects. That was the only time point where it was shown, but the study was actually designed to show the opposite, so it was a very interesting finding, while with all the other time points there were no differences between the platelet inhibitory effects between the two drugs.
The other thing that we did look at, which gives a little bit of a novelty to this study is, we went beyond just looking at ADP induced effects, which is the target for these two drugs, we looked at other signalling pathways which one would not believe to be necessarily affected by P2Y12 inhibitors, and we found these also to be reduced by both drugs to a similar extent.
Fascinating. I'm going to get to your second point a bit later. First, that first finding that surprisingly Ticagrelor appeared to perform better using one of the specific assays and so on, I'd really like Gabriel's opinion there. What do you think is the overall clinical implications or what was the message that the editorial board was hoping to get across to the audience? Because I noticed you invited an editorial as well, a beautiful one written by Dr. [Star-ee-an 11:36] Parker. What was the thinking behind that?
I think this is really a very important paper and I'm delighted that Dominick Angiolillo and his team submitted it to Circulation, in fact to be frank, we invited that paper after seeing his presentation at the ACC earlier this year. The reason that paper caught everybody's attention in the editorial board was that it's addressing a frequent and deadly disease, diabetes, that kills really patients with cardiovascular disease. There's a critical issue in the treatment because of the limitations of Clopidogrel because of the increased platelet reactivity in diabetics, and there's tremendous interest in the novel P2Y12 inhibitors Prasugrel and Ticagrelor, and of course any hint of differences between these agents has major clinical implications. In addition, I think I can state that Dominick's team is really one of the premiere international teams looking at this exact issue, platelet reactivity in diabetics. What they did was really state of the art rigorous clinical investigation by a highly skilled team, looking rigorously at a double blind crossover designed four different assays looking at platelet function and platelet response, looking both at the effect of a loading dose and the maintenance dose.
To me, the message is not a minute difference between the treatments, in fact I think that even though it's the primary outcome and it does show a slightly greater response with Ticagrelor than with Prasugrel, the overall most of the other assays at the other time points show a consistent good response with both agents. To us, and to me, the message is that the novel agents are clearly superior to Clopidogrel as we've seen in the clinical trials, but they are fairly consistent in their benefit, and it's reassuring to see this not in healthy volunteers but in actual patients with stable coronary artery disease. I think it was really important to show that. Certainly platelet reactivity doesn't summarize entirely the effects of any drug, and there might be platelet independent effects of Ticagrelor mostly and possibly Prasugrel, but I think on the platelet side, I think that this paper really nails it.
I read that editorial and really agree that that puts everything in perspective really well. I particularly like the figure that accompanied the editorial. In case any of our listeners out there don't really remember all the different pathways and how Prasugrel and Ticagrelor and Clopidogrel are metabolized differently, I'd really refer everyone to that figure as well. Just want to pick up on one of the points that both of you mentioned, and that is the non ADP induced platelet reactivity that Prasugrel and Ticagrelor both seem to have an affect on and so on, and if they're so effective, Dominick, is there still a role for aspirin co-administration with these new anti-platelet agents?
The study clearly puts a little bit more beef, let's put it this way, to some of the ongoing clinical studies looking at whether we need aspirin in the patients treated with one of these newer P2Y12 receptor inhibitors. There are a series of ongoing studies out there. There's a laundry list, so I'm not going to go into the details. It does highlight that maybe when you have ultimate P2Y12 blockade, which is a key signalling pathway and blocks other responses by virtue of the fact that there's an interplay between this pathway and others, maybe you do not need this additional anti-platelet agent such as aspirin, which we know there's associated with potential bleeding particularly gastrointestinal side effects.
Having said that, this is not something that I'm advocating at time, but what I am saying is that we'll need to look into the results of the clinical trials. I believe that this study is an additional piece of evidence from an ex vivo standpoint to prior in vitro studies showing that aspirin is not associated with additional platelet inhibitory effects, at least not substantial platelet inhibitory effects. One can say that you may get away with just one of these newer agents. Again, this is based on pharmacodynamic findings, let's just wait for the clinical trial results.
I think that's so fairly put, and I learnt so much just listening to this conversation. Thank you so much for joining me today. Any last words from Gabriel?
Yeah, I'd like to make a couple of points as an Associate editor for Circulation. The first one is, this paper was picked up when we saw Dominick's team's presentation at the ACC, and I think it exemplifies that we really want to pick up the best science from the meetings, either before the meetings and publish it simultaneously as much as possible, but sometimes also at the meetings, so expect to see Circulation Editors at your presentations and maybe you'll seduce them enough with your science that we'll get good science submitted to the journal. The other aspect to it is also that I think with the new editorial board there's really a focus on trying to make the journal very international in it's approach, and I think it's fitting that I am Associate Editor from Europe and I think there's no more international a scientist than Dominick Angiolillo who's not only a good friend but also has been trained in Italy, has practiced in Spain, and now works in the US. I think he embodies how science transcends boundaries and borders. I think there's a definite international outlook to Circulation, and we're looking for great science from anywhere in the world, not solely the US.
Thank you so much Gabriel. Thank you so much Dominick. Thank you listeners for listening today, you've been listening to Circulation on the Run. Don't forget to join us next week for more summaries and highlights.