Dec 12, 2022
This week, please join author Trisha Singh as she discusses her article "Manganese-Enhanced Magnetic Resonance Imaging in Takotsubo Syndrome."
Dr. Carolyn Lam:
Welcome to Circulation on the Run, your weekly podcast summary and backstage pass for the journal and its editors. We're your co-hosts. I'm Dr. Carolyn Nam, Associate Editor from the National Heart Center and Duke National University of Singapore.
Dr. Greg Hundley:
And I'm Dr. Greg Hundley, Associate Editor, director of the Pauley Heart Center at VCU Health in Richmond, Virginia.
Carolyn, very interesting feature discussion this week. Many times we hear in magnetic resonance imaging the use of gadolinium contrast. And remember, gadolinium is an extracellular agent. And when we apply it in the heart, we look for infarcts, or areas of the heart that are perhaps dead, or scarred over. This week's feature discusses manganese as a contrast agent and it is an intracellular contrast agent. And very interestingly, it identifies calcium handling, so it's a marker of viability. And these authors are going to apply manganese as well as gadolinium in trying to understand mechanisms behind Takotsubo cardiomyopathy.
But before we get to that, how about we grab a cup of coffee and jump into some of the other articles in the issue?
Dr. Carolyn Lam:
Oh, I'd love to tell you about the other articles. But just have to first say, I loved your description of the feature paper. It's right up your alley and I can't wait to learn more.
But my first paper today I want to talk about pulse field ablation. Now, what is that? Pulse field ablation, or PFA, is a unique and novel technique to treat atrial fibrillation. It has a unique safety profile largely related to its preferentially for myocardial tissue ablation. And thus, sparing the esophagus and thus, deemed to have a unique safety profile. Now, a pentaspline catheter was the first such PFA system studied for AF ablation. And in the initial trials the catheter was used for pulmonary vein isolation and left atrial posterior wall ablation.
However, following its regulatory approval in Europe, in clinical practice, physicians have ablated both these locations and expanded lesions that could be in closer proximity to the coronary arteries. Now, this is an unstudied important issue since preclinical and maybe some clinical data have raised the potential for coronary arterial spasm. Hence, the investigators led by Dr. Vivek Reddy from Icahn School of Medicine at Mount Sinai and colleagues studied the vasal spastic potential of PFA lesion sets, both remote from and adjacent to coronary arteries.
Dr. Greg Hundley:
Wow, Carolyn, this is a really interesting question. So what did they find?
Dr. Carolyn Lam:
In this retrospective analysis of a series of 25 patients undergoing PFA for atrial fibrillation in whom coronary angiography was performed pre, during and post ablation, they found that during pulmonary vein isolation and left atrial posterior wall ablation, coronary spasm did not occur. However, cavotricuspid isthmus ablation provoked severe subtotal vasospasm in five out of five consecutive patients. And this was relieved by in coronary nitroglycerin. ST elevation was not observed. No patient had severe spasm if first pretreated with parenteral nitroglycerin, either intracoronary or intravenous.
And so in summary, coronary vasospasm was not provoked during PFA at locations remote from the coronary arteries. But when the energy is delivered adjacent to a coronary artery, like in cavotricuspid isthmus ablation, PFA did provoke subclinical vasospasm. And the phenomenon was attenuated by nitroglycerine administered either post hoc to treat spasm or as prophylaxis. And this is discussed in accompanying editorial, I like it, “Coronary Vasospasm in PFA Primum Non Nocere” by Drs. Estes and Sundeep and Saba.
Dr. Greg Hundley:
Very nice Carolyn. Very important research in this area using that particular methodology.
Well Carolyn, my next study comes to us again from preclinical science. And Carolyn, this study evaluated mechanisms responsible for pulmonary hypertension.
So as background, pulmonary hypertension is associated with increased expression of VEGFA and it's receptor VEGFR-2. But whether and how activation of VEGFA signal participates in the pathogenesis of pulmonary hypertension, that's unclear. And so these authors led by Dr. Yangxin Chen from Sun Yat-Sen Memorial Hospital and Sun Yat-Sen University evaluated VEGFA, VEGFR-2 signal activation and VEGFR-2 Y949 dependent vascular leak in lung samples from patients with pulmonary hypertension as well as in mice exposed to hypoxia.
Dr. Carolyn Lam:
Another one of those excellent translational pieces, isn't it Greg? So what did they find?
Dr. Greg Hundley:
Right Carolyn. So these authors found that pulmonary hypertension led to excessive pulmonary vascular leak in both patients and hypoxic mice. And this was owing to over activated VEGFA and VEGFR-2 Y949 signaling axis. Abolishing VEGFR-2 Y949 signaling via a specific point mutation was sufficient to prevent pulmonary vascular permeability and inhibit macrophage infiltration and Rac1 activation in smooth muscle cells under hypoxia exposure. This, in turn, led to alleviation of pulmonary hypertension manifestations including muscularization of distal pulmonary arterials, elevation of right ventricular systolic pressure and right ventricular hypertrophy.
And so Carolyn, in summary, these results suggest that VEGFA, VEGFR-2 Y949 dependent vascular permeability is an important determinant in the pathogenesis of pulmonary hypertension and might serve as an attractive therapeutic target pathway for this disease.
Dr. Carolyn Lam:
Aw, thanks Greg for explaining that so well.
The next paper talks about transcatheter aortic valve replacement of TAVR, recognizing that it is a well established treatment now for high and intermediate risk patients with severe symptomatic aortic stenosis. However, the question asked here is what makes some, but not all patients improve their left ventricular ejection fraction following TAVR associated after load reduction?
Now, hypothesizing that circulating microRNAs may play a role here, the authors led by corresponding authors, Dr. Hosen and Jansen from University of Bonn and their colleagues profiled the differential expression of microRNAs in circulating extracellular vesicles in patients after TAVR. And in particular, the novel role of circulating microRNA 1225p in cardiomyocytes.
Dr. Greg Hundley:
Oh wow. So Carolyn, important study. So what did they find?
Dr. Carolyn Lam:
Well, first aortic stenosis increases circulating microRNA 1225p, which correlated with a lack of improvement of the EF in patients after TAVR. Extracellular vesicles harbored microRNA 1225p and facilitated its startling into the cardiomyocytes. Vesicular shuttling of this particular microRNA was regulated by a direct interaction with a multifunctional RNA binding protein called heterogeneous nuclear ribonucleoprotein U in a sequence specific manner. Extracellular vesicles containing the specific microRNA post transcriptionally repressed BCL2 an anti-apoptotic gene, which is central to cell viability and apoptosis.
So in summary, Greg, an increase in extracellular vesicle microRNA 1225p in patients with aortic stenosis represents a novel mechanism for the deterioration of cardiac function in patients following TAVR. And pharmacological manipulation of this axis may improve ejection fraction and cardiac function in patients with aortic stenosis by improving the viability of cardiomyocytes, which opens the door to a potential therapeutic approach in patients with limited EF improvement following TAVR.
Dr. Greg Hundley:
Oh Carolyn, beautiful, beautiful description of that wonderful preclinical science.
Well, let's reach into the mail bag and see what else is in the issue. And first, there's a research letter by Professor van Raalte entitled “Kidney Hemodynamic Effects of Angiotensin Receptor Blockades Sodium Glucose Co-transporter 2 Inhibition Alone and in Their Combination: A Crossover Randomized Trial in People with Type 2 Diabetes.”
And Carolyn, there's also an In Depth piece from Dr. Marx entitled “GLP1 Receptor Agonist for the Reduction of Atherosclerotic Cardiovascular Risk in Patients with Type 2 Diabetes.”
Dr. Carolyn Lam:
Very, very nice papers, those two. There's also an exchange of letters between Drs. Hou and Sedej regarding the article, “Fine Tuning Cardiac Insulin Like Growth Factor 1 Receptor Signaling to Promote Health and Longevity.” As well as a Perspective by Dr. Eagle, “Comments on the 2022 Aortic Guidelines: Seeking More Precision in Aortic Care.”
Now, let's go onto the feature discussion of all things MRI, shall we?
Dr. Greg Hundley:
You bet. More on manganese.
Welcome listeners to this very interesting feature discussion on December 13th. And we have with us Dr. Trisha Singh from the University of Edinburgh in Edinburgh, Scotland.
Welcome, Trisha. This is a fascinating study incorporating manganese cardiovascular magnetic resonance to study some of the mechanistic underpinnings of hypokinesis left ventricular hypokinesis in patients with Takotsubo syndrome. So maybe just describe for us some of the background information that went into the preparation of your study, and what was the hypothesis that you wanted to address?
Dr. Trisha Singh:
Yes, of course. So we know with patients with Takotsubo syndrome, it predominantly affects middle aged women, patients present with a degree of left ventricular dysfunction, which is transient. And, unfortunately, it can be quite difficult to diagnose because it can phenotypically present very similar to an acute coronary syndrome. We know from previous studies that these patients do have ongoing symptoms despite normalization of their LV function. And actually their outcomes are not as benign as previously thought.
In terms of manganese enhanced MRI imaging, we at Edinburgh University have imaged patients with other cardiac conditions such as hypertrophic cardiomyopathy, and dilated cardiomyopathy. And have established that it can be used as a surrogate marker of myocardial calcium uptake and handling. So we were very interested to see whether or not patients with acute Takotsubo syndrome have got a myocardial calcium dysfunction and more importantly whether or not this translates into long-term dysfunction and perhaps could explain their symptoms and worse prognosis in long-term.
Dr. Greg Hundley:
Trisha, manganese MRI. Now, we hear about gadolinium MRI, how is manganese different? You mentioned it's a nice marker for calcium handling. Is this widely used clinically? What kind of contrast does it provide?
Dr. Trisha Singh:
So manganese was actually one of the first contrast agents to be used with magnetic resonance imaging. It kind of came about in the 1970s and 1980s. And previous animal models have looked at how it is essentially an intracellular contrast agent. And what I mean by that is manganese is a calcium analog and therefore, in cells where they are viable and there's intact cell function, they will be taken up through a voltage gated calcium channels. So, for example, in the heart. So the theory is that manganese, when you've got normal viability, manganese is taken up into the myocardium via voltage gate calcium channels. And several studies have shown that if you then have disease myocardium, these tissues do not take up the manganese as normal tissue would.
And the main difference between manganese and gadolinium is they are both paramagnetic, which is why they're helpful and useful in MRI. But gadolinium, as a compound, is too big and it cannot cross an intact cell membrane and therefore, gadolinium is more extracellular. And as, we know, accumulates in tissues where there is increased edema, or water content. So gadolinium, for all intents and purposes, is incredibly useful contrast agent, certainly what we use predominantly at the moment in clinical practice, but it is extracellular. So the theory behind manganese is that it is an intracellular contrast agent as opposed to gadolinium. And where gadolinium accumulates in disease tissue, manganese accumulates in viable tissue. So they behave almost kind of in contrast to each other.
And currently, manganese is not used in clinical practice. I think the only clinical compound contrast agent utilizing manganese was mangafodipir, otherwise known as Teslascan, which I believe came off the market in 2012 and that was predominantly used for imaging liver metastasis.
Dr. Greg Hundley:
Well Trisha, thank you for clarifying for us the difference between manganese, the intracellular contrast agent, and gadolinium, the extracellular contrast agent, that's so widely used clinically.
Well, with that description, can you describe for us now, your study population and your study design?
Dr. Trisha Singh:
Perfect. So the study population was we aimed to recruit 20 patients with acute Takotsubo syndrome. The diagnosis of Takotsubo syndrome was based on a clinical diagnosis, so all our patients underwent a baseline echocardiography and invasive coronary angiography.
Now, for us, the coronary angiography was quite important because we wanted to ensure we ruled out anyone with an acute myocardial infarction, which can often be tricky in this cohort of patients.
So after recruiting 20 patients during the acute phase of Takotsubo, they all underwent a baseline gadolinium enhanced MRI scan followed by a manganese enhanced MRI scan. And these were done at least 48 hours a part. And then about three months roughly after the acute index, they were all invited to participate in a second manganese enhanced MRI scan.
Dr. Greg Hundley:
Very good. So two exams separated longitudinally over time. What were your study results?
Dr. Trisha Singh:
Our results demonstrated that during the acute phase as one would expect, patients had a degree of left ventricular dysfunction. The majority of our patients had afibrillar Takotsubo, so had afibrillar ballooning with preservation of the basal segments. With this, we also noted that in the areas that were affected by Takotsubo, so kind of the mid ventricular wall and the apex that all patients had significantly elevated native T1 and associated T2 as well. And as we expected there was reduced uptake of manganese and therefore kind of reduced calcium uptake in the myocardium in the area affected by Takotsubo syndrome.
Interesting, what we also noticed was that all these patients had significantly elevated LV mass, which has been described in previous Takotsubo papers, certainly by Professor Dawson. And when you measured the left ventricular wall thickness, the LV wall thickness is elevated in the affected and actually not even in the non-affected areas, which I suspect explains why in the acute phase people almost doubles up which kind I guess fit with kind of acute myocardial edema and intense water content.
And then, three months later when these patients returned for their follow-up scan, a lot of the acute changes had resolved. So native T2 values had improved and gone back to baseline. Native T1 and post contrast T1 values had remained elevated compared to the control population. And what we found was that manganese uptake, though it had improved, it still remained abnormal and reduced compared to the control population, which is a finding that we weren't expecting to find.
Dr. Greg Hundley:
Very interesting. So acutely we've got extracellular water there, elevation of myocardial T2, and also impaired manganese uptake. So intracellular abnormalities with calcium handling. Then later, so three months later, we have restoration of myocardial T2 so the extra water content is absent, but we have impaired manganese uptake indicating an abnormality with calcium handling. So how do we put this all together mechanistically? What does this tell us about the pathophysiology of Takotsubo syndrome?
Dr. Trisha Singh:
For one thing, I think we can say that there is, as described before, there is obviously intense myocardial edema present in patients with acute Takotsubo. And I think the significant elevation in T2 and LV mass kind of all fits together. Actually interestingly, as native T2 improves in their follow-up scans, the LV mass actually all return back to normal baseline. So I think the acute edema does resolve.
And as you said, interestingly, despite all of these patients, their LV function completely recover. And despite that their myocardial calcium uptake, or handling remain normal. And I think that's not been demonstrated before. And I think it just points to that there is obviously, still something going on in the myocardium and it's not behaving completely normally despite completely normal kind of gross LV function. And potentially, this might point in the direction of why these patients have ongoing symptoms. So, certainly, from our observational cohort group, about 70% of patients had ongoing symptoms and this was predominantly breathlessness and palpitations. And potentially, might be related to why patients have worse outcomes compared to the general population.
Dr. Greg Hundley:
Very nice. And Trisha, can you describe, was there a therapeutic intervention between the acute and then the three month later measurements? Were these patients administered any type of medical therapy and were there differences in what those therapies may have been between different patients in your study?
Dr. Trisha Singh:
So predominantly, most of the patient population that were started on some combination of heart treatment due to the baseline LV dysfunction. And this kind of was a combination of most of them were on Ramipril, a few of them were also on spironolactone or eplerenone. And then, every single one was on furosemide. And interestingly, I mean I appreciate, I think the population group was quite small, so it's very difficult to compare those that were on kind of full heart failure treatment versus those who were just on beta blocker and ramipril therapy. But even in that cohort there was a split of about, I think predominantly, I think 17, 16 patients were on kind just beta blockers and ramipril as opposed to beta blocker, ramipril, spironolactone. And there was no difference kind of in the recovery in manganese uptake in that cohort. But, again, the numbers are quite small, so I think it's difficult to extrapolate any kind of true meaning in that.
Of course, we know there's a lack of randomized control trial data looking at how to best treat patients with acute Takotsubo syndrome and certainly, what treatment may prevent these patients from having a recurrence of Takotsubo. And I know some of the TACA registry data has looked at actually despite the fact patients of being on beta blocker, or ramipril therapy, they still go having recurrence of Takotsubo and certainly of our cohort, one of our patients went on having a recurrent episode of Takotsubo within a year of her index event and she was on aspirin, beta blocker, spironolactone as well.
Dr. Greg Hundley:
Very nice.
And then lastly, when you made these measurements looking at the manganese uptake or lack thereof, were these in the regions of myocardium where you mentioned many had apical LV wall motion abnormalities, were they in those regions or did you also measure regions remote to where the wall motion abnormality occurred?
Dr. Trisha Singh:
Of course. So we took measurements in the affected regions of the heart that kind of demonstrated spironolactone syndrome. And we also took measurements in kind of, so to speak, the remote segments of the heart.
Now, for the remote segments of the heart, we could only measure native T1 and post contrast T1 at 30 minutes and to measure manganese uptake well, unfortunately, what we have to do is take a measurement over time, so we'd do every two and a half minutes for 30 minutes after the manganese contrast. So we weren't able to calculate manganese uptake in the remote regions. But what we could do was measure the native T1 in the remote region, and then the post contrast T1 and see how it differed with the region of interest in the affected portion of the heart, so to speak.
Dr. Greg Hundley:
Very good.
Well, Trisha, with this really exciting research and very nice methodology, what do you see as the next study to be performed in patients with Takotsubo?
Dr. Trisha Singh:
So I think, in terms of manganese enhanced imaging, I think it'd be really interesting to re-scan these patients at one year or at two years. And the question there is whether or not their manganese uptake ever recovers really. I know we previously talked about this and thought about whether or not these patients who go onto developing Takotsubo syndrome might actually have a kind of an underlying cardiomyopathy that puts them at risk of developing Takotsubo with stress. So it'd be interesting to see whether or not actually their calcium uptake ever recovers in the long-term, or whether actually they have more of a chronic heart failure type like picture.
And I think another area of interest would be to see potentially using manganese imaging as a noninvasive measure of kind of myocardial calcium activity and to see whether or there's any changes with therapy over the course of months to years or so.
Dr. Greg Hundley:
Very nice.
Well listeners, we want to thank Dr. Trisha Singh from University of Edinburgh in Edinburgh, Scotland for bringing us this really interesting article in patients with Takotsubo syndrome demonstrating that there is a marked perturbation of myocardial manganese uptake, which is most evident in the acute phase of Takotsubo presentation, but also persists for at least three months despite apparent restoration of normal left ventricular ejection fraction and resolution of myocardial edema. All of this suggesting that abnormal myocardial calcium handling may be implicated in the pathophysiology of Takotsubo syndrome.
Well, on behalf of Carolyn and myself, we want to wish you a great week. And we will catch you next week on the run.
This program is copyright of the American Heart Association 2022. The opinions expressed by speakers in this podcast are their own and not necessarily those of the editors or of the American Heart Association. For more, please visit ajjournals.org.