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Dr Wessel: I think different
centers have evolved slightly differ-ent strategies for
the assessment of patients who they think are at some
risk of having elevated pulmonary vascular resistance
as a part of their congenital heart disease. In general,
if patients come to us with a large lesion that should
represent a large left to-right-shunt, and they have no
signs or symptoms of congestive heart failure, that certainly
raises a red flag that pulmonary vascular resistance may
be ele-vated. Now how much one investigates that preop-eratively
in my mind depends in part on the age of the patients.
If it is quite a young patient (in the first months of
life) with a large defect and no evidence of congestive
heart failure, I think the recommenda-tion is still going
to be intervene, operate on that patient; it doesn’t necessarily
mean that the child is going to have significant PH as
a postoperative prob-lem. Cardiac catheterization is not
necessarily mandatory. However, in an older patient who
comes to us with a larger lesion at the ventricular level
or even the ductus level, if one sees PH either indirectly
inferred by the echocardiogram or by the absence of signs
and symptoms of congestive heart failure, then I think
the bur-den is on us to quantify the pulmonary vascular
resistance and the extent of the pulmonary vascular disease
because it does have pretty substantial implications for
postoperative morbidi-ty, mortality and the long-term
outcome. So, I would recom-mend that after a child gets
substantially beyond the first year of life with evidence
of elevated pulmonary vascular resistance, then before
intervention we catheterize those patients or get a better
handle on the quantitative aspects of pulmonary vascu-lar
resistance. I believe in testing for vasoreactivity because
in PPH we know that these outcomes are related to the
vasoreac-tivity of the patient during testing. I think
that carries over to the perioperative period for the
child with secondary pulmonary hypertension as well.
Dr Barst: Now what about
those patients who have PAH out of proportion to their
pulmonary venous hypertension? Is there an age at which
you would not operate? Do you do preoperative cardiac
catheterizations on these patients or do you just say,
“We’re going to operate because we know it is reversible
and then we’ll deal with the postoperative issues.”
Dr Wessel: In general we
would do a preoperative catheteriza-tion in those patients,
usually because the disease that causes severe PH is one
in which there is other physiologic information or an
opportunity for intervention that requires catheterization.
It has always been my impression (in children) that if
one can repair the left-side heart disease, that the PH
will not present a major problem and cause death. In the
postoperative period it is treatable and generally worth
the risk of intervention. The simplest answer to your
question is that we are very optimistic that in children
with PH related to left-side heart disease if one can
intervene and repair the heart disease, then the PH gener-ally
regresses.
Dr Barst: Is there a PVRI
that you consider “operable” versus “inoperable”? And
if you do, are you calculating the PVRI using measured
oxygen consumption or assumed oxygen consump-tion? Are
there some times when you think it is important to leave
a small interatrial communication as a “pop-off valve”
in the immediate perioperative period?
Dr Bridges: If by doing
vasodilator testing I can’t get the PVR somewhere
in the neighborhood of six Wood units indexed, I have
not sent them for repair. What I have done in several
of those cases is referred them for a pulmonary artery
band if they have a lesion suitable for banding. So let’s
consider a patient with an unre-strictive post-tricuspid
valve shunt who has a base-line, indexed PVR of 12 Wood
units, which I think we may all agree is not repairable,
and with vasodilator testing I can reveal some reactivity,
but still not to an indexed PVR below six Wood units.
In such cases I have referred the patient for a pul-monary
artery band and subsequently brought the patient back
for reevaluation for complete repair. That approach has
been very successful in some cases, in that the pulmonary
artery pressure and PVR falls after the band, and the
patient can go on to repair.
Dr Wessel: I think it depends
in part on the level of the shunt (ie, atrial or ventricular)
as well as the demonstrated reactivity. We might be more
liberal with atrial level shunts and accept a higher PVR.
Let’s consider children with a large VSD, or trun-cus
arteriosus, or AV canal, and a ventricular level shunt.
We are probably a little bit less conservative than Nancy
has described, but if we can get the pulmonary vascular
resistance to less than 8 units, corrected for body surface
area then we would be inclined to have a shunt undergo
a surgical repair. If it is between 8 and 12 U/m 2 , then
we want to assess not only their age, because in younger
patients we are more likely to want to intervene than
in older patients, but also their reactivity. I think
to be fixed at 12 U/m 2 is a little bit different than
to have a pulmonary vascular resistance that may start
at 12 but drop down to 8 or 9 U/m 2 . Above 12 U/m 2 ,
I think that we are reluc-tant to operate. Then again
there have been occasional younger children for whom we
performed a repair in the operating room or placed a device
in the cath lab to close the left to right shunt, even
though the PVR was 12 U/m 2 . What I have tried to incor-porate
into our evaluation is whether we turn them into a left
to right shunt during catheterization with vasodilator
testing. So if a young patient has high resistance, but
one can demonstrate by pulmonary vasodilator testing that
one can turn the shunt into a left-to-right shunt I think
that there are more opportuni-ties for intervention and
long-term therapy for PH. We do from time to time leave
a small atrial septal communication when closing a large
VSD in a high-resistance patient. Frankly, I don’t think
that helps so much minute to minute in the postoperative
perod as it might help during an acute decompensation
or even resuscitation. I think that if one can provide
an opportunity for blood to fill the left ventricle by
going right to left at the atrial level, it provides a
better opportunity to get through that acute decompensation
or even resuscitation as opposed to being faced with completely
separated circuits when there is a very intense pulmonary
vasoconstriction and a right heart that just can’t manage
through the pulmonary hypertensive crisis.
Dr Barst: I completely agree
with everything that has been said, including if a patient
has borderline resistance, if we can decrease the shear
stress or pressure, we are more aggressive about operating
on these patients. We may leave an interatrial communication
as a pop-off valve. The next question is since we keep
throwing around the term “vasodilator testing”, are you
including oxygen as well as inhaled nitric oxide, aerosolized
ilo-prost, intravenous epoprostenol, or intravenous adenosene?
Dr Ivy: We use measured
oxygen consumption in all of these patients and we use
a combination of oxygen and nitric oxide, as previously
shown to be the most effective strategy by Dr Wessel.
Dr Wessel: In preoperative
patients we have found that using nitric oxide and oxygen
together gives us the best pulmonary vasodilating response.
Dr Barst: How confident
are you that using a measured oxygen consumption in room
air will be accurate for calculating PVRI with inhaled
nitric oxide and supplemental oxygen?
Dr Wessel: PVR is a calculated
variable and can have enormous error especially when oxygen
consumption is assumed and not measured. That is why we
must be flexible when determining operability. If one
looks at all of the data that have been accu-mulated over
the years with nitric oxide, it does appear that, in the
absence of large changes in cardiac output, inhaled nitric
oxide does not change oxygen consumption. There is much
experience to substantiate this assumption. So I am reasonably
confident that in the absence of extreme right-heart failure
and very low cardiac output that giving NO to patients
to breathe does not substantially change the oxygen consumption
and introduce an error in PVR calculation that is based
on a meas-ured oxygen consumption at baseline before nitric
oxide.
Dr Bridges: I agree with
that. And I think there are two other things that may
be worth saying here. One is that even the measured oxygen
consumption that one gets in the cath lab is not completely
accurate. I think we just have to remember that all of
these measurements that we make in the cath lab are just
estimates, or snapshots, even after we have done our best
to create standardized conditions. And the second thing
is that, from my view, almost all of the vasodilator testing
that I do in the cath lab is done with very pragmatic
endpoints in mind. For example, I know that in some labs,
hyperventilation is used to test for pulmonary vasoreactivity.
I don’t see what the point of that is, frankly, because
it is not a therapy that I am going to use in the postoperative
period or for long-term therapy for the patient who is
not having surgery. I try to use oxygen, I use nitric
oxide, I use calcium channel blockers. I try to test with
the same things that I think I might reasonably use for
therapy for the patients.
Dr Barst: The therapies
that we should discuss include calci-um channel blockers,
epoprostenol intravenously, treprostinil subcutaneously,
oral beraprost, iloprost (which is available in Europe
for both intravenous and inhaled administration), inhaled
nitric oxide, oral endothelin-receptor antagonists, and
oral phosphodiesterase inhibitors.
Dr Ivy: I would just like
to start by saying that evaluation of PH is very important
before even considering therapy. We have patients who
have repaired congenital heart disease, who are later
found to have other exacerbating factors for pulmonary
hypertension, such as thromboembolic disease, ulcerative
coli-tis, or thyroid dusease. The treating physician shouldn’t
assume that because the child has congenital heart disease,
the con-genital lesion is the only cause of the patient’s
pulmonary hypertension. With regard to therapy, we do
not use calcium channel blockers in patients who are not
reactive to short-act-ing vasodilators at cardiac catheterization,
have low or border-line cardiac output, or have high right
atrial pressure. We don’t test calcium channel blockers
in those patients. So, I think it is important for the
general pediatric cardiologist who is going to perform
vasoreactivity testing to use calcium channel blockers
only in patients who are reactive.
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