Circulation July 28, 2020 Issue

Dr Carolyn 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.


Dr Greg Hundley: And I'm Dr Greg Hundley, associate editor,
Director of the Pauley Heart Center from VCU Health in Richmond,
Virginia.


Dr Carolyn Lam: Our feature paper today discusses trans-ethnic
genome-wide association studies and the insights in the genetic
architecture and heritability of long QT syndrome, a massive
study that we will be digging into, but only after we talk a
little bit about the other papers in this week's issue. And I'm
going to start, Greg. Are you ready with your coffee?


Dr Greg Hundley: I am.


Dr Carolyn Lam: The first original paper really represents
seminal work, showing that the endothelium can directly regulate
obesity and insulin resistance. Now, as obesity develops, there
is a decline in adipose tissue vascularity, which seems
counterintuitive, and an increase in fibrosis.


So authors, led by Dr Chen from the Irell and Manella Graduate
School of Biological Sciences in the City of Hope, speculated
that the reduction in vascularity in this adipose tissue might
have an adverse effect on adipose tissue function. Now, these
authors previously identified Argonaute-1, or AG01, a key
component of microRNA-induced silencing complex, as a crucial
regulator in hypoxia-induced angiogenesis.


So in the current study, they aim to determine the AG01-mediated
endothelial cell transcriptome, the functional importance of
AG01-regulated endothelial function in vivo, and the relevance to
adipose tissue function and obesity.


A new mouse model with genetic deletion of AG01 in the
endothelium was useful to investigate the importance of
endothelial regulation of adipose tissue function. The findings
were that in mice fed high fat, high sucrose diet, the
suppression of endothelial AG01 promoted adipose tissue browning,
and led to an anti-obesity phenotype. Endothelial cell AG01
thrombospondin-1 pathway was induced in the endothelium from
human donors with insulin resistance.


In total, this study suggests a novel mechanism, by which
endothelial cells through AG01 thrombospondin-1 pathway controls
vascularization and function of adipose tissues, insulin
sensitivity, and whole-body metabolic state.


Dr Greg Hundley: Interesting, Carolyn. So tell me about this
clinically. Where do we take this from here?


Dr Carolyn Lam: I thought you would ask. So endothelial
dysfunction, per se, can cause metabolic dysregulation, rendering
targeting dysfunctional endothelium, a potential therapeutic
strategy to counteract obesity, and metabolic disorders. So this
study really opens a door to that.


Dr Greg Hundley: Very nice. Well, I've got another basic science
paper, and it evaluates single-cell RNA sequencing to dissect the
immunological network of autoimmune myocarditis. And it comes
from Dr Jiangping Song from the State Key Laboratory of
Cardiovascular Disease of Fuwai Hospital, and the National Center
for Cardiovascular Disease, Chinese Academy of Medical Sciences,
and Peking Union Medical College.


So Carolyn, the study aimed to investigate the immunological
network during the transition from myocarditis to cardiomyopathy,
and to identify the genes contributing to the inflammatory
response to myocarditis.


So mice were treated with myosin heavy chain alpha-peptides to
generate an experimental autoimmune myocarditis model. The
investigators performed single-cell RNA sequencing analysis of
CD45 plus cells extracted from mouse hearts during different
experimental autoimmune myocarditis phases, including normal
control, acute inflammation, subacute inflammation, and then in
the myopathy phase. Also, human heart tissues were collected from
surgically removed hearts of patients who had undergone heart
transplantation.


Dr Carolyn Lam: So what did they find, Greg?


Dr Greg Hundley: Well, Carolyn, a comparison of the single-cell
RNA sequencing data from different experimental autoimmune
myocarditis phases suggested that some cell clusters, such as
macrophage cluster 2 and Th17 cells, were associated with the
inflammatory response in the experimental autoimmune myocarditis
model.


The HIF1A expression level correlated with the extent of the
inflammatory response, and PX-478, a HIF1A inhibitor, alleviated
the inflammation during the different experimental autoimmune
myocarditis phases.


Immunohistochemical staining revealed that HIF1A expression was
upregulated in autoimmune myocarditis from the tissue samples
from the explanted hearts. Thus, the HIF1A inhibitor alleviated
inflammatory cell infiltration, and that may serve as a potential
therapeutic target in clinical practice.


Dr Carolyn Lam: Wow. That is some serious clinical implications.
Well, my next paper is really the first systematic
echocardiographic evaluation of consecutive patients requiring
hospitalization due to COVID-19, and it comes from Dr Topilsky
and colleagues from Tel Aviv Medical Center.


Dr Greg Hundley: So Carolyn, what did they find in this series?


Dr Carolyn Lam: So among a hundred consecutive patients diagnosed
with COVID-19 infection who underwent complete echocardiographic
evaluation, within 24 hours of admission, only 32% had a normal
echocardiogram at baseline. The most frequent abnormality was
right ventricular dilatation or dysfunction.


Among patients developing clinical deterioration during
follow-up, which were 20% of these hospitalized patients,
repeated echocardiograms showed further deterioration of the
right ventricular parameters, probably related to increased
pulmonary resistance. Five of these patients had deep vein
thrombosis.


Dr Greg Hundley: Carolyn, my next study comes from Dr Stephen
Fremes, and it's a modeling study out of the University of
Toronto. It modeled TAVR versus SAVR valve durability to
determine the effects on life expectancy across a broad range of
age.


Dr Carolyn Lam: Interesting. And what were the results?


Dr Greg Hundley: Well, based on their simulation models, the
durability of TAVR valves must be 70% shorter than that of
surgically replaced valves to result in reduced life expectancy
in patients with similar demographics to recent trials.


However, in younger patients, the threshold for TAVR valve
durability was substantially higher. In younger patients, life
expectancy was reduced when TAVR durability was 30%, 40% and 50%
shorter than surgical valves in 40, 50 or 60-year-old patients,
respectively.


So Carolyn, these findings suggest that durability concerns
should not influence the initial treatment decision regarding
TAVR versus SAVR in older low-risk patients, based on current
evidence supporting TAVR valve durability. However, in younger
low-risk patients, valve durability must be weighed against other
patient factors, such as life expectancy.


Dr Carolyn Lam: Thanks Greg, for that summary. Well, let me tell
you about other papers in this issue. There are a pair of letters
to the editor by Dr Opotowsky, and a response by Dr Goldberg
regarding the paper results of the Fontan Udenafil Exercise
Longitudinal, or FUEL trial.


There's a research letter by Dr Strik, Validating QT-Interval
Measurement Using the Apple Watch ECG to Enable Remote Monitoring
During the COVID-19 Pandemic. There are two On My Mind papers,
the first, Telemedicine and Forgotten America by Dr Julien, and
the second, The COVID-19 Pandemic: Ethical and Scientific
Imperatives for "Natural" Experiments by Dr Lewis.


Dr Greg Hundley: Very nice. Well, Carolyn, I've got a research
letter evaluating the effect of evolocumab on atherogenic
lipoproteins during the peri and early post-infarction period.
It's a placebo-controlled randomized trial from Dr Gary
Gerstenblith.


Sarah Cuddy also worked through a tough case of cardiac amyloid
when a fat biopsy was negative, but imaging studies of the heart
suggested cardiac amyloid.


Carolyn, I've also got an On My Mind piece, and it's entitled,
Can Old Ally Defeat a New Enemy? And it's by Dr Paul Gurbel, and
he discusses the use of inhaled aspirin to treat patients with
COVID-19.


And then finally, Carolyn, I have a prospective piece from Dr
Robert Lefkowitz who discusses β-arrestin-biased angiotensin II
receptor agonists for treatment of COVID-19. Well, Carolyn, what
a great issue, and let's get onto that feature discussion.


Dr Carolyn Lam: Yay. Let's go, Greg.


Dr Greg Hundley: Well, listeners. Now we're turning to our
feature discussion, and we are very fortunate to have Professor
Connie Bezzina from Amsterdam University Medical Center to talk
to us about her paper related to long QT syndrome.


Welcome, Connie. And I was wondering, before we get started in
discussing your paper, could you tell us a little bit about the
background in this area? And then, what was the hypothesis that
you wanted to address?


Prof Connie Bezzina: So over the last 20 to 30 years, we've
learned a lot about the genetic underpinnings of inherited
cardiac disorders associated with sudden cardiac arrest. And
basically, we've learned a lot about mutations in specific genes
that co-segregate with these disorders within families.


However, two outstanding features have remained unresolved.
Essentially, the first unresolved issue is the fact that we
observe, oftentimes, a low disease penetrance and variable
disease expression within families, which means that not
everybody within a family that carries a familial mutation is
affected by the disorder.


But two, so among those that are affected, some are affected more
severely than others. So some people would have only the ECG
abnormality, whereas other people, for instance, would have the
ECG abnormality and arrhythmic events. And you could also have
individuals, indeed, who don't even manifest any disease
manifestations. This is one of the outstanding challenges.


The other outstanding challenge is the fact that, despite
extensive genetic testing of the known genes in some probands and
some families, they remain genetically lucid, in that we don't
find a likely genetic defect in a minority of families. And of
course, that hinders genetic testing and implementation of
genetic testing in such families.


Dr Greg Hundley: What was the question you were going to answer
with your study? And tell us a little bit about your study design
and your study population.


Prof Connie Bezzina: Yeah, so essentially, we figured that
assigning these disorders to one large genetic defect might be an
oversimplification of biological phenomenon. So we hypothesized
that even in these Mendelian disorders, the inheritance of
additional genetic factors alongside the familial mutation could
contribute to risk. Of course, there will be other factors such
as environmental factors, which we did not tackle in the study.


The central hypothesis of the study was that common genetic
variation, which is present in the germ population, could
modulate the effect of the familial genetic defect of the
Mendelian mutation.


So in order to do this, we assembled a large consortium of
investigators from multiple centers in Europe, in North America
and Japan, worldwide, to bring together about 1700 probands with
the long QT syndrome. So we tested this hypothesis in the long QT
syndrome because we figured, among the rare inherited rhythm
disorders, it's one of the more common disorders. Also, because
each individual center has too few patients. To do this locally,
we put this group of investigators together to come up with 1700
probands.


The study design was a genome-wide association study with a
case-control design, where we tested the association of millions
of SNPs littered across the genome with susceptibility for the
disorder. So this led us to identify three single-nucleotide
polymorphisms that are associated with susceptibility for the
long QT syndrome.


What we immediately saw is that, actually, these three SNPs,
perhaps not surprisingly at all, had been previously associated
with the extent of the QT interval, with QT interval in the
general population. This is not surprising, of course, because
repolarization is a central part of physiological mechanism in
the long QT syndrome. So this basically indicated overlap between
genetic control of the QT interval in the germ population and
susceptibility to the long QT syndrome.


So the fact that the three SNPs that we identified as long QT
syndrome susceptibility SNPs had been associated with QT interval
duration in the germ population, we felt that that was pointing
to assure genetic underpinnings between these two phenotypes.


So we went on to investigate that by looking at the correlation
between the odds ratio for long QT syndrome susceptibility and
the effect that these SNPs have on QT interval in the germ
population. And in fact, we found a very high correlation between
those. So essentially, this pointed to sure genetic factors
between QT interval in the germ population and long QT syndrome
susceptibility.


Of course, we wanted to look for disease variability. The next
thing we wanted to do was whether these SNPs could actually
explain disease variability. Now, this was perhaps the most
disappointing part of the study, because when we constructed a
polygenic risk score based on SNPs that impact on the QT in the
germ population, we found no relation to QT interval among
patients, and also no relation to life-threatening arrhythmic
events among the patients.


We think that this is because our patients... or probrands.
They're primarily probands, so they are all more sick. So we
didn't have enough variability in our patient set to identify an
association with disease variability. And in fact, this is at
variance with previous studies that tested individual SNPs, and
even our own studies with smaller polygenic risk scores that did
find an association between a polygenic risk score based on QT
SNPs and QT prolongation and events among patients.


So we think that this is certainly something to study further in
the future, in larger patient sets where we not only have the
probands, but also their relatives, their mutation-carrying
relatives, which will give us a bigger variability to actually
test this hypothesis. So we think that looking at probands
actually was a very good design to find susceptibility variance
but was not maybe a good design to find SNPs or polygenic risk
scores to test their effect on disease variability.


Dr Greg Hundley: It sounds like you've found certain gene low PSI
that indicate a predilection for prolongation of the QT interval,
but not necessarily are those gene low PSI consistent with who's
going to experience an adverse cardiovascular event as a result
of their genetic constitution. Is that a fair statement?


Prof Connie Bezzina: Well, I think that the setting, because we
had probands, they were the most sick people in their families. I
think to have stronger conclusions on that, we need to test the
polygenic risk scores in families where there are people who are
differentially affected.


Dr Greg Hundley: I see. I-


Prof Connie Bezzina: We had too-narrow of a variability in a
probands-only design, as opposed to a study where we would have
probands who are severely affected and mutation-carrying
relatives who are less severely affected.


Dr Greg Hundley: Very nice. So that puts that clearly into
context. This was a massive effort. You have quite a list of
investigators, and you mentioned you had to gather so many sites.
How would you conduct that next study? Would you need another
large collection of individuals and many sites to take that on?


Prof Connie Bezzina: Yes. I'm a geneticist, and geneticists
always want larger, larger numbers, and I'm also one of those. So
I'm interested in explaining as much as possible into individual
variability. And I think to do that properly, I think we should
go preferably for a similar design where we will approach the
same centers. And hopefully, we can organize the next study,
which will have these probands and their relatives.


Dr Greg Hundley: Now, just quickly, for us working in the clinic,
how should we approach genetic testing in patients with long QT?


Prof Connie Bezzina: At the moment, I think our findings don't
have an immediate impact. I think our findings tell us about the
genetic architecture of the disorder. And actually, one thing I
haven't gone into yet is the fact that what we also found is that
patients who do not have mutations in the no-long QT genes, which
were called mutation-negative, which are about 20% of all long QT
syndrome probands, actually have a higher burden of these common
variants that prolong the QT interval.


So we think, actually, that mutation-negative long QT syndrome
probands will not have a Mendelian large effect variant but will
have perhaps a higher burden of these QT-prolonging alleles.


Therefore, I think this has direct implications for clinical
genetics of these patients, because if you have a proband in whom
you don't find a mutation in the known genes, you could think
that maybe it is not monogenic, which has implications because
you don't have a single genetic defect to test on that family.
One would need to keep follow-up of more family members until we
understand more about the genetics of those individuals.


Dr Greg Hundley: So Connie, this has been just a wonderful
discussion. Any additional studies examining the genetic
architecture of individuals that we need to think about for the
future?


Prof Connie Bezzina: Sure. So for long QT syndrome in particular,
as additional SNPs that modulate the QT interval in the germ
population are identified, it will be very important to
incorporate these into larger polygenic risk scores, and see
whether we could have a better discriminative capacity of such
polygenic risk scores in discriminating between severely affected
and less severely affected people, or who is more at risk for an
arrhythmic event.


Outside of long QT syndrome, I think there's a lot of work to be
done with respect to the likely complex inheritance of many of
these disorders that we previously considered to be Mendelian. So
for instance, ongoing work in our group concerns Brugada
syndrome, where we're seeing the same kind of thing, and
hypertrophic cardiomyopathy, where we're seeing the same kind of
inheritance.


Dr Greg Hundley: Well listeners, on behalf of both Carolyn and
myself, we look forward to catching you on the run next week.
Take care. This program is copyright the American Heart
Association 2020.