Good evening, everyone.
It's a pleasure to be here, and I thank you
all for coming tonight.
So what I'm going to try to address over
the next few minutes is answer the question,
can MRI aid decision-making in the borderline small left
ventricle?
So here's the outline for the next few minutes.
I'm going to begin with some overview
comments about univentricular versus biventricular
repair in patients with borderline size left heart
structures and the decision-making around that.
I'll then present results of a recent research
study we did to try to answer the question about whether MRI
can help with this decision-making.
And then I'll show you a case example
where some of the results from that research study
are applied in clinical practice.
So clearly, this is a challenging decision,
trying to outweigh the benefits and risks of going down
a one ventricle pathway versus a two ventricle pathway.
Each road potentially has some pitfalls to it.
Going down a single ventricle approach
all the way to a Fontan clearly is associated
with some risks of morbidity.
You can see the list here up on the left side
of the slide here.
You're all familiar with those.
That cumulative morbidity results over the long term
into mortality.
And that's, of course, something that we're
trying to improve upon.
On the other hand, trying to go down
a two-ventricle route in a patient that may not
be an optimal candidate runs the risk of the patient developing
ventricular and valvular dysfunction,
pulmonary hypertension related to insufficiency
of the left heart structures, and pressure building up
in causing that pulmonary hypertension.
There may be a need for multiple procedures over time,
and with that, the risk of neurodevelopmental deficits,
as well as psychosocial challenges that
come with multiple hospitalizations and prolonged
medical care.
So how do we approach these difficult decisions?
Well, a key element to this, of course,
is a detailed diagnostic assessment.
This involves echocardiography, of course,
both two-dimensional and three-dimensional data,
cardiac catheterization.
And many of our patients also get a cardiac MRI study.
In addition, when we're making these decisions,
we want to take into account some patient specific factors.
For example, if the patient has trisomy 21 that
might be a situation where we might try a little bit harder
or take some more risks in order to try to get to that two
ventricle repair.
There's also this concept of reversibility.
If we make a decision to go down one particular road,
will we be able to change our minds if things
don't go as we had hoped?
So for example, if we take some steps toward a two ventricle
repair, will we be able to go back and still offer
that patient a one ventricle repair
if things don't continue to develop for the left side?
In practice, what we do with these cases is
we have a multidisciplinary review.
We have a meeting once a week where we review these cases
and discuss them.
And of course, a key element in all of this
is to have parental involvement and buy-in with the decision
making.
I can't emphasize how important that is when we're
trying to make these decisions.
So we have a challenging decision that
has some major consequences.
And we were wondering whether the use of MRI
can enhance this decision-making, given
its ability to measure ventricular volumes very
accurately and reproducibly.
Also its ability to measure blood flow
at comparing the right heart circulation with the left heart
circulation, would that be of any added value.
And of course, MRI has the ability
to assess myocardial fibrosis, as well.
So we recently published a study looking at these factors
to try to see whether MRI could help us
with decision-making in patients with borderline left hearts.
Just want to highlight the work of the first author
on this paper and my colleague, Dr. Puja Banka.
And I'm going to just briefly present
the results of that study to you.
So this was a retrospective study.
And in this group, we had two anatomic classifications,
two sets of patients, really.
The first was patients with borderline left heart
structures.
And the second group was patients
with a right-dominant atrioventricular canal defect.
If patients had a conotruncal abnormality,
such as transposition of the great arteries or double outlet
right ventricle, they were excluded from the study.
In addition, all the patients in this study,
there had to be some uncertainty amongst the care team
regarding whether or not the left heart could support
a biventricular circulation.
And the final inclusion criteria is all the patients
had to have had a CMR prior to the surgical or catheterization
procedure that converted them from a one ventricle
to two ventricle circulation, because we wanted them right
before the procedure.
And then we were going to assess the outcome
of those surgical interventions and see
which parameters would predict success in that two ventricle
conversion.
So let me deal with each anatomic group separately.
So we're going to begin with the borderline hypoplastic left
heart group.
You can see an example of a four-chamber view
up on the screen here.
You've got a hypoplastic mitral valve.
The distal leaflets are tethered down.
The left ventricle is small.
You can see it doesn't reach the apex.
You have some mitral regurgitation
in a dilated left atrium.
This is just an example of one of the patients in the cohort.
So in this group, we had a total of 22 patients.
The median age at the time of CMR was 39 months.
But note there was a fairly broad range in the age group
here right before they had their surgical procedure
to convert them.
Their circulation at the time of the CMR
ranged all across the spectrum of different single ventricle
palliation.
So there were three that were on prostaglandins
with no prior surgical or catheter intervention.
There were three that had undergone their stage 1.
The majority of the patients, 15 of them,
had already had their bidirectional Glenn.
And there was one patient who had completed their Fontan
procedure.
So it's also important to note that 17 of the 22 patients
had had a prior procedure to increase LV flow.
More specifically, 13 had an additional source
of pulmonary flow put in, such as a Blalock-Taussig shunt
or an RV-PA conduit.
And 16 had their ASD restricted.
And many of the patients had both of these things done.
So let me just pause here for a second just
to make sure you're following what I just said there.
So for example, here's a patient with borderline left heart
structures who's undergone their stage 1 and also
a Glenn procedure.
So for example, the procedures that
are being done to recruit the left side
could include an RV-PA connection.
That's going to increase the blood flow
to the pulmonary arteries, to the lungs,
and also back to the left atrium.
And then patients often had their atrial septum restricted.
And as a result of that, increased blood
was pushed into the left ventricle
to help promote growth.
All right, so let's return to our patient cohort.
So they had their MRIs.
Then they underwent their biventricular conversion
procedure.
And we had a median post-op follow-up from that conversion
procedure of 40 months.
And at last follow-up, we had 16 of the 22 patients
with a biventricular circulation.
And the other six were unsuccessful conversions.
Specifically, there were three deaths, two takedowns to a one
ventricle circulation, and one patient
underwent a heart transplant.
So then when we looked back at the CMR predictors,
we looked to see which imaging parameters were associated
with transplant-free biventricular survival
over that follow-up period.
So looking at the CMR parameters,
the things that came out as significant were increased
left ventricular end-diastolic volume.
So let me refer you over here to the graph.
We have end-diastolic volume on the vertical axis.
And then we have the two outcome groups--
those with a successful biventricular
conversion at last follow-up and those
who didn't have transplant-free biventricular survival
over here in the No group.
And you can see that the volume was statistically significantly
larger than in the successful group.
Similarly, those patients with an increased LV
to RV stroke volume ratio also had a greater chance
of success.
And along with that, those patients
had had an increased mitral valve to tricuspid valve inflow
flow ratio, also that was associated
with successful conversion.
On the echo side, LV end-diastolic volume
was also predictive of a transplant-free biventricular
survival.
So with each of those parameters that I just went through,
we did an ROC and survival analysis.
And with that, we were able to identify cut-off parameters
for each of those that either optimized sensitivity
for predicting successful conversion
or optimized specificity.
And then we could apply those going forward
in terms of decision making.
The other thing I wanted to touch on with this study
is the MRI assessment of fibrosis
using the late gadolinium enhancement technique.
15 of those 22 patients had late gadolinium enhancement.
And you can see a typical example here.
The bright area here in the subendocardium
is a fibrotic region in the short axis and the long axis.
Now when we looked at this, having that pattern,
that endocardial fibroelastosis, wasn't
associated with transplant-free biventricular survival.
However, interpretation of this result
is confounded by the fact that with their conversion surgery,
all 15 of the patients had EFE resection.
So we really don't know what would
have happened if it hadn't been resected
at the time of the operation.
All right, let me now just turn to the other anatomic group
in our study.
That's the right-dominant atrioventricular canal group.
You can see a representative example up here
on the screen, a four-chamber view.
You can see the common AV valve, mostly
filling the right ventricle here,
and this hypoplastic left ventricle that doesn't quite
make it to the apex.
Similarly, you can appreciate this in the short axis views,
as well.
So in this group, we had 10 patients.
The median age at their CMR study right
before their biventricular conversion procedure
was six months.
You can see this group is a younger
group than the small left heart group
and that their circulation at the time of CMR
also had a range of different types of palliations.
There were two patients who had undergone a stage 1, three
who had had a pulmonary artery band,
and five who had undergone a bidirectional Glenn.
So in terms of their surgical results,
all had a successful biventricular repair
at the time of hospital discharge.
Patients were then followed for a median post-op period
of 28 months.
Over that follow-up time, there was one late death.
That was 12 months post-op in a patient with mitral stenosis
and left ventricular outflow tract
obstruction who passed away during a respiratory illness.
There was one other patient who underwent mitral valve
replacement.
And all the surviving patients at last follow-up
were known to have a right ventricular pressure
less than one half systemic.
So since we only had 10 patients,
this was too small a sample size to come up and analyze
for predictors of success.
However, it's interesting to note
the range of the left ventricle end-diastolic volumes went
all the way down to 22 mls per meter squared.
And the LV to RV stroke volume ratio,
the lower end of that range went down to 0.19.
Just giving you a sense of what might be feasible.
So in the last portion of this discussion,
I just want to share a case with you
to show you how you can potentially
use these parameters with your decision making.
This is a two and a half year old
with mitral and aortic stenosis who
underwent a stage 1 with an RV-PA conduit
and then had the conduit taken down
and underwent their bidirectional Glenn procedure.
They were referred to us at two and a half years
of age for consideration of left ventricular
recruitment with the hope that you'd
get to a biventricular repair.
So here you can see the patient's four chamber
and short axis images.
You can see there's mitral valve hypoplasia.
The LV is narrow and doesn't make it all the way
to the apex of the heart.
And you can also appreciate in short axis
that the left ventricle's quite hypoplastic.
Here are some of the MRI data looking
at the inflow parameters.
I think you can appreciate that just even qualitatively
that there's much more tricuspid valve inflow
than there is mitral inflow here.
In addition, patient had late gadolinium enhancement imaging.
And here it's important to note that there
is no late gadolinium enhancement in this patient.
It's just normal appearing myocardium
by the late gadolinium enhancement technique.
So we reviewed this information and what you see in this chart
are the patient's values for those three CMR parameters
that we found in our study to be predictive.
You can see their value, and you can
see the threshold values that were established for the best
specificity.
And as you go through each of those parameters,
you see none of them meet those threshold values
in terms of them being acceptable for consideration
of biventricular conversion.
So along with review of the echo data and the cath data,
rather than doing a biventricular conversion
at that point, we did a series of procedures in one operation
to help recruit the left side of the heart.
Specifically the patient underwent
placement of a Blalock-Taussig shunt, atrial septal defect
restriction, and aortic valvuloplasty.
Patient then went home.
And then 12 months later, they came back for a reassessment.
And I'll share with you the MRI results comparing the MRI
pictures before the recruitment procedure and those 12 months
after the recruitment procedure.
So again, on the top row, you have the MRI data
that I showed you earlier from before the recruitment
procedure.
Here is 12 months after the recruitment procedure.
You can see in the four-chamber view, as well as a short axis
view, you can just get the sense clearly
that the LV size has increased.
The mitral annulus diameter has increased.
And then just qualitatively looking at the inflow,
you can see there's better mitral valve inflow.
So if we go forward and take a look, what I'm showing you here
in the table is the pre-recruitment numbers.
And then 12 months after that procedure, the parameters
for that, and then again the same threshold
values that I showed you before.
And if you start going through those,
you can see those now reached the acceptable range
on all of those parameters.
But we don't just rely on the MRI data alone.
We reviewed the cath and the echo data as well.
And with that, we made the decision
to go ahead and advance and proceed with a biventricular
conversion procedure which included a Ross procedure.
And in two and a half years of follow-up after that,
there have been no subsequent cardiac procedures.
So to summarize, the CMR parameters
can guide decision-making regarding one
versus two ventricle repairs.
It can also help assess the impact of procedures
that are designed to rehabilitate
the small left ventricle and left heart.
And we're certainly still working
on refining our selection criteria
for this type of procedure, and it's
an ongoing area of research.
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