Jan 20, 2020
Dr. Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. I'm Carolyn Lam, Associate Editor from National Heart Center at Duke National University of Singapore.
Dr. Greg Hundley: And I'm Greg Hundley, Associate Editor, Director of the Pauley Heart Center in Richmond, Virginia.
Dr. Carolyn Lam: Greg, it is so good to be back. I just love doing these podcasts with you and what more when we get to feature a paper like the one that we have this week. It's all about high sensitivity, cardiac troponin and the universal definition of myocardial infarction, one of these evergreen topics that we truly need to understand better. But before we go onto that, I want to share my first paper. It's a preclinical paper and it provides an important breakthrough discovery that could protect the heart against progressive left ventricular systolic dysfunction following injury. Want to hear about it?
Dr. Greg Hundley: Absolutely.
Dr. Carolyn Lam: Okay. It's from course wanting authors, Drs Sabourin and Benitah from INSERM University, Paris, as well as Doctors Foster and Beech from University of Leeds.
Dr. Carolyn Lam: Now, whereas store operated calcium entry has recently gained attention in cardiac pathophysiology, the role of the prototypic store operated channel known as Orai1 remains elusive. So these authors used a novel genetically modified mouse that specifically disrupts the Orai1 channel in cardiomyocytes and showed that functional inhibition of Orai1 preserved alterations of calcium homeostasis, fibrosis and systolic function without affecting hypertrophy. A novel in vivo small molecule Orai1 channel inhibitor, in fact, markedly improve left ventricular systolic function and calcium handling after pressure overload without causing adverse effects.
Dr. Greg Hundley: Tell me, how does this help me as a clinician?
Dr. Carolyn Lam: All right, you always ask the tough questions. Well, these results really suggest that Orai1 inhibition has the potential for favorable hemodynamic value in the protection of the heart from maladaptive hypotrophy, and therefore might represent a new way to provide inotropic support to help relieve systolic dysfunction.
Dr. Greg Hundley: Very good. Well Carolyn, my first paper is from Dr Peter Kudenchuk from University of Washington Medical Center and this study evaluates the overall survivor after out of hospital cardiac arrest from shock refractory ventricular fibrillation or pulseless ventricular tachycardia related to the route of accessory drug administration. So to accomplish this, the investigators had 2,358 individuals that had received Amiodarone, lidocaine or placebo study drugs and randomized to an IV route.
Dr. Greg Hundley: And then they also included 661 patients that received the same medications, but they were randomized to an intraosseous route.
Dr. Carolyn Lam: So what were the results, Greg?
Dr. Greg Hundley: Well, Carolyn, while no significant effect modification by drug administration route was observed point estimates for the effects of both drugs, both the lidocaine and the Amiodarone, compared to placebo were greater for the IV, as opposed to the intraosseous route and that was across all outcomes. And they had significant increases in survival to hospital admission and discharge and favored improved neurological outcomes with the IV administration.
Dr. Greg Hundley: Unfortunately, however, the study was underpowered to examine for an interaction between the route of vascular access and drug effectiveness and thus additional studies are needed to determine whether Amiodarone in lidocaine may be lifesaving drugs in patients with shock refractory out of hospital cardiac arrest when given IV, but not necessarily intraosseous.
Dr. Carolyn Lam: Very interesting. Well, my next paper is really focused on HIV infection and asks the question, is HIV infection associated with abnormal cardiac repolarization that may contribute to a greater risk for sudden arrhythmic death? Well, corresponding author Wendy Post, our very own from Johns Hopkins University School of Medicine and her colleagues studied 1,123 men, 589 of whom were HIV positive and they were from the multicenter AIDS cohort study and they were studied using the ZioXT ambulatory ECG patch.
Dr. Greg Hundley: Wow. Carolyn, this study sounds like it's the largest study of QT variability in HIV today.
Dr. Greg Hundley: Is that right? And what did the authors find?
Dr. Carolyn Lam: Yeah, it's right. It's huge. And basically they found that HIV positive men had greater beat to beat variability in the QT interval compared to HIV negative men, especially in the setting of HIV viremia and heightened inflammation.
Dr. Carolyn Lam: Among HIV positive men, a higher QT interval variability suggests ventricular repolarization lability which could increase susceptibility to arrhythmias. However, lower heart rate variability also may signal a component of autonomic dysfunction.
Dr. Greg Hundley: Ah, Carolyn. My next paper goes back to the world of basic science and it's from Dr. Chen Yan from University of Rochester. And in this study, Dr. Yon and colleagues examine the role of cyclic nucleotide phosphodiesterase in isolated adult mouse cardiomyocytes and fibroblasts as well as in preclinical mouse models of hypertrophy and/or heart failure. And they found that phosphodiesterase 10A expression is significantly induced in mouse and human failing hearts.
Dr. Greg Hundley: It directly promotes cardiomyocyte hypertrophic growth as well as cardio fiber-blast activation, proliferation, migration and extracellular matrix production. In addition, phosphodiesterase 10A deficiency, so not as much of it, ameliorates cardiac hypertrophy fibrosis and/or dysfunction in different preclinical mouse cardiac disease models. And finally inhibiting phosphodiesterase 10A activity with a compound labeled T P 10 effectively antagonizes the pathological cardiac remodeling in LVH.
Dr. Carolyn Lam: Huh, that's interesting Greg. And now I'll ask you, so what are the clinical implications?
Dr. Greg Hundley: Well, phosphodiesterase 10A inhibitors have been evaluated in phase two clinical trials for treatment of schizophrenia, suggesting that these agents are safe, druggable, if you will, targets. And therefore the results with TP 10 suggests a potential therapeutic effect of targeting phosphodiesterase 10A on antagonizing the development of pathological cardiac remodeling. Perhaps as suggested by Dr. Ezekowitz last week, this could represent another new agent in the treatment of the adverse effects of heart failure syndromes, more pharmacological agents coming to treat heart failure.
Dr. Carolyn Lam: Wow. That is interesting. But okay, let's talk about what else is in this issue. So let me tell you about an online mine by Dr. Kalra and it's called the Cardiovascular Science India Tour. And what this talks about is a multi-pronged initiative bringing together professionals and diverse expertise to allow better understanding of the issues driving the ever-rising cardiovascular disease burden in South Asia.
Dr. Greg Hundley: Oh, very good. And from the mailbag, I've got a research letter, Carolyn from Dr. Julian Luetkens from the University of Bond, who investigates a surrogate of frailty by examining the fat fraction within skeletal muscle at the L three L four level. So it's from an axial CT that's acquired at the time of CT scanning for TAVR pre-evaluation and uses the fat muscle fraction to forecast TAVR outcomes. Well. Carolyn, that's a great wrap up. How about we get onto our feature article?
Dr. Carolyn Lam: You bet.
Dr. Amit Khera: Hi, this is Amit Khera. I am digital strategies editor for circulation and today with our featured podcast we have Dr. Andrew Chapman from the university of Edinburgh, UK who is the first author of a study entitled high sensitivity cardiac proponent and the universal definition of myocardial infarction. Welcome Dr. Chapman. Thanks for joining us.
Dr. Andrew Chapman: Good morning. It's a pleasure. Thank you.
Dr. Amit Khera: This is obviously a very interesting study and timely and on the backs of the prior work that your group has published. Maybe we can start by you telling us a little bit about the impetus, the background which led to this work.
Dr. Andrew Chapman: We've been using high sensitivity cardiac troponin in Europe now for some years, and the way that we diagnose myocardial infarction has, of course changed. We now recognize that myocardial infarction can occur in the context of an occluded coronary artery, be that a STEMI or an NSTEMI, also known as a type one myocardial infarction.
Dr. Andrew Chapman: But increasingly with the use of more sensitive cardiac troponin, we're recognizing myocardial infarction can occur in other conditions. So for example, after arrhythmia or after severe infection with hypoxia. So the real rationale and background for this study is trying to understand better the different subtypes of myocardial infarction. As proposed in the universal definition.
Dr. Andrew Chapman: And we were in quite a unique position to evaluate this as, when we implemented high sensitivity cardiac troponin testing in Scotland as part of a randomized controlled trial. We did so across different hospitals and two of our major cities, Edinburgh and Glasgow, and the trial which formed the basis for this study was called the high States trial and we enrolled 48,000 patients of who we initially used a contemporary sensitive cardiac troponin on an IRC and we then implemented a high sensitivity cardiac troponin IRC.
Dr. Andrew Chapman: And that allowed us to evaluate what impact implementing this high sensitivity test hard firstly on the prevalence of different subtypes in myocardial infarction, but also on the investigations and the treatments received. And finally of course the clinical outcomes of these patients.
Dr. Amit Khera: So obviously at a really sizable study and good forethought on your group to implement this as this step wedge type study design. As you pointed out, the goal here was to understand the different subgroups of myocardial infarction, the prevalence and implications. Tell us a little bit about what you found in this study.
Dr. Andrew Chapman: As I mentioned, we had over 48,000 consecutive patients and that was the real benefit of this step wedge design is that rather than recruiting patients between say nine and five where we had research nurses available, we enrolled all consecutive patients. So we think this is quite a representative population for our area. So of those patients, we found around 10,000 had elevation in the high sensitivity cardiac troponin concentration, and we adjudicated these diagnoses in parallel. So two independent clinicians look through every case, all the clinical information. And we had a consensus from a third when there was disagreement. So in short we found that around half of all elevations in cardiac troponin in this study were to take one myocardial infarction, that is that the blocked artery phenotype and the type two myocardial infarctions or an acute or chronic myocardial injury and myocardial injury being elevation and cardiac troponin, either acute with a rise or fall or chronic with a stable concentration with no evidence of myocardial ischemia and occurred in the other 50% of patients.
Dr. Andrew Chapman: So looking between the phases of the study, we found introducing high sensitivity troponin disproportionately increased the diagnosis of Type II MI or acute or chronic myocardial injury. So there's just an 11% increase in the diagnosis of Type I MI, and I think again that's highlighting that these more sensitive tests are finding myocardial damage in areas that previously it might not have been recognized.
Dr. Andrew Chapman: So moving forward from that, we evaluated the primary outcome of the trial, which was future myocardial infarction or cardiovascular death by subgroup. And we also evaluated unimportant non-cardiovascular death. If I may for just 30 seconds, I'll just discuss why this is important.
Dr. Andrew Chapman: So evaluating future cardiovascular events is very important and in different subgroups of myocardial infarction. However, we know patients with Type II MI and acute or chronic myocardial injury are different. So they tend to be older, they're more commonly female, they have more comorbidities, they're on more medications to start with.
Dr. Andrew Chapman: And these patients are ar increased risk of a competing events to cardiovascular death or a myocardial infarction. And that is that these patients can go on and die, will primarily from their primary illness, be an infection or a pulmonary embolism or what have you. But also they are at increased risk of death from other non-cardiovascular causes.
Dr. Andrew Chapman: So in this study we were able to evaluate future cardiovascular risks using quite advanced competing risks modeling. And I was very grateful for the input of a number of experts and we managed to find that actually, Type I myocardial infarction patients with occlusion or partial occlusion of the coronary artery were at the highest risk of cardiovascular events going forward.
Dr. Andrew Chapman: But interestingly, even despite the vast excess in non-cardiovascular death, patients with Type II MI, and acute or chronic injury also had quite a high cardiovascular risk over three folds out of patients without myocardial injury. And we noticed that these patients did not stand to receive increases in investigations or treatments for coronary heart disease and we speculate and we hypothesize that actually in a proportion of these patients there is some clinical coronary artery disease which has manifested itself during this physiological stress test of an alternative illness. We wonder and we hope that moving forward this might be an opportunity for better targeting it in an investigation and perhaps even improving clinical outcomes.
Dr. Amit Khera: Well, you just shared a ton of important findings there and I'm going to unpackage a few of them. I guess the first is this sort of type I versus type II MI, and I think one of the fears with implementing these high sensitivity troponin would be perhaps an explosion in these type II MIs. And I think, if you look, although you mentioned proportionally, the absolute numbers of increase in type I and type II MI was relatively small so it didn't seem we had this explosion that I think people had feared was implementation.
Dr. Andrew Chapman: Yes, that's a fair point. And also need to bear in mind this is a population of patients from Scotland and our high sensitivity troponin testing is quite selective. You would find differences in the impact of high sensitivity if you're testing practices were different and I know there's prior work from the United States showing that less selective testing or to put it in a different way, testing troponin in more patients. Perhaps some of them may not have symptoms of chest pain or symptoms suggestive of myocardial infarction, is likely to change the prevalence of these different groups and you are likely to pick up more secondary injury or type II MI, but I think we don't need to panic. There's no need for alarm. I don't think there is going to be an explosion in recognition of these patients. If you check a temperature, you'll find a fever, but provided we're sensible and who we're testing, then I don't think practice needs to change dramatically.
Dr. Amit Khera: That was a great way to say it. Unfortunately, we're always looking for fevers in the U.S. So as you pointed out, the prevalence increase may increase a bit, but definitely reassuring from what you're finding in your population was more judicious testing.
Dr. Amit Khera: The second point that you brought up was the event rates, type I versus type II MI. I guess this does remind us again that patients with type II have almost comparable cardiovascular deaths and MI rates as type I, so certainly a higher risk group. As you pointed out, there's many comorbidities there and this gets to your point about treatments. I guess the question is now the event rates are higher, these are higher risk group or what to do about it I think is one of the vexing problems. As you pointed out, there's, there's not a lot of secondary prevention treatments, but what should those treatments be and where do we go from here in terms of these type II MI?
Dr. Andrew Chapman: That's the million dollar question I suppose and something that we've explored in another recent circulation review under the [00:17:07] lead author is what we do for these patients. When we've looked at different strategies, it seems the most reasonable initial approach is determining, does my patient with type II MI or myocardial injury actually have a cardiac problem?
Dr. Andrew Chapman: Now I don't think we have the evidence to support routine and baited testing in this population yet and indeed that might expose patients to harm and that's one of the tensions with this diagnosis.
Dr. Andrew Chapman: For example, consider the patient with gastrointestinal hemorrhage and could it have gone forward for an angiogram. Giving them heparin might not be the best thing to do in their acute illness. However, whether or not these patients would benefit from noninvasive tests such as a CT scan to delineate the coronary anatomy and identify those that might benefit from an iron platelet agent or a statin or indeed an echocardiogram to determine which patients have left ventricular impairment and could benefit from the many number of treatments we have now for LV impairment and that would be my initial thinking is that we need to firstly risk profile these patients.
Dr. Andrew Chapman: What is their pretest probability or likelihood of coronary artery disease? It's not intermediate or high. Let's have a think about investigating their coronary arteries. In the first instance, I think a noninvasive test is going to be most appropriate for the majority of people, but we need a personalized approach. It may be that someone's just had a very brief run of an arrhythmia and that's resulted in a disproportionate level of ischemia and a very high cardiac troponin.
Dr. Andrew Chapman: Your index of suspicion for that patient having coronary disease is going to be significantly higher. So a personalized approach, I think, is where we're heading. And there are trials which are coming in this area. So yeah, two trial is being led by Derek Chu of Melbourne in Australia and they're evaluating the use of CT or invasive angiography to identify coronary disease and target treatment to see if that can improve outcomes.
Dr. Andrew Chapman: And certainly here in Scotland, we're hoping to evaluate the use of a personalized approach to target treatment in patients with type II MI and again, try and improve cardiovascular outcomes. So things are coming.
Dr. Amit Khera: Well, I appreciate that and I think as you pointed out, as we wait for these additional data and additional studies, sort of a thoughtful. algorithmic approach would be helpful and we certainly will make sure the readers and listeners look out for that paper that you mentioned in circulation.
Dr. Amit Khera: I should also point out that your paper here is an excellent editorial by David Morrow, which has a nice figure and illustration of your central findings. So we appreciate that. As we wrap up here, maybe you can tell us what are the main take homes? What should they take away from this study?
Dr. Andrew Chapman: What we've shown is that high sensitivity troponin are useful and we've shown that they increase recognition of patients who have myocardial jury or type II myocardial infarction, where in the past this may not have been found and we've shown quite clearly that these are prognostic. Not only predicting non-cardiovascular disease, but also going on to identify patients at increased risk of myocardial infarction, cardiovascular death.
Dr. Andrew Chapman: So I think moving forward, clinicians using these tests and identifying these patients should be considering investigations to identify coronary or structural heart disease. And until we have that high quality randomized controlled trial data, we need to be pragmatic and we need to evaluate secondary prevention on an individual patient basis, be that an antiplatelet agent or be that a statin as the primary ones. This may even go on to include an ACE inhibitor or a beta blocker if there's LV impairment, but our aim ultimately has to be to try and reduce the cardiovascular event rates in this population who, to date, have been under investigated and undertreated.
Dr. Amit Khera: That summarizes it quite well. And I want to thank Dr. Andrew Chapman for his excellent discussion today and that's why we do these backstage passes to get an inside look as to what the authors were thinking and some behind the scenes on their papers.
Dr. Amit Khera: Again, I'm Omnicare digital strategies editor for circulation, and thank you for joining us on this circulation on the run podcast.
Dr. Greg Hundley: This program is copyright, the American heart association 2020.