Jan 9, 2017
Dr. 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. This episode marks the six month milestone of our run together, a run that has taken us around the world from the United States to Europe, South Africa, and Asia, and one that is shared by listeners all over the world.
On behalf of the editors, and from the bottom of my heart, I want to thank you for your support and request that you please subscribe to our podcast and share it with your friends and colleagues. We commit to bringing you the best of cardiovascular science in the most accurate and digestible way possible, thus suiting the busy cardiologist on the run.
Dr. Lam: All right, here are your highlights of this week's issue.
The first paper looks at tissue plasminogen activator, or TPA treatment in ischemic stroke, addressing two aspects that are still unclear. Number one, the degree of additional benefit accrued with treatment in the first 60 minutes after onset of ischemic stroke; and number two, the shape of the time-benefit curve through 4.5 hours. First author, Dr. Kim, corresponding author Dr. Saver and colleagues from UCLA stroke center analyzed more than sixty-five thousand acute ischemic stroke patients treated with intravenous TPA within 4.5 hours of onset from the "Get With the Guidelines" Stroke U.S. National Program.
They found that 878 of these over sixty-five thousand patients were treated within the first 60 minutes after onset, a ten-fold increase over previously available data. Thrombolytic treatment within the first 60 minutes was associated with the highest rates of favorable discharge outcomes. The shape of the time-benefit curve throughout the first 4.5 hours was non-linear for some outcomes. Discharge to home and discharge free of disability decayed more rapidly in the first hundred to a hundred and seventy minutes after onset than later. While independent ambulation at discharge and in-hospital mortality declined in a steady fashion through the time window.
These findings reinforce the importance of quality improvement programs to accelerate door to needle time for thrombolytic therapy in acute ischemic stroke.
Dr. Lam: The next study sheds light on mechanisms underlying red blood cell mediated hypoxic vasodilation. A highly conserved response coupling oxygen delivery to metabolic demands of the tissues, and very clinically relevant in states of systemic hypoxemia and impairment in oxygen delivery, such as in patients suffering from cardiovascular, pulmonary, or hemolytic diseases.
In this paper, Dr. Bailey and colleagues from University of British Columbia Okanagan in Canada studied ten healthy participants who were randomly assigned to a normoxic, or 21% oxygen, and hypoxic, or 10% oxygen trial with measurements performed at rest and following 30 minutes of cycling at 70% of maximal power output. Blood was sampled simultaneously from the brachial artery, internal jugular, and femoral veins with plasma and red blood cell nitric oxide metabolites measured. Cerebral and femoral venous blood flow were determined by transcranial doppler ultrasound and constant infusion thermodilution respectively.
The authors found that hypoxia was associated with a mild increase in both cerebral and femoral blood flow, with further more pronounced increases observed in femoral blood flow during exercise. Plasma nitrite gradients reflecting consumption were accompanied by red blood cell iron nitrosyl hemoglobin formation at rest in normoxia, during hypoxia and especially during exercise, with the most pronounced gradients observed across the femoral circulation. In contrast, there were no gradients consistent with S-nitrosohemoglobin consumption.
Collectively, these findings suggest hypoxia, and to a far greater extent exercise, independently promote arteriovenous delivery gradients of intravascular nitric oxide with deoxyhemoglobin mediated nitrite reduction, identified as the dominant mechanism underlying hypoxic vasodilation. This is as opposed to the competing hypothesis of S-nitrosohemoglobin formation.
In summary, by distinguishing between the two competing mechanisms that underpinned endocrine nitric oxide vasoregulation, that is, the S-nitrosohemoglobin hypothesis versus the nitrite reductase hypothesis, these data help us to understand the dynamic interplay that takes place between nitric oxide metabolites as a function of oxygen demand in vivo, and will help to establish the most specific and sensitive prognostic markers of vascular health and therapeutic interventions that optimize tissue oxygenation.
Dr. Lam: The next study addresses the controversial issues of thrombus aspiration during percutaneous coronary intervention, or PCI, for the treatment of ST elevation myocardial infarction, or STEMI.
Dr. Jolly and colleagues from Hamilton General Hospital in Ontario, Canada performed an individual patient meta-analysis of three eligible large randomized trials that is the TAPAS, TASTE and TOTAL trials including more than eighteen thousand patients who underwent PCI for STEMI. They found that as a routine strategy thrombus aspiration did not reduce cardiovascular mortality for STEMI patients undergoing primary PCI, and that exploratory analysis of patients with high thrombus burden suggested that thrombus aspiration may improve cardiovascular mortality but at the price of an increased risk of stroke or transient ischemic attack.
In summary, these data suggest that thrombus aspiration should not be used as a routine strategy in patients with STEMI, however in patients with high thrombus burden, further large randomized trials are needed to determine if improved forms of thrombus aspiration can reduce cardiovascular mortality and to determine its safety with regards to stroke.
Dr. Lam: The next paper is the first study to look at coronary artery calcium imaging as a tool to personalize systolic blood pressure treatment goals.
Dr. McEvoy and colleagues from Johns Hopkins University School of Medicine in Baltimore, Maryland studied 3,733 participants from the multi-ethnic study of atherosclerosis with systolic blood pressure between 120 to 179 millimeters of mercury. Within subgroups categorized by both systolic blood pressure and estimated ten year atherosclerotic cardiovascular disease risk, they compared multi-variable adjusted hazards ratios for the composite outcome of incident atherosclerotic cardiovascular disease or heart failure after further stratifying by coronary artery calcium.
The authors found that combining coronary artery calcium imaging and assessment of global atherosclerotic cardiovascular disease risk had potential to guide personalized systolic blood pressure goals, particularly among adults with an estimated risk between five to fifteen percent, and pre-hypertension, or mild hypertension.
For example, among those with an atherosclerotic cardiovascular disease risk of less than fifteen percent and who had systolic blood pressure between 140 and 159, those with a coronary artery calcium score up to 100 were at two times the risk, while those with a coronary artery calcium score more than 100 were at 5.7 times the risk of events, all compared to a coronary artery calcium score of zero. Thus, information on coronary artery calcium burden may be considered when making personalized treatment decisions about blood pressure targets, particularly among patients with an estimated cardiovascular risk between five and fifteen percent, and who have either pre-hypertension or mild hypertension.
In summary, information on coronary calcium burden may be considered when making personalized treatment decisions about blood pressure targets, for example, choosing a traditional goal of 140 or a more intensive goal of 120 millimeters of mercury. The authors ended by calling for a precision medicine clinical trial evaluating risk-based blood pressure treatment goals, preferably incorporating coronary artery calcium.
Well, those were your highlights, now for your feature discussion.
Dr. Lam: On today's episode we are going to be discussing the very important issue of type-two myocardial infarction, very important yet usually neglected compared to type-one myocardial infarction. As a reminder to our listeners, type-two MIs are the ones where there is myocardial demand-supply mismatch whereas type one is the usual acute coronary artery plaque rupture and thrombosis. To discuss this I am really honored to have two James' on the podcast. The first is Dr. James Januzzi from Massachusetts General Hospital, the second is Dr. James de Lemos, executive editor of Circulation from UT Southwestern.
Welcome to you both.
Dr. Januzzi: Thank you very much Carolyn, really great to be speaking with you.
Dr. de Lemos: Thanks Carolyn, it's great to be on.
Dr. Lam: Dr. Januzzi, could you please let us know what you found in this paper, it's really extraordinary. Just give us a top line of the results.
Dr. Januzzi: Basically we set out to examine the question of how frequent type-two myocardial infarction is in a population of patients followed longitudinally after they have taken a trip to the cath lab for one reason or another. Really with the goal to better understand the type-two MI syndrome. It was our hypothesis that type-two MI was perhaps more common than people may have recognized, and that type-two MI would be higher risk in terms of the likelihood for ischemic complications than what people had previously recognized. As you point out, type-two MI is often neglected from a management perspective.
What we found, basically, was among a cohort of patients, 1,250 patients coming through the cath lab at the Massachusetts General Hospital Heart Center, in follow up over a several year follow up period with a maximum of eight years of follow up, with a mean of about 3.4, a median of 3.4 years follow up. Out of the 1,251 patients that we enrolled and followed, 152 actually had an incident type-two myocardial infarction during follow up. Additionally, type-two MI was actually quite recurrent in many patients, and in each of the cases whether individual or in most patients with recurrent type-two MI, the mortality risk was really quite striking. Patients that had a type-two MI, partially because they were more complicated medically speaking, as one might have expected, they were older and had lower blood pressure, more coronary disease, heart failure and other medical comorbidities. The likelihood for a major adverse cardiovascular event was more than doubled in patients that suffered an incident type-two MI, the risk for mortality was actually remarkably almost ten-fold higher with a cardiovascular death rate that was around nine-fold higher, heart failure was tripled.
Really just illustrates the very morbid nature of the type-two myocardial infarction, and illustrates the fact that studies are urgently needed to better understand how we should manage these patients.
Dr. Lam: Dr. Januzzi when I manage patients I find this diagnosis of type two-MI to be a very dirty one to make, if you know what I mean. It's hard to really be sure what's happening, and what to attribute rises in troponin to, and so on. Could you tell us a little bit more about how difficult it was to adjudicate the events, and what's the risk of misclassification in your study?
Dr. Januzzi: It's a challenge, and that's something that came up during the peer-review process. We really wanted to make sure that we got this right, so in fact we went back and did a cross-sectional re-review of cases to make sure that our adjudication process was accurate. It's not a very straightforward thing to judge, obviously. A rise and/or fall in troponin may be from a type-one myocardial infarction. There's increasing interest in a syndrome of myocardial injury in the absence of a classical myocardial infarction. Then lastly, we recognized that troponin may rise and fall, for example, in patients with heart failure, possibly due to non-coronary mechanisms. You are correct, it may be a challenge to classify these patients solely on the basis of the presence of a rise or fall of troponin.
What we did was classify them utilizing the Universal Definition of MI Task Force criteria, which includes symptoms and signs, as well as a rise and/or fall of troponin, plus evidence for loss of myocardial function on non-invasive testing. We were pretty strict, actually, in terms of how we judged them, and when we went back and re-reviewed ten percent of the cases, we actually found that all of the fifteen cases that we went back and re-reviewed met the criteria that we had articulated in the front end. We feel pretty confident that we got the diagnosis correct, but obviously it's a challenge in every day practices, as you rightfully point out.
Dr. Lam: It does certainly sound very rigorous, indeed. Dr. de Lemos, you managed this. He mentioned reviewers giving him a hard time, what was it like managing this paper?
Dr. de Lemos: It was fascinating because the Universal Definition that introduced type-two MI into the classification scheme is only a decade old. It's remarkable how little we know about the problem, and how much we struggle in clinical practice. We thought this paper was one of the first and most comprehensive evaluations to put some construct around the problem. As you pointed out, Carolyn, it is a messy diagnosis. Even when you do it in an organized, researched fashion this reflects what we all deal with in clinical practice where it's not so easy to define myocardial infarction even when given the criteria of the Universal Definition. The challenge really is that only a minority of the troponin elevations that are the classic type-one MIs that we know what to do with. The rest of them are either these troponin elevations NOS, type-two MI, or something on a continuum on this spectrum that's really hard to differentiate.
This paper's important because it really highlights that these non-type-one MIs whatever they are, are common and associated with really high risk, and it's sort of a call to arm that we better start to understand and sub-classify these if we're going to be able to reduce risk in this very high risk population. That's really why we were so interested in the paper, and why we worked so closely with Jim and his team to address some of the issues that you just raised.
Dr. Lam: I completely agree, in fact it's beginning to remind me of the world of HFpEF when we first started realizing that people with heart failure, even though ejection fraction's normal are definitely not doing well. James Januzzi, if you don't mind, what do you think are the implications for treatment, what are the things that you think need to be examined going forward?
Dr. Januzzi: Carolyn I laughed when you mentioned HFpEF because at one of the recent Universal Definition of MI Task Force meetings, I actually said that type-two MI is the HFpEF of the myocardial infarction world. To answer your question, I have approached this question very much the way we do in the heart failure space relative to heart failure with preserved EF. In order to develop a strategy for treatment for type-two MI, we need considerable advances still in our understanding of just what exactly is a type-two MI, what types of patients have type-two MI, and on an individual level, the treatment strategies may follow.
The problem here is if you look just at all comers who suffered a type-two MI in our study, the majority were actually taking statins, they were taking aspirin, they were more likely to be taking beta-blockers. So the patients themselves were actually on the very treatments that we might think about prescribing in those folks that have a type -wo MI, and yet they still suffered the MI, and they had worse outcomes. One might think about coronary disease and revascularization, and indeed one of the nice things about our study is we enrolled patients at the time of coronary angiography, and then followed them subsequently, so we actually had detailed coronary angiograms on every one. Those suffering an incident type-two MI certainly had more coronary disease, so one might argue revascularization might either be protective if done prior to the onset of type-two MI, or at the time of type-two MI a revascularization-driven strategy might be a logical approach.
I think more fundamentally, bringing it back to heart failure and to the HFpEF analogy, I think that in order to better understand treatment we need to better understand just who these patients really are. So much like has been done in the heart failure space we're now doing cluster phenotype analyses where we're looking at the various phenotypes of patients with type-two MI using network analyses, which is one way to approach a problem when you've got a mix of various diseases that fall under the same title. So in those patients with preserved ejection fraction heart failure, there are patients that are younger obese patients, there are the patients with advanced diabetes, et cetera.
Our hypothesis for our present research is to examine this question within the type-two MI diagnosis to see if we can identify specific clusters of phenotypes that might be treated in specific ways. The coronary patients might deserve revascularization, the heart failure patients might deserve a different approach for their care. That, I think, might be the way forward, exactly taking a page from the playbook that you just mentioned with respect to preserved ejection fraction heart failure.
Dr. Lam: Wow, how terribly exciting. Congratulations again for this paper, I really think it's a landmark and will open the door to many more important papers. I would like to switch tracks a little bit at the moment. We are coming to six months into the new Circulation editors that have been under the leadership of Joe Hill and James de Lemos, and I'd actually like to start by asking you, Dr. Januzzi, what was it like working with our new Circulation team? Then handing the mic over to Dr. de Lemos to tell us a little bit more about what the journey has been so far in the last six months.
Dr. Januzzi: Thanks for asking, it was an absolute pleasure. I trained with Dr. Hill and with Dr. de Lemos in one degree or another during all of our respective residency and/or fellowship training, so I've known these guys for a long long time. I think that the most important aspect in the peer review process is a collaborative and collegial process where the division between author and editor can allow for communication. In this experience with this manuscript, it was a very easy-going and collaborative process where the paper from beginning to end grew in its quality, and ultimately landed in the journal, and the way that it did was, I think, a substantial likelihood for heavy citation. That says a lot about the editors who really help us to bring it to this final product.
Dr. Lam: Dr. de Lemos?
Dr. de Lemos: We're now six months in to the new Circulation editor team's tenure, and I think all of us are having a blast. I think we've put together this team of diverse international experts that build off each other and thrive off each other, so from the team perspective, we're just having great fun, working hard, learning a great deal. We hope that those of you out there that are listening and reading, and submitting papers, and using our journal for your own research, are noticing the changes that we've made and think we're headed in the right direction. We'd love to hear from you about the things you like, and those things you don't like. We do think we've, in many ways, modestly changed the focus of the journal. There's so many new content categories that are designed to speak to the global burden of cardiovascular disease, the international aspect of cardiovascular research, and new clinically relevant problems, translating basic science so that clinicians can understand it. We hope that clinically active, as well as basic investigators are finding these changes useful in their own daily lives.
Dr. Lam: Thank you both so much for spending time with me on Circulation on the Run. Thank you everyone, don't forget to tune in next week.