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ORIGINALLY PUBLISHED December 9, 2024

Circulation on the Run: December 10, 2024

  • W. Gregory Hundley , MD
  • Peder L. Myhre , MD, PhD

This week offers a double-feature of author interviews. First, please join author Gregg Stone as he discusses the article "Inter-Atrial Shunt Treatment for Heart Failure: The Randomized RELIEVE-HF Trial." Then, please join author Sung-Min Cho and our Circulation on the Run podcast host Greg Hundley as they discuss the article "Clinical Use of Bedside Portable Ultra-Low-field Brain Magnetic Resonance Imaging in Patients on Extracorporeal Membrane Oxygenation: The Results from Multicenter SAFE MRI ECMO Study."

Transcript

Dr. Gregg Stone:

Well thanks Greg. So first, the sponsor of this study, which is V-Wave, which has recently been purchased by Johnson & Johnson will take these data and submit them to the Food and Drug Administration for approval in patients with heart failure with reduced ejection fraction. And that will be a very interesting scenario to see how the FDA responds given that the overall trial was negative and usually that's the end of the story. But there was such a marked interaction according to ejection fraction and there was such a marked reduction in events in the HFrEF group with really no safety concerns identified that I think it's going to make for fascinating discussion. Now that being said, we would all like additional randomized data in patients with reduced ejection fraction both with or either with this device and other interatrial shunt devices that are under investigation. And such trials are being planned.

And finally it raises the specter as what to do about preserved ejection fraction. I mean, our data really suggests that patients might be harmed by interatrial shunt treatment if they have preserved ejection fraction because the heart is very stiff in that condition and the right side of the heart couldn't tolerate the extra left to right blood flow, which raised pulmonary artery pressures and decreased cardiac output. But this was a particular patient population that we enrolled in this study that were very, very sick. It's possible that less sick patients with preserved ejection fraction, those who have normal or near normal pulmonary vascular resistance and right ventricular function may be able to tolerate that increased left or right blood flow and actually have a symptomatic or cardiovascular event prognostic benefit. But trials will have to be done in such a selective group and a different sponsor is doing such a trial. Actually two other sponsors are doing such a trial now with different shunts.

Dr. Greg Hundley:

Well Gregg, we really want to thank you for having this discussion with our listeners highlighting your study, which found that transcatheter interatrial shunt implantation was safe, but overall did not improve outcomes in patients with heart failure. However, a very important caveat as you raised that the results from your pre-specified exploratory analyses and that stratifying on an EF of 40%, shunt implantation was beneficial in those with the reduced EF that is below 40%. But was harmful in patients with a preserved or an EF of greater than 40%. Well, on behalf of Peder and myself, we want to wish you a great week and we will catch you next week on the run.

 

Dr. Peder Myhre:

Welcome listeners to this week's feature discussion, and this is in fact the double feature issue and today we are going to discuss the use of portable MRI machines. Can you believe that? These machines use ultra-low field technology and they enable sensitive imaging. So we'll discuss and learn a lot about this new technology and more specifically, we're going to look at it in the intensive care units, especially patients treated with ECMO. So very exciting and to discuss this study and the results I'm so fortunate to have with me the corresponding author, Sung Min Cho from Johns Hopkins University School of Medicine, but also our old friend Greg Hundley, who is my co-host and the handling editor of this paper from VCU Health Richmond, Virginia. Welcome both. Sung Min, perhaps you can give us a head start here by covering a little bit about the background to this study. What is this portable MRI? What kind of technology do we use here? And what was the aim of your study?

Dr. Sung Min Cho:

Thank you so much. I'm happy to be here today. So I'll start with a portable MRI, ultra-low field portable MRI, which has 0.06 per tesla. It's a technology that enables clinical meaningful sensitive imaging in the presence of ferromagnetic materials in complex clinical settings such as ICU and ECMO patients. Because it has a much smaller magnetic field footprint compared to conventional MRI, this technology allows for the use of MRI incompatible equipment as close as a few feet of the system. It decreases specific absorption rate with the heating and conductive devices and implants. So it really decreases the heating and the migration of this materials that's traditionally not possible with conventional MRI. In our study, we did first human multi-center study. Previously we have conducted preclinical phantom and animal studies at Hopkins, which have shown the safety and compatibility of portable MRI with the ECMO circuit without any deleterious sequelae of the magnetic forces or heating.

And we published our first human ECMO case series in adults in 2022 and then proceeded with this multi-center study. This study was important because currently our knowledge regarding the timing and true prevalence of acute brain injury, I'm going to call this ABI, are very limited because assessing neurologic status in ECMO patient is challenging and often delayed. ECMO patients are critically ill, often receives heavy sedation and often paralytics. Therefore, we have really limited neurologic exam and assessment in these patients. Even if you use standardized neuromonitoring protocol such as NIRS, EEG and TCD, which may improve the detection of ABI, we still have a lot of issues with persistent cardiopulmonary instability that doesn't allow the patient to be transported out of ICU. And it turns out more than 30% of patients do not receive HCT in these patients because of the transport issue and the lack of portable imaging system in the ICU.

Even when possible a patient goes to... ECMO patients go to CT scanner. The issue is the CT scan does not detect hyperacute and acute ischemic changes early on and you may miss early detection of hyperacute and acute ischemic injuries. Currently, of course the traditional or conventional gold standard imaging system is a 1.5 tesla to 3.0 tesla, excuse me, conventional MRI, but that's not possible with extra corporeal life support circuits. So that's the aim of the study to prove or determine the safety of portable MRI across all major cannulation strategies in ECMO patients. And we also wanted to investigate the frequency and type of ABI during the ECMO support.

Dr. Peder Myhre:

Oh, wow. This is such an exciting topic and it sounds almost like science fiction. We all think of these MRI machines as huge machines locked in a room and here you're actually bringing it into the ICU to assess brain damage during ECMO. Fantastic. So you already explained a little bit about the design and the objectives of your study, but can you please elaborate a little more on the patients you enrolled and what kind of outcome measures you use?

Dr. Sung Min Cho:

Absolutely. This was a multi-center prospective observational study between two centers. We included Johns Hopkins and UT Houston, both their tertiary ECMO centers, high volume centers. We included adults only, more than 18 years of age, both VA and VB ECMO, major cannulation strategies. We excluded patients with well-known country indication for conventional MRI. The list goes on, that's in the supplement trail, but except for Swan-Gunz catheter and intra aortic balloon pump. Because we previously already demonstrated at the time of the study in the beginning safety of these devices with portable MRI, we did not include LVAD and Impella in this particular study. That's important to mention because Impella is being used commonly with ECMO support. Our primary outcome again was the safety of using portable MRI in patients during ECMO support defined as completion of portable MRI exam without any serious adverse events and the validation of clinically useful legible imaging acquisition. Secondary outcome was the frequency and type of ABI.

Dr. Peder Myhre:

All right, very nice. And now let's hear the results. What did you find in this study, Sung Min?

Dr. Sung Min Cho:

Yeah, so in the beginning we had 53 eligible patients. So three patients were not scanned due to a large size of the head that did not fit within the head coil of the magnet. So that was one of the limitations of this technology at this time. The portable MRI was performed in 50 patients between two centers, 34 patients with VA-ECMO and 16 patients with VV-ECMO. Of course, in VA-ECMO we included both central and peripheral cannulation strategies. And also in VV-ECMO, both single lumen and double lumen cannulation strategies. The primary outcome was adverse events which occurred in three patients, that's 6%. With two minor events, one was ECMO suction event. This was the very first patient we actually scanned because of the groin flexion when we moved the patient to the scanner in the ICU bed. And we realized that any flexion of the groin at the side of cannulation can cause a suction event.

So there was a learning curve with the very first patient and the second event was minor also, transition low ECMO flow during the MRI scan which was occurring before already, before the scan. So we didn't think it was related to the scanner. One event was serious event, which was a balloon pump MRI function, which was attributable to EKG artifact. One thing that MRI causes is EKG artifact and in this particular patient balloon pump was actually the trigger was EKG, so we learned it. So in this patient you cannot actually have EKG trigger for the balloon pump when you try to scan with an MRI and we pull out the pin because balloon pump stopped working and we changed the trigger to internal set rate 75 bits per minute. And then we scan this patient with MRI without any issues afterwards. And the secondary outcome was type of ABI and prevalence.

Surprisingly or strikingly ABI was observed in 22 patients, that is 44% of the patients during the ECMO support. Most commonly ischemic stroke early 6% followed by ICH or hemorrhagic stroke 6% and anoxic brain injury 4%. We had 18 patients who had both portable MRI and CT scan within 24 hours. And ABI was observed in nine patients with a total of 10 events, eight ischemic and two hemorrhagic events. Of the eight ischemic events, portable MRI observed all eight ischemic events and head CT observed only four events. For ICH or hemorrhagic stroke, portable MRI observed only one of them and head CT observed both two hemorrhagic events. So it may represent that ischemic stroke, portable MRI was much more sensitive than head CT. And hemorrhagic stroke, although it's only two events, head CT may be more sensitive than portable MRI.

Dr. Peder Myhre:

Oh, wow. Congratulations. So many interesting results there. And now we are all very happy to introduce the discussant, Greg, thank you so much for discussing and handling this paper for circulation. And now Greg, I'm curious, as an expert in MRI, why did you find this paper important and what you think are the clinical implications of the findings from Sung Min and team?

Dr. Greg Hundley:

Right. So thanks very much Peder for the introduction. And Sung Min, first I want to congratulate you and your team at Johns Hopkins for pursuing this work. At Circulation, we really like to highlight impactful science and I think the science that you present here and this methodology could be transformative in the future, particularly as many centers today develop the resources to manage cardiogenic shock. And the implementation of ECMO, the implementation of other means of support are sometimes complicated by intracranial events. And you have described it very nicely, that moving those patients through our hospital systems with all the extra support down to a CT scanner or even if the CT scanner is in close proximity to the ICU setting is really a tour de force. And so what you're bringing to this solution is practically well, can we move the imaging device to the close proximity in the ICU?

And I thought that was really intriguing, Peder. And something to discuss further. One thing Sung Min, and we might talk a little bit about this in sort of the next segment, is how do you move a big device like this through an ICU, right? You've got to have hallways, passages, what kind of room size is necessary to really fit this type of device? And we've all been in ICU settings with all this extra equipment, particularly in patients with cardiogenic shock. We might want to elaborate a little bit more on what those items are. I think also another key piece of this relates to your comparison with the other imaging. Now I realize that was only 10 or so patients, but I thought it was striking that the MRI technology identified the ischemic strokes. And we might want to elaborate a little bit further on why it might've missed the hemorrhagic stroke.

Because if we're managing a patient we see that there's a stroke, we're not sure which. And so we want to think a little bit further about that. The low field, for our listeners, low field imaging, we've typically thought about that application with the open magnets, the ones that don't have the confining nature to them. And that's really been primarily worldwide, the application of low field. But here what you've done is taken that low field concept and used it in a new way. And I think that was actually quite clever and creative and it'll be interesting to see how this moves forward. So I think Sung Min maybe think a little bit, what do we need to actually implement this and then also what do you see as the limitation there for why we missed that one hemorrhagic stroke and could that be overcome in the future?

Dr. Sung Min Cho:

Yeah, thanks for the questions. That's really, really insightful. I'll go to that hemorrhagic stroke question first. Of course, the portable MRI, not surprisingly, it was much sensitive to ischemic stroke compared to CT scan. We know that in conventional MRI, of course ischemic strokes were the MRI system is much more sensitive to ischemia than head CT. In portable MRI, two hemorrhagic events, those are really small events, one was a trace. I think both of them are trace actually, subarachnoid hemorrhages. So I think that's probably the reason that actually that was missed in MRI. One of them, of course, the technology is evolving. This already software that the portable MRI, this hyperfine company is using at the time of study is already outdated. Of course there is a continuous advancement in the technology of imaging system, but we also know from conventional imaging system, not portable, but CT scan and MRI, that conventional CT scan also is more sensitive to hemorrhagic stroke than portable MRI is some way. So I think it's not that surprising that portable MRI scan missed one of the two hemorrhages compared to conventional CT head.

And I think your first question on how to move this device into the ICU bed is pretty easy. This portable device is small. If you think of an average male human 175 centimeter, okay, I'm going by centimeter, it's smaller than that and the width is a little bit wider than average human size. So you actually slide the portable MRI near the ICU bed door, and then you actually move the patient in the ICU, the head of the bed will be towards the door of the ICU. So you slide in the MRI and then move the patient right into the scanner. So that's how we have done that, all the scans between the two centers. In the beginning we did require some training to do that, nurses and perfusionist and RTs, but after a couple cases it was pretty smooth transition.

And after the training, not too hard to move this scanner into the ICU bed. Of course there's some questions. This is the US centers right now. So US centers are equipped with a lot of resources. And some ICUs globally, they're divided by curtain, not by the wall. So there is some limitations on that, but I don't suspect even if the patients beds are divided by curtain, there should not be a safety issue with portable MRI.

Dr. Peder Myhre:

Oh, wow. What a wonderful discussion. Thank you both. And now we are getting close to an end, unfortunately. But Greg, I want to challenge you about your thoughts of the future in this field. Where are we going? Can you look into the crystal ball for us, Greg?

Dr. Greg Hundley:

I think a fascinating presentation. One of the issues that we often encounter in this type of patient is the concomitant use of ECMO and Impella, right? Because we're supporting the circulation and the heart's contractility is very limited, but as the heart recovers contractility, oftentimes we also place an Impella device to reduce the afterload from the left ventricle. So I think kind of a next thing we'd like to see is, oh, in that really complex patient, as we're advancing Impella's forward circulatory flow, but we also have the ECMO, can you identify...? Because that's a lot more equipment to move and I think that would be a next study to consider. And then of course larger numbers of patients will be I think a next evolutionary step as well.

Dr. Peder Myhre:

Oh, wow. What an exciting field this is and undoubtedly important research coming from you, Sung Min. Thank you so much for publishing with us in Circulation. And for all the listeners, I recommend everyone to pick up this paper to see the figures. In figure one, you're actually allowed to see one of these machines in the ICU and in figure two you're even allowed to see the comparison of images between the MRI and CT scans. Very interesting. Thank you so much, Sung Min and Greg, for taking the time to discuss this with us today. And thank you audience for joining us. Well, on behalf of Circulation on The Run team, thank you for listening and please tune in again next week.

 

This program is copyright of the American Heart Association, 2024. The opinions expressed by speakers in these podcasts are their own and not necessarily those of the editors or of the American Heart Association. For more, please visit ahajournals.org.

Circulation on the Run

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Cite As

"Circulation on the Run: December 10, 2024", December 9, 2024.

DOI: 10.1161/podcast.20241209.320025