Mar 23, 2020
Dr Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast soiree and backstage pass to the journal and its editors. I'm Dr Carolyn Lam, Associate Editor for the National Heart Center and Duke National University of Singapore.
Dr Greg Hundley: And I'm Greg Hundley, Associate Editor from the Pauley Heart Center at VCU Health in Richmond, Virginia. Well, Carolyn, this week we're going to talk about carotid stenosis, and you remember how we measure those a lot with ultrasound, and what that thickness is, and IMT? Well, we're going to talk about getting some thresholds and an update in that with our feature discussion today. But before we get there, how about grab a cup of coffee and we get started with other papers.
Dr Carolyn Lam: All right. Well, I've got my coffee and I'm ready to tell you about two papers. They're both on left ventricular hypertrophy. One is basic and one is clinical. I will start with the basic paper because it is a super cool one that uncovers a novel mechanism underlying myocardial hypertrophy. And this involves S-nitrosylation, a prototypic, redux-based post-translational modification, S-nitrosylation.
So this is from co-corresponding authors, Drs Xie, Han, and Ji from Nanjing Medical University, who performed a series of elegant experiments using myocardial samples from patients and animal models exhibiting myocardial hypertrophy, and they demonstrated that S-nitrosylation of muscle limb protein plays a crucial role in myocardial hypertrophy.
This muscle limb protein modification enhanced binding to toll-like receptor 3 and receptor interacting protein kinase 3, which stimulated NOD-like receptor pyrin domain containing 3 or NLRP3 inflammasome activation and consequent caspace-1 and interleukin 1 beta activation, ultimately promoting myocardial hypertrophy. They further showed that the deficiency of S-nitrosylated muscle limb protein governed toll-like receptor 3 really alleviates pathological myocardial hypertrophy.
Okay Greg, I can see the look on your face. You're like what? That was a lot. What are the clinical implications, right?
Dr Greg Hundley: Yeah, Carolyn, you are taking me back to molecular biology course 410, that I would take as a senior in college. Wow. So tell me what are the clinical implications?
Dr Carolyn Lam: All right, here's a take-home. The data really identify that S-nitrosylated muscle limb protein is a key regulator, which together with toll-like receptor 3 made therefore serve as putative therapeutic targets in treating pathological myocardial hypertrophy in heart failure. That's the take-home. Before any further comments, let's go to the clinical study.
Now, this one focuses on a malignant subphenotype of left ventricular hypertrophy in which minimal elevations of cardiac biomarkers identify individuals with left ventricular hypertrophy at high risk for developing heart failure. And this is from corresponding author Dr James de Lemos from UT Southwestern. He and his colleagues tested the hypothesis that a higher prevalence of the malignant left ventricular hypertrophy phenotype among blacks may contribute to racial disparities in heart failure risk. So they pooled data from three large multi-ethnic cohorts, that is Eric, Dallas Heart Study, and MESA, totaling more than 15,700 participants. These participants were then classified into three groups: One, those without ECG left ventricular hypertrophy; two, those with ECG left ventricular hypertrophy but normal biomarkers; and three, those with ECG left ventricular hypertrophy and at normal levels of two biomarkers, high sensitivity troponin T above six nanogram per liters, or NT-proBNP above 100 picograms per milliliter. And that last group were the malignant left ventricular hypertrophy group.
They found that the prevalence of malignant left ventricular hypertrophy was threefold higher among black men and women versus white men and women. Compared to participants without left ventricular hypertrophy, the adjusted hazard ratio for heart failure was 2.8 in those with malignant ventricular hypertrophy and only 0.9 in those with left ventricular hypertrophy and normal biomarkers. And these were similar findings in each race and sex subgroups.
Mediation analysis indicated that 33% of the access hazard of heart failure among black men and 11% of the excess hazard among black women was explained by the higher prevalence of malignant left ventricular hypertrophy in blacks.
Dr Greg Hundley: So Carolyn, race could be a really important issue in left ventricular hypertrophy. What did the authors conclude? I mean, how should this help us perhaps manage these patients? What was the take-home?
Dr Carolyn Lam: So this really shows that a higher prevalence of the malignant hypertrophy phenotype may in part, explain the higher risk of heart failure among blacks compared to whites. And what it means too is that when left ventricle hypertrophy is detected by ECG or cardiac imaging, perhaps we should consider measuring high sensitive troponin T or NT-proBNP, which will help distinguish those in whom risk for heart failure is favorable from those at a much higher risk.
Dr Greg Hundley: Very, very interesting. Well Carolyn, I'm going to switch. I've got a basic paper and it's going to focus on dysfunctional adipocytes and how they might talk to cardiomyocytes in the situation of ischemia reperfusion injury. And the corresponding author is Xin-Liang Ma, from Thomas Jefferson University in Pennsylvania.
So Carolyn, do you have any thoughts regarding how patients with diabetes might experience a greater degree of myocardial ischemia reperfusion injury in the setting of an MI?
Dr Carolyn Lam: Oh my goodness, you're really putting me on this spot here. Well, I know things that come to mind would be oxidative stress, microvascular disease.
Dr Greg Hundley: Very good. Open-ended questions for Carolyn's quiz. I'm going to give you a 90. That was very good. So Carolyn, this current study attempted to clarify whether and how small extracellular vesicles may mediate pathological communication between diabetic adipocytes and cardiomyocytes, exacerbating myocardial ischemia reperfusion injury. And to do this, adult male mice were fed a normal or high fat diet for 12 weeks.
The small extracellular vesicles from diabetic serum, diabetic adipocytes, high glucose, high lipid-challenged, non-diabetic adipocytes were injected then, intramyocardially, distal of the site of a coronary ligation.
Dr Carolyn Lam: Okay. So Greg, I would not have guessed it was about extracellular vesicles, but very interesting. What did they find?
Dr Greg Hundley: Intramyocardial injection of diabetic serum small extracellular vesicles or these SEVs, in the nondiabetic heart, significantly exacerbated myocardial ischemia reperfusion injury, as evidenced by poor cardiac function recovery, larger infarct size, and greater cardiomyocyte apoptosis. And administration of small extracellular vesicles, biogenesis inhibitors, significantly mitigated the myocardial ischemia reperfusion injury in diabetic mice. And mechanistic investigations in these studies identified that MIR 130B3P is a common molecule, significantly increased in diabetic serum of small extracellular vesicles and mediated the pathological communication between the dysfunctional adipocytes and the cardiomyocytes. Therefore, if in the future, we could interfere with this molecule, that could perhaps be a novel strategy for attenuating diabetic exacerbation of myocardial ischemia reperfusion injury. Really, a clever study, I think. What else did you find in this issue of the journal?
Dr Carolyn Lam: Yeah, Greg, this week's issue is packed with other papers too. For example, there's the research priorities for HFpEF by NHLBI working group summary by Dr Shah, et al. There's a research letter by Dr Kaltman on the disparities in congenital heart disease mortality based on proximity to a specialized pediatric cardiac center. There's also another research letter by Dr Irisawa, on the impact of low-flow duration on favorable neurological outcomes of extracorporeal CPR, after out-of-hospital cardiac arrest, and this is a multicenter prospective study.
Dr Greg Hundley: It sounds like a lot's in the mailbag. In the couple of things that I wanted to talk about, Dr Giulia Rivasi from the University of Florence, and William White from University of Connecticut, exchange a series of letters back and forth regarding a previous publication on the effects of intensive versus standard ambulatory blood pressure control on cerebrovascular outcomes in older individuals.
I have another research letter entitled, The Cardiac Cell Therapy Rejuvenates the Infarcted Rodent Heart via Direct Injection, but not by Vascular Infusions. And that is from Dr Jeffrey Molkentin from Cincinnati Children's Hospital Medical Center.
Finally, though Carolyn, there's a very interesting piece from Dr Carl Bakker at the Ann and Robert H. Lurie Children's Hospital of Chicago, discussing are we now in a time, in the United States, where congenital heart surgery should be coalesced or regionalized? And that really comes on the back of a discussion of there have been several high-profile articles in the national media, reporting on US congenital heart surgery programs. And that's led to, the author describes, some closure of several centers and at least in five programs. So a great discussion on, should this be regionalized? But we've got a great feature article coming ahead and how about if we head to that.
Dr Carolyn Lam: Let's go, Greg.
Dr Greg Hundley: Welcome everyone, to this feature discussion where we are going to discuss the use of diagnostic ultrasound in the carotid arteries and how that pertains to selection of patients for vascular surgery. And with us today, we have Dr Jesse Columbo from the Geisel School of Medicine at Dartmouth University in Hanover, New Hampshire. We also have Dr Bob Zwolak, from the Manchester VA at the Dartmouth School of Medicine and we have our own Josh Beckman from Vanderbilt University, one of our associate editors at Circulation. And Bob, let's get started with you. Could you tell us a little bit, what was the background of this study and what hypothesis were you looking to test?
Dr Robert Zwolak: It goes without saying that stroke is still a huge health problem in the United States. If there is any good news, it's that stroke incidence is falling slightly, but there are still over 100,000 deaths from stroke each year in United States and as many as 700,000 new strokes each year, and a significant proportion of those derive from atherosclerotic plaque in the carotid bifurcations.
Carotid duplex ultrasound is a fantastic way to assess the presence of plaque in the carotid bifurcations because it does not use any ionizing radiation, does not require any contrast. Ultrasound is a relatively less expensive technology than CT or MR, and the study can be repeated so we can follow people over time, who are found to have significant atherosclerotic plaque in their bifurcations.
The hypothesis of our study though, was that there is variation in the diagnostic thresholds used by various carotid ultrasound testing laboratories, such that it may impact the healthcare and the treatment plans of people who undergo the studies. Jesse will tell you the details, but specifically, we hypothesized that people who undergo this carotid ultrasound test may or may not be inducted into a surveillance program and intensive therapy based on the diagnostic criteria that were used by the individuals conducting their ultrasound study. And even more substantially, we hypothesized that individuals who undergo carotid endarterectomy or potentially carotid stenting, could also have their procedure influenced, whether or not they undergo surgery or stenting based on the carotid ultrasound results. It might vary from one facility to another. So it potentially could be that an individual would be inducted into ultrasound surveillance or even undergo carotid surgery, depending on the vascular laboratory in which they were tested.
Dr Greg Hundley: Jesse, could you tell us a little bit, what was your study population and how did you design this to address the hypothesis that Bob just stated?
Dr Jesse Columbo: Sure. A review of the published literature really shows a variability in that ultrasound criteria that's used for diagnosing carotid stenosis. And so our first objective was to see if we could obtain as many in-use criteria as possible. Our first step was to partner with the Intersocietal Accreditation Commission, the commission that accredits vascular labs. We partnered with them and obtained a 25% random sample of ultrasound criteria in use across the US. And so that kind of gave us the starting point for the criteria upon which to look at.
We then wanted to apply those to a couple of different groups. As Dr Zwolak mentioned, there's really two primary breakpoints here. One, you either have mild stenosis, where you get medical therapy, but no further surveillance, or moderate stenosis, at which point you then are dedicated to long-term surveillance per the AAJ recommendations, or then, the break point between moderate and severe stenosis where surgery is considered.
What we wanted to do is examine the impact of moderate and severe stenosis thresholds. For the severe stenosis thresholds, we use the Vascular Quality Initiative Registry, which collects information on patients who underwent carotid endarterectomy. When we studied patients specifically that we thought the percent stenosis would be the major deciding factor in who got surgery, those are the asymptomatic stenosis and we applied the range of severe stenosis criteria from the IAC to those patients. We then wanted to study other individuals who might be committed to long-term surveillance based on the criteria used. And so for that, we used participants in the Cardiovascular Health Study, which had their induction into the study, had baseline data on carotid stenosis collected. And so that kind of formed our basis of the study, applying the criteria to those two different groups of individuals.
Dr Greg Hundley: And so how many subjects did you have in the two cohorts? And then tell us what were your study results?
Dr Jesse Columbo: Sure. Once we narrowed down that patients in the vascular quality initiative to those who underwent surgery for asymptomatic carotid stenosis, we had about 28,000 patients. And then when we examined the Cardiovascular Health Study, we had about 4,800 or 5,000 patients in that group. What we found was pretty interesting.
If you look at individuals who underwent surgery, and you take the carotid threshold criteria and apply it to them, and if you say, "Well, we're going to take criteria in the fifth percentile versus criteria in the 95th percentile," what you'll find is that 10% of patients who got surgery, fall between that range. And what that means is that there are patients, approximately 10% of patients, who are undergoing surgery that may not have been offered surgery if they had gone to a different institution, which we thought a pretty important finding.
The second part was studying patients who maybe committed to long-term surveillance. And if we took centers that were in the fifth percentile versus those in the 95th percentile for their carotid stenosis thresholds, we found a twofold difference in the number of patients that would be committed to long-term surveillance. And remember, this is the difference between getting aspirin and a statin and medical therapy, but no longer surveillance and getting carotid ultrasound every six months to a year for a long period of time. That twofold difference really could have a meaningful impact on patients.
Dr Greg Hundley: It sounds like we've got a variance issue here and that could really impact clinical care. So while ultrasound's very portable and advantageous, how do we use these results to more effectively select how we're going to implement ultrasound to monitor these patients?
Dr Joshua Beckman: I have to say the results of this study, when I read them the first time were eye opening. One point that doesn't come out clearly to those folks who aren't necessarily in the field, is that these are the labs that have been accredited and they are the top labs in the United States. This doesn't include at least half of the rest of the labs in the United States and suggest that if there's variation in the very best of labs, you know that there's even more variation that's being practiced routinely around the United States. So when I read this, I thought that there was a huge problem that they were uncovering. There are many, many millions of patients with atherosclerosis.
And so what we have to figure out now is how to standardize the measurement and reading of these studies so that ultrasound can be deployed routinely, without a fear of your treatment varying based on which doctor you decide to see and where you decided to go. And I think the fact that these guys highlighted that in such a nice and clear way, really raises the alarm and raises the flag that attention needs to be paid here quite soon because it's quite important.
Dr Greg Hundley: So what study could we perform next? And maybe I'll ask, Bob, you just start off. What study could we perform next to help clarify and guide us to the better use of ultrasound in this situation?
Dr Robert Zwolak: Well, I think there are two issues. The first issue that this manuscript points out is the one of variation and it's real and the results speak for themselves. The second issue is the one of accuracy, and the question of what are the best thresholds? And there are several ways that this can be standardized. I'm pleased to say that the Intersocietal Accreditation Commission, the IAC, that Jesse mentioned, is actually tackling this problem.
Dr Robert Zwolak: But what's the gold standard? 40 years ago when ultrasound was developed, these thresholds that people are discussing, were related to measurements on contrast arteriograms. And the catheter-based contrast arteriogram, a relatively invasive study, was the source and we compared ultrasound velocities to the measurements on the contrast arteriograms to determine these thresholds that Jesse has investigated. That resulted in substantial variation depending on the individual authors. The question is, over time, have the machines changed? Is there really a central focus that we can look at? Most of these studies were very small and so it accounts for the variation in recommendations.
Dr Robert Zwolak: The IAC now, is going back and collecting contemporary contrast arteriograms, not so many of which are done anymore and so, it's taken a very substantial multicenter effort. But trying to look again, to see if there are more accurate results that could be published, studied in a way such that they would be universally accepted and potentially promulgated by professional societies within guidelines. And standardized such that various specialties, whether it's vascular surgeons who run the labs, or a cardiologist, or radiologist, would agree on a set of both accurate and reproducible and constant velocity thresholds to standardize this technology, which is otherwise a very, very good technology and eliminate this variation that we've seen.
Dr Greg Hundley: Well, this has been a phenomenal discussion in a very interesting piece of research. Jesse, can you give us sort of a point forward from here, how do we move forward with some of these results and what you anticipate seeing going forward?
Dr Jesse Columbo: Well, a duplex ultrasound for carotid stenosis is really important. There are lots of studies done. It's a great way to follow patients over time, in a noninvasive manner. And I might hope that this paper would open the eyes of some of the listeners as to what the carotid ultrasound really means. Instead of just looking at the percent stenosis on the report, to perhaps look at the raw velocities and interpret them in the context of the patient, because I think that has really important impact on how we might manage some of these individuals, for each person that you see.
Dr Greg Hundley: Well, listeners, we want to thank Dr Jesse Columbo, Dr Bob Zwolak, also Dr Josh Beckman, for discussing this very informative research related to the use of ultrasound for assessing carotid stenosis.
Dr Greg Hundley: On behalf of both Carolyn and myself, we wish you a great week and see you next week. This program is copyright, the American Heart Association 2020.