Aug 5, 2019
Dr Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. We're your cohosts, I'm Dr Carolyn Lam, associate editor from National Heart Center and Duke National University of Singapore
Dr Gregory Hundley: And I'm Greg Hundley, associate editor from the Pauley Heart Center in Richmond, Virginia at VCU Health. Our feature article today really invokes thought regarding LVAD bridging to heart transplantation. I really look forward to the conversation with Dr Veli Topkara from Columbia University, the corresponding author and our associate editor, Dr Mark Drazner from UT Southwestern. And it's regarding the outcomes from their study, evaluating patients waiting for transplant that are bridged with an LVAD versus not. But before we get to that, let's dive into some of our other original articles with our little coffee chat. Do you have an article that you'd like to discuss?
Dr Carolyn Lam: You bet I do Greg and I have my coffee here. Have you ever wondered, does microvascular disease, in any location in the body, increase the risk of lower limb amputation? Well, this was looked at in the paper that I chose first today. It's from Dr Beckman from Vanderbilt University Medical Center in Tennessee and his colleagues, and they basically examined 125,674 participants in the Veterans Aging Cohort Study from 2003 to 2014 and analyzed the effect of prevalent microvascular disease defined as retinopathy, neuropathy and nephropathy and peripheral artery disease status on the risk of incident amputation events, of which there were 1,185 amputations over a median of 9.3 years.
Dr Gregory Hundley: Wow, Carolyn. What did this study find? What did Josh and his colleagues find?
Dr Carolyn Lam: They found that the presence of microvascular disease increases the risk of amputation significantly in the absence of peripheral artery disease. As many as one in six below knee amputations may result from microvascular disease, even without peripheral artery disease. Microvascular disease also potentiates the amputation risk in persons with peripheral artery disease to more than 20-fold, compared to persons with neither peripheral artery disease nor microvascular disease. Further research is really needed to understand the mechanisms by which this occurs. And in the meantime, clinicians should bear this increased risk in mind when screening for and managing lower extremity disease.
Dr Gregory Hundley: Ah. Well Carolyn, my first paper is somewhat related because we're going to talk about triglycerides. And this paper is from Zahid Ahmad from UT Southwestern Medical Center. He's the corresponding author. And can you imagine Carolyn an antibody that could correct elevations in serum triglycerides?
Dr Carolyn Lam: Tell us about it, Greg.
Dr Gregory Hundley: Well, I'm going to give you a little background first. Low levels of triglycerides and other lipids are observed in individuals with loss of function mutations in angiopoietin-like protein 3 which inhibits lipoprotein lipase activity, increasing triglycerides and other lipids, and providing a rationale for development of a monoclonal antibody therapy.
Dr Carolyn Lam: Interesting. What did this study do Greg?
Dr Gregory Hundley: It evaluated evinacumab. They looked at the safety of this. This is a fully human angiopoietin-like protein 3 antibody, and it was compared with placebo, with no serious treatment emergent adverse events, no events related to death or treatment discontinuation was reported. They did two phase one studies evaluating single and multiple ascending doses. In addition, substantial and sustained percent reductions from baseline versus placebo were observed and triglycerides with absolute levels reaching about 50 milligrams per deciliter for several of the evinacumab doses at specific time points in both studies. And therefore, the data from these two phase one studies in this one paper support further clinical evaluation of this new antibody in larger studies of hypertriglyceridemic individuals.
Dr Carolyn Lam: Definitely a space to look out for. Well Greg, my next paper is a basic paper. Genome wide association studies have identified chromosome 14 Q32 as a locus for coronary artery disease. The disease associated variants fall in a hitherto uncharacterized gene called Hedgehog Interacting Protein Like 1, or HHIPL1. the function of this gene and its role in atherosclerosis has previously been unknown, well, until today's paper. But Greg, here's your quiz. What do you know about the hedgehog proteins?
Dr Gregory Hundley: Well, I know hedgehogs are friendly little animals and I know they must have great proteins because they're so friendly.
Dr Carolyn Lam: Why did I expect that? Oh, let me tell you a little bit about them. The mammalian hedgehog proteins like sonic hedgehog, desert hedgehog, and Indian hedgehog are secreted molecules that exert a concentration and time dependent effect on target cells following binding and complex signal transduction pathways. They induce the transcription of target genes, primarily involved in cell proliferation, survival, and fate specification.
Now in adults, the hedgehog signaling is involved in the maintenance of adult vasculature and ischemia induced neovascularization, including after myocardial infarction. Today's authors, however, including Tom Webb from University of Leicester and colleagues, report the first experimental investigation of HHIPL1 and the present evidence that it is a secreted proatherogenic protein that regulates smooth muscle cell proliferation and migration. So, that's novel.
Through a series of experiments involving coronary artery disease, relevant human cells and mouse models, they showed that HHIPL1 is a secreted protein that interacts with sonic hedgehog and is a positive regulator of hedgehog signaling. In murine models, HHIPL1 deficiency attenuates the development of atherosclerosis by reducing smooth muscle cell proliferation and migration. The clinical implications are two-fold. First, this study supports HHIPL1 as the causal gene at that 14 Q32 coronary artery disease locus that we did not really understand previously. And secondly, HHIPL1 is a promising therapeutic target that affects a pathogenic mechanism not addressed by current mechanisms for coronary artery disease. Room for novel development.
Dr Gregory Hundley: Very interesting Carolyn. Well, I've got another basic science paper, and this is from Dr Kenneth Walsh at University of Virginia and it's going to look at the role of neutrophils, not necessarily macrophages but neutrophils and their role in pressure overload induced cardiac dysfunction. While the complex roles of macrophages in myocardial injury is widely appreciated, the function of neutrophils in nonischemic cardiac pathology has received relatively little attention. This study examined the regulation and function of neutrophils in pressure overload induced cardiac hypertrophy as mice underwent treatment with Ly6G antibody to deplete neutrophils and then subjected them to transverse aortic constriction or TAC.
Dr Carolyn Lam: Huh? What did they find?
Dr Gregory Hundley Caroline, the study revealed that neutrophils played a critical role in the hypertrophy of the left ventricle that results from pressure overload in this murine model of heart failure and identified that a non-canonical Wnt protein is essential for the recruitment of neutrophils to the injured myocardium.
Dr Carolyn Lam: Hmm. What do you think are the clinical implications of this?
Dr Gregory Hundley This study demonstrates how neutrophils contribute to the hypertrophy of the left ventricle under conditions that do not involve ischemia or myocardial necrosis. Also, since cardiac hypertrophy is a risk factor for the development of heart failure, this study implicates WnT5a mediated neutrophil infiltration as an early step in the progression of this disease.
Dr Carolyn Lam: Wow, thanks Greg. That was so cool. But let's hurry on to our feature discussion, shall we?
Dr Gregory Hundley You Bet.
Dr Carolyn Lam: Bridge to transplant with left ventricular assist devices is a mainstay of therapy for heart failure in patients awaiting heart transplantation. The criteria for heart transplantation listing does not differ between patients medically managed versus mechanically bridged to heart transplant. However, are there differences in post-transplant outcomes between medically managed and mechanically bridged patients? Well, today's paper provides important data to address this question. So pleased to have with us the corresponding author, Dr Veli Topkara from Columbia University Medical Center, New York Presbyterian as well as Dr Mark Drazner, associate editor from UT Southwestern. Welcome gentleman. Veli, this is an important question. Could you please tell us how you addressed it and what you found?
Dr Veli Topkara: We decided to visit an old question of whether bridging with LVAD confers at risk for post-transplant mortality. Because the field and pump technology has been rapidly changing. There has been a significant increase in utilization of devices nationwide to the extent that more than 50% of patients already have an LVAD in place by the time they receive a heart transplant. And patients also wait much longer on these pumps before they could get a heart.
Currently, available devices provide continuous flow and patients essentially live without a pulse for many months to years waiting for a heart. And with this unique physiology, they also have unique complications such as RV failure and there has also been pre-survey reports including one from our center suggesting an increase in the primary graft failure rates after heart transplant. And mostly seen in patients who were bridge to transplant with an LVAD.
To address some of these questions, we took advantage of the UNOS database, which is the largest prospective transplant data registry in the United States. We were able to identify more than 14,000 patients who are either medically or mechanically bridged to transplant. We then derived a cohort from patients who were LVAD baseline by propensity score and we looked at their outcomes.
And what we found was that patients who were mechanically bridged to transplant with an LVAD, had 9.5% mortality at one year, compared to 7.2% in patients who were medically bridged. And this is more than 30% increase in relative risk of death for LVAD patients. When we looked at the specific cause of death at one year, LVAD patients had a higher number of cardiovascular death secondary to primary graft failure, confirming findings of the recent studies at a larger scale.
Next, we looked at whether mortality risk factors were similar in the mechanical versus medical bridged patients. And this is a very important question clinically because the criteria for transplant listing do not distinguish between the two patient cohorts. For example, at my center age cutoff transplant listing is less than 72 years of age and that is whether or not patients are on VAD support. And same applies for example, GFR cutoff for renal function or PVR cutoff for pulmonary hypertension. And all the cutoffs that are utilized are essentially identical for transplant candidates irrespective of the bridging strategy.
But what we found in this paper, however, what's quite different that if we apply the same thresholds for mechanical versus medical bridged patients, for some of these risk factors, you end up having outcomes that are remarkably different. For example, for patients with a normal renal function, the mortality risk is similar going into transplant with or without an LVAD, but for patients with borderline renal function observed mortality has more than doubled for those going into transplant with an LVAD, as opposed to medical therapy.
And we also observed similar trends for recipient age, BMI and PVR, in which numerical increase in these factors would translate to high risk of mortality in LVAD patients going into heart transplant. Despite the limitations of this large registry analysis, I think these findings suggest that we may need to think of it differently when it comes to listing or transplanting patients who are on LVAD. And there seems to be a group of patients who are perhaps maybe better served by staying on an LVAD as opposed to moving on to heart transplant and we need to better identify who these patients are.
Dr Carolyn Lam: Oh Wow. Veli, thank you. First, congratulations on a very important paper and also how you beautifully summarized. Mechanically bridging patients associated with a higher risk of early post-transplant mortality and even providing data on the cause and risk factors associated with that mortality. Mark, could I bring you in here? Not just as AE (associate editor), but as a doc[tor] who manages many of these patients. What were your perspectives?
Dr Mark Drazner: As I step back and as Veli said, there's an increasing number of patients who are being bridged with a VAD, so the question clearly is important, and we don't really have any randomized data available to us in terms of how the bridging strategy may impact outcomes. When you look at the groups of patients who are supported with VADs or not, they're very different and so you need to do some statistical manipulation which here they did propensity matching, to try to come up with equal groups as you look at their outcomes. That was nicely done.
And then theoretically I think you could argue there may be reasons why patients bridged with VADs may do better or they may do worse. They may do better because you may restore their functionality, you may improve renal function and, but they may do worse because they have coagulopathies, the VAD itself may lead to complications and so it's a question you can't really answer just logically. You really need some data which is I think the best study that's been brought forward so far as the one we're discussing today. Veli, let me ask you because the obvious question then is why do you think the outcomes are worse among the patients who are bridged?
Dr Veli Topkara: I think they are doing worse for multiple different reasons. Having an LVAD is clearly an additional surgery which technically makes the second transplant surgery more complicated. But when we looked at the risk factors for primary graft failure at our institutions, the predictors of primary graft failure in LVAD patients were also very similar to factors we identified in this nationwide analysis which included renal failure, RV dysfunction, as well as trans-transplant and increased time on device support. I think it's clear that some subset of LVAD patients who have these risk factors are at higher risk for increased post-transplant mortality for some of the mechanistic reasons are unclear at this point.
Dr Mark Drazner: Do you think their continuous flow exposure is part of it?
Dr Veli Topkara: That's clearly one of the hypotheses that we have been talking about because as we discussed, these patients are exposed to continuous flow for a long time and one of the concerns is whether they lose their peripheral arterial venous-reactivity over time. And this could potentially also be the reason why patients who are on pump support for longer times are at higher risk for PGF. That's a possible underlying mechanism. But in this data set, we didn't have fair data with regards to pulse pressure and pulsatility, which could have helped answering this question.
Dr Mark Drazner: And just for clarification for the listeners, this was pre-HeartMate 3 data, is that correct?
Dr Veli Topkara: Yes. This analysis doesn't include any HeartMate 3 patients.
Dr Carolyn Lam: And Mark, if you don't mind, could you also clarify for the listeners why you specifically pointed out HeartMate 3 in the setting of the pulsatility?
Dr Mark Drazner: There is some degree of pulsatility reintroduced with the HeartMate 3, whether that has any physiological consequences is not yet known. Certainly, in terms of the impact of transplants. But as Veli said, the dataset available didn't yet include the HeartMate 3 so that's, remains an unanswered question for us currently, but certainly an important one.
Dr Veli Topkara: We would probably be able to do this analysis now that we have accumulated more patients with HeartMate 3. At the time of the study we didn't have any HeartMate 3 patients in the registry. In terms of primary graft failure, we have implanted over 160 patients with HeartMate 3 at my center, but we still see primary graft failure in HeartMate 3 patients going into heart transplant, but that would clearly be an interesting follow up project.
Dr Mark Drazner: Yeah, for sure. Another point that people, as they looked at your paper and asked me, is in terms of the impact of the VAD complications, whether the patients who are doing worse or those who, because they are patients who had VAD who have had complications and then went on a transplant and the impact of that, in terms of your findings. I know you did some analyses on that. Could you just clarify that for our listeners as well?
Dr Veli Topkara: Sure, so we wanted to look at for the LVAD patients, if there were any VAD related factors that would impact the posttransplant mortality and one of the things that we looked at was, their specific complications on LVAD support and were able to pull that data by looking at their reason for 1A upgrade status which clarifies the complication pipe. And when we looked at, based on complication type, we didn't see any impact of complication on the post LVAD mortality. In other words, the other patients who are transplanted with an infection or they were transplanted because of device thrombosis, they did not have any difference in terms of their posttransplant mortality.
We also compared patients who were supported by axial flow devices versus centrifugal flow devices and again, there was no significant difference in terms of posttransplant mortality. One factor that we found that was significant was the duration of the LVAD support and patients who stayed on the LVAD for longer times clearly had increased higher risk of posttransplant mortality. And this is also something that we had found in our institutional data.
Dr Mark Drazner: And Veli that would potentially speak to the impact of the continuous flow if duration of VAD is a risk factor.
Dr Veli Topkara: That's our hypothesis Mark. And I think we all tend to think that continuous flow is not natural, and we have pulse style flow for a reason. Now it's possible that if our bodies and end organs and vessels are exposed to continuous flow for a long time, that may be potentially a reason for, increased risk of PGF or raise of PGF after heart transplant. But I don't think we have enough data yet.
Dr Mark Drazner: Veli, one of the other interesting findings was the lack of impact on long-term outcomes. I'd be interested in your thoughts about that, why there was an impact on the first year but not long term.
Dr Veli Topkara: Absolutely. And that was a critical part of the findings and when we looked at our survival, when we visually looked at the curve, it seemed like the curves really separated early on and they sort of remain parallel to each other after one year. And for that reason, we did a conditional survival analysis starting from one year and then we compared starting for one year. There was actually no difference between the LVAD versus medical group. Again, confirming that the adverse impact of survival was really early, within the first year after transplant and I think that really has to do with primary graft failure as well as vasoplegia which are, typically seen early posttransplant. And I think the reason the VAD support is increasing mortality is most likely through increasing risk of PGF as well as vasoplegia. Now that's my read on the early risk rather than the late impact.
Dr Mark Drazner: Do you think that speaks to maybe not as big an impact on the immunological milieu of VADs as one might anticipate?
Dr Veli Topkara: Certainly, I mean the immunology, one thing we know is that LVAD patients have higher HLA sensitization going into transplant. However, primary graft failure is typically very early after transplant. And in general, we don't find, obviously we don't see any rejection in these patients. The mechanism is not related to HLA mediated rejection.
Dr Mark Drazner: That's interesting.
Dr Carolyn Lam: Well Mark and Veli, thanks so much. This is such an important and interesting discussion. Could I wrap it up now by asking each of you, you've already covered possibly the important areas for future research including the pulsatile devices, but what should clinicians take home right now? Veli, if I could start with you, because you had already said earlier that perhaps these patients need to be more carefully considered. What do you mean by that? What's the take home for now?
Dr Veli Topkara: I think the question is whether we should be listing or transplanting LVAD patients who are high-risk, and I think the research should focus on developing tools to better identify LVAD patients who are too high-risk for transplant. In this project, we only worked with a limited number of variables that were available in the UNOS registry, but there may be more specific clinical risk factors or even biomarkers predicting outcome in this unique cohort of LVAD patients potentially transitioning into transplant. I think that's an important question to figure out.
And another important question is whether we should be using identical cutoffs for listing patients with or without LVAD and if not, what would be the ideal cutoff for each one of these risk factors? Because what I read from this paper is that, a creatinine level of 1.8 may signal a different risk in an LVAD patient versus another patient on a minor trump. That's another important question.
And also, since October of last year, the new heart allocation policy has been in place, which now defines LVAD patients to appear status three or four based on their complication profile. And it will be interesting to see how the new allocation system would impact patients are on LVAD support waiting for an organ. And it's possible that these patients may end up waiting longer compared to patients who are with cardiogenic shock and are assigned to higher tier status. And if LVAD patients wait longer as we see from this data, they will have worse posttransplant outcomes. It's going to be very interesting to see how the new allocation policy impacts.
Another point I want to make is that with the recent MOMENTUM-3 trial patients receiving HeartMate 3 LVADs, had a 13.4% mortality risk at one year and this is actually lower than 17.6% mortality at one year in high risk LVAD patients in our study. Again, questioning transitioning from LVAD to transplant in high risk patients.
Dr Mark Drazner: I might take a step back even further. It's an important, it touches on a critical question in my mind, which is if you have a patient who needs to go into transplant and they're not crashing and burning. I'm assuming if they're crashing and burning, you need to go onto an LVAD, the following comments won't apply to that group. If you're a patient who's relatively stable, is it a better strategy to try and get them to transplant directly? Or is it better to go through and VAD and then transplant them? And ultimately that strategy question I think would require randomization to really answer that. But the data that we have discussed today, I think are opening that question and touch upon that in terms of the strategy of the impact of bridging people with VADs itself, which is why I think this is such an important question.
Dr Carolyn Lam: Thanks again, Mark and Veli. That was an amazing discussion.
Thank you, audience, for joining us. You've been listening to Circulation On The Run. Don't forget to tune in again next week.
This program is copyright American Heart Association 2019.